Preliminary methods for wearable neuro-vascular assessment with non-invasive, active sensing

In this study, a non-invasive and active sensing scheme that is ultimately aimed to be integrated in a wearable system for neuro-vascular health assessment is presented with preliminary results. With this system, vascular tone is modulated by local heating and cooling of the palm, and the resulting changes in local hemodynamics are monitored via impedance plethysmography (IPG) and photoplethysmography (PPG) sensors interfaced with custom analog electronics. Proof-of-concept measurements were conducted on three subjects using hot packs / ice bags to modulate the palmar skin temperature. From ensemble averaged and smoothed versions of pulsatile IPG and PPG signals, the effects of local changes in skin temperature on a series of parameters associated with neuro-vascular mechanisms (heart rate, blood volume, blood flow rate, blood volume pulse inflection point area ratio, and local pulse transit time) have been observed. The promising experimental results suggest that, with different active temperature modulation schemes (consisting of heating / cooling cycles covering different temperature ranges at different rates), it would be possible to enhance the depth and specificity of the information associated with neuro-vascular health by using biosensors that can fit inside a wearable device (such as a sleeve). This study sets the foundation for future studies on designing and testing such a wearable neuro-vascular health assessment system employing active sensing.