Performance of near-infrared spectroscopy in measuring local O(2) consumption and blood flow in skeletal muscle.

The aim of this study was to investigate local muscle O(2) consumption (muscV(O(2))) and forearm blood flow (FBF) in resting and exercising muscle by use of near-infrared spectroscopy (NIRS) and to compare the results with the global muscV(O(2)) and FBF derived from the well-established Fick method and plethysmography. muscV(O(2)) was derived from 1) NIRS using venous occlusion, 2) NIRS using arterial occlusion, and 3) the Fick method [muscV(O(2(Fick)))]. FBF was derived from 1) NIRS and 2) strain-gauge plethysmography. Twenty-six healthy subjects were tested at rest and during sustained isometric handgrip exercise. Local variations were investigated with two independent and simultaneously operating NIRS systems at two different muscles and two measurement depths. muscV(O(2)) increased more than fivefold in the active flexor digitorum superficialis muscle, and it increased 1.6 times in the brachioradialis muscle. The average increase in muscV(O(2(Fick))) was twofold. FBF increased 1.4 times independent of the muscle or the method. It is concluded that NIRS is an appropriate tool to provide information about local muscV(O(2)) and local FBF because both place and depth of the NIRS measurements reveal local differences that are not detectable by the more established, but also more global, Fick method.