Development of wearable optical-based fibre sensor system for pulse transit time measurement

Abstract

This paper presents the development of an optical-based fibre sensor system for pulse transit time (PTT) measurement. PTT is a promising method for cuffless continuous blood pressure (BP). In this study, the time delay between the R-wave peak of the Electrocardiogram (ECG) and the peak of the Photoplethysmogram (PPG) was measured and denoted as PTT. A conductive fabric based ECG electrode was deployed to measure the ECG on the chest. A plastic optical fibre (POF) was deployed as a medium to transport and receive light for PPG detection. A green LED (525 nm) was deployed as a light source to illuminate the skin tissue, and a phototransistor was deployed to measure the reflected light intensity. A cuff-based blood pressure (Ostar, P2) was used to measure blood pressure simultaneously with the PTTs. The ECG and the PPG signals were synchronized using a Nexus-10 MK II data acquisition device along with Matlab software for subsequent analysis. In this study, the PTT at three different positions (finger, wrist and foot) were recorded along with the BP measurement during a tilt table experiment. The results show that the system is able to monitor the PTT during a tilt table moving from supine position to tilt-up position (0° to 70°). A statistical analysis was performed by using SPSS software to compare the mean of BP and the PTT in supine and tilt-up position. The novelty of the developed system lies in the miniaturization of the POF system and the combination of POFs and textile electrodes that are well suited to smart textile applications.