Feasibility of monitoring vascular ageing by multi-site photoplethysmography

The aim of this pilot study was to determine the expected normative values of two main features from multi-site photoplethysmography (PPG) waveforms, namely the pulse transit times to foot (PTTf) and to peak (PTTp), and explore their overall trends with ageing. These measures reflect the presence of arterial stiffness and peripheral arterial disease, important factors in cardiovascular risk. PPG waveforms were acquired from the right and left ear lobes, index fingers, and great toes in 31 healthy subjects (19 males and 12 females, mean age 50 years old and range 30–70 years). The electrocardiogram was also simultaneously recorded to provide a cardiac timing reference for the computation of PTTf and PTTp. Values from right and left sides were averaged for subsequent analysis. Linear regressions with age were investigated utilising Pearson's correlation analysis. PTTf for ear, finger and toe sites were 139±10 ms, 192±14 ms, and 282±24 ms, respectively. For PTTp the values were 460±67 ms, 431±40 ms, and 510±29 ms, respectively. Toe PTTf significantly decreased with age (r=−0.59, p<0.001). In contrast, finger PTTp significantly increased with age (r=0.46, p<0.01). In conclusion, multi-site PPG shows potential to assess the increase in cardiovascular risk linked to physiological or early vascular ageing.