Optical non-invasive blood pressure : PPG waveform-based estimation and verification

Abstract

Photoplethysmograph (PPG) is an optical measurement technique that can be used to detect blood volume (BV) changes in the micro vascular bed of tissue. It has widespread clinical application, with the technology utilized in commercially available medical devices. PPG waveform is believed to have significant information regarding the patient’s cardiovascular condition which has not been fully utilized in the current clinical practice.The objective of the current study is to assess the feasibility of using multiple features derived from the finger PPG waveform as markers of BP. The specific objectives are; first, to study the change in PPG waveform during BP change from patients in emergency room and intensive care unit based on a blood flow model and to evaluate their potentials as non-invasive indicators of cardiovascular diseases (CVDs), second, to evaluate the potential use of the finger PPG waveform derived BP as a non-invasive indicator of BV and vascular resistance (VR) by investigating its association with progressive change in the central BV and the total peripheral resistance (TPR) induced by cardiac stimulants, third, to investigate the propriety of using normalized PPG derived the finger PPG waveform to track variations in contact force (CF) change at measurement area and progressive changes in PPG waveform induced by forced gradual cooling and heating, forth, to develop an automated method of detecting BP from the finger PPG waveform and evaluate the reliability of the measurement by direct comparison with the BP measured from clinical non-invasive blood pressure (NIBP) equipment.The results from current study clearly show the possibility of finger PPG waveform as a noninvasive determine tool for BP change. BP detection model were verified by the relationship study, which involved change of cardiovascular status from a group of healthy human subject that constituted blood pressure change and a group of healthy animal subject that induced via commonly used cardiac stimulants. The results from these studies have supported that morphological features derived from the finger PPG waveform could be very useful for detecting the change in central BP, and the trends of features might be possible to identify not only the local BV change but also the VR change in peripheral vasculature. The relationship between effects of environment and the finger PPG waveform was confirmed that CF and skin surface temperature (SST) changes in groups of healthy subjects produced the progressive PPG waveform change. The clinical study focused on long-term comparison and has shown that morphological features of the finger PPG waveform could be potential markers of BP change, which may help to patients who are interested in monitoring their daily BP.In terms of clinical application, this approach is best way to identify BP change as easily as possible, because we can apply the long-term monitoring possibility of BP measurement system. In this perspective, the finger PPG waveform-based technique may prove to be extremely valuable detection technique of BP. The technique proposed in the current study may be applied in home and mobile healthcare phase, so that whenever and wherever the patient are, BP assessment can be more convenient with very simple monitoring procedures. When the simple, comfortable and totally noninvasive BP measurement is required, PPG waveform will be the ideal application for continuous BP monitoring of the patient.