Blood pressure contour analysis after exercise by the photoplethysmogram using a Transfer Function method

Blood pressure monitoring is routinely required in many mobile health applications, but the present cuff based measuring system (Finapres) is often unsuitable due to being too big and uncomfortable. An alternative method is to measure the digital volume pulse, which can be non-invasively recorded using the photoplethysmography (PPG), and predict the blood pressure waveform from that of PPG. The benefit is that the PPG components are easy to embed in many portable and wearable devices. In this study, we predicted the peripheral blood pressure waveform of young healthy adults after exercise from that of the PPG pulse using a General Transfer Function (GTF) method, which had been proved effective for this prediction task at steady state before. To this end, we measured the simultaneous blood pressure and PPG pulses of twelve subjects at steady state and immediately after exercise. Three tests were performed to verify the GTF method. Results showed that a single best-fit GTF (GTFb) derived from all subjects and all measurement phases could predict the blood pressure waveform precisely, both at steady state and after exercise. The prediction performance was further improved when phase dependant GTFs were applied.