The Role of Fluorescence and Human Factors in Quantitative Transdermal Blood and Tissue Analysis Using NIR Raman Spectroscopy.

摘要

This research is part of an ongoing project aimed at the application of combined near infrared (NIR) Raman and fluorescence spectroscopy to noninvasive in vivo blood analysis including but not limited to glucose monitoring. Coping with practicalities of human factors and exploring ways to obtain and use knowledge gained about autofluorescence to improve algorithms for blood and tissue analysis are the general goals of this research. Firstly, the study investigated the various sources of human factors pertinent to our concerns, such as fingerprints, turgor, skin hydration and pigmentation. We then introduced specialized in vivo apparatus including means for precise and reproducible placement of the tissues relative to the optical aperture, i.e., the position detector pressure monitor (PDPM). Based on solid instrumental performances, appropriate methodology is now provided for applying and maintaining pressure to keep surface tissues immobile during experiments while obtaining the desired blood content and flow. Secondly, in vivo human fingertip skin autofluorescence photobleaching under 200 mW 830 nm NIR irradiation is observed and it is characterized that: i) the majority of the photobleached fluorescence originates from static tissue not blood, ii) the bleaching (1/e point) occurs in 101-102 sec timescale, and also iii) a photobleached region remains bleached for at least 45 min but recovers completely within several hours. A corresponding extensive but not exhaustive in vitro systematic study narrowed down the major contributors of such fluorescence and bleaching to collagen, melanin, plasma and hemoglobin: two major static tissue constituents and two major blood proteins. Thirdly, we established that measuring the inelastic and elastic emissions simultaneously leads to a sensitive probe for volume changes of both red blood cells and plasma. An algorithm based on measurements obtained while performing research needed for this thesis, as well as some empirical calibration approaches, was presented. The calibrated algorithm showed real potential to track hematocrit variations in cardiac pulses, centrifugal loading, blood vessel blockage using tourniquet, and even during as subtle an occurrence as in a Valsalva maneuver. Finally, NIR fluorescence and photochemistry of pentosidine, a representative of the advanced glycation endproducts (AGEs) which accumulate with age and hyperglycemia, was studied. The results indicate that oxygen plays a pivotal role in its photobleaching process. We hypothesized and offered proofs showing that pentosidine is a 1O2 sensitizer that is also subject to attack by the 1O2 resulting in the photobleaching that is observed when probing tissue using NIR. The photobleaching reaction is kinetically first order in pentosidine and ground state oxygen, and in vivo effectively first order with NIR irradiation also.