Effects Of Using A Light Shield On Near Infrared Spectroscopy Measurements Of Skeletal Muscle Oxygenation During Cycling

Near Infrared Spectroscopy (NIRS) measures oxygenated (O2Hb) and deoxygenated (HHb) hemoglobin in skeletal muscle. Tissue Saturation Index (TSI) measures oxygenated hemoglobin as a percentage of total hemoglobin. Ambient light affects the sensitivity of NIRS measurements. There is limited literature quantifying the effects of stray light. PURPOSE: Determine the effect of a light blocker on NIRS measurements. METHODS: Lactate threshold tests were performed on participants (n=23) on a cycling ergometer, followed by a repeated protocol of an on/off kinetics test, with and without a light blocker. The order of the light blocker was randomized. ΔO2Hb, ΔHHb, and ΔTSI were measured across the 3 on/off periods for both the light blocker being on and off. VO2 was measured using a metabolic cart. Work to rest was calculated as the difference between work and rest steady state of sequential sections and is referred to as delta (Δ). RESULTS: Paired T-tests were used to compare the light blocker on vs. off conditions. ΔHHb was lower in the light shield on condition (p=0.002) and ΔTSI was higher in the light shield on condition (p=0.001). There were no significant differences in ΔO2Hb between light shield status (p=0.08). Cronbach Alpha coefficients for NIRS measurements demonstrated excellent reliability (0.96-0.99). Cronbach alpha coefficients for VO2 were acceptable to excellent, (.71-.99). Repeated measures ANOVAs revealed significant differences between the 3rd on/off cycle and the first two cycles (P<.05) CONCLUSIONS: NIRS measurements are reliable with or without a light shield. VO2 reliability measurements were acceptable to excellent with more variability during the 3rd on/off cycle. This suggests eliminating the 3rd cycle. The ΔHHb measurements were lower with a light blocker, however, ΔTSI was larger with potential for improving minimal detectable clinical changes. Using the ΔTSI values is an absolute measure that considers total hemoglobin and changing blood flow and volume. SC INBRE Award Number: P20GM103499