Quantitative muscle oxygenation measurement using NIRS with correction for the influence of a fat layer: Comparison of oxygen consumption rates with measurements by other techniques

The inhomogeneity of tissue structure greatly affects the sensitivity of tissue oxygenation measurement by near-infrared spectroscopy (NIRS). We have proposed a method for correcting the influence of a subcutaneous fat layer on muscle oxygenation measurements. In this study, we validated our correction method by measuring oxygen consumption rates of the forearm muscle (Vo(2)mus) and comparing the measurements with those obtained by other techniques: P-31-magnetic resonance spectroscopy (P-31-NMR) and positron emission tomography (PET). In NIRS, Vo2mus was obtained from the falling rate of oxygenation in ischemia tests. The values of Vo(2)mus were corrected using a curve of measurement sensitivity against fat layer thicknesses, which were measured by ultrasonography. The corrected Vo(2)mus showed greater values and less variation between individuals (0.21 +/-0.03 ml 100g(-1) min(-1)) than did the uncorrected one (0.17+/-0.04 ml 1000g(-1) min(-1)). In the P-31-NMR measurements on 10 subjects, Vo(2)mus was estimated from changes in phosphocreatine (PCr). The corrected Vo(2)mus in NIRS correlated well with the measurements by P-31-NMR (r = 0.61), compared to the uncorrected Vo(2)mus (r=-0.26). This result suggested that our correction method is valid. Vo2mus was also measured using PET in one of the authors. The measured values by NIRS (with correction), P-31-NMMR, and PET were 0.22, 0.17, 0.24 ml 100g(-1) min(-1) respectively. The measurement by NIRS using our correction method was in an acceptable range.