Aging and Postural Changes Influence the Agreement Between Pulse Rate Variability and Heart Rate Variability

OBJECTIVE: Pulse rate variability (PRV) derived from photoplethysmography is often used as a surrogate for heart rate variability (HRV) in daily monitoring. However, their interchangeability in older adults and under postural change remains uncertain, potentially leading to misinterpretation in practical usage. Moreover, the mechanisms underlying HRV-PRV differences are incompletely understood. APPROACH: We evaluated HRV-PRV interchangeability across 18 features during four kinds of orthostatic tests in 35 younger and 42 older adults. Bland-Altman analysis assessed the interchangeability in different postural change conditions. Linear mixed models (LMMs) quantified the effects of age, sex, and postural changes. Mediation analysis examined whether mean arterial compliance, total peripheral resistance, and cardiac contractility mediated these effects. RESULTS: 16 features were interchangeable at individual level in younger adults, while only seven in older adults. Both aging and posture significantly reduced the interchangeability. A significant age-sex interaction was identified for metrics reflecting slow variation, with older females exhibiting a most pronounced HRV-PRV agreement decline. Mediation analysis showed that while hemodynamic parameters differed significantly across subgroups, they cannot explain the age- or posture-related decline in HRV-PRV consistency. SIGNIFICANCE: Our findings demonstrate that PRV cannot reliably substitute HRV in older adults, especially for features reflecting rapid physiological dynamics. The significant age-sex interaction highlights the necessity for calibration models particularly for monitoring elderly populations. These insights are essential for daily-life monitoring, emphasizing the need for reliable HRV assessment in older adults and after posture change.