A Low-cost, Smartphone-only Pulse Transit Time Measurement System Using Cardio-mechanical Signals and Optical Sensors*

This paper presents a smartphone-only solution for measuring pulse transit time (PTT). An application based on an Android smartphone is developed to collect seismocardiogram (SCG), gyrocardiogram (GCG), and photoplethysmography (PPG) recordings. The system does not need any other external system for measurements, so the total cost and system complexity are minimized. PTT metrics are calculated as the time difference between the aortic valve opening points in the SCG or GCG signals recorded by the accelerometer or gyroscope of a smartphone respectively, and the fiducial points in the PPG signal recorded by a modified optical sensor connected to the audio input. A digital signal processing (DSP) system is developed in a post-processing environment and experimentally validated on ten healthy subjects at rest. Our results indicate that a smartphone-only PTT measurement system is feasible and comparable with stand-alone sensor node systems.