(885.11) A NIRS-derived Skeletal Muscle Oxygen Consumption Method Accurately Reflects the Gold Standard Direct Fick Method during Single-leg Knee Extension Exercise

Poster Board Number: E309

Jesse Craig (University of Utah), Ryan Broxterman (University of Utah), Zachary Barret-OKeefe (University of Utah), D. Walter Wray (University of Utah), Thomas Barstow (Kansas State University), Russell Richardson (University of Utah), Joel Trinity (University of Utah)

Background: Quantifying the oxygen consumption (V̇O2) of skeletal muscle, which represents the largest metabolically-active tissue mass, is an important assessment in exercise physiology. The gold standard for quantifying muscle V̇O2 in the exercising human is the direct Fick method, however, technical challenges (e.g. arterial catheter insertion) preclude the widespread use of this technique, justifying the need for alternative approaches for the quantification of muscle V̇O2. Recently, we developed a noninvasive method of quantifying muscle V̇O2 using Doppler ultrasound measurements of blood flow (Q̇) and near-infrared spectroscopy (NIRS)-derived deoxygenated-[Heme] in a modified Fick method calculation, but, to date, this has not been validated against the gold standard method. Purpose and Hypotheses: Therefore, the purpose of this investigation was to compare NIRS-derived and direct Fick quantification of muscle V̇O2 at multiple levels of single-leg knee-extensor exercise. We tested the hypotheses that: 1) the muscle V̇O2 assessed by direct Fick and the NIRS-derived muscle V̇O2 would not be statistically different from each other across work rates, and 2) the V̇O2 assessed by the two techniques would be strongly related.

Methods: Seven healthy young volunteers (3 women, 4 men; 24 ± 5 years) performed an incremental work rate test on a dynamic single-leg knee-extensor ergometer. Measurements of femoral artery Q̇ (Doppler ultrasound), vastus lateralis deoxygenated-[Heme] (NIRS), and femoral artery and vein oxygen content were taken at rest, 0, 5, 10, 15, and 20 Watts (W) and used to estimate direct Fick and NIRS-derived muscle V̇O­2.

Results: NIRS-derived V̇O2 was not different from direct Fick V̇O2 at any point (rest: 45 ± 21 vs 25 ± 17 ml/min; 0 W: 153 ± 70 vs 133 ± 68 ml/min; 5 W: 188 ± 81 vs 160 ± 65 ml/min; 10 W: 242 ± 123 vs 214 ± 91 ml/min; 15 W: 279 ± 131 vs 247 ± 89 ml/min; 20 W: 343 ± 163 vs 319 ± 122 ml/min; all P = 0.26 – 0.44). Muscle V̇O2 determined by the two techniques was strongly related (r2: 0.97 ± 0.03) with a slope of 1.1 ± 0.3 and Y-intercept of -21 ± 22 ml/min.

Discussion: Taken together, these findings indicate that the NIRS-derived, noninvasive assessment of skeletal muscle V̇O2 accurately reflects the gold standard quantification of muscle V̇O2 over a range of work rates (with a constant ≈20 ml/min offset). This investigation provides the first evidence to support the use of the NIRS-derived muscle V̇O2 estimate during free-flow conditions (i.e. not using venous or arterial occlusions like previous work), introducing a novel, noninvasive technique to quantify exercising skeletal muscle V̇O2.

Veterans Affairs VA Merit Award I01 CX001999, National Heart, Lung, and Blood Institute Grant R01 HL142603 and National Research Service Award T32 HL139451



Individual (dashed lines) and group mean (bold line) oxygen consumption (VO2) quantified by NIRS-derived and direct Fick techniques. The dotted line represents the line of identity.