Comparison Of Near-infrared Spectroscopy Measured Muscle Oxygen Consumption With Whole-body Oxygen Consumption

Research has shown that an altered rate of skeletal muscle (SM) metabolism is associated with illness, disease, and mortality, especially with aging. Near-Infrared Spectroscopy (NIRS) allows for non-invasive assessment of SM oxygen consumption, but few studies have evaluated the relationship between the rate of oxygen consumption in the muscle and whole-body oxygen consumption rate. PURPOSE: To explore the relationship between whole-body oxygen consumption (wbVO2) and skeletal muscle oxygen consumption (mVO2) using NIRS during rest and ambulation. METHODS: A NIRS device was placed on the belly of the medial gastrocnemius (MG) muscle of participants (n = 13, age = 29 ± 10 yrs) and a pneumatic rapid inflation cuff was placed proximal to the testing site to occlude arterial blood flow. Resting MG mVO2 was measured after 5 min of rest in a supine position during three rounds of 30s arterial occlusion and 30s of rest, and ambulatory mVO2 was measured during a 5 s arterial occlusion immediately after 6 min of walking at usual gait speed over a 40 m course. The rate of mVO2 (%/s-1) was calculated from the difference in oxygenated and deoxygenated hemoglobin (Hbdiff) during occlusion. Resting wbVO2 was measured by indirect calorimetry after an overnight fast and ambulatory wbVO2 was measured by portable indirect calorimetry during the 6 min walk. Muscle and whole-body oxygen consumption at rest and during ambulation were compared through Pearson correlations. RESULTS: No significant correlation (β = -0.05, p = 0.87) was found between resting wbVO2 (avg: 3.1 ± 0.3 mL/kg/min) and mVO2 (avg: 0.09 ± 0.05 %/s). However, a significant correlation (β = 0.76, p = 0.003) was found between ambulatory wbVO2 (avg: 14.1 ± 2.9 mL/kg/min) and mVO2 (avg: 1.5 ± 0.8 %/s). CONCLUSION: NIRS can successfully be used to assess mVO2 rate during ambulation. At rest, however, the direct contribution of the MG to wbVO2 is limited as other organs and tissues are contributing substantially to resting metabolism. Supported by Towson University (TU) School of Emerging Technology and TU College of Health Professions