Photoplethysmography-derived Heart Rate Variability as a Marker of Physiological Stress in Korean American Home Care Workers Providing Dementia Care

This pilot study explored the longitudinal relationship between daily dementia caregiving and physiological stress, assessed through heart rate variability (HRV) measured using a wearable device, among Korean American home care workers (HCWs). Fifteen HCWs wore the Ōura ring for 21 days, providing 14 days of valid nocturnal HRV data after baseline calibration. HRV was quantified as the root mean square of successive differences (RMSSD) derived from photoplethysmography (PPG)-based interbeat intervals. To minimize interindividual variability, HRV values were standardized within participants. Multilevel linear models examined within- and between-person associations of dementia caregiving (yes or no and total hours) with HRV, adjusting for covariates. All were women, and the majority of HCWs (86.96%) were unsure about the type of dementia their care recipients had. Of 210 potential daily observations, 198 (94.3%) were valid. HRV displayed substantial within-person day-to-day fluctuations (intraclass correlation = 0.20) despite relatively low baseline self-reported stress. Although dementia caregiving was not significantly associated with HRV, the estimated coefficients suggested small-to-moderate within-person effect sizes. These findings highlight the dynamic nature of physiological stress and underscore both the feasibility and limitations of nocturnal PPG-derived HRV for real-world stress assessment. The study provides preliminary methodological guidance for wearable-based HRV research in understudied caregiver populations.