Optical spectroscopic method for in vivo measurement of cardiac myoglobin oxygen saturation

A fiber-optic-based spectrophotometer was developed to acquire optical reflectance spectra from a living dog heart. A bullseye concentric optical probe with a 3 mm source-to-detector fiber separation was designed to obtain a 1.5 mm average tissue depth of light penetration. Spectra were analyzed in the near-infrared region from 660 to 840 nm. Myoglobin oxygen saturation was determined by partial least-squares analysis using a calibration spectral data set developed irt vitro. Comparison of in vivo and in vitro spectra by Mahalanobis distance and residual ratio tests demonstrated good similarity, justifying use of partial least-squares analysis. Coronary perfusion with an oxygenated blood substitute, Fluosol(R), was used to demonstrate that hemoglobin had little effect on the analysis. An increase in myoglobin saturation of 5% was noted when the animals were changed from inspired room air to 100% oxygen. Occlusion of the coronary artery resulted in prompt decrease in myoglobin saturation, and release of the occlusion was followed by rapid increase in saturation to a value above baseline. These experiments demonstrate that it is feasible to use partial least-squares analysis of near-infrared reflectance spectra to determine myoglobin saturation in the blood-perfused, beating heart.