Edmond Zahedi

Finger photoplethysmogram pulse amplitude changes induced by flow-mediated dilation

This study was conducted to investigate the utility and efficacy of finger photoplethysmogram pulse amplitude (PPG-AC) in comparison with the standard Doppler ultrasound in assessing an endothelial function via flow-mediated dilation (FMD). High-resolution B-mode scanning of the right brachial artery (BA) of 31 healthy subjects aged 39.7 +/- 11.3 (range 22-64) years and 52 risk subjects aged 47.7 +/- 10.8 (range 30-65) years were performed before and after 4 min of upper arm occlusion. Concurrent with the ultrasound measurement (where color Doppler imaging was used to enhance arterial boundary detection), PPG signals were recorded from both index fingers for cross evaluation and comparison. Our results show that the finger PPG-AC exhibits a similar response to that of the well-known BA dilation: following the release of pressure (cuff around the BA), the PPG-AC increases abruptly before slowly decreasing toward the baseline. The peak PPG-AC is reached significantly faster than the peak FMD measured by ultrasound among healthy and risk groups (P < 0.001). The proposed technique using a finger photoplethysmogram can be applied in a rapid and non-invasive assessment of peripheral vascular functions as an alternative low-cost and less operator-dependent tool compared to ultrasound.

The application of empirical mode decomposition for the enhancement of cardiotocograph signals.

Cardiotocograph (CTG) is widely used in everyday clinical practice for fetal surveillance, where it is used to record fetal heart rate (FHR) and uterine activity (UA). These two biosignals can be used for antepartum and intrapartum fetal monitoring and are, in fact, nonlinear and non-stationary. CTG recordings are often corrupted by artifacts such as missing beats in FHR, high-frequency noise in FHR and UA signals. In this paper, an empirical mode decomposition (EMD) method is applied on CTG signals. A recursive algorithm is first utilized to eliminate missing beats. High-frequency noise is reduced using EMD followed by the partial reconstruction (PAR) method, where the noise order is identified by a statistical method. The obtained signal enhancement from the proposed method is validated by comparing the resulting traces with the output obtained by applying classical signal processing methods such as Butterworth low-pass filtering, linear interpolation and a moving average filter on 12 CTG signals. Three obstetricians evaluated all 12 sets of traces and rated the proposed method, on average, 3.8 out of 5 on a scale of 1(lowest) to 5 (highest).

Diagnosis of Early Alzheimer's Disease Based on EEG Source Localization and a Standardized Realistic Head Model

In this paper, distributed electroencephalographic (EEG) sources in the brain have been mapped with the objective of early diagnosis of Alzheimers disease (AD). To this end, records from a montage of a high-density EEG from 17 early AD patients and 17 matched healthy control subjects were considered. Subjects were in eyes-closed, resting-state condition. Cortical EEG sources were modeled by the standardized low-resolution brain electromagnetic tomography (sLORETA) method. Relative logarithmic power spectral density values were obtained in the four conventional frequency bands (alpha, beta, delta, and theta) and 12 cortical regions. Results show that in the left brain hemisphere, the theta band of AD subjects shows an increase in the power, whereas the alpha band shows a decreased activity (P-value <;0.05). In the right brain hemisphere of AD subjects, a decreased activity is observed in all frequency bands. It was also noticed that the right temporal region shows a significant difference between the two groups in all frequency bands. Using a support vector machine, control and patient groups are discriminated with an accuracy of 84.4%, sensitivity 75.0%, and specificity of 93.7%.

Computerized Fetal Heart Rate Baseline Estimation Based on Number and Continuity of Occurrences

Continuous monitoring of the fetal heart rate using cardiotocography was introduced into clinical practice in the late 1960s and since then it has been considered as an indispensable tool for fetal surveillance. Fetal heart rate patterns are recognized manually by obstetricians during the process of cardiotocographs analyses. Difference in opinion and delay in detecting a significant pattern and subsequent clinical intervention, especially during high-risk pregnancies, increases the maternal and fetal complications. In this work, we present a method for estimating baseline, one of the important features present in the fetal heart rate (FHR) signal, taking into account the number of occurrences of a particular FHR and its continuity of occurrence. The results are compared with the opinion of two experts’ baseline estimation. Similar results on baseline estimation between the algorithm and the experts were obtained in all except one of the 15 data samples.

Classification of vascular function in upper limb using bilateral photoplethysmographic signals

Bilateral PPG signals have been used for comparative study of two groups of healthy (free from any cardiovascular risk factors) and diabetic (as cardiovascular disease risk group) subjects in the age-matched range 40-50 years. The peripheral blood pulsations were recorded simultaneously from right and left index fingers for 90 s. Pulses have been modeled with the ARX440 model in the interval of 300 sample points with 100 sample points overlap between segments. Model parameters of three segments based on the highest fitness (higher than 80%) of modeled segments were retained for each subject. Subsequently, principal component analysis (PCA) was applied to the parameters of retained segments to eliminate the existing correlation among parameters and provide uncorrelated variables. The first principal component (contains 78.2% variance of data) was significantly greater in diabetic than in control groups (P < 0.0001, 0.74 +/- 2.01 versus -0.53 +/- 1.66). In addition the seventh principal component, which contains 0.02% of the data variance, was significantly lower in diabetic than in control groups (P < 0.05, -0.007 +/- 0.03 versus 0.005 +/- 0.03). Finally, linear discrimination analysis (LDA) was used to classify the subjects. The classification was done using the robust leaving-one-subject-out method. LDA could classify the subjects with 71.7% sensitivity and 70.2% specificity while the male subjects resulted in a highly acceptable result for the sensitivity (81%). The present study showed that PPG signals can be used for vascular function assessment and may find further application for detection of vascular changes before onset of clinical diseases.

An Age Index for Vascular System Based on Photoplethysmogram Pulse Contour Analysis

An approach based pulse on contour analysis is proposed for the development of an aging index for the vascular system. The approach is non-invasive, using photoplethysmography (PPG), which is in wide clinical use. A probe is applied to the subject’s finger-tip to provide a measure of the pulse waveform. The measured waveforms are filtered, digitized and post-processed. Individual pulses are extracted and the best pulse was selected by using the best pulse selection algorithm. Pulse contour analysis is then performed with specially formulated PPG fitness equation. Results of measurements taken from 72 subjects are reported. The age range of the subjects was from 19 to 68 years, all of them are healthy (free from cardiovascular related risks and diseases). There are linear relationship between the PPG fitness and the age recorded from the 72 individuals. The gradient of the line of best fit tends to decrease with increasing age. An age index, which indicates vascular age, is thus proposed based on the slope of this line of best fit for a given individual.

Effects of Physical Exercise on the Photoplethysmogram Waveform

Photoplethysmography is a non-invasive method which is suitable to estimate vascular compliance. Photoplethysmogram (PPG) waveform has been used to evaluate vascular characteristic changes due to exercise. Quantification of the primary and secondary peak position is of interest as a potential objective, individualized measure of the level of exercise that a subject has achieved with respect to a baseline status, prior to the beginning of the exercise session. The modified bicycle ergonomic protocol was selected for this experiment. Two different signal processing methods were employed in processing the PPG waveform to characterize its changes through a single parameter. Both, the visual inspection of the recorded PPG and the results of the analyses reinforce our opinion about the existence of continuous changes in PPG waveform through an exercise session. The experiment results confirm that PPG can be a potential approach in quantifying cardiovascular characteristics or properties of an individual.

A comparative review of blood pressure measurement methods using pulse wave velocity

Continuous and non-invasive blood pressure (BP) measurement systems generally utilize applanation tonometry. Besides their relatively higher cost compared to conventional cuff-based systems, these are not yet practical during movement of the subject. This may explain their application to clinical researches instead of operation rooms. Another approach is based on measurement of the pulse transit time (PTT). Although the precision and accuracy of the presented models are reported to be acceptable in the literature, devices purely based on PTT have not yet been released commercially. One of the most important reasons is that these methods need calibration at regular intervals. In this paper a number of PTT-based methods have been reviewed. Two definitions of the PTT related to the systolic and diastolic pressures are presented, based on the current literature. The accuracy of these models was evaluated using their correlation coefficient of systolic and diastolic BP with these PTT. Results show that Fungs algorithm can estimate BP more accurately than other algorithm based on its correlation coefficient of 94.8% for systolic and 92.46% for the diastolic BP respectively.

Design and Implementation of A PC-Based Digital Synchronous Detection System for Biological Signal Measurement

A PC-based digital lock-in amplifier was implemented completely in software (Labview) for photoplethysmograph (PPG) measurement. Experiments carried out to evaluate the performance of the amplifier show that the system can recover the signals up to 40 dB below the interference (ambient light). This system can be customized later to measure the trans-abdominal PPG signal of pregnant women for fetal heart rate detection.

Mathematical modeling of heart rate and blood pressure variations due to changes in breathing pattern

Analysis of the heart rate (HR) variation due to respiration, known as respiratory sinus arrhythmia (RSA), is a method to assess the autonomic nervous system (ANS) function. In this paper a physiologically-based mathematical model consisting of the cardiorespiratory system and ANS control has been used in order to study the cardiovascular response (mean arterial blood pressure and HR) to breathing with different respiration rates and tidal volumes. Simulation results show that RSA has its maximal amplitude at the respiration frequency of 0.12 Hz and that RSA amplitude varies linearly by tidal volume. These results are in agreement with real data from the literature. In addition, the amplitude of the variations of the simulated blood pressure (BP) in each respiratory cycle is maximum at almost the same respiratory rate as RSA.