Near-infrared estimation of O-2 supply and consumption in forearm muscles working at varying intensity

We estimated a blood flow index, O-2 supply index, and O-2 consumption index from near-infrared (NIR) signals during venous occlusion imposed at rest and immediately after handgrip exercise with loads equal to 5, 10, 15, 20, 25, and 30% of the maximum voluntary contraction. We also estimated forearm blood flow (BFfa) by strain-gauge plethysmography and forearm O-2 consumption (VO2(fa),) by the invasive method. There was a significant correlation between the rate of increase in total hemoglobin during venous occlusion obtained from NIR signals and BFfa in each subject (r = 0.853 similar to 0.981, P < 0.001). There was also a significant correlation (r = 0.854 similar to 0.944, P < 0.001) between the O-2 consumption index estimated from NIR signals and VO2fa. The mean values for O-2 supply index in five subjects increased with exercise intensity, while the O-2 consumption index showed no further increase above 25% of maximum voluntary contraction. We found significant positive correlations between the O-2 supply index and BFfa(r = 0.986, P < 0.001) and the O-2 consumption index and VO2fa (r = 0.976, P < 0.001) during exercise at 5-30% of maximum voluntary contraction. These results demonstrate that analysis of NIR signals during venous occlusion provides an advantageous method of estimation of O-2 supply and consumption in working muscles during exercise of varying intensity.