Non-invasive measurements of O2 availability in human skeletal muscle with near-infrared spectroscopy.

The availability of O2 in the human vastus lateralis muscle has been investigated with non-invasive near-infrared spectroscopy (NIRS) using a commercially available unit (RunMan, NIM Inc. Philadelphia). The measuring probe placed above the skin illuminates the underlying tissue and measures the reflected light at two wavelengths (760 and 850 nm). Due to differences in the absorption spectra between HbO2 and Hb the difference in light intensity at these two wavelengths will be a relative index of tissue oxygenation. Prolonged arterial occlusion and static contraction have been studied. Arterial occlusion resulted in a decreased O2 saturation with a half-time of 2.3 +/- 0.2 min (mean +/- SE, n = 4). Restoration of blood flow resulted in a rapid tissue reoxygenation with a half-time of 24 +/- 2 s. Reoxygenation after static contraction occurred with a half time of 19-37 s. The half-time of reoxygenation subsequent to exercise and/or ischemia may be a valuable parameter in sports medicine and in the evaluation of peripheral vascular disease.