Microvascular Tissue Oxygenation and Oxidative Metabolism Changes in the Pedicled Latissimus Dorsi Muscle During Graded Hypoxia: Correlation Between Near Infrared and 31P Nuclear Magnetic Resonance Spectroscopy

BackgroundIn this study, the microvascular tissue oxygenation and oxidative muscle metabolism during graded hypoxia and reoxygenation were examined in a rabbit model by near-infrared (NIR) spectroscopy and correlated with high-energy phosphates measured by 31P nuclear magnetic resonance (NMR) spectroscopy.Materials and MethodsGraded hypoxia was performed in a New Zealand rabbit model (n = 20, 2.0 ± 0.4 kg) by a stepwise reduction of the fraction of inspired oxygen (FiO2) from 0.3 to 0.05 (intervention group versus control group). Recovery and reoxygenation were achieved using FiO2 of 0.3. A noninvasive NIR spectroscopy sensor and NMR probe was positioned on the surface of the prepared pedicled latissimus dorsi muscle. Microvascular tissue oxygenation (oxyhemoglobin, HbO2; deoxyhemoglobin, HHb) and redox state of cytochrome oxidase (CytOx) were measured by NIR spectroscopy and correlated with standard values of oxidative muscle metabolism (phosphocreatine, PCr; adenosine triphosphate, ATP) measured by time-resolved 31P NMR spectroscopy (4.7T).ResultsSignificant correlation was found between PCr and HbO2 (r = 0.85, P < 0.001) and HHb (r = −0.75, P < 0.001). β-ATP levels correlated significantly with CytOx (r = 0.87, P < 0.001).ConclusionsThe data suggest that changes in high-energy phosphates (PCr- and ATP-levels) correlate closely with microvascular tissue oxygenation (HbO2, HHb, CytOx) measured by NIR spectroscopy.