Dingchang Zheng

Analysis of heart rate variability using fuzzy measure entropy

This paper proposed a new entropy measure, Fuzzy Measure Entropy (FuzzyMEn), for the analysis of heart rate variability (HRV) signals. FuzzyMEn was calculated based on the fuzzy set theory and improved the poor statistical stability in the approximate entropy (ApEn) and sample entropy (SampEn). The simulation results also demonstrated that the FuzzyMEn had better algorithm discrimination ability when compared with the recently published fuzzy entropy (FuzzyEn), The validity of FuzzyMEn was tested for clinical HRV analysis on 120 subjects (60 heart failure and 60 healthy control subjects). It is concluded that FuzzyMEn could be considered as a valid and reliable method for a clinical HRV application.

Modeling carotid and radial artery pulse pressure waveforms by curve fitting with Gaussian functions

Abstract Modeling arterial pressure waveforms holds the potential for identifying physiological changes. There is a clinical need for a simple waveform analysis method with a high accuracy in reproducing the original waveforms. The aim of this study was to determine the accuracy of modeling carotid and radial pulses using Gaussian functions, making no physiological assumptions. Carotid and radial pulses were recorded from 20 normal volunteers. Ten consecutive beats from each volunteer were analyzed to determine beat-to-beat variability. Each pulse was decomposed using seven combinations of up to three Gaussian functions. The first function was always positive, but the second or third could be either positive or negative. Three positive Gaussian functions reproduced the original waveforms best with a mean absolute error (MAE) of 1.2% and 1.3% for the carotid and radial pulses respectively, and a maximum residual error of only 4.1% for both. This model had significantly smaller errors than any of the other six (all P

Effect of respiration, talking and small body movements on blood pressure measurement.

It is accepted that accuracy of auscultatory blood pressure (BP) measurement is influenced by measurement conditions. However, there is little comparative quantitative clinical data. The aim of this study was to provide these data. Auscultatory systolic and diastolic BPs (SBPs and DBPs) were measured in 111 healthy subjects under five different conditions (resting, deeper breathing, talking, head and arm movement). The measurement sequence was randomized, and repeated three times. BPs and their within-subject variabilities were compared with resting values. SBP and DBP changed significantly in comparison with the resting condition: decreasing by 4.4 and 4.8 mm Hg, respectively, with deeper breathing (both P<0.001), increasing by 3.7 and 5.0 mm Hg with opposite arm movement, and increasing by 5.3 and 6.2 mm Hg with talking (all P<0.001). The mean differences between deeper breathing and talking were 9.7 and 11.0 mm Hg for SBP and DBP. The within-subject variability for repeat measurement of SBP and DBP under resting condition were 3.7 and 3.2 mm Hg and increased for non-resting conditions (all P<0.05, except for DBP while talking). We have shown that measurement conditions significantly influence manual auscultatory BPs and their measurement variabilities, and we provide quantitative data to allow comparison of the effects.

Peripheral arterial volume distensibility: significant differences with age and blood pressure measured using an applied external pressure

A new arterial distensibility measurement technique was assessed in 100 healthy normotensive subjects. Arterial transmural pressures on the whole right arm were reduced with a 50 cm long cuff inflated to 10, 20, 30 and 40 mmHg. The electrocardiogram, and finger and ear photoplethysmograms were recorded simultaneously. Arm pulse propagation time, pulse wave velocity (PWV) and arterial volume distensibility were determined. With a 40 mmHg reduction in transmural pressure, arm pulse propagation time increased from 61 to 83 ms, PWV decreased from 12 to 8 m s(-1) and arterial distensibility increased from 0.102% to 0.232% per mmHg (all P < 0.0001). At all cuff pressures, arterial distensibility was significantly related to resting mean arterial pressure (MAP), diastolic blood pressure (DBP) and age, and for systolic blood pressure at 30 and 40 mmHg (all P < 0.05). At 40 mmHg cuff pressure, arterial distensibility fell by 54% for a MAP increase from 75 to 105 mmHg, 57% for a DBP increase from 60 to 90 mmHg and 47% for an age increase from 20 to 70 years. These changes were more than double than those without cuff pressure. Our technique showed that systemic volume distensibility of the peripheral arm artery reduced with age, with a greater effect at higher external and lower transmural pressures.

Body surface potential mapping for detection of myocardial infarct sites

Using the additional information from multi-lead body surface potential recordings we aimed to study ECG features to predict the extent of infarcted myocardium as part of the 2007 PhysioNet/Computers in Cardiology Challenge. We studied potential and QT maps through key stages of the ventricular cycle assessing the 2 training and 2 test cases. Clinical assessment of the ECGs was provided by three cardiologists. QRS axis was abnormal in training case 1. ST was elevated in training case 1 and test case 2. T wave axis was abnormal in training case 2 and test case 1. T wave axis was different to QRS axis in training case 1. Cardiologists agreed that training cases 1 and 2 were anterior and inferior infarctions respectively, while they considered both test cases to be normal variations. The maps, however, showed significant abnormalities in the test cases.

Gaussian fitting for carotid and radial artery pressure waveforms: comparison between normal subjects and heart failure patients

It has been reported that Gaussian functions could accurately and reliably model both carotid and radial artery pressure waveforms (CAPW and RAPW). However, the physiological relevance of the characteristic features from the modeled Gaussian functions has been little investigated. This study thus aimed to determine characteristic features from the Gaussian functions and to make comparisons of them between normal subjects and heart failure patients. Fifty-six normal subjects and 51 patients with heart failure were studied with the CAPW and RAPW signals recorded simultaneously. The two signals were normalized first and then modeled by three positive Gaussian functions, with their peak amplitude, peak time, and half-width determined. Comparisons of these features were finally made between the two groups. Results indicated that the peak amplitude of the first Gaussian curve was significantly decreased in heart failure patients compared with normal subjects (P<0.001). Significantly increased peak amplitude of the second Gaussian curves (P<0.001) and significantly shortened peak times of the second and third Gaussian curves (both P<0.001) were also presented in heart failure patients. These results were true for both CAPW and RAPW signals, indicating the clinical significance of the Gaussian modeling, which should provide essential tools for further understanding the underlying physiological mechanisms of the artery pressure waveform.

Effects of handgrip exercise or inorganic nitrate supplementation on 24-h ambulatory blood pressure and peripheral arterial function in overweight and obese middle age and older adults: A pilot RCT

INTRODUCTION Hypertension is a major contributor to the global burden of cardiovascular diseases and its prevalence increases progressively with ageing. Therefore the identification of effective, age-friendly exercise and nutritional interventions which lower blood pressure (BP) is a research priority. OBJECTIVE To undertake a pilot RCT examining the efficacy of isometric handgrip exercise (IHGE) and beetroot juice (a rich source of inorganic nitrate) consumption in modifying clinic and 24-h ambulatory BP (24-h ABP), peripheral arterial function and plasma asymmetric dimethylarginine (ADMA) in older overweight and obese adults. DESIGN Thirty middle age and older adults (62±5 years) were randomised to: (a) bilateral IHGE at 50% of maximal voluntary contraction (8 min/day), (b) 140 ml/day of concentrated beetroot juice, or (c) no-intervention (control group), for 7 days. All groups followed a standardised diet to control nitrate intake. Clinic and 24-h ABP, peripheral arterial function quantified by pulse wave velocity (PWV) and arterial volume distensibility were assessed before and after intervention. SETTING Clinical ageing research unit, Newcastle University. RESULTS At baseline, there were no between-group differences in age, handgrip strength, clinic or 24-h ABP, BMI, waist circumference, fat mass, physical activity level, energy intake or urinary and plasma nitrate concentrations. After intervention, there were no significant effects on clinic systolic and diastolic BP or 24-h ABP, PWV (p=0.54), arterial volume distensibility (p=0.89), or ADMA (p=0.45). CONCLUSIONS IHGE or beetroot juice consumption for 7 days did not affect BP or peripheral arterial function in overweight and obese middle age and older adults. Ageing may reduce the effects of these interventions on vascular function and studies are needed to test this hypothesis.

Extracting fetal heart beats from maternal abdominal recordings: selection of the optimal principal components.

This study presents a systematic comparison of different approaches to the automated selection of the principal components (PC) which optimise the detection of maternal and fetal heart beats from non-invasive maternal abdominal recordings.A public database of 75 4-channel non-invasive maternal abdominal recordings was used for training the algorithm. Four methods were developed and assessed to determine the optimal PC: (1) power spectral distribution, (2) root mean square, (3) sample entropy, and (4) QRS template. The sensitivity of the performance of the algorithm to large-amplitude noise removal (by wavelet de-noising) and maternal beat cancellation methods were also assessed. The accuracy of maternal and fetal beat detection was assessed against reference annotations and quantified using the detection accuracy score F1 [2*PPV*Se / (PPV + Se)], sensitivity (Se), and positive predictive value (PPV). The best performing implementation was assessed on a test dataset of 100 recordings and the agreement between the computed and the reference fetal heart rate (fHR) and fetal RR (fRR) time series quantified.The best performance for detecting maternal beats (F1 99.3%, Se 99.0%, PPV 99.7%) was obtained when using the QRS template method to select the optimal maternal PC and applying wavelet de-noising. The best performance for detecting fetal beats (F1 89.8%, Se 89.3%, PPV 90.5%) was obtained when the optimal fetal PC was selected using the sample entropy method and utilising a fixed-length time window for the cancellation of the maternal beats. The performance on the test dataset was 142.7 beats(2)/min(2) for fHR and 19.9 ms for fRR, ranking respectively 14 and 17 (out of 29) when compared to the other algorithms presented at the Physionet Challenge 2013.

T-wave alternans: A comparison of different measurement techniques

T-wave alternans (TWA) is characterized by a pattern of beat-to-beat alternations in the amplitude of the T-wave of the electrocardiogram (ECG). However, TWA is usually very small and hard to detect or measure. Our aim was to develop and compare three automated TWA measurement algorithms. 100 ECG recordings provided by the 2008 PhysioNet/Computers in Cardiology Challenge were analysed. After ECG pre-processing`moving four-beat window technique (FBW), fast Fourier transform (FFT) spectral analysis and principal component analysis (PCA) were used for TWA determination and quantification. These estimates were then ranked from 1 to 100, separately for each method, and the correlation between the results of each method analysed. The correlation of the ranking of TWA estimates between FBW and FFT was 0.65, between FFT and PCA 0.33, and between FBW and PCA 0.24. With TWA criteria applied, the number of ECGs with TWA was for FBW 29, FFT 29, and PCA 38. Only 7 of the ECG records had TWA detected by all three techniques. In conclusion, we have shown that different analysis techniques produced substantially different results.

Non-invasive in vivo assessment of changes in peripheral arterial properties with estimation of arterial volume compliance

Arterial volume compliance reduces with age and with arterial disease and its easy non-invasive measurement will be of significant clinical value in monitoring the development of cardiovascular disease or evaluating therapy. However, the relationship between arterial volume compliance and pressure is not fully understood. To enable us to examine changing arterial characteristics, we studied the effect of naturally occurring pressure change, and in this pilot study investigated the effect of ectopic beats. Twenty-five subjects were studied. The electrocardiogram and the peripheral pulses, detected optically at the right ear and right finger, were recorded for subsequent analysis. The difference in pulse transit times between the finger and ear allowed the arm pulse propagation time to be determined, as the effect of ventricular ejection time was common to both measurements and hence removed. Finally, the relative arterial volume compliance changes were estimated based on the Moens-Korteweg equation. The arm pulse propagation time for sinus beats was 58 +/- 11 ms (mean +/- SD). Ectopic beats induced a significant increase of 7.2 +/- 6.9 ms (p < 0.001), those ectopic beats with short coupling intervals to the previous sinus beats a significant increase of 11.4 +/- 10.2 ms (p < 0.001) and post-ectopic sinus beats a significant fall of 3.4 +/- 4.6 ms (p = 0.001), all relative to the initial sinus beats. Ectopic beats induced a mean 14% increase in the arm pulse propagation time, equivalent to a 31% increase in relative arterial volume compliance. In conclusion, we have demonstrated that dynamic changes in arterial characteristics can be detected at a beat-to-beat level by the measurement of the arm pulse propagation time.