Chronic hypoxia as a factor of enhanced autofluorescence of endogenous porphyrins in soft biological tissues

This report, as a continuation of 8-years research on the problem of noninvasive clinical fluorescence diagnostics efficiency, discusses a hypothesis of influence of a chronic hypoxia state in soft alive tissues on the intensity of a laser-induced endogenous porphyrins' autofluorescence in a red region of optical spectra. Earlier this hypothesis was proposed on the basis of analysis of fluorescence activity for erosive-ulcerative impairments of the upper part of a gastrointestinal tract (SPIE Proc., vol. 4613, 2002. - p.286-294). Today the hypothesis additionally is confirmed by means of observation after patients with another illness and by means of analysis of some well-known literature data. An authors' methodology of clinical trails to verify the hypothesis using an up-to-date noninvasive fluorescence diagnostic technique is presented as well. Both theoretical reasons and all new clinical data show that the chronic hypoxia state can be one of the major factors of appearance of a large and abnormal laser-induced autofluorescent signal from biotissues in the spectrum range 600-800 nm, which is associated with abnormally high accumulation of endogenous porphyrins in the tissues. So, the noninvasive autofluorescent diagnostic technique could be a powerful tool to estimate in vivo a chronic hypoxia condition in soft biotissues. For that purpose a classification of chronic hypoxia levels versus in vivo autofluorescence contrast coefficients in tissues is proposed as well.