We recently reported the first noninvasive, label free measurement of pH in a bodily fluid in vivo using only Raman spectra i.e. in vivo rat model measurements probing the immediate vicinity of a contusive spinal cord injury (SCI) in the first minutes and hours after injury. Calibrated and assigned using Raman spectra of authentic materials, in the rat model we were not able to sample the cerebrospinal fluid (CSF) to allow comparison with an independent measurement of the pH. Swine presents a better model because they allow physical sampling of CSF, although still not ideal for our purposes. We were only able to physically sample CSF from the fourth cerebral ventricle of 2 different animals, before and after all spectral measurements on cords were completed. One measurement each for 2 different animals on physically sampled CSF averaged a pH of 7.001±0.106 (N=2) as per standard laboratory instrumentation. Using a dynamic analysis and the Henderson-Hasselbalch equation, the average of (N=12) noninvasive Raman-based pH measurements of CSF was 7.073±0.156 and at >95% confidence there is no statistically significant difference between the Raman-based and the physically sampled results. We discuss the difference between the dynamic and static analysis, the implications for our understanding of SCI, the accuracy, precision, calibration, general applicability of this approach and future work.
We previously reported a new algorithm “PV[O]H” for continuous, noninvasive, in vivo monitoring of hematocrit changes in blood and have since shown its utility for monitoring in humans during 1) hemodialysis, 2) orthostatic perturbations and 3) during blood loss and fluid replacement in a rat model. We now show that the algorithm is sensitive to changes in hemoglobin oxygen saturation. We document the phenomenology of the effect and explain the effect using new results obtained from humans and rat models. The oxygen sensitivity derives from the differential absorption of autofluorescence originating in the static tissues by oxy and deoxy hemoglobin. Using this approach we show how to perform simultaneous, noninvasive, in vivo, continuous monitoring of hematocrit, vascular volume, hemoglobin oxygen saturation, pulse rate and breathing rate in mammals using a single light source. We suspect that monitoring of changes in this suite of vital signs can be provided with improved time response, sensitivity and precision compared to existing methodologies. Initial results also offer a more detailed glimpse into the systemic oxygen transport in the circulatory system of humans.
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