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USB Based Data Acquisition System for Heart Rate Variability through ECG & PPG Signals Vibhuti Bagga1, Tanvi Kalra2, Abhinav 3, Sneh Anand 3 1- Faculty of Sciences, Jamia Hamdard, New Delhi 2- Department of Biomedical Engineering, Rayat & Bahra Institute of Engineering & Bio-Technology, Punjab 3- Centre for Biomedical Engineering, IIT DELHI What is HRV? •Refers to the variation in beat-to-beat pacing intervals of heart rate • It is a measure of heart's ability to respond to normal regulatory impulses that affect its rhythm • HRV analysis is an important parameter for assessment of the cardiovascular autonomic nervous system • Bears clinical relevance for both diagnostic & prognostic purposes as they are directly influenced by the sympathetic and parasympathetic systems Electrocardiograph Refers to the electrical activity of the heart represented as a vector between two point charges It measures the rate and regularity of heart beats PHOTOPLETHYSMOGRAPHY Optical measurement technique used to detect blood volume changes in the microvascular bed of the tissues during cardiac cycle PPG signal contains components that are synchronous with respiratory and cardiac rhythms It can be used as a replacement of ECG for HRV analysis in healthy subjects. It is also a measure of vessel stiffness. Systolic peak Dicrotic notch Reflective Type - PPG the yellow region shows the path of the photons (emitted by the source) which reach the detector after scattering and absorption into the various layers of the skin HRV analysis can be done using ECG and PPG Pulse Transit Time The time taken for pulse wave to travel from the left ventricle to the peripheral site Noninvasive measure of arterial compliance The PTT can be computed from the ECG and PPG waveforms as the time delay in between R wave peak of ECG and upstroke of corresponding PPG pulse . Can be used for continuous monitoring of vascular reactivity PTT varies in pace with respiration & so can be used for respiration monitoring Features include: USB based ; no external power supply needed Simultaneous plot of both ECG & PPG Small size, compact ; portable Signal processing at the press of a button.* * Under process… Functional Block Diagram ECG MEASURING CIRCUIT ACQUISITION BOARD PPG MEASURING CIRCUIT PC GRAPHICAL USER INTERFACE ECG Measurement Module • BUFFER RA ELECTRODE • PREAMPLIFIER DIFFERENTIAL AMPLIFIER • BUFFER LA ELECTRODE • PREAMPLIFIER BAND PASS FILTER # INVERTING SIGNAL # GAIN # REFERENCE VOLTAGE This three leads ECG system includes: 3 Electrodes • RA, RL, LL • Lead II Pre-amplifier • signal from the RA & LL electrodes buffered , preamplified • Gain : 5 Differential amplifier • differential o/p of the signal with reference to the third electrode (LA). Filter Output stage • 2nd order Butterworth band-pass filter • Pass Band : 1.2 Hz – 40 Hz • filtered signal is inverted • amplified • output given with respect to a reference voltage. The PPG system includes: Light Source • IR LED • 920 nm Detector • Phototransistor Amplifier • Gain of 20 Filter Output stage • 2nd order Butterworth band-pass filter • Pass Band : 0.05 Hz – 10 Hz • amplified • output given with respect to a reference voltage. Acquisition Module VOLTAGE SHIFTING AMPLIFIER PROGRAMMABLR GAIN AMPLIFIER ANALOG INPUT VOLTAGE CONVERTER (INVERTING) COMPUTER MICROCONTROLLER Acquisition Module Graphical User Interface A visual basic, windows based application. Reads data from the USB port in bulk and displays it on the monitor. Features include : Two selectable channels No of samples :10-500 Selectable time base: 10 us – 1000 ms Data can be stored as a text file and processed as desired. Signal plotted can be smoothened, averaged and inverted Discussion The acquisition system & the GUI successfully acquire and plot the noise free ECG signal. Further improvisations in the plotting software include User selectable acquisition duration Continuous and dynamic plotting Integration of the various data processing features for HRV analysis References : Selvaraj, N., Jaryal, A. K., Santhosh, J., Deepak, K. K. and Anand, S.(2009)'Influence of respiratory rate on the variability of blood volume pulse characteristics',Journal of Medical Engineering & Technology Allen, J., 2007, Photoplethysmography and its application in clinical physiological measurement. Physiological Measurement, 28, R1–R39. Foo, J.Y.A. and Lim, C.S., 2006, Pulse transit time as an indirect marker for variations in cardiovascular related reactivity. Technology and Health Care, 14, 97–108. Johansson, A., Ahlstrom, C., Lanne, T. and Ask, P., 2006, Pulse wave transit time for monitoring respiration rate. Medical & Biological Engineering & Computing, 44, 471–478. Selvaraj, N., Jaryal, A., Santhosh, J., Deepak, K.K. and Anand, S., 2008, Assessment of heart rate variability derived from finger-tip photoplethsmography as compared to electrocardiography. Journal of Medical Engineering & Technology.