Vascular reactivity characterized by PPG-derived pulse wave velocity

Vascular reactivity is the capacity of the blood vessels to adapt under physiological and environmental stimuli. Heat stress causes changes at vascular level affecting pulse wave velocity (PWV), which can be non-invasively obtained using pulse photoplethysmography (PPG). The study aim is to characterize non-invasive and reliable PPG-derived PWV surrogates that are able to assess vascular reactivity, using data from fifteen healthy male volunteers under heat stress conditions. Pulse arrival time (PAT) is a recognized PWV surrogate measure, but our study explores further by including pulse transit time difference (PTTD) and pulse wave decomposition analysis (PDA). Our results indicate a significant linear decrease in PAT and PDA under heat stress, with an approximate 15% reduction compared to the relax phase, closely correlating with heart rate (HR) alterations. This correlation is likely influenced by factors such as the pre-ejection period or stroke volume changes. In contrast, PTTD demonstrates a distinct pattern: it exhibits significant and rapid changes during the initial exposure to heat stress, with an approximate 30% reduction, yet shows minimal intra-stage variations (around 0 ms/min compared to 2.5 ms/min in PAT). This suggests that PTTD, in measuring acute sympathetic activation responses, effectively minimizes the impact of HR-related phenomena that significantly influence PAT and PDA measurements. Our study highlights PTTD as an underexplored yet promising measure for accurately assessing vasoconstriction and vascular reactivity. • HR, PAT, PDA, and PTTD change under heat stress.. • PAT and PDA reduce slowly upon exposure, correlating with HR increase. • PTTD shows distinct behavior from PAT, PDA, and HR. • PTTD suddenly drops ≈ 30% at stress onset and remains stable. • PTTD may better reflect vasoconstriction than PAT or PDA.