Reflective PPG Sensor Measures Heart Rate Through Clothing During Driving

Abstract

This article presents the development and validation of a reflective photoplethysmography (PPG) sensor designed for unobtrusive heart rate monitoring through clothing in automotive environments. The sensor is integrated into the backrest of a car seat and uses an optimized hardware configuration to enhance signal acquisition and mitigate motion artifacts during driving. Its performance was evaluated in two scenarios: a validation study with 12 participants driving for a total of 316 min and a longitudinal field study encompassing 1080 min of driving across three European countries. The validation study demonstrated a concordance correlation coefficient (CCC) of 0.89, a mean absolute error (MAE) of 2.51 bpm, and a mean absolute percentage error (MAPE) of 3.07%. Gender-specific analysis revealed minimal differences in performance, with an overall coverage rate of 77.60%. The longitudinal study confirmed the sensor's reliability over prolonged periods, achieving a CCC of 0.976, MAE of 0.844 bpm, and MAPE of 1.04%, with a 95.92% coverage rate across diverse driving conditions.