Comparison of Multi-Wavelength PPG at Wrist and Finger for Non-Invasive Vascular Aging Assessment Using APG Analysis

Abstract

Vascular aging, characterized by progressive arterial stiffening, is an independent predictor of cardiovascular risk. Acceleration plethysmography, which is obtained from the second derivative of the photoplethysmographic signal, allows for the non-invasive extraction of vascular aging indices from five fiducial points. However, the morphology of the photoplethysmographic waveform varies with the wavelength of the light source and with the anatomical measurement site, which may influence the derived vascular aging indices and limit their use in wearable devices. To the best of our knowledge, the combined influence of these two factors has not previously been evaluated. In this study, photoplethysmographic signals were acquired simultaneously from the wrist and the finger at four wavelengths (red, infrared, green and blue) in 44 healthy volunteers with no known cardiovascular disease, aged 22 to 94 years, using a custom multi-wavelength wearable prototype. The green and blue wavelengths yielded significantly stronger correlations with chronological age than red and infrared, and the finger yielded stronger and more consistent correlations than the wrist (c/a index: r $= -0.513$ , p < 0.001 for blue and r $= -0.497$ , p < 0.001 for green; (b−e)/a index: r = 0.451, p < 0.01 for blue and r = 0.443, p < 0.01 for green). However, consistent trends were also observed at the wrist, suggesting that this site may still be suitable for tracking age-related changes in wearable devices.