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.