Reflectance Measurement Of Heart Muscle Oxygenation
Clyde H. Barlow, Katherine A. Kelly, Emily Bailey and Jeffrey J. Kelly
C.H. Barlow, K.A. Kelly, E. Bailey and J.J. Kelly "Reflectance measurement of heart muscle oxygenation". 25th Annual Conference of the International Society on Oxygen Transport to Tissue. Milwaukee, Wisconsin. August, 1997. Measurements of hemoglobin (Hb) and myoglobin (Mb) saturations and mitochondrial cytochrome reduction in heart muscle allow effects of oxygen in three tissue compartments of heart muscle to be monitored simultaneously. Rat hearts, perfused with solutions containing no blood and with 7% hematocrit sheep red blood cells, were used in these studies.
Reflectance spectra, 450-650 nm, were recorded during normoxic and anoxic states of hearts under working, potassium-arrested, and cyanide-inhibited conditions to develop spectral basis sets for Mb, MbO2, Hb, HbO2, and reduced cytochromes. Using matrix inversion techniques, these basis sets were used to analyze spectral data sets from perfused hearts undergoing titrations of oxygen concentration. Hemoglobin and myoglobin saturation and fractional cytochrome reduction were calculated at each point in the titration.
Plots of Mb and Hb saturations and cytochrome reduction vs arterial PO2, showed Hb saturation titrating separately and at higher PO2's than Mb saturation and cytochrome reduction which were tightly coupled in their behavior. Apparent P50's for all three components shifted to higher PO2 with increased work. Plots of cytochrome reduction vs Mb saturation for blood-free perfused working hearts followed an identity relationship consistent with the presence of negligible tissue volumes with oxygen concentrations between the P50's for mitochondrial cytochromes and myoglobin.
Under conditions of decreased work, as in potassium arrest, plots of cytochrome reduction vs myoglobin saturation deviate from an identity relationship in a direction consistent with significant volumes of tissue containing fractional cytochrome reduction higher than myoglobin desaturation. These observations may be interpreted in terms of changes in oxygen gradients within heart muscle as a function of oxygen demand.
Research was supported by grant HL47924 from the National Institutes of Health.
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