Shoe Insole Ballistocardiography as a Tool for Heart Rate Variability Estimation in Smart Insoles

Heart rate variability (HRV) is a noninvasive tool for assessing cardiovascular health, typically measured using ECG and PPG, which require direct skin contact.Ballistocardiogram (BCG) offers an alternative by measuring whole-body recoil forces through a piezoelectric sensor embedded in a shoe insole, eliminating the need for direct contact.This study explores the use of insole BCG to estimate HRV from short-term recordings of at least 5 min in a seated position.Simultaneous ECG and BCG recordings were obtained for 7 min from 7 subjects in sitting position.A template matching technique was used for heartbeat detection, with automatic correction for incorrect heart rate (HR) values.Temporal and spectral HRV parameters from both methods were calculated and compared.Bland-Altman analysis showed a 95% confidence interval of 1.66 bpm between BCG and ECG HR values, within the AAMI standard accuracy limit of 5 bpm.High statistical correlation was found in HRV parameters between the two techniques.BCG from a shoe insole is a noninvasive, comfortable, and reliable method for ambulatory cardiovascular monitoring