Diffuse Optical Spectroscopy Assessment of Resting Oxygen Metabolism in the Leg Musculature

We lack reliable methods to continuously assess localized, resting-state muscle activity that are comparable across individuals. Near-infrared spectroscopy (NIRS) provides a low-cost, non-invasive means to assess localized, resting-state muscle oxygen metabolism during venous or arterial occlusions (VO_2VO and VO_2AO, respectively). However, this technique is not suitable for continuous monitoring, and its utility is limited to those who can tolerate occlusions. Combining NIRS with diffuse correlated spectroscopy (DCS) enables continuous measurement of an index of muscle oxygen metabolism (VO_2i). Despite the lack of previous validation, VO_2i is employed as a measure of oxygen metabolism in the muscle. Here we characterized measurement repeatability and compared VO_2i with VO_2VO and VO_2AO in the medial gastrocnemius (MG) in 9 healthy adults. Intra-participant repeatability of VO_2i, VO_2VO, and VO_2AO were excellent. VO_2i was not significantly correlated with VO_2AO (p = 0.15) nor VO_2VO (p = 0.55). This lack of correlation suggests that the variability in the calibration coefficient between VO_2i and VO_2AO/VO_2VO in the MG is substantial across participants. Thus, it is preferable to calibrate VO_2i prior to every monitoring session. Important future work is needed to compare VO_2i against gold standard modalities such as positron emission tomography or magnetic resonance imaging.