Abstract
A monitor for simultaneous recording of heart and respiratory rates has been developed using digital filters and photoplethysmography (PPG) with plastic optical fiber. PPG signal includes both heart and respiratory synchronous components. Digital filtering technique was employed to differentiate between those. With increasing heart and respiratory rates, the cut-off frequency of filter was changed empirically. Finite impulse response digital filters were designed using the Remez exchange algorithm. One filter for the heart-related signal was 40th order of Chebyshev type and the other filters for the respiration-related signal were 60th order of Chebyshev type. A suitable cut-off frequency of filter was selected empirically. The heart-related signal was detected by using a impulse response, while the respiration-related signal was detected by three impulse responses. One out of three impulse response was selected for the respiration-related signal. Heart and respiratory rate were increased with whole body heart stress i. e. bathing. The heart rates from 65 to 87 beats/min and the respiratory rates from 13 to 27 breath/min agreed with those obtained with ECG and thermistor. The digital filtering technique may provide on-line monitor for heart and respiratory rates.
