| 1. |
- Bachi, Lorenzo, et al.
(författare)
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ECG Modeling for Simulation of Arrhythmias in Time-Varying Conditions
- 2023
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Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294. ; 70:12, s. 3449-3460
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Tidskriftsartikel (refereegranskat)abstract
- The present paper proposes an ECG simulator that advances modeling of arrhythmias and noise by introducing time-varying signal characteristics. The simulator is built around a discrete-time Markov chain model for simulating atrial and ventricular arrhythmias of particular relevance when analyzing atrial fibrillation (AF). Each state is associated with statistical information on episode duration and heartbeat characteristics. Statistical, time-varying modeling of muscle noise, motion artifacts, and the influence of respiration is introduced to increase the complexity of simulated ECGs, making the simulator well suited for data augmentation in machine learning. Modeling of how the PQ and QT intervals depend on heart rate is also introduced. The realism of simulated ECGs is assessed by three experienced doctors, showing that simulated ECGs are difficult to distinguish from real ECGs. Simulator usefulness is illustrated in terms of AF detection performance when either simulated or real ECGs are used to train a neural network for signal quality control. The results show that both types of training lead to similar performance.
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| 2. |
- Barquero-Perez, Oscar, et al.
(författare)
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On the influence of heart rate and coupling interval prematurity on heart rate turbulence
- 2017
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 64:2, s. 302-309
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Heart rate turbulence (HRT) has been successfully explored for cardiac risk stratification. While HRT is known to be influenced by the heart rate (HR) and the coupling interval (CI), nonconcordant results have been reported on how the CI influences HRT. The purpose of this study is to investigate HRT changes in terms of CI and HR by means of an especially designed protocol. Methods: A dataset was acquired from 11 patients with structurally normal hearts for which CI was altered by different pacing trains and HR by isoproterenol during electrophysiological study (EPS). The protocol was designed so that, first, the effect of HR changes on HRT and, second, the combined effect of HR and CI could be explored. As a complement to the EPS dataset, a database of 24-h Holters from 61 acute myocardial infarction (AMI) patients was studied for the purpose of assessing risk. Data analysis was performed by using different nonlinear ridge regression models, and the relevance of model variables was assessed using resampling methods. The EPS subjects, with and without isoproterenol, were analyzed separately. Results: The proposed nonlinear regression models were found to account for the influence of HR and CI on HRT, both in patients undergoing EPS without isoproterenol and in low-risk AMI patients, whereas this influence was absent in high-risk AMI patients. Moreover, model coefficients related to CI were not statistically significant, p > 0.05, on EPS subjects with isoproterenol. Conclusion: The observed relationship between CI and HRT, being in agreement with the baroreflex hypothesis, was statistically significant (p < 0.05), when decoupling the effect of HR and normalizing the CI by the HR. Significance: The results of this study can help to provide new risk indicators that take into account physiological influence on HRT, as well as to model how this influence changes in different cardiac conditions.
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| 3. |
- Demidova, Marina, et al.
(författare)
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T wave alternans in experimental myocardial infarction: Time course and predictive value for the assessment of myocardial damage.
- 2013
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Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 46:3, s. 263-269
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: T-wave alternans (TWA) is associated with prognosis after myocardial infarction (MI), however its link to the extent of ischemic injury has not been clarified. We analyzed the course of TWA and its relation to myocardial damage in experimental myocardial infarction. METHODS: In 21 pigs, infarction was induced by 40-minute long balloon inflation in LAD under continuous 12-lead ECG monitoring. TWA was assessed in a 32-beat sliding window, using periodic component analysis and the Laplacian Likelihood Ratio method. Myocardium at risk (MaR) and infarct size (IS) were evaluated by SPECT and magnetic resonance imaging respectively. RESULTS: TWA appeared at 7.2±4.5minutes of occlusion, reached its maximum at 12.7±6.3 and lasted until 26.5±9.2minutes. The maximal level of TWA was associated with both MaR (r=0.499, p=0.035) and IS (r=0.65, p=0.004). CONCLUSION: TWA magnitude is associated with both MaR and IS in experiment, which encourages further studies in clinical settings.
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| 4. |
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| 5. |
- Gil, Eduardo, et al.
(författare)
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Heart Rate Turbulence Analysis Based on Photoplethysmography
- 2013
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 60:11, s. 3149-3155
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Tidskriftsartikel (refereegranskat)abstract
- The goal of this paper is to determine whether the photoplethysmography (PPG) can replace the ECG-based detection of heart rate turbulence. Using the PPG, classification of ventricular premature beats (VPBs) is accomplished with a linear classifier. The two conventional parameters turbulence onset and slope are studied together with a recently introduced parameter characterizing turbulence shape. Performance is studied on a dataset with 4131 VPBs, recorded from a total of 27 patients in different clinical contexts (hemodialysis treatment, intensive care monitoring, and electrophysiological study). The sensitivity/specificity of VPB classification was found to be 90.5/99.9%, with an accuracy of 99.3%, suggesting that classification of VPBs can be reliable made from the PPG. The main difference between the two types of turbulence analysis stems from the fact that the pulse transit time varies largely immediately after the VPB. Out of the 22 patients which had a sufficient number of VPBs, the outcome of the ECG-and PPG-based analysis was identical in 21. It is concluded that the PPG may serve as a surrogate technique for the ECG in turbulence analysis.
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| 6. |
- Gomez, Neurys, et al.
(författare)
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Changes in T-Peak-to-T-End Morphology Measured by Time-Warping are Associated with Ischemia-Induced Ventricular Fibrillation in a Porcine Model
- 2023
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Ingår i: Computing in Cardiology, CinC 2023. - 2325-8861 .- 2325-887X. - 9798350382525
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Konferensbidrag (refereegranskat)abstract
- In this work, we use a time-warping-based morphology variation index, d_{w}, computed between the peak and the end of the T-wave, and assess its association with the occurrence of ventricular fibrillation (VF) episodes in ischemic conditions. ECG recordings from 26 pigs under-going a 40-minute coronary occlusion were analyzed. The d_{w} series was obtained by quantifying the morphological differences between the final part of the T wave at different stages of the occlusion and a reference T wave in the control recording. During control recordings, d_{w} remained stationary with a median value along each recording of 1.76 ms, IQR of 1.80, while during artery occlusion followed a well-marked gradual increasing trend as ischemia progressed, with median of 15.47 ms, IQR of 18.53. At the 20-to-25 min period from occlusion onset (and during 5 min prior to VF episode) dw averages in the VF group was significantly higher than in the non-VF group with median values of 40.0 (and 34.4) vs 7.8 (and 7.7) ms, with p-values of 0.002 (and 0.001), respectively. In conclusion, dynamic increases of the d_{w} index during ischaemia progression in pigs are associated with VF occurrence.
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| 7. |
- Gomez, Neurys, et al.
(författare)
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T-wave Peak-to-End Changes Quantified by Time-Warping Predicts Ventricular Fibrillation in a Porcine Myocardial Infarction Model
- 2024
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Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294. ; , s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Background: The T-peak-to-T-end ($\mathrm{T}_{pe}$) interval has shown potential in predicting ventricular arrhythmic risk. It is an appealing index to be measured during ischemia since it is less influenced by ST-segment changes than the early part of the T wave. A time-warping-based index, derived from a spatially transformed PCA lead, $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$, quantifying changes in the $\mathrm{T}_{pe}$ morphology, has previously demonstrated utility in tracking repolarization changes induced by a 5-minute ischemia model in humans. The value of $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ as a predictor of ventricular fibrillation (VF) episodes is assessed in a porcine model of myocardial ischemia with ischemia maintained for 40 minutes. Methods: From 32 pigs undergoing a coronary occlusion, pre-occlusion and occlusion ECG recordings from 10 pigs suffering a VF episode after 10 min of occlusion (Delayed VF) and 16 that did not had any episode during the recording were analyzed. The $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ series was measured by comparing $\mathrm{T}_{pe}$ morphologies at different stages of the occlusion relative to the peak-to-end morphology of a baseline T-wave. Results: During baseline, $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ remained stationary with an intra-recording median [IQR] value of 1.60 [1.33] ms. During artery occlusion, $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ followed a well-marked gradual increasing trend as ischemia progressed, reaching a median of 14.58 [17.72] ms. $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ averages were significantly higher (${p< 0.05}$) in the VF group than in the Non-VF group at time intervals 0-5, 5-10, 10-15, 15-20, 20-25 min after occlusion onset and at 10-15, 5-10 and 5-0 minutes prior to VF episode, with median values of 12.5, 18.8, 26.8, 24.0, 31.0, 18.6, 25.0 and 28.8 vs 6.3, 7.6, 8.0, 7.8, 7.8, 8.5, 7.2 and 6.0 ms, respectively. The $\mathrm{T}_{pe}^{\text{PCA}}$ interval was also significantly higher in the VF group at all analyzed time periods, but with a lower significance level. Pigs with maximum $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ $\geq$ 20.0 ms and $\mathrm{T}_{pe}^{\text{PCA}}$ $\geq$ 85.4 ms had significantly higher risk for VF occurring in the early 5-10 minutes interval, with 90.0%/75.0% and 80.0%/69.0% sensitivity/specificity, respectively. Univariate Cox analysis yielded hazard ratios of 12.5 for $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$ vs 5.5 for $\mathrm{T}_{pe}^{\text{PCA}}$. Conclusions and Significance: The time-warping-based index, $d^{{\kern0.28436pt}\text{PCA}}_{w,{\scriptscriptstyle \mathrm{T}_{pe}}}$, is a stronger VF predictor than $\mathrm{T}_{pe}^{\text{PCA}}$ during ischemia in a porcine model, advising for further clinical exploration studies in humans.
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| 8. |
- Martinez, Juan Pablo, et al.
(författare)
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Assessment of QT-measurement accuracy using the 12-lead electrocardiogram derived from EASI leads
- 2007
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Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 40:2, s. 172-179
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the present study is to assess QT-interval measurements from the EASI 12-lead electrocardiogram (ECG) as compared with the standard 12-lead ECG. The QT interval was automatically determined in simultaneously recorded standard and EASI 12-lead ECGs, using a validated wavelet-based delineator. The agreement between the 2 sets of measurements was quantified both on a lead-by-lead basis and a multilead basis with global definitions of QRS onset and T-wave end. The results show that the agreement between QT-interval measurements from the 2 lead systems is acceptable, with negligible mean differences and with correlation coefficients ranging from 0.91 to 0.98 depending on the lead studied. Although the SD shows a clear dependence on the selected lead (ranging from 9.2 to 26.4 milliseconds), differences are within the accepted tolerances for automatic delineation. In a few patients, large differences were found, mainly because of changes in morphology present in both lead systems. QT intervals measured by the multilead approach were considerably more stable than single-lead measurements and resulted in a much better agreement between the 2 lead systems (correlation coefficient, 0.98; QT difference, 1.1 +/- 9.8 milliseconds). Thus, the EASI 12-lead ECG may be used for reliable QT monitoring when the multilead delineation approach is adopted. (c) 2007 Elsevier Inc. All rights reserved.
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| 9. |
- Martínez, Juan Pablo, et al.
(författare)
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The STAFF III Database : ECGs recorded during acutely induced myocardial ischemia
- 2017
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Ingår i: Computing in Cardiology. - 2325-8861. ; 44
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Tidskriftsartikel (refereegranskat)abstract
- The STAFF III database was acquired with the aim of better understanding the ECG signatures observed during acute ischemia, with special focus on high-frequency QRS components. The database contains recordings from 104 patients undergoing elective balloon percutaneous coronary intervention. The database has not only been analyzed in numerous clinical studies, but also turned out to be an excellent tool for methodological development. Its use has, by far, exceeded the original aim. Inspired by this fact, the database has now been made publicly available at Physionet.
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| 10. |
- Pablo Martinez, Juan, et al.
(författare)
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Detection Performance and Risk Stratification Using a Model-Based Shape Index Characterizing Heart Rate Turbulence
- 2010
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Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 1573-9686 .- 0090-6964. ; 38:10, s. 3173-3184
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Tidskriftsartikel (refereegranskat)abstract
- A detection-theoretic approach to quantify heart rate turbulence (HRT) following a ventricular premature beat is proposed and validated using an extended integral pulse frequency modulation (IPFM) model which accounts for HRT. The modulating signal of the extended IPFM model is projected into a three-dimensional subspace spanned by the Karhunen-Loeve basis functions, characterizing HRT shape. The presence or absence of HRT is decided by means of a likelihood ratio test, the Neyman-Pearson detector, resulting in a quadratic detection statistic. Using a labeled dataset built from different interbeat interval series, detection performance is assessed and found to outperform the two widely used indices: turbulence onset (TO) and turbulence slope (TS). The ability of the proposed method to predict the risk of cardiac death is evaluated in a population of patients (n = 90) with ischemic cardiomyopathy and mild-to-moderate congestive heart failure. While both TS and the novel HRT index differ significantly in survivors and cardiac death patients, mortality analysis shows that the latter index exhibits much stronger association with risk of cardiac death (hazard ratio = 2.8, CI = 1.32-5.97, p = 0.008). It is also shown that the model-based shape indices, but not TO and TS, remain predictive of cardiac death in our population when computed from 4-h instead of 24-h ambulatory ECGs.
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| 11. |
- Perez, Cristina, et al.
(författare)
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Evaluation of a QT Adaptation Time Estimator for ECG Exercise Stress Test in Controlled Simulation
- 2023
-
Ingår i: Computing in Cardiology, CinC 2023. - 2325-887X .- 2325-8861. - 9798350382525
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Konferensbidrag (refereegranskat)abstract
- Slowed adaptation of the QT interval to sudden abrupt heart rate (HR) changes has been identified as a marker of ventricular arrhythmic risk. However, abrupt HR changes are difficult to induce in patients. Quantifying the QT adaptation time in gradual HR changes, as observed in ECGs recording during an exercise stress test, has been recently proposed. The time lag between the QT series and an instantaneous memoryless HR-dependent QT series along stress test was computed as QT memory. Here, this method was evaluated in a control scenario using simulated exercise stress test ECG signals presenting different QT adaptation times. The method robustness was studied by contaminating the ECGs with muscular noise (MN) signals with different Signal-to-Noise ratio (SNR) values, either synthetic or extracted from real recordings. We found that delineation of the T-wave end point in the first transformed lead from Periodic Component Analysis offers the best performance for low SNR. Moreover, we confirmed that the estimator provides an unbiased estimate of the QT memory introduced in the simulations for the studied range of SNR values (25 to 50 dB).
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| 12. |
- Sandberg, Frida, et al.
(författare)
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Prediction of hypotension in hemodialysis patients
- 2014
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Ingår i: Physiological Measurement. - : IOP Publishing. - 0967-3334 .- 1361-6579. ; 35:9, s. 1885-1898
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Tidskriftsartikel (refereegranskat)abstract
- Intradialytic hypotension (IDH) is the most common adverse complication during hemodialysis. Its early prediction and prevention will dramatically improve the quality of life for patients with an end stage renal disease. In a recent study, changes in the normalized envelope of the test statistic of the photoplethysmograpic (PPG) signal were found to predict acute symptomatic IDH. In the present study, the PPG-based predictor is generalized to include a patient-dependent threshold which incorporates on-line information on heart rate variability and heart rate turbulence. From datasets with patients prone and resistant to IDH, the results show that symptomatic IDH could be correctly predicted in 9 out of 14 cases, while 5 out of 24 were falsely predicted. In a subset of the data containing only patients prone to IDH, acute symptomatic IDH could be correctly predicted in 5 out of 5 cases, with one false prediction out of 14. When testing the robustness of the predictor, no significant changes were observed in the test statistic when controlled changes occurred in dialysis fluid temperature, ultrafiltration rate and body position.
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| 13. |
- Sandberg, Frida, et al.
(författare)
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Prediction of intradialytic hypotension using PPG and ECG
- 2013
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Ingår i: 2013 Computing in Cardiology. - 9781479908844 ; 40, s. 1227-1230
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Konferensbidrag (refereegranskat)abstract
- Intradialytic hypotension (IDH) is the most common complication during hemodialysis; early prediction and prevention of IDH would dramatically improve the living conditions for patients with end stage renal disease. A recently published study suggests that a decrease in the envelope of the photoplethysmograpy (PPG) signal can be used for predicting acute symptomatic IDH. In the present study, the PPG based method is extended by introducing a patient dependent detection threshold, which involves information on heart rate variability (HRV) and heart rate turbulence (HRT) from the current dialysis session. This is motivated since several studies have found significant differences in HRV and HRT between hypotension-prone and hypotension-resistant patients. Recordings from 15 patients during 38 hemodialysis sessions were used to evaluate the method. Symptomatic IDH was correctly predicted in 9 out of 14 cases, while 5 out of 24 cases were falsely predicted. The performance was better for acute symptomatic IDH, 5 out of 5 cases were correctly predicted. The present method represents a novel approach to combining information derived from ECG and PPG signals.
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| 14. |
- Smith, Danny, et al.
(författare)
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Model-Based Detection of Heart Rate Turbulence Using Mean Shape Information
- 2010
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 57:2, s. 334-342
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Tidskriftsartikel (refereegranskat)abstract
- A generalized likelihood ratio test (GLRT) statistic is proposed for detection of heart rate turbulence (HRT), where a set of Karhunen-Loeve basis functions models HRT. The detector structure is based on the extended integral pulse frequency modulation model that accounts for the presence of ectopic beats and HRT. This new test statistic takes a priori information regarding HRT shape into account, whereas our previously presented GLRT detector relied solely on the energy contained in the signal subspace. The spectral relationship between heart rate variability (HRV) and HRT is investigated for the purpose of modeling HRV "noise" present during the turbulence period, the results suggesting that the white noise assumption is feasible to pursue. The performance was studied for both simulated and real data, leading to results which show that the new GLRT detector is superior to the original one as well as to the commonly used parameter turbulence slope (TS) on both types of data. Averaging ten ventricular ectopic beats, the estimated detection probability of the new detector, the previous detector, and TS were found to be 0.83, 0.35, and 0.41, respectively, when the false alarm probability was held fixed at 0.1.
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| 15. |
- Solem, Kristian, et al.
(författare)
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Model-based detection of heart rate turbulence.
- 2008
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 55:12, s. 2712-2722
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the integral pulse frequency modulation model is extended to account for the presence of ectopic beats and heart rate turbulence (HRT). Based on this model, a new statistical approach to the detection and characterization of HRT is presented. The detector structure involves a set of Karhunen-LoEve basis functions and a generalized likelihood ratio test statistic T(x) . The three most significant basis functions reflect the difference in heart rate prior to a ventricular ectopic beat (VEB) compared to after HRT, the "average" HRT, and a delayed contribution to HRT, respectively. Detector performance was studied on both simulated and ECG signals. Three different simulations were performed for the purpose of studying the influence of SNR, QRS jitter, and ECG sampling rate. The results show that the HRT test statistic T(x) performs better in all simulations than do the commonly used parameters known as turbulence onset (TO) and turbulence slope (TS). In order to attain the same performance as T(x), TS needs at least twice the amount of VEBs for averaging, and TO at least four times. The detector performance was also studied on ECGs acquired from eight patients who underwent hemodialysis treatment with the goal to discriminate between patients considered to be hypotension-resistant (HtR) and hypotension-prone (HtP). The results show that T(x) exhibits larger mean values in HtR patients than in HtP, suggesting that HRT is mostly present in HtR patients. The overlap between the two groups was larger for TO and TS than for T(x).
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| 16. |
- Ahlström, Christer, 1977-
(författare)
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Nonlinear phonocardiographic Signal Processing
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work has been to develop signal analysis methods for a computerized cardiac auscultation system, the intelligent stethoscope. In particular, the work focuses on classification and interpretation of features derived from the phonocardiographic (PCG) signal by using advanced signal processing techniques.The PCG signal is traditionally analyzed and characterized by morphological properties in the time domain, by spectral properties in the frequency domain or by nonstationary properties in a joint time-frequency domain. The main contribution of this thesis has been to introduce nonlinear analysis techniques based on dynamical systems theory to extract more information from the PCG signal. Especially, Takens' delay embedding theorem has been used to reconstruct the underlying system's state space based on the measured PCG signal. This processing step provides a geometrical interpretation of the dynamics of the signal, whose structure can be utilized for both system characterization and classification as well as for signal processing tasks such as detection and prediction. In this thesis, the PCG signal's structure in state space has been exploited in several applications. Change detection based on recurrence time statistics was used in combination with nonlinear prediction to remove obscuring heart sounds from lung sound recordings in healthy test subjects. Sample entropy and mutual information were used to assess the severity of aortic stenosis (AS) as well as mitral insufficiency (MI) in dogs. A large number of, partly nonlinear, features was extracted and used for distinguishing innocent murmurs from murmurs caused by AS or MI in patients with probable valve disease. Finally, novel work related to very accurate localization of the first heart sound by means of ECG-gated ensemble averaging was conducted. In general, the presented nonlinear processing techniques have shown considerably improved results in comparison with other PCG based techniques.In modern health care, auscultation has found its main role in primary or in home health care, when deciding if special care and more extensive examinations are required. Making a decision based on auscultation is however difficult, why a simple tool able to screen and assess murmurs would be both time- and cost-saving while relieving many patients from needless anxiety. In the emerging field of telemedicine and home care, an intelligent stethoscope with decision support abilities would be of great value.
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| 17. |
- Baalsrud Hauge, Jannicke Madeleine, et al.
(författare)
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Learning Analytics Architecture to Scaffold Learning Experience through Technology-based Methods
- 2015
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Ingår i: International Journal of Serious Games. - : Serious Games Society. - 2384-8766. ; 2:1, s. 29-44
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Tidskriftsartikel (refereegranskat)abstract
- The challenge of delivering personalized learning experiences is often increased by the size of classrooms and online learning communities. Serious Games (SGs) are increasingly recognized for their potential to improve education. However, the issues related to their development and their level of effectiveness can be seriously affected when brought too rapidly into growing online learning communities. Deeper insights into how the students are playing is needed to deliver a comprehensive and intelligent learning framework that facilitates better understanding of learners' knowledge, effective assessment of their progress and continuous evaluation and optimization of the environments in which they learn. This paper discusses current SOTA and aims to explore the potential in the use of games and learning analytics towards scaffolding and supporting teaching and learning experience. The conceptual model (ecosystem and architecture) discussed in this paper aims to highlight the key considerations that may advance the current state of learning analytics, adaptive learning and SGs, by leveraging SGs as an suitable medium for gathering data and performing adaptations.
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| 18. |
- Bailon, Raquel, et al.
(författare)
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Analysis of heart rate variability during exercise stress testing using respiratory information
- 2010
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Ingår i: Biomedical Signal Processing and Control. - : Elsevier BV. - 1746-8094. ; 5:4, s. 299-310
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a novel method for the analysis of heart rate variability (HRV) during exercise stress testing enhanced with respiratory information. The instantaneous frequency and power of the low frequency (LF) and high frequency (HF) bands of the HRV are estimated by parametric decomposition of the instantaneous autocorrelation function (ACF) as a sum of damped sinusoids. The instantaneous ACF is first windowed and filtered to reduce the cross terms. The inclusion of respiratory information is proposed at different stages of the analysis, namely, the design of the filter applied to the instantaneous ACF, the parametric decomposition, and the definition of a dynamic HF band. The performance of the method is evaluated on simulated data as well as on a stress testing database. The simulation results show that the inclusion of respiratory information reduces the estimation error of the amplitude of the HF component from 3.5% to 2.4% in mean and related SD from 3.0% to 1.7% when a tuned time smoothing window is used at an SNR of 15 dB. Results from the stress testing database show that information on respiratory frequency produces HF power estimates which closely resemble those from the simulations which exhibited lower SD. The mean SD of these estimates with respect to their mean trends is reduced by 84% (from 0.74 x 10(-3) s(-2) to 0.12 x 10(-3) s(-2)). The analysis of HRV in the stress testing database reveals a significant decrease in the power of both the LF and HF components around peak stress. (C) 2010 Elsevier Ltd. All rights reserved.
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| 19. |
- Bailon, R., et al.
(författare)
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Analysis of heart rate variability using time-varying frequency bands based on the respiratory frequency
- 2007
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Ingår i: Proc. IEEE Conf. Eng. Med. Biol.
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Konferensbidrag (refereegranskat)abstract
- In this paper a methodological approach for the analysis of nonstationary heart rate variability (HRV) signals using time-varying frequency bands based on respiratory frequency is presented. Spectral analysis of HRV is accomplished by means of the Smoothed Pseudo Wigner Ville distribution. Different approaches to the definition of the low frequency (LF) and high frequency (HF) bands are considered which involve respiratory information, derived either from a respiratory signal or from the ECG itself. Results are presented which derive from recordings acquired during stress testing and induced emotion experiments.
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| 20. |
- Castells, Francisco, et al.
(författare)
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Principal component analysis in ECG signal processing
- 2007
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Ingår i: Eurasip Journal on Applied Signal Processing. - : Springer Science and Business Media LLC. - 1110-8657. ; , s. 74580-74580
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Tidskriftsartikel (refereegranskat)abstract
- This paper reviews the current status of principal component analysis in the area of ECG signal processing. The fundamentals of PCA are briefly described and the relationship between PCA and Karhunen-Loeve transform is explained. Aspects on PCA related to data with temporal and spatial correlations are considered as adaptive estimation of principal components is. Several ECG applications are reviewed where PCA techniques have been successfully employed, including data compression, ST-T segment analysis for the detection of myocardial ischemia and abnormalities in ventricular repolarization, extraction of atrial fibrillatory waves for detailed characterization of atrial fibrillation, and analysis of body surface potential maps.
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| 21. |
- Celotto, Chiara, et al.
(författare)
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Dependence of Atrial Fibrillatory Rate Variations Induced by Head-Up/Down Tilt-Test on Autonomic Action
- 2023
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Ingår i: Computing in Cardiology, CinC 2023. - 2325-887X .- 2325-8861. - 9798350382525 ; 50
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Konferensbidrag (refereegranskat)abstract
- In atrial fibrillation (AF), autonomic nervous system (ANS) differences among individuals may have a substantial influence on the varying effectiveness of anti-AF treatments. This work aimed to assess the relationship between changes in autonomic balance and in atrial fibrillatory rate (AFR) oscillations (F_{mathrm{f}}(t)) induced by head-up (HUT) and head-down (HDT) tilt test. 22 persistent AF (psAF) patients underwent a tilt test protocol and ECGs were recorded and analyzed to extract F_{mathrm{f}}(t) and its respiratory modulation (Delta F_{mathrm{f}}). Electrophysiological simulations of stable reentrant rotors in 2D human atrial psAF tissues were performed. Combinations of different levels of parasympathetic stimulation (PSS) by acetylcholine (ACh) and sympathetic stimulation (SS) by isoproterenol (Iso) were tested. The respiratory-related modulation of ACh was modeled by a cyclic temporal variation of ACh. In the patients, HUT/HDT resulted in an increase/decrease in AFR with respect to baseline (BL). Variations in Delta F_{mathrm{f}} from HDT/HUT to BL/HDT were significantly positively correlated with the variations in mean F_{mathrm{f}}(t)(overline{F}_{mathrm{f}}). In the simulations, higher Iso and/or ACh led to an increase in overline{F}_{mathrm{f}}, while Delta F_{mathrm{f}} was correlated to the range of ACh variation. HUT/HDT increased/decreased AFR, which could be explained by an increase/reduction in SS. The concomitant variation in Delta F_{mathrm{f}} could be linked to changes in PSS.
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| 22. |
- Celotto, Chiara, et al.
(författare)
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Effects of Acetylcholine Release Spatial Distribution on the Frequency of Atrial Reentrant Circuits : a Computational Study
- 2022
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Ingår i: 2022 Computing in Cardiology, CinC 2022. - 2325-887X .- 2325-8861. - 9798350300970 ; 2022-September
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Konferensbidrag (refereegranskat)abstract
- The frequency of the ECG fibrillatory f-waves (Ff) in atrial fibrillation (AF) shows significant variations over time. Cardiorespiratory interactions through the autonomic nervous system have been suggested to play a role in such variations. Here, we tested whether the spatial distribution associated with the release of the parasympathetic neurotransmitter acetylcholine (ACh) could affect the frequency of atrial reentrant circuits. Computational simulations in a human persistent-AF 3D atrial model were performed. We evaluated two different patterns of atrial innervation: ACh release restricted to the area of the ganglionated plexi (GP) and the nerves departing from them, following the so-called octopus hypothesis, and ACh release distributed uniformly randomly throughout the atria. In both cases, ACh release sites occupied 8% of the atria. The temporal pattern of ACh release was simulated following a sinusoidal waveform of frequency 0.125 Hz (respiratory frequency). Different mean levels and peak-to-peak variation ranges of ACh were tested. We found that variations in the dominant frequency Ff followed the simulated temporal ACh pattern in all cases, with Ff modulation being more pronounced for increasingly larger ACh variation ranges. For the tested percentage of ACh release sites (8%), the spatial distribution of ACh did not have an impact on Ff modulation.
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| 23. |
- Celotto, Chiara, et al.
(författare)
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Relationship between Atrial Oscillatory Acetylcholine Release Pattern and f-wave Frequency Modulation : A Computational and Experimental Study
- 2020
-
Ingår i: 2020 Computing in Cardiology, CinC 2020. - 2325-887X .- 2325-8861. - 9781728173825 ; 2020-September
-
Konferensbidrag (refereegranskat)abstract
- The frequency of fibrillatory waves (f-waves), Ff, exhibits significant variation over time, and previous studies suggest that some of this variation is related to respiratory modulation through the autonomic nervous system. In this study, we tested the hypothesis that this variation (?Ff) could be related to acetylcholine concentration ([ACh]) release pattern. Electrocardiograms were recorded from seven patients during controlled respiration before and after full vagal blockade, from which f-wave frequency modulation was characterized. Computational simulations in human atrial tissues were performed to assess the effects of [ACh] release pattern on Ff and compared to experimental results in humans. A cross-stimulation protocol was applied onto the tissue to initiate a rotor while cyclically varying [ACh] following a sinusoidal waveform of frequency equal to 0.125 Hz. Different mean levels (0.05, 0.075µM/l) and peak-to-peak ranges (0.1, 0.05, 0.025 µM/l) of [ACh] variation were tested. In all patients, an f-wave frequency modulation could be observed. In 57% of the patients, this modulation was significantly reduced after vagal blockade. Simulations confirmed that rotor frequency variations followed the induced [ACh] patterns. Mean Ff was dependent on mean [ACh] level, while?Ffwas dependent on [ACh] variation range.
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| 24. |
- Celotto, Chiara, et al.
(författare)
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The frequency of atrial fibrillatory waves is modulated by the spatiotemporal pattern of acetylcholine release : a 3D computational study
- 2024
-
Ingår i: Frontiers in Physiology. - 1664-042X. ; 14
-
Tidskriftsartikel (refereegranskat)abstract
- In atrial fibrillation (AF), the ECG P-wave, which represents atrial depolarization, is replaced with chaotic and irregular fibrillation waves (f waves). The f-wave frequency, F f, shows significant variations over time. Cardiorespiratory interactions regulated by the autonomic nervous system have been suggested to play a role in such variations. We conducted a simulation study to test whether the spatiotemporal release pattern of the parasympathetic neurotransmitter acetylcholine (ACh) modulates the frequency of atrial reentrant circuits. Understanding parasympathetic involvement in AF may guide more effective treatment approaches and could help to design autonomic markers alternative to heart rate variability (HRV), which is not available in AF patients. 2D tissue and 3D whole-atria models of human atrial electrophysiology in persistent AF were built. Different ACh release percentages (8% and 30%) and spatial ACh release patterns, including spatially random release and release from ganglionated plexi (GPs) and associated nerves, were considered. The temporal pattern of ACh release, ACh( t), was simulated following a sinusoidal waveform of frequency 0.125 Hz to represent the respiratory frequency. Different mean concentrations ( A C h ¯ ) and peak-to-peak ranges of ACh (ΔACh) were tested. We found that temporal variations in F f, F f( t), followed the simulated temporal ACh( t) pattern in all cases. The temporal mean of F f( t), F ¯ f , depended on the fibrillatory pattern (number and location of rotors), the percentage of ACh release nodes and A C h ¯ . The magnitude of F f( t) modulation, Δ F f, depended on the percentage of ACh release nodes and ΔACh. The spatial pattern of ACh release did not have an impact on F ¯ f and only a mild impact on Δ F f. The f-wave frequency, being indicative of vagal activity, has the potential to drive autonomic-based therapeutic actions and could replace HRV markers not quantifiable from AF patients.
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| 25. |
- Garde, Ainara, et al.
(författare)
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Assessment of respiratory flow cycle morphology in patients with chronic heart failure
- 2017
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Ingår i: Medical & Biological Engineering & Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 55:2, s. 245-255
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Tidskriftsartikel (refereegranskat)abstract
- Breathing pattern as periodic breathing (PB) in chronic heart failure (CHF) is associated with poor prognosis and high mortality risk. This work investigates the significance of a number of time domain parameters for characterizing respiratory flow cycle morphology in patients with CHF. Thus, our primary goal is to detect PB pattern and identify patients at higher risk. In addition, differences in respiratory flow cycle morphology between CHF patients (with and without PB) and healthy subjects are studied. Differences between these parameters are assessed by investigating the following three classification issues: CHF patients with PB versus with non-periodic breathing (nPB), CHF patients (both PB and nPB) versus healthy subjects, and nPB patients versus healthy subjects. Twenty-six CHF patients (8/18 with PB/nPB) and 35 healthy subjects are studied. The results show that the maximal expiratory flow interval is shorter and with lower dispersion in CHF patients than in healthy subjects. The flow slopes are much steeper in CHF patients, especially for PB. Both inspiration and expiration durations are reduced in CHF patients, mostly for PB. Using the classification and regression tree technique, the most discriminant parameters are selected. For signals shorter than 1 min, the time domain parameters produce better results than the spectral parameters, with accuracies for each classification of 82/78, 89/85, and 91/89 %, respectively. It is concluded that morphologic analysis in the time domain is useful, especially when short signals are analyzed.
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| 26. |
- Grigonyte, Egle, et al.
(författare)
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Relative peripheral blood volume changes in response to ventricular premature beats during dialysis
- 2013
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Ingår i: [Host publication title missing]. - 2325-8861. ; 40, s. 209-212
-
Konferensbidrag (refereegranskat)abstract
- The goal of this study is to determine whether peripheral blood volume fluctuations triggered by ventricular premature beats (VPBs) are significantly related to hypotensive symptoms during dialysis treatment. Patients treated with hemodialysis often suffer from cardiovascular disorders and uremic neuropathy, increasing the propensity to homeostatic imbalance that, in turn, may result in intradialytic hypotension, cramps, nausea, dizziness, headache and other complications. VPBs, being abundant in hemodialysis patients, can be viewed as an internal disturbance leading to imbalance through acute blood pressure drop and prolonged tissue deoxygenation. The present study investigates and quantifies VPB-induced relative peripheral blood volume changes, measured from the fingertip photoplethysmographic (PPG) waveform, and their significance for characterization of physiological recovery of a disturbed circulatory state. The mean decrease in PPG amplitude, corresponding to an initial post-ectopic drop in blood volume delivered to the periphery, was 4 ± 3% in asymptomatic treatments, whereas 17 ± 3% in symptomatic dialysis treatments. This result indicates that significant differences exist between the two groups of treatment, providing a potential for development of intradialytic risk predictors.
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| 27. |
- Grigonytė, Eglė, et al.
(författare)
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Relative peripheral blood volume changes induced by premature ectopic beats and their role in hemodialysis
- 2017
-
Ingår i: Biomedical Signal Processing and Control. - : Elsevier BV. - 1746-8094. ; 31, s. 524-528
-
Tidskriftsartikel (refereegranskat)abstract
- Hemodialysis patients often suffer from cardiovascular disorders and uremic neuropathy, increasing the propensity to homeostatic imbalance that, in turn, may result in intradialytic complications like cramp, nausea, and, worse, hypotension. Ectopic beats, being abundant in such patients, may lead to imbalance through repeated, sudden drops in blood pressure. By exploring the properties of postectopic peripheral circulation recovery, treatment sessions prone to intradialytic complications may be better identified. This paper introduces a novel method for quantifying changes in peripheral blood volume due to ventricular or supraventricular premature beats (VPBs or SVPBs). Using the fingertip photoplethysmographic pulse waveform, VPB and SVPB-induced changes in relative peripheral blood volume are quantified by the postectopic pulse amplitude. Two parameters are proposed for characterizing (i) the initial drop in peripheral blood volume following an ectopic beat, and (ii) the degree of postectopic peripheral circulation recovery. A small set of data from 16 hemodialysis sessions in 9 hypotension-prone patients are used to illustrate the method. In asymptomatic sessions, the first parameter was found to be 8 ± 13% (mean ± std), whereas, in symptomatic sessions, it increased to 32 ± 13%, suggesting that postectopic pulse amplitude recovery is related to intradialytic complications; similar results were obtained for the second parameter. Postectopic pulse amplitude recovery may also be of interest in other applications where relative changes in peripheral blood volume play a role.
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| 28. |
- Kontaxis, Spyridon, et al.
(författare)
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Investigating Respiratory Rate Estimation during Paroxysmal Atrial Fibrillation Using an Improved ECG Simulation Model
- 2020
-
Ingår i: 2020 Computing in Cardiology, CinC 2020. - 2325-887X .- 2325-8861. - 9781728173825 ; 2020-September
-
Konferensbidrag (refereegranskat)abstract
- The present study addresses the problem of respiratory rate estimation from ECG-derived respiration (EDR) signals during paroxysmal atrial fibrillation (AF). Novel signal-to-noise ratios between various components of the ECG including the influence of respiration, measured by QRS ensemble variance, the amplitude of fibrillatory waves (f-waves), and the QRS amplitude are introduced to characterize EDR performance. Using an improved ECG simulation model accounting for morphological variation induced by respiration, the results show that 1. the error in estimating the respiratory rate increases as a function of the time spent in AF, 2. the leads farthest away from the atria, i.e., V_{4}, V_{5}, V_{6}, exhibit the best performance due to lower f-wave amplitudes, 3. lower errors in leads with similar f-wave amplitude are due to a more pronounced respiratory influence, and 4. the respiratory influence is higher in V_{2}, V_{3}, and V_{4} compared to other precordial leads.
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| 29. |
- Laguna, Pablo, et al.
(författare)
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Eigenvalue-based time delay estimation of repetitive biomedical signals
- 2018
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Ingår i: Digital Signal Processing. - : Elsevier BV. - 1051-2004. ; 75, s. 107-119
-
Tidskriftsartikel (refereegranskat)abstract
- The time delay estimation problem associated with an ensemble of misaligned, repetitive signals is revisited. Each observed signal is assumed to be composed of an unknown, deterministic signal corrupted by Gaussian, white noise. This paper shows that maximum likelihood (ML) time delay estimation can be viewed as the maximization of an eigenvalue ratio, where the eigenvalues are obtained from the ensemble correlation matrix. A suboptimal, one-step time delay estimate is proposed for initialization of the ML estimator, based on one of the eigenvectors of the inter-signal correlation matrix. With this approach, the ML estimates can be determined without the need for an intermediate estimate of the underlying, unknown signal. Based on respiratory flow signals, simulations show that the variance of the time delay estimation error for the eigenvalue-based method is almost the same as that of the ML estimator. Initializing the maximization with the one-step estimates, rather than using the ML estimator alone, the computation time is reduced by a factor of 5M when using brute force maximization (M denoting the number of signals in the ensemble), and a factor of about 1.5 when using particle swarm maximization. It is concluded that eigenanalysis of the ensemble correlation matrix not only provides valuable insight on how signal energy, jitter, and noise influence the estimation process, but it also leads to a one-step estimator which can make the way for a substantial reduction in computation time.
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| 30. |
- Laguna, Pablo, et al.
(författare)
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The STAFF III ECG database and its significance for methodological development and evaluation
- 2014
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Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 47:4, s. 408-417
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Forskningsöversikt (refereegranskat)abstract
- The development of new techniques for detection and characterization of transient myocardial ischemia has benefited considerably from the STAFF database, acquired in patients receiving elective prolonged percutaneous transluminal coronary angiography. The present article reviews a range of techniques developed and/or evaluated on the ECG signals of this database, including techniques for exploring abnormal intra-QRS potentials, QRS slopes, QRS angles, T wave morphology, T wave alternans, spatiotemporal ECG information, as well as heart rate dynamics. The detection of changes in body position is also briefly reviewed as it is intimately related to ischemia detection. (c) 2014 Elsevier Inc. All rights reserved.
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| 31. |
- Lázaro, Jesús, et al.
(författare)
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ECG-Derived Respiratory Rate in Atrial Fibrillation
- 2020
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 67:3, s. 905-914
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: The present study addresses the problem of estimating the respiratory rate from the mor- phological ECG variations in the presence of atrial fibrilla- tory waves (f-waves). The significance of performing f-wave suppression before respiratory rate estimation is investi- gated. Methods: The performance of a novel approach to ECG-derived respiration, named “slope range” (SR) and de- signed particularly for operation in atrial fibrillation (AF), is compared to that of two well-known methods based on ei- ther R-wave angle (RA) or QRS loop rotation angle (LA). A novel rule is proposed for spectral peak selection in respira- tory rate estimation. The suppression of f-waves is accom- plished using signal- and noise-dependent QRS weighted averaging. The performance evaluation embraces real as well as simulated ECG signals acquired from patients with persistent AF; the estimation error of the respiratory rate is determined for both types of signals. Results: Using real ECG signals and reference respiratory signals, rate estima- tion without f-wave suppression resulted in a median error of 0.015 ± 0.021 Hz and 0.019 ± 0.025 Hz for SR and RA, respectively, whereas LA with f-wave suppression resulted in 0.034 ± 0.039 Hz. Using simulated signals, the results also demonstrate that f-wave suppression is superfluous for SR and RA, whereas it is essential for LA. Conclusion: The results show that SR offers the best performance as well as computational simplicity since f-wave suppression is not needed. Significance: The respiratory rate can be robustly estimated from the ECG in the presence of AF.
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| 32. |
- Lazaro, Jesus, et al.
(författare)
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Electrocardiogram derived respiration from QRS slopes : Evaluation with stress testing recordings
- 2013
-
Ingår i: 2013 Computing in Cardiology. - 9781479908844 ; 40, s. 655-658
-
Konferensbidrag (refereegranskat)abstract
- A method for respiratory rate estimation from electrocardiogram (ECG), based on variations in QRS complexes slopes, is evaluated over stress testing recordings. Besides the 12 standard, and the 3 vectorcardiogram (VCG), 2 additional leads derived from the VCG are analyzed. A total of 34 slope series were studied, 2 for each lead: slopes between the peaks of the Q and R waves, and between the peaks of the R and S waves. Respiratory rate is estimated by using a time-frequency based algorithm which can combine information from several derived respiration signals. Evaluation was performed over a database containing ECG and respiratory signals simultaneously recorded from 30 subjects spontaneously breathing during a stress test. Respiratory rate estimation is performed with information of 4 different combinations of QRS slope series. The best results in respiratory rate estimation error terms are -1.07 ± 8.86% (-11.47 ± 37.97 mHz). These results suggest that proposed methods based on QRS slopes are highly suitable for respiratory rate estimation from ECG signal, specially at very non-stationary and noise scenarios as stress test.
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| 33. |
- Leandersson, Susanna, et al.
(författare)
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Estimation of respiration frequency using spatial information from the VCG
- 2003
-
Ingår i: Medical Engineering & Physics. - 1873-4030. ; 25:6, s. 501-507
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Tidskriftsartikel (refereegranskat)abstract
- A new method for extracting respiratory signals from the ECG/VCG is presented. The method is based on the alignment of an observed VCG loop to a reference loop with respect to the transformations of rotation and time synchronisation. The resulting series of estimated rotation angles reflects respiratory-induced changes in the electrical axis of the heart. The respiratory frequency is estimated by power spectral analysis of the derived respiration signal. The value of respiratory modulation of the heart rate is considered by analysing the cross power spectrum of the signals related to rotation angles and heart rate. For comparison, a respiratory signal derived from the QRS area of two different leads is implemented. The performance of the methods is validated on a database with simultaneously recorded VCG and respiratory signals acquired from 20 healthy subjects. The agreement between the respiratory frequencies obtained from the derived and the respiratory signals is presented. The angle-based respiratory signal is found to produce the best agreement with a gross median error of only 4.2%.
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| 34. |
- Martin-Yebra, Alba, et al.
(författare)
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QT interval Adaptation to Heart Rate Changes in Atrial Fibrillation as a Predictor of Sudden Cardiac Death
- 2022
-
Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294. ; 69:10, s. 3109-3118
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: The clinical significance of QT interval adaptation to heart rate changes has been poorly investigated in atrial fibrillation (AF), since QT delineation in the presence of f-waves is challenging. Therefore, the objective of the present study is to investigate new techniques for QT adaptation estimation in permanent AF. Methods: A multilead strategy based on generalized periodic component analysis is proposed for QT delineation, involving a spatial, linear transformation which emphasizes Twave periodicity and attenuates f-waves. QT adaptation is modeled by a linear, time-invariant filter, whose impulse response describes the dependence between the current QT interval and the preceding RR intervals, followed by a memoryless, possibly nonlinear, function. The QT adaptation time lag is determined from the estimated impulse response. Results: Using simulated ECGs in permanent AF, the transformed lead was found to offer more accurate QT delineation and time lag estimation than did the original ECG leads for a wide range of f-wave amplitudes (the time lag estimation error was found to be -0.2+/-0.6 s for SNR = 12 dB). In a population with chronic heart failure and permanent AF, the time lag estimated from the transformed lead was found to have the strongest, statistically significant association with sudden cardiac death (SCD) (hazard ratio = 3.49), whereas none of the original, orthogonal leads had any such association. Conclusions: Periodic component analysis provides more accurate QT delineation and improves time lag estimation in AF. A prolonged adaptation time of the QT interval to heart rate changes is associated with a high risk for SCD. Significance: This study demonstrates that SCD risk markers, originally developed for sinus rhythm, can also be used in AF, provided that Twave periodicity is emphasized. The time lag is a potentially useful marker for identifying patients at high risk for SCD, guiding clinicians in adopting effective therapeutic decisions.
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| 35. |
- Martínez Cortés, Juan Pablo, et al.
(författare)
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Risk stratification in congestive heart failure patients using a model-based approach to heart rate turbulence characterization
- 2009
-
Ingår i: Computers in Cardiology 2009, CinC 2009. - 9781424472819 ; 36, s. 337-340
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Konferensbidrag (refereegranskat)abstract
- Heart rate turbulence (HRT) is commonly assessed by two parameters: turbulence onset (TO) and turbulence slope (TS), both obtained by averaging RR tachograms following a ventricular premature beat (VPB). It has been recently shown that a model-based detection-theoretical approach results in HRT indices outperforming TO/TS in identifying the presence or absence of HRT. The aim of this work is to evaluate the risk stratification ability of this approach, as compared with the classical parameters TO and TS, in a population of 96 ischemic patients with mild to moderate congestive heart failure. We found signifi-cant differences (Mann-Withney U test) between survivors and cardiac death groups for TS and the new parameter TΣ(x). Survival analysis showed that TΣ(x) is the HRT index with highest association to risk of cardiac death (hazard ratio=2.8, p =0.008). Results show improved risk stratification of the new description of HRT with respect to classical parameters.
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| 36. |
- Minchole, Ana, et al.
(författare)
-
Detection of body position changes from the ECG using a Laplacian noise model
- 2014
-
Ingår i: Biomedical Signal Processing and Control. - : Elsevier BV. - 1746-8094. ; 14, s. 189-196
-
Tidskriftsartikel (refereegranskat)abstract
- Body position changes (BPCs) are manifested as shifts in the electrical axis of the heart, which may lead to ST changes in the ECG, misclassified as ischemic events. This paper presents a novel BPC detector based on a Laplacian noise model. It is assumed that a BPC can be modelled as a step-like change in the two coefficient series that result from the Karhunen-Loeve transform of the QRS complex and the ST-T segment. The generalized likelihood ratio test is explored for detection, where the statistical parameters of the Laplacian model are subject to estimation. Two databases are studied: one for assessing detection performance in healthy subjects who perform BPCs, and another for assessing the false alarm rate in ECGs recorded during percutaneous transluminal coronary angiography. The resulting probability of detection (P-D) and probability of false alarm (P-F) are 0.94 and 0.00, respectively, whereas the false alarm rate in ischemic recordings is 1 event/h. The proposed detector outperforms an existing detector based on the Gaussian noise model which achieved a P-D/P-F of 0.90/0.01 and a false alarm rate of 2 events/h. Analysis of the log-likelihood function for the Gaussian and Laplacian noise models show that latter model is more adequate. (C) 2014 Published by Elsevier Ltd.
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| 37. |
- Pueyo, Esther, et al.
(författare)
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QRS slopes for early ischemia detection and characterization
- 2008
-
Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 55:2, part 1, s. 468-477
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the upward (IUS) and downward (IDS) slopes of the QRS complex are proposed as indices for quantifying ischemia-induced electrocardiogram (ECG) changes. Using ECG recordings acquired before and during percutaneous transluminal coronary angioplasty (PTCA), it is found that the QRS slopes are considerably less steep during artery occlusion, in particular for IDS. With respect to ischemia detection, the slope indices outperform the often used high-frequency index (defined as the root mean square (rms) of the bandpass-filtered QRS signal for the frequency band 150-250 Hz) as the mean relative factors of change are much larger for IUS and IDS than for the high-frequency index (6.9 and 7.3 versus 3.7). The superior performance of the slope indices is equally valid when other frequency bands of the high-frequency index are investigated (the optimum one is found to be 125-175 Hz). Employing a simulation model in which the slopes of a template QRS are altered by different techniques, it is found that the slope changes observed during PTCA are mostly due to a widening of the QRS complex or a decrease of its amplitudes, but not a reduction of its high-frequency content or a combination of this and the previous effects. It is concluded that QRS slope information can be used as an adjunct to the conventional ST segment analysis in the monitoring of myocardial ischemia.
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| 38. |
- Ringborn, Michael, et al.
(författare)
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Evaluation of depolarization changes during acute myocardial ischemia by analysis of QRS slopes.
- 2011
-
Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 44:4, s. 416-424
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: This study evaluates depolarization changes in acute myocardial ischemia by analysis of QRS slopes. METHODS: In 38 patients undergoing elective percutaneous coronary intervention, changes in upward slope between Q and R waves and downward slope between R and S waves (DS) were analyzed. In leads V1 to V3, upward slope of the S wave was additionally analyzed. Ischemia was quantified by myocardial scintigraphy. Also, conventional QRS and ST measures were determined. RESULTS: QRS slope changes correlated significantly with ischemia (for DS: r = 0.71, P < .0001 for extent, and r = 0.73, P < .0001 for severity). Best corresponding correlation for conventional electrocardiogram parameters was the sum of R-wave amplitude change (r = 0.63, P < .0001; r = 0.60, P < .0001) and the sum of ST-segment elevation (r = 0.67, P < .0001; r = 0.73, P < .0001). Prediction of extent and severity of ischemia increased by 12.2% and 7.1% by adding DS to ST. CONCLUSIONS: The downward slope between R and S waves correlates with ischemia and could have potential value in risk stratification in acute ischemia in addition to ST-T analysis.
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| 39. |
- Romero, Daniel, et al.
(författare)
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Characterization of ventricular depolarization and repolarization changes in a porcine model of myocardial infarction
- 2012
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Ingår i: Physiological Measurement. - : IOP Publishing. - 0967-3334 .- 1361-6579. ; 33:12, s. 1975-1991
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Tidskriftsartikel (refereegranskat)abstract
- In this study, several electrocardiogram (ECG)-derived indices corresponding to both ventricular depolarization and repolarization were evaluated during acute myocardial ischemia in an experimental model of myocardial infarction produced by 40 min coronary balloon inflation in 13 pigs. Significant changes were rapidly observed from minute 4 after the start of coronary occlusion, achieving their maximum values between 11 and 22 min for depolarization and between 9 and 12 min for repolarization indices, respectively. Subsequently, these maximum changes started to decrease during the latter part of the occlusion. Depolarization changes associated with the second half of the QRS complex showed a significant but inverse correlation with the myocardium at risk (MaR) estimated by scintigraphic images. The correlation between MaR and changes of the downward slope of the QRS complex, I-DS, evaluated at the two more relevant peaks observed during the occlusion, was r = -0.75, p < 0.01 and r = -0.79, p < 0.01 for the positive and negative deflections observed in I-DS temporal evolution, respectively. Repolarization changes, analyzed by evaluation of ST segment elevation at the main observed positive peak, also showed negative, however non-significant correlation with MaR: r = -0.34, p = 0.28. Our results suggest that changes evaluated in the latter part of the depolarization, such as those described by I-DS, which are influenced by R-wave amplitude, QRS width and ST level variations simultaneously, correlate better with the amount of ischemia than other indices evaluated in the earlier part of depolarization or during the ST segment.
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| 40. |
- Romero, Daniel, et al.
(författare)
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Depolarization Changes During Acute Myocardial Ischemia by Evaluation of QRS Slopes: Standard Lead and Vectorial Approach
- 2011
-
Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 58:1, s. 110-120
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Tidskriftsartikel (refereegranskat)abstract
- Diagnosis and risk stratification of patients with acute coronary syndromes can be improved by adding information from the depolarization phase (QRS complex) to the conventionally used ST-T segment changes. In this study, ischemia-induced changes in the main three slopes of the QRS complex, upward (I-US) and downward (I-DS) slopes of the R wave as well as the upward (I-TS) slope of the terminal S wave, were evaluated as to represent a robust measure of pathological changes within the depolarization phase. From ECG recordings both in a resting state (control recordings) and during percutaneous coronary intervention (PCI)-induced transmural ischemia, we developed a method for quantification of I-US, I-DS, and I-TS that incorporates dynamic ECG normalization so as to improve the sensitivity in the detection of ischemia-induced changes. The same method was also applied on leads obtained by projection of QRS loops onto their dominant directions. We show that I-US, I-DS, and I-TS present high stability in the resting state, thus providing a stable reference for ischemia characterization. Maximum relative factors of change (R-I) during PCI were found in leads derived from the QRS loop, reaching 10.5 and 13.7 times their normal variations in the control for I-US and I-DS, respectively. For standard leads, the relative factors of change were 6.01 and 9.31. The I-TS index presented a similar behavior to that of I-DS. The timing for the occurrence of significant changes in I-US and I-DS varied with lead, ranging from 30 s to 2 min after initiation of coronary occlusion. In the present ischemia model, relative I-DS changes were smaller than ST changes in most leads, however with only modest correlation between the two indices, suggesting they present different information about the ischemic process. We conclude that QRS slopes offer a robust tool for evaluating depolarization changes during myocardial ischemia.
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| 41. |
- Romero, Daniel, et al.
(författare)
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Detection and quantification of acute myocardial ischemia by morphologic evaluation of QRS changes by an angle-based method
- 2013
-
Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 46:3, s. 204-214
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: In acute myocardial ischemia changes within the QRS complex can add valuable information to that from the repolarization phase. This study evaluates three angles obtained from the main slopes of the R-wave within the QRS complex to assess acute myocardial ischemia. Methods: The QRS angles, denoted by empty set(R) (R-wave angle), empty set(U) (up-stroke angle) and empty set(D) (down-stroke angle), were evaluated in 12-lead electrocardiogram (ECG) recordings of 79 patients before and during coronary occlusion by elective percutaneous coronary intervention (PCI). In a subset of 38 patients, ischemia was quantified by myocardial scintigraphy. Results: At baseline the QRS angles presented low variations. During occlusion, empty set(U) and empty set(D) developed a fast and abrupt change, whereas empty set(R) showed a smaller and gradual change. There were significant correlations between both maximal and sum of positive change in empty set(R) and ischemia: r = 0.67; p < 0:001 and r = 0.78; p <0.001, for extent, and r = 0.60; p < 0.001 and r = 0.73; p <0.001, for severity, respectively. Prediction of extent and severity of ischemia increased by 50% by adding empty set(R) changes to ST-segment changes, for LCX occlusions, whereas increased by 12.1% and 24.6% for LAD and RCA occlusions, respectively. No significant correlation was seen between empty set(u) and empty set(D) angles and ischemia. Conclusions: Evaluation of QRS angles from the standard 12-lead ECG represents a sensitive marker for detection of acute myocardial ischemia, whereas, empty set(R) changes can be used for prediction of its extent and severity. (C) 2013 Elsevier Inc. All rights reserved.
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| 42. |
- Solem, Kristian, et al.
(författare)
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Detection of Heart Rate Turbulence Using an Extended IPFM Model
- 2006
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Ingår i: [Host publication title missing]. - 0276-6574. ; 33, s. 905-908
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Konferensbidrag (refereegranskat)abstract
- In this study, the IPFM model is extended to account for the presence of ectopic beats and heart rate turbulence (HRT). Based on the model extension, a new approach to characterize HRT is presented based on a set of Karhunen- Loeve (KL) basis functions. The three most significant basis functions possess attractive physiological interpretations which reflect the difference in heart rate prior to the ventricular ectopic beat (VEB) compared to after HRT, an “average” HRT, and a delayed “average” HRT, respectively. HRT detection is based on the IPFM model extension, and involves a test statistic that results from a linear model. The HRT test statistic was studied on patients who underwent hemodialysis treatment. The goal was to distinguish between patients considered to be hypotensionresistant (HtR) and hypotension-prone (HtP). The results show that the test statistic of the two groups formed two non-overlapping clusters. The HtR-cluster exhibited much larger values than did the HtP-cluster (mean values 51 and 2, respectively), suggesting that HRT is mostly present in HtR patients.
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| 43. |
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| 44. |
- Solem, Kristian, et al.
(författare)
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Handling of ectopic beats in heart rate variability analysis using the heart timing signal
- 2004
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Ingår i: IFMBE Proceedings MEDICON and HEALTH TELEMATICS 2004 "X Mediterranean Conference on Medical and Biological Engineering".
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Konferensbidrag (refereegranskat)abstract
- The problem of analyzing heart rate variability in the presence of ectopic beats is revisited. Based on the IPFM model and the closely related heart timing signal, a new technique is introduced which corrects for the occasional presence of such beats. The correction technique, which involves the occurrence times of a certain number of beats preceding the ectopic, is computationally very efficient. Based on actual heart rate data, the results suggest that the power spectrum, and related clinical indices, are more accurately estimated.
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| 45. |
- Solem, Kristian, et al.
(författare)
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Performance evaluation of heart rate turbulence detection using an extended IPFM model
- 2007
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Ingår i: Computers in Cardiology. - 0276-6574. - 9781424425334 ; 34, s. 821-824
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Konferensbidrag (refereegranskat)abstract
- The well-known integral pulse frequency modulation (IPFM) model is used to generate the occurrence times of normal sinus rhythm. In a previous study, we extended the model to account for ectopic beats and subsequent variation in sinus rhythm that may accompany an ectopic beat; a phenomenon known as heart rate turbulence (HRT). Inspired by the extended model, a new approach to characterize HRT was presented, being based on Karhunen-Loeve basis functions. An HRT detection procedure was developed which involves a test statistic T(x), resulting from the generalized likelihood ratio test of a linear model. In this study, detector performance of T(x) is evaluated on both simulated and ECG data, and compared to the performance of turbulence onset (TO) and turbulence slope (TS). Two types of simulations were performed, both adding simulated heart rate variability and HRT to the input of the extended model. The first simulation evaluated HRT detection performance at different signal-to-noise-ratios (SNRs). The second simulation evaluated the influence of QRS detection inaccuracies on HRT detection. The performance was also studied on ventricular ectopic beats (VEBs) selected from 31 patients with myocardial ischemia. The relation between HRT and the degree of blood pressure reduction induced by a VEB (estimated as proportional to the sum of the coupling interval and the compensatory pause), as well as the relation between HRT and heart rate, were analysed. The simulation results at different SNRs showed that T(x) performs dramatically better than TO and TS. With a 95% sensitivity (Sn), the specificity (Sp) at 5 dB SNR was 94% for T(x), 51% for TO, and 64% for TS. The detection performance of T(x) was equally superior when assuming that QRS jitter was Gaussian with 1 ms std: with Sn=95%, Sp was 99% for T(x), 40% for TO, and 68% for TS. Based on the ECG data, it was found that the degree of blood pressure reduction is essentially proportional to the magnitude of the HRT; this finding was reflected by T(x), TO, as well as TS. Moreover, the three HRT parameters were found to be linearly related to heart rate: low heart rates was associated with large HRT and high heart rates with small HRT. This linear relation is probably due to that a VEB during low heart rates induces a larger blood pressure reduction than during high heart rates.
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| 46. |
- Sornmo, Leif, et al.
(författare)
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Spectral Analysis of Heart Rate Variability in Time-Varying Conditions and in the Presence of Confounding Factors
- 2022
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Ingår i: IEEE Reviews in Biomedical Engineering. - 1937-3333. ; , s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- The tools for spectrally analyzing heart rate variability (HRV) has in recent years grown considerably, with emphasis on the handling of time-varying conditions and confounding factors. Time–frequency analysis holds since long an important position in HRV analysis, however, this technique cannot alone handle a mean heart rate or a respiratory frequency which vary over time. Overlapping frequency bands represents another critical condition which needs to be dealt with to produce accurate spectral measurements. The present survey offers a comprehensive account of techniques designed to handle such conditions and factors by providing a brief description of the main principles of the different methods. Several methods derive from a mathematical/statistical model, suggesting that the model can be used to simulate data used for performance evaluation. The inclusion of a respiratory signal, whether measured or derived, is another feature of many recent methods, e.g., used to guide the decomposition of the HRV signal so that signals related as well as unrelated to respiration can be analyzed. It is concluded that the development of new approaches to handling time-varying scenarios are warranted, as is benchmarking of performance evaluated in technical as well as in physiological/clinical terms.
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| 47. |
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| 48. |
- Varon, Carolina, et al.
(författare)
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A Comparative Study of ECG-derived Respiration in Ambulatory Monitoring using the Single-lead ECG
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Cardiorespiratory monitoring is crucial for the diagnosis and management of multiple conditions such as stress and sleep disorders. Therefore, the development of ambulatory systems providing continuous, comfortable, and inexpensive means for monitoring represents an important research topic. Several techniques have been proposed in the literature to derive respiratory information from the ECG signal. Ten methods to compute single-lead ECG-derived respiration (EDR) were compared under multiple conditions, including different recording systems, baseline wander, normal and abnormal breathing patterns, changes in breathing rate, noise, and artifacts. Respiratory rates, wave morphology, and cardiorespiratory information were derived from the ECG and compared to those extracted from a reference respiratory signal. Three datasets were considered for analysis, involving a total 59 482 one-min, single-lead ECG segments recorded from 156 subjects. The results indicate that the methods based on QRS slopes outperform the other methods. This result is particularly interesting since simplicity is crucial for the development of ECG-based ambulatory systems.
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