The PVOH device: our first stop on the path to small and very small physical embodiments of the PV[O]H algorithm

Several years ago we proposed a new algorithm, PV[O]H, to allow noninvasive in vitro and in vivo spectroscopic analysis of mildly turbid i.e. optically thin or dilute samples that can be considered two phase systems such as plasma and red blood cells (RBCs). The goal was to provide a method for measuring the volume fraction of the sample for each of the two phases noninvasively without physical sampling or labeling. The first application of this approach was to calculate the volume fractions of plasma and RBCs for blood in the peripheral vasculature of skin, to calculate the hematocrit (Hct) of the blood as an early indicator of blood loss. Having validated PV[O]H in completely defined in vitro systems and then for bacterial cultures in various media, we began to envision potential uses for PV[O]H in medicine and biotech applications. Every potential application presents special requirements but nearly all require the embodiment to be physically small and light and have a minimum power footprint. Some applications require retaining the capacity to perform Raman spectroscopy while utilizing PV[O]H and others do not. We describe our first attempt to design and fabricate a small device that can implement PV[O]H without Raman capability. Among many potential uses, we intend PVOH for medical uses involving indications of 1) potential undetected internal bleeding, 2) hematocrit variation during dialysis and 3) infection and inflammation in spinal cord injury. PV[O]H also has potential utility in wellness, exercise science and physiological monitoring of small vessel plasma and red cell volumes continuously over time.