| 1. |
- Berg, Jonathan, et al.
(författare)
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Ventricular longitudinal function by cardiovascular magnetic resonance predicts cardiovascular morbidity in HFrEF patients
- 2022
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Ingår i: ESC Heart Failure. - : Wiley. - 2055-5822. ; 9:4, s. 2313-2324
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Ventricular longitudinal function measured as basal-apical atrioventricular plane displacement (AVPD) or global longitudinal strain (GLS) is a potent predictor of mortality and could potentially be a predictor of heart failure-associated morbidity. We hypothesized that low AVPD and GLS are associated with the combined endpoint of cardiovascular mortality and heart failure-associated morbidity. Methods and results: Two hundred eighty-seven patients (age 62 ± 12 years, 78% male) with heart failure with reduced (≤40%) ejection fraction (HFrEF) referred to a cardiovascular magnetic resonance exam were included. Ventricular longitudinal function, ventricular volume, and myocardial fibrosis or infarction were analysed from cine and late gadolinium enhancement images. National registries provided data on causes of cardiovascular hospitalizations and cardiovascular mortality for the combined endpoint. Time-to-event analysis capable of including reoccurring events was employed with a 5-year follow-up. HFrEF patients had EF 26.5 ± 8.0%, AVPD 7.8 ± 2.4 mm, and GLS −7.5 ± 3.0%. In contrast, ventricular longitudinal function was approximately twice as large in an age-matched control group (AVPD 15.3 ± 1.6 mm; GLS −20.6 ± 2.0%; P < 0.001 for both). There were 578 events in total, and the majority were HF hospitalizations (n = 418). Other major events were revascularizations (n = 64), cardiovascular deaths (n = 40), and myocardial infarctions (n = 21). One hundred fifty-five (54%) patients experienced at least one event (mean 2.0, range 0–64). Of these patients, 119 (71%) had three events or fewer, and the first three events comprised 51% of all events (295 events). Patients in the bottom AVPD or GLS tertile (<6.8 mm or >−6.1%) overall experienced more than 3 times as many events as the top tertile (>8.8 mm or <−8.4%; P < 0.001). Patients in this tertile also faced more cardiovascular deaths (P < 0.05), HF hospitalizations (P = 0.001), myocardial infarctions (only GLS: P = 0.032), and accumulated longer in-hospital length-of-stay overall (AVPD 20.9 vs. 9.1 days; GLS 22.4 vs. 6.5 days; P = 0.001 for both), and from HF hospitalizations (AVPD 19.3 vs. 8.3 days; GLS 19.3 vs. 5.4 days; P = 0.001 for both). In multivariate analysis adjusted for significant covariates, AVPD and GLS remained independent predictors of events (hazard ratio 1.12 per-mm-decrease and 1.13 per-%-increase) alongside hyponatremia (<135 mmol/L), aetiology of HF, and LV end-diastolic volume index. Conclusions: Low ventricular longitudinal function is associated with an increase in number of events as well as longer in-hospital stay from cardiovascular causes. In addition, AVPD and GLS have independent prognostic value for cardiovascular mortality and morbidity in HFrEF patients.
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| 2. |
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| 3. |
- Cordtz, Joakim, et al.
(författare)
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Central venous oxygen saturation and thoracic admittance during dialysis: New approaches to hemodynamic monitoring
- 2008
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Ingår i: Hemodialysis International. - : Wiley. - 1542-4758 .- 1492-7535. ; 12:3, s. 369-377
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Tidskriftsartikel (refereegranskat)abstract
- Intradialytic hypotension (IDH) is one of the most important short-term complications to hemodialysis (HD). Inadequate cardiac filling due to a reduction in the central blood volume is believed to be a major etiological factor. The aim of this study was to evaluate whether these pathophysiologic events are reflected in the central venous oxygen saturation (ScO2) and thoracic admittance (TA) during dialysis. Twenty ambulatory HD patients, 11 hypotension prone (HP) and 9 hypotension resistant, with central vascular access, were monitored during 3 HD sessions each. ScO2, TA, finger blood pressure (BP), and relative change in blood volume (Delta BV) were measured and sampled continuously. The relative TA decrease and Delta BV were both largest in the HP group (p < 0.05 for both), whereas ScO2 decreased only in HP patients (p < 0.001). Baseline TA was lower in the HP group (p < 0.01). Changes in ScO2 and TA correlated much closer than did changes in ScO2 and Delta BV (r=0.43 and 0.18, respectively). Our results suggest that an intradialytic decrease in cardiac output, as reflected by a fall in ScO2, is a common feature to HD patients prone to IDH. In patients using a central vascular access, ScO2 and TA measurements may be more specific to the pathophysiologic events preceding IDH than Delta BV-the current standard monitoring method.
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| 4. |
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| 5. |
- Holmer, Mattias
(creator_code:cre_t)
-
Detecting blood path disruption in extracorporeal blood processing
- 2015
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Patent (övrigt vetenskapligt/konstnärligt)abstract
- A device monitors a blood path from a blood vessel access of a human subject through an extracorporeal blood processing apparatus and back to the blood vessel access. A pumping device in the blood path is operable to pump blood through the blood path from the blood withdrawal device to the blood return device. The monitoring device obtains pressure data from a pressure sensor arranged upstream of the pumping device in the blood path, and processes the pressure data for detection of a disruption of the blood path downstream of the pumping device, e.g. caused by VND (Venous Needle Dislodgement). The disruption is detected by evaluating presence/absence of cross-talk pulses at the pressure sensor, where the cross-talk pulses originate from one or more pulse generators in the extracorporeal blood processing apparatus and have propagated on a propagation path in a direction downstream of the pumping device through the blood return device, the blood vessel access and the blood withdrawal device to the pressure sensor.
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| 6. |
- Holmer, Mattias, et al.
(författare)
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Determining Heart Activity Present in the Pressure Sensors of a Dialysis Machine
- 2013
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Ingår i: Computing in Cardiology. - 2325-8861. ; , s. 217-220
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Konferensbidrag (refereegranskat)abstract
- Determination of heart status during dialysis can im- prove patient monitoring. Pressure sensors in the dialysis machine measures the heart pulses that propagates in the body and enter the extracorporeal blood circuit. A peri- staltic blood pump, located in the same circuit, introduces strong periodic pressure pulses that interfere with the much weaker cardiac component. These signal characteristics make the extraction of the heart activity challenging. In the present study, we explore the possibility to extract and analyze the cardiac component using simulated data. The accuracy of the timing of each heartbeat is analyzed. Ad- ditionally, the heart component is extracted from patient pressure recordings, and compared to the heart rate com- puted from a photoplethysmogram. The results show that heart timings can be accurately determined using the pres- sure sensors of a dialysis machine.
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| 7. |
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| 8. |
- Holmer, Mattias, et al.
(författare)
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Extracting a Cardiac Signal From the Extracorporeal Pressure Sensors of a Hemodialysis Machine
- 2015
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 62:5, s. 1305-1315
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Tidskriftsartikel (refereegranskat)abstract
- Although patients undergoing hemodialysis treatment often suffer from cardiovascular disease, monitoring of cardiac rhythm is not performed on a routine basis. Without requiring any extra sensor, this study proposes a method for extracting a cardiac signal from the built-in extracorporeal venous pressure sensor of the hemodialysis machine. The extraction is challenged by the fact that the cardiac component is much weaker than the pressure component caused by the peristaltic blood pump. To further complicate the extraction problem, the cardiac component is difficult to separate when the pump and heart rates coincide. The proposed method estimates a cardiac signal by subtracting an iteratively refined blood pump model signal from the signal measured at the extracorporeal venous pressure sensor. The method was developed based on simulated pressure signals, and evaluated on clinical pressure signals acquired during hemodialysis treatment. The heart rate estimated from the clinical pressure signal was compared to that derived from a photoplethysmographic reference signal, resulting in a difference of 0.07 +/- 0.84 beats/min. The accuracy of the heartbeat occurrence times was studied for different strengths of the cardiac component, using both clinical and simulated signals. The results suggest that the accuracy is sufficient for analysis of heart rate and certain arrhythmias.
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| 9. |
- Holmer, Mattias, et al.
(författare)
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Heart Rate Estimation from Dual Pressure Sensors of a Dialysis Machine
- 2015
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Ingår i: 2015 Computing in Cardiology Conference (CinC). - 2325-8861. ; 42, s. 29-32
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Konferensbidrag (refereegranskat)abstract
- Dialysis patients often suffer from cardiovascular dis- eases, motivating the use of continuous monitoring of car- diac activity in clinical routine. Cardiac pressure pulses propagate through the vascular system and enter the ex- tracorporeal blood circuit of a dialysis machine, where the pulses are captured by pressure sensors. The cardiac pulses are obscured by the much stronger pressure pulses originating from the peristaltic blood pump. We have pre- viously shown that a cardiac signal can be extracted from the venous pressure signal. However, that method has been found to perform less well at very low cardiac pressure pulse amplitudes. In the present study, we propose a novel method which addresses this issue by using the signals from both the arterial and the venous pressure sensors. The method is compared to the previous method on clini- cal data using a photoplethysmogram as reference. The re- sults suggests that heart rate can be estimated more accu- rately from pressure signals with lower cardiac signal am- plitude when both arterial and venous pressure are used, compared to when only the venous signal is used.
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| 10. |
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| 11. |
- Holmer, Mattias, et al.
(författare)
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On-line Heart Rate Monitoring Using the Extra-corporeal Pressure Sensors of a Dialysis Machine
- 2012
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Ingår i: Biomedical engineering – 2012 : proceedings of international conference. - 2029-3380.
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Konferensbidrag (refereegranskat)abstract
- Heart rate can be extracted from the extracorporeal venous pressure signal of a dialysis machine. The results are of comparable accuracy and reliability to the ones obtained by the PPG reference signal from a pulse oximeter. Difficulties that occur during heart rate estimation were determined, and some can be overcome by a slight adjustment of blood flow rate. The described techniques, after being implemented into the dialysis machines, would help to improve current hemodialysis safety throughout the treatment by on-line monitoring of the cardiac activity.
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| 12. |
- Olde, Bo
(creator_code:cre_t)
-
Filtering of a time-dependent pressure signal
- 2015
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Patent (övrigt vetenskapligt/konstnärligt)abstract
- A device removes first pulses in a pressure signal of a pressure sensor which is arranged in a fluid containing system to detect the first pulses, which originate from a first pulse generator, and second pulses, which originate from a second pulse generator. The first pulse generator is known to operate in a sequence of pulse cycles, each pulse cycle resulting in at least one first pulse. The device repetitively obtains a current data sample, calculates corresponding a reference value and subtracts the reference value from the current data sample. The reference value is calculated as a function of other data sample(s) in the same pressure signal.; These data sample(s) may be either cycle-synchronized so as to have a corresponding location in one or more other pulse cycles (e.g. in a preceding pulse cycle) as the current data sample, or be located in proximity to the current data sample. The fluid containing system may include an extracorporeal blood flow circuit, e.g. as part of a dialysis machine, and a cardiovascular system of a human patient.
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| 13. |
- Sandberg, Frida, et al.
(författare)
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Estimation of Respiratory Information from the Built-In Pressure Sensors of a Dialysis Machine
- 2014
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Ingår i: [Host publication title missing]. - 0276-6574. ; 41, s. 853-856
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Konferensbidrag (refereegranskat)abstract
- The purpose of the present study is to determine the feasibility of estimating respiratory information from the built-in pressure sensors of a dialysis machine. The study database consists of simultaneous recordings of pressure signals and capnographic signals from 6 patients during 7 hemodialysis treatment sessions. Respiration rates were estimated using respiratory induced variations in the beat- to-beat interval series of the cardiac component of the pressure signal and respiratory induced baseline varia- tions in the pressure signal, respectively. The estimated respiration rates were compared to a reference respira- tion rate determined from the capnograhpic signal. The root-mean-square error of the estimated respiration rate from the baseline variations of the pressure signal was 2.10 breaths/min; the corresponding error of the estimated res- piration rate from the beat-to-beat interval series of the cardiac component was 4.95 breaths/min. The results sug- gest that it is possible to estimate respiratory information from the pressure sensors.
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| 14. |
- 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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| 15. |
- 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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| 16. |
- Seemann, Felicia, et al.
(författare)
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Quantification of left ventricular contribution to stroke work by longitudinal and radial force-length loops
- 2020
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Ingår i: Journal of Applied Physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 129:4, s. 880-890
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Tidskriftsartikel (refereegranskat)abstract
- Left ventricular (LV) stroke work (SW) is calculated from the pressure-volume (PV) loop. PV loops do not contain information on longitudinal and radial pumping, leaving their contributions to SW unknown. A conceptual framework is proposed to derive the longitudinal and radial contributions to SW, using ventricular force-length loops reflecting longitudinal and radial pumping. The aim of this study was to develop and validate this framework experimentally and to explore these contributions in healthy controls and heart failure patients. Thirteen swine underwent cardiovascular magnetic resonance (CMR) and LV pressure catheterization at baseline (n = 7) or 1 wk after myocardial infarction (n = 6). CMR and noninvasive PV loop quantification were performed on 26 human controls and 14 patients. Longitudinal and radial forces were calculated as LV pressure multiplied by the myocardial surface areas in the respective directions. Length components were defined as the atrioventricular plane and epicardial displacements, respectively. Contributions to SW were calculated as the area within the respective force-length loop. Summation of longitudinal and radial SW had excellent agreement with PV loop-derived SW (ICC = 0.95, R = 0.96, bias + SD = = 4.5 + 5.4%) in swine. Longitudinal and radial contributions to SW were ~50/50% in swine and human controls, and 44/56% in patients. Longitudinal pumping required less work than radial to deliver stroke volume in swine (6.8 + 0.8 vs. 8.7 + 1.2 mJ/mL, P = 0.0002) and in humans (11 + 2.1 vs. 17 + 4.7 mJ/mL, P < 0.0001). In conclusion, longitudinal and radial pumping contribute ~50/50% to SW in swine and human controls and 44/56% in heart failure patients. Longitudinal pumping is more energy efficient than radial pumping in delivering stroke volume.
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| 17. |
- Smith, Danny, et al.
(författare)
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Heart Rate Turbulence Detection Using Mean Shape Information
- 2009
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Ingår i: CINC: 2009 36th Annual Computers in Cardiology Conference. - 0276-6574. ; , s. 153-156
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Konferensbidrag (refereegranskat)abstract
- In this study, we propose a generalized likelihood ratio test statistic for detection of heart rate turbulence (HRT) based on a linear signal model. The new test statistic, which expands our previous original detector; takes a priori information regarding HRT shape into account. The detector structure is based on the extended integral pulse frequency modulation model which accounts for the presence of ectopic beats and HRT 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 performance was studied for both simulated data and real data obtained from the Long-Term ST database. The results show that the new detector is superior to the original one as well as to the commonly used parameter turbulence slope (TS) on both types of data.
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| 18. |
- 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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| 19. |
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| 20. |
- Solem, Kristian, et al.
(författare)
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An efficient method for handling ectopic beats using the heart timing signal
- 2006
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 53:1, s. 13-20
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Tidskriftsartikel (refereegranskat)abstract
- The problem of analyzing heart rate variability in the presence of ectopic beats is revisited. Based on the integral pulse frequency modulation model and the closely related heart timing signal, a new technique is introduced which corrects for the occasional presence of ectopic beats. The correction technique, which involves the occurrence times of a certain number of beats preceding the ectopic beat, is computationally very efficient. From actual heart rate data, the results show that the new technique is associated with a much lower computational complexity (flops reduced by a factor of about 3000) than the original heart timing technique, while producing similar performance. It is also shown that the power spectrum and related clinical indices obtained by the new technique are more accurately estimated than by other methods.
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| 21. |
- Solem, Kristian, et al.
(författare)
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An electrocardiogram-based method for early detection of abrupt changes in blood pressure during hernodialysis
- 2006
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Ingår i: ASAIO Journal. - : Ovid Technologies (Wolters Kluwer Health). - 1538-943X .- 1058-2916. ; 52:3, s. 282-290
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Tidskriftsartikel (refereegranskat)abstract
- Clinical techniques for early detection of acute hypotension during conventional hemodialysis treatment are lacking, even though intradialytic hypotension is the most common acute complication. In this article, intradialytic hypotension is identified by means of signal analysis of data recorded at two clinics. The database consists of 30 treatments with concurrently acquired signals: the 12-lead electrocardiogram, continuous blood pressure, hematocrit, oxygen saturation, relative blood volume, and important hemodialysis variables. This article presents two characteristics, a heart rate turbulence (HRT) measure called turbulence slope (TS), and the LF/HF ratio, which provide information, at the beginning of hemodialysis treatment, on the patient's propensity to hypotension (TS: p = 0.0038, and LF/HF ratio: p = 0.0028). The authors also present a novel dynamic echocardiography-based method for detecting intradialytic hypotension using complementary information on heart rate variability (HRV) and ectopic beat patterns. These two types of information reflect different mechanisms of cardiac activity. It is essential that both types are used for the detection of hypotension, because HRV analysis is inappropriate when several ectopic beats are present. The proposed dynamic echocardiography-based method offers early identification of the cases with acute intradialytic hypotension of the database.
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| 22. |
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| 23. |
- Solem, Kristian, et al.
(författare)
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Detection of Heart Rate Turbulence Using an Extended IPFM Model
- 2006
-
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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| 24. |
- Solem, Kristian, et al.
(författare)
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Detection of hypotension during hemodialysis using the ECG
- 2004
-
Ingår i: [Host publication title missing]. - 0780389271 ; 31, s. 717-720
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Konferensbidrag (refereegranskat)abstract
- There is today a lack of clinical techniques for detecting acute hypotension during conventional hemodialysis treat -ment, despite the fact that hypotension remains the - mosr common acute complication during hemodialysis. Hypotension is often followed by nausea, vomiting, and even fainting, not only strenuous for the patient but requires considerable attention from the nursing staf. The problem of detecting hypotension was studied by means of a multimodal database. The database consists of 30 treatments in which each treatment includes several simultaneously acquired signals. Acute .symptomatic hypotension occurred in 2 of the 30 treatments. An ECG-based method for detecting hypotension has been developed. n e method involves information on heart rate variability (HRV) and ectopic beat patterns. The proposed method does not only detect the two cases of acute hypotension but also provides information of the patient's propensity to hypotension at an early stage of hemodialysis.
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| 25. |
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| 26. |
- Solem, Kristian, et al.
(författare)
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Handling of ectopic beats in heart rate variability analysis using the heart timing signal
- 2004
-
Ingår i: IFMBE Proceedings MEDICON and HEALTH TELEMATICS 2004 "X Mediterranean Conference on Medical and Biological Engineering".
-
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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| 27. |
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| 28. |
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| 29. |
- 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
-
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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| 30. |
- 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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| 31. |
- Solem, Kristian, et al.
(författare)
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Prediction of Intradialytic Hypotension Using Photoplethysmography
- 2010
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 57:7, s. 1611-1619
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Tidskriftsartikel (refereegranskat)abstract
- Intradialytic hypotension is the most common acute complication during conventional hemodialysis treatment. Prediction of such events is highly desirable in clinical routine for prevention. This paper presents a novel prediction method of acute symptomatic hypotension in which the photoplethysmographic signal is analyzed with respect to changes in amplitude, reflecting vasoconstriction, and cardiac output. The method is based on a statistical model in which the noise is assumed to have Laplacian amplitude distribution. The performance is evaluated on 11 hypotension-prone patients who underwent hemodialysis treatment, resulting in seven events with acute symptomatic hypotension and 17 without. The photoplethysmographic signal was continuously acquired during treatment as was information on blood pressure and oxygen saturation. Using leave-one-out cross validation, the proposed method predicted six out of seven hypotensive events, while producing 1 false prediction out of 17 possible. The performance was achieved when the prediction threshold was chosen to be in the range 57%-65% of the photoplethysmographic envelope at treatment onset.
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| 32. |
- Solem, Kristian
(författare)
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Signal Modeling and Detection in Nephrologic and Cardiac Applications
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This doctoral thesis is comprised of five parts in the field of biomedical signal processing with focus on methods for use in hemodialysis as well as in cardiac applications. The problem of predicting hypotension is the main concern in the parts were data from patients undergoing hemodialysis are used. In Part I, a newly developed method for heart rate variability (HRV) analysis in the presence of ectopic beats, based on the recently published heart timing (HT) signal, is presented. The derived HRV method deals efficiently with the ectopic beats and is shown to have better performance than other existing methods as well as to be computationally very efficient. In Part II, the method from Part I is used to analyze the problem of hypotension on a database acquired from patients during hemodialysis. In addition, Part II also investigates other aspects from the ECG signal, namely, heart rate turbulence (HRT) and ectopic beat count (EBC). A method for early detection of hypotension, involving HRV and EBC analysis, is introduced, found to detect the cases of acute dialysis induced hypotension. It is suggested that the LF/HF ratio of the HRV spectrum and HRT are useful quantities for classifying patients as being either resistant or prone to hypotension. The integral pulse frequency modulation (IPFM) model is extended to account for the presence of ectopic beats and HRT in Part III. Based on this model, a new test statistic to detect and characterize HRT is presented. Three simulations were performed for the purpose of studying the influence of signal-to-noise ratio (SNR), QRS jitter, and ECG sampling rate on detector performance. The results show that the test statistic performs better in all simulations than do the commonly used parameters turbulence onset (TO) and turbulence slope (TS). In Part IV, the detector structure presented in Part III is further developed. A new detector, obtained from introducing a priori information to the detector structure, is presented. The a priori information consists of the average HRT shape and magnitude reflected in a weight vector. The results showed that the performance of the new detector outperformed that of the previously presented test statistic and TS on both simulations and real ECG data. Part V introduces a new method for prediction of intradialytic hypotension based on pulse oximetry. The method is based on a measure denoted relative magnitude of capillary pulse (RMCP), which reflects capillary vasoconstriction and cardiac output. The proposed method is able to predict all the cases in this study with acute intradialytic hypotension without producing any false alarms. In general, the prediction occurs early in time, allowing clinical staff to take actions to prevent the onset of hypotension or to alleviate symptoms.
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| 33. |
- Sörnmo, Leif, et al.
(författare)
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Noninvasive techniques for prevention of intradialytic hypotension
- 2012
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 5, s. 45-59
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Tidskriftsartikel (refereegranskat)abstract
- Episodes of hypotension during hemodialysis treatment constitutes an important clinical problem which has received considerable attention in recent years. Despite the fact that numerous approaches to reducing the frequency of intradialytic hypotension (IDH) have been proposed and evaluated, the problem has not yet found a definitive solution--an observation which, in particular, applies to episodes of acute, symptomatic hypotension. This overview covers recent advances in methodology for predicting and preventing IDH. Following a brief overview of well-established hypotension-related variables, including blood pressure, blood temperature, relative blood volume, and bioimpedance, special attention is given to electrocardiographic and photoplethysmographic (PPG) variables and their significance for IDH prediction. It is concluded that cardiovascular variables which reflect heart rate variability, heart rate turbulence, and baroreflex sensitivity are important to explore in feedback control hemodialysis systems so as to improve their performance. The analysis of hemodialysis-related changes in PPG pulse wave properties hold considerable promise for improving prediction.
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