| 1. |
- 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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| 2. |
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| 3. |
- Corino, V. D. A., et al.
(författare)
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A Gaussian mixture model for time-frequency analysis during atrial fibrillation electrocardiograms
- 2007
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Ingår i: 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS 2007.. - 1557-170X. - 9781424407880 ; , s. 271-274
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Konferensbidrag (refereegranskat)abstract
- During atrial fibrillation (AF), time-frequency analysis of atrial signal has been applied to describe fibrillatory frequency trends. Recently, temporal changes in spectral shape have been investigated using the spectral profile technique. This profile is computed recursively by fitting each short-time log-spectrum to a spectral template, using amplitude scaling and frequency shifting. The purpose of the present study was to develop a Gaussian mixture model of the spectral profile in order to characterize the shape of AF waveforms. A novel index is introduced, the so-called harmonic index (HI), which reflects properties of the fundamental frequency peak and related harmonics peaks as estimated from the model. The index was tested on recordings from 9 patients with persistent AF, obtained before and after exercise testing. The HI succeeded in monitoring the response to exercise, i.e. change in the spectral profile to a less harmonic pattern, which is consistent with a reduction in AF organization (HI: 0.61±0.11 vs. 0.50±0.19, rest vs. exercise; p≪0.05).
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| 4. |
- Floreby, L, et al.
(författare)
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Boundary finding using Fourier surfaces of increasing order
- 1998
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Ingår i: Proceeedings of the Fourteenth International Conference on Pattern Recognition. - 1051-4651. - 0818685123 ; 1, s. 465-467
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Konferensbidrag (refereegranskat)abstract
- Boundary finding in simulated medical images is performed by optimizing the Fourier coefficients in a parametric surface representation with respect to an objective function. The deformable model is fitted to the data using the brightness gradient component which is normal to the surface. A low order (<10) Fourier series expansion offers a sufficiently accurate representation for many inherently smooth objects that occur in medical imaging. Experimental results are presented for simulated image objects corresponding to organs of the anthropomorphic Zubal phantom. Two different optimization methods are studied concerning robustness and computational efficiency. The effect of increasing the Fourier expansion order is investigated for various noise levels
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| 5. |
- Floreby, L, et al.
(författare)
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Deformable Fourier surfaces for volume segmentation in SPECT
- 1998
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Ingår i: Proceeedings of the Fourteenth International Conference on Pattern Recognition. - 1051-4651. - 0818685123 ; 1, s. 358-360
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Konferensbidrag (refereegranskat)abstract
- Three-dimensional boundary finding based on Fourier surface optimization is presented as a method for segmentation of SPECT images. Being robust against noise and adjustable with respect to its detail resolution, it forms an interesting alternative in this application area. A three-dimensional approach can also be assumed to increase the possibility of delineating low contrast regions, as compared to a two-dimensional slice-by-slice approach. We apply boundary finding to Monte Carlo simulated SPECT images of the computer-based anthropomorphic Zubal phantom in order to evaluate the influence of object contrast and noise on the segmentation accuracy. Segmentation is also performed in real patient images
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| 6. |
- Gil, E., et al.
(författare)
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Detection of heart rate turbulence in photoplethysmographic signals
- 2011
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Ingår i: 2011 Computing in Cardiology. - 9781457706127 - 9781457706110 ; 38, s. 665-668
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Konferensbidrag (refereegranskat)abstract
- In this study, alterations in the cardiovascular system caused by ventricular premature beats (VPBs) are investigated by analyzing the photoplethysmographic (PPG) signal. A simple algorithm for PPG-based detection of VPBs is devised and evaluated, and then employed for the analysis of heart rate turbulence (HRT), here labelled "pulse rate turbulence" (PRT). The pulse transit time is also studied as it constitutes the main difference between HRT and PRT. The data sets included a total of 3872 VPBs and 13169 normal beats. The results showed that VPBs can be detected from the PPG signal with a sensitivity of 92.8%, a specificity of 99.8% and an accuracy of 99.3%, using six features and a simple linear classifier. The shape of PRT was found to resemble that of HRT, the latter type of turbulence resulting from ECG-based analysis, suggesting that PRT analysis can be used as a replacement for HRT analysis when the ECG is not available.
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| 7. |
- Hernando, D., et al.
(författare)
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Heart rate variability during hemodialysis and its relation to hypotension
- 2011
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Ingår i: Computing in Cardiology 2011, CinC 2011. - 9781457706127 ; 38, s. 189-192
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Konferensbidrag (refereegranskat)abstract
- Acute hypotensive episodes are common during dialysis sessions, and represent a serious problem. Spectral analysis of heart rate variability (HRV) and barorrefle x sensitivity (BRS) is performed to study the behaviour of the autonomic nervous system (ANS) during the hemodialysis. The ratio between the low frequency (LF) and high frequency (HF) power of HRV, as well as BRS in the HF band, are significantly different in patients being prone and resistant to hypotension (p<0.001 and p<0.05, respectively). Moreover, a very low frequency (VLF) modulation visible in HRV, blood pressure and the series of rotation angles of the heart's electrical axis have been studied. It turns out that the VLF component is more pronounced and with higher coherence in prone patients (p<0.05), suggesting a possible relation with altered or imbalanced ANS regulation.
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| 8. |
- Holmer, M, et al.
(författare)
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Cardiac signal estimation based on the arterial and venous pressure signals of a hemodialysis machine
- 2016
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Ingår i: Physiological Measurement. - 0967-3334. ; 37:9, s. 1499-1515
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Tidskriftsartikel (refereegranskat)abstract
- Continuous cardiac monitoring is usually not performed during hemodialysis treatment, although a majority of patients with kidney failure suffer from cardiovascular disease. In the present paper, a method is proposed for estimating a cardiac pressure signal by combining the arterial and the venous pressure sensor signals of the hemodialysis machine. The estimation is complicated by the periodic pressure disturbance caused by the peristaltic blood pump, with an amplitude much larger than that of the cardiac pressure signal. Using different techniques for combining the arterial and venous pressure signals, the performance is evaluated and compared to that of an earlier method which made use of the venous pressure only. The heart rate and the heartbeat occurrence times, determined from the estimated cardiac pressure signal, are compared to the corresponding quantities determined from a photoplethysmographic reference signal. Signals from 9 complete hemodialysis treatments were analyzed. For a heartbeat amplitude of 0.5 mmHg, the median absolute deviation between estimated and reference heart rate was 1.3 bpm when using the venous pressure signal only, but dropped to 0.6 bpm when combining the pressure signals. The results show that the proposed method offers superior estimation at low heartbeat amplitudes. Consequently, more patients can be successfully monitored during treatment without the need of extra sensors. The results are preliminary, and need to be verified on a separate dataset.
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| 9. |
- Husser, O., et al.
(författare)
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Exercise testing for non-invasive assessment of atrial electrophysiology in patients with persistent atrial fibrillation
- 2006
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Ingår i: 2006 Computers in Cardiology, CIC. - 1424425328 - 9781424425327 ; 33, s. 21-24
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Konferensbidrag (refereegranskat)abstract
- The abstract with its heading should not be more than 75 mm long. This is equivalent to 18 lines of text. Leave 1 line space at the bottom of the abstract before continuing with the next heading. The autonomic nervous system modulates atrial electrophysiology in atrial fibrillation (AF). The purpose of this study was (1) to non-invasively characterize the effects of exercise on atrial fibrillatory rate as marker of atrial refractoriness in patients with persistent AF and (2) to identify clinical and electrocardiographic predictors for rate response. In 15 patients with persistent AF, mean fibrillatory rate assessed by spatiotemporal QRST cancellation and time-frequency analysis remained unchanged with exercise. There were, however, 6 responders (rate change > 2.5%), with either a rate increase (N=5, 25±9 fpm) or decrease (N=1, -13 fpm). Absolute fibrillatory rate change (%) correlated inversely with baseline fibrillatory rate (r= -0.543, p=.045). In conclusion, sympathetic activation by exercise modulates atrial electrophysiology in some patients which can be monitored using time-frequency analysis. Higher baseline fibrillatory rates are associated with less autonomic modulation indicating advanced electrical remodeling.
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| 10. |
- Iozzia, L., et al.
(författare)
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Atrial Impulses at the Atrioventricular Node: Arrival versus Conduction during Atrial Fibrillation
- 2015
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Ingår i: 16th Nordic-Baltic Conference on Biomedical Engineering. - Cham : Springer International Publishing. - 9783319129662 - 9783319129679 ; , s. 100-103
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Konferensbidrag (refereegranskat)abstract
- The atrioventricular (AV) node plays a central role during atrial fibrillation (AF).We have recently proposed a statistical AV node model defined by parameters characterizing the arrival rate of atrial impulses, the probability of an impulse choosing the slower of the two AV nodal pathways, the refractory periods of the pathways, and the prolongation of refractory periods. All model parameters are estimated from the RR series using maximum likelihood estimation, except for the mean arrival rate of atrial impulses which is estimated by the AF frequency derived from the f-waves. The aim of this study is to assess the relationship between the probability γ of an atrial impulse to arrive at the slow pathway with the probability α (used in the model) of an impulse to pass through that pathway. A theoretical equation was derived to relate α with γ and viceversa, highlighting the dependence on both refractory periods and their prolongation. Results based on simulations show that the equation was correct, with an average absolute error of 0.0034 ± 0.0008.
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| 11. |
- 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
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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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| 12. |
- Trägårdh, Elin, et al.
(författare)
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Högfrekvens-EKG
- 2006
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Ingår i: Elektrokardiologi : klinik och teknik. - 9789144006154 ; , s. 273-273
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 13. |
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