Determinants of skeletal muscle oxygen consumption assessed by near-infrared diffuse correlation spectroscopy during incremental handgrip exercise

Abstract

Near-infrared diffuse correlation spectroscopy (DCS) is a rapidly evolving optical imaging technique for the assessment of skeletal muscle O₂ utilization (mVO₂). We compared DCS-derived determinants of mVO₂ with conventional measures [blood flow by brachial artery Doppler ultrasound and venous O₂ saturation (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>S</mml:mtext><mml:msub><mml:mtext>V</mml:mtext><mml:mrow><mml:msub><mml:mtext>O</mml:mtext><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:msub></mml:mrow></mml:math>)] in eight volunteers at rest and during incremental handgrip exercise. Brachial artery blood flow and DCS-derived blood flow index (BFI) were linearly related (R² = 0.57) and increased with each workload, whereas <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>S</mml:mtext><mml:msub><mml:mtext>V</mml:mtext><mml:mrow><mml:msub><mml:mtext>O</mml:mtext><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:msub></mml:mrow></mml:math> decreased from 65.3 ± 2.5% (rest) to 39.9 ± 3.0% (light exercise; <i>P</i> < 0.01) with no change thereafter. In contrast, DCS-derived tissue O₂ saturation decreased progressively with each incremental stage (<i>P</i> < 0.01), driven almost entirely by an initial steep rise in deoxyhemoglobin/myoglobin, followed by a linear increase thereafter. Whereas seemingly disparate at first glance, we believe these two approaches provide similar information. Indeed, by plotting the mean convective O₂ delivery and diffusive O₂ conductance, we show that the initial increase in mVO₂ during the transition from rest to exercise was achieved by a greater increase in diffusive O₂ conductance versus convective O₂ delivery (10-fold vs. 4-fold increase, respectively), explaining the initial decline in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>S</mml:mtext><mml:msub><mml:mtext>V</mml:mtext><mml:mrow><mml:msub><mml:mtext>O</mml:mtext><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:msub></mml:mrow></mml:math>. In contrast, the increase in mVO₂ from light to heavy exercise was achieved by equal increases (1.8-fold) in convective O₂ delivery and diffusive O₂ conductance, explaining the plateau in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>S</mml:mtext><mml:msub><mml:mtext>V</mml:mtext><mml:mrow><mml:msub><mml:mtext>O</mml:mtext><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:msub></mml:mrow></mml:math>. That DCS-derived BFI and deoxyhemoglobin/myoglobin (surrogate measure of O₂ extraction) share the same general biphasic pattern suggests that both DCS and conventional approaches provide complementary information regarding the determinants of mVO₂.<b>NEW & NOTEWORTHY</b> Near-infrared diffuse correlation spectroscopy (DCS) is an emerging optical imaging technique for quantifying skeletal muscle O₂ delivery and utilization at the microvascular level. Here, we show that DCS provides complementary insight into the determinants of muscle O₂ consumption across a wide range of exercise intensities, further establishing the utility of DCS.