Volumetric index for non-invasive vascular characterization based on the finger pulse response to flow mediated dilation

In this paper, a new index is defined for the characterization of the vascular response to a predefined stimulus using the finger photoplethysmogram (PPG) as input. To this end, two different wavelengths (red and infrared) were employed. To show the feasibility of this concept, PPG signals were acquired from two subjects: a healthy and a diabetic with obesity. A normalization procedure was implemented so as to eliminate the effects of confounding factors such as tissue thickness and skin pigmentation. To elucidate a valid response from the vascular bed, a standard stimulus leading to reactive hyperemia was applied to the subjects. Obtained results show a clear difference between the response of the subjects´ PPG after normalization. Moreover, a significant difference is observed between the red and infrared channels. We submit that this proof of concept work may lay down the foundations of affordable and operator-independent techniques for non-invasive vascular characterization.