Limited Interchangeability Between Pulse and Heart Rate Variability Influenced by Aging and postural change

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 physiological mechanisms underlying HRV-PRV differences, particularly in relation to aging, are poorly understood. Approach: We evaluated HRV-PRV interchangeability across 18 features during different postural changes using four orthostatic tests in 31 younger and 20 older adults. Bland-Altman analysis assessed the interchangeability in different postural change conditions. Linear mixed models (LMMs) quantified the effects of aging and postural changes. Mediation analysis examined whether pulse arrival time variability (PATV) and mean systolic/diastolic blood pressure (BP) mediated these effects. Results: Short-term features were mostly interchangeable in younger adults but largely non-interchangeable in older adults. Features reflecting long-term variability generally met the threshold in both age groups. Aging and posture significantly reduced interchangeability, with aging effects partly mediated by increased PATV. Significance: Our findings demonstrate that PRV cannot reliably substitute HRV for short-term variability, with limitations further aggravated by postural changes and aging. For long-term variability, HRV and PRV were interchangeable in both age groups, although interchangeability was consistently lower in older adults. These insights are essential for daily-life monitoring, emphasizing the need for reliable HRV assessment especially in older adults and during postural transitions.