Abstract
Wrist based photoplethysmography (PPG) is widely used for heart rate (HR) monitoring in daily life and in the clinical follow up of cardiac patients, yet accuracy differs strongly between individuals. About 30-50% of users consistently produce unreliable data even under optimal conditions, suggesting that PPG performance reflects a personal physiological trait rather than a technical or demographic issue. Growing evidence points to vascular factors, but the mechanisms remain unclear.
This project investigates why PPG HR monitoring works well in some individuals and fails in others, and reframes wearable HR monitoring as a question of vascular physiology rather than device design. It separates device related from person related influences and studies how optical, vascular and mechanical characteristics shape wrist based HR accuracy. Three coordinated steps combine multi device crossover testing, detailed physiological characterisation and controlled modulation of vascular tone through hyperemia, thermal stress and pharmacologic interventions. Endothelial assessment using pulse amplitude testing and dynamic retinal vessel analysis will link peripheral PPG performance to broader microvascular health.
By identifying determinants of individual variability and testing causal vascular pathways, the project aims to build the first physiologically grounded model of PPG compatibility, supporting more reliable and personalised use of wearable HR monitoring in clinical care.
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