Near Infrared Optical Monitoring of Cat Skeletal Muscle during Hypercapnia
Circulatory effects of CO2 have been previously examined in a variety of tissues,1,2,3,4 however, prior efforts to evaluate oxygen transport to skeletal muscle during hypercapnia using non-specific or invasive methods have reported sometimes contrasting conclusions.4,5,6 The recent development of near infrared (NIR), multiple wavelength, differential spectrophotometry has allowed non-invasive assessment of oxygen sufficiency in intact tissues including skeletal muscle7,8 by allowing continuous in situ monitoring of the reduction-oxidation (redox) state of the terminal member of the mitochondrial “respiratory chain”, cytochrome a,a 3. Oxidized cytochrome a,a 3 has an absorption band in the NIR region which is not present when the molecule is reduced. NIR multiple wavelength spectrophotometry allows ongoing assessment of the redox state of a population of cytochrome a,a 3 molecules in a tissue being monitored, with absorption of NIR light increasing as the concentration of oxidized cytochrome a,a 3 increases and absorption decreasing as more molecules in the population become reduced. Furthermore, changes in regional blood volume and saturation can be monitored simultaneously to provide ancillary information useful for interpreting changes in the redox signal. The present study examines the effect of hypercapnia on the steady state of reduction-oxidation of cytochrome a,a 3 and also on the blood volume (t-BV) and hemoglobin plus myoglobin (Hb + Mb and HbO2 + MbO2) saturation responses in intact hindlimb muscles of the cat.
KeywordsMetabolic Acidosis Indocyanine Green Hypercapnic Acidosis Gallamine Triethiodide Regional Blood Volume
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