Noninvasive in vivo monitoring of plasma volume and hematocrit using the FRD-PVOH device: From Cozy to Cold

The FRD-PVOH algorithm/medical device enables continuous noninvasive spectroscopic analysis and monitoring of physiology induced changes in the peripheral vasculature in vivo in humans, specifically red blood cell and plasma volume fractions. Previously, FRD-PVOH demonstrated a correlation between mean arterial pressure (MAP) and vascular plasma volume with tilt-table experiments, indicating physiological relevance. Continuous monitoring of plasma volume and hematocrit (Hct) with a total bandwidth of 0-0.3 Hz in volar side fingertip capillary beds, reveals MAP fluctuations superimposed on slower background. These MAP fluctuations isolated from slower vascular volume shifts and the cardiac pulse create a time series associated with vasodilation/vasoconstriction i.e., thermoregulation, an autonomic path to homeostasis. We consistently observe random walk dynamics i.e., the amplitudes of the fluctuations in the time domain are distributed as a Gaussian while Fourier analysis simultaneously confirms the presence of circulatory physiology in the results i.e., breathing effects and the Baroflex response. Lorenz plots indicate linear dynamics control short and long timescale fluctuations across both test subjects. ANOVA analysis of data from a small, on-going, study using a mild external thermoregulation protocol (2 supine subjects, 16 total hours of monitoring for each subject, in 8 sessions of 2 hours each) demonstrates that the number of fluctuations per unit time varies across the two subjects with 95% significance with or without the thermoregulation challenge. Also, the mean number of fluctuations per monitoring session was significantly greater for sessions that included an external thermoregulation challenge compared to those that did not, for both subjects at 95% confidence.