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

Near-infrared diffuse correlation spectroscopy (DCS) is a rapidly evolving optical imaging technique for the assessment of skeletal muscle O 2 utilization (mVO 2 ). We compared DCS-derived determinants of mVO 2 with conventional measures [blood flow by brachial artery Doppler ultrasound and venous O 2 saturation ( S V O 2)] in eight volunteers at rest and during incremental handgrip exercise. Brachial artery blood flow and DCS-derived blood flow index (BFI) were linearly related (R 2  = 0.57) and increased with each workload, whereas S V O 2decreased from 65.3 ± 2.5% (rest) to 39.9 ± 3.0% (light exercise; P < 0.01) with no change thereafter. In contrast, DCS-derived tissue O 2 saturation decreased progressively with each incremental stage ( P < 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 O 2 delivery and diffusive O 2 conductance, we show that the initial increase in mVO 2 during the transition from rest to exercise was achieved by a greater increase in diffusive O 2 conductance versus convective O 2 delivery (10-fold vs. 4-fold increase, respectively), explaining the initial decline in S V O 2. In contrast, the increase in mVO 2 from light to heavy exercise was achieved by equal increases (1.8-fold) in convective O 2 delivery and diffusive O 2 conductance, explaining the plateau in S V O 2. That DCS-derived BFI and deoxyhemoglobin/myoglobin (surrogate measure of O 2 extraction) share the same general biphasic pattern suggests that both DCS and conventional approaches provide complementary information regarding the determinants of mVO 2 . NEW & NOTEWORTHY Near-infrared diffuse correlation spectroscopy (DCS) is an emerging optical imaging technique for quantifying skeletal muscle O 2 delivery and utilization at the microvascular level. Here, we show that DCS provides complementary insight into the determinants of muscle O 2 consumption across a wide range of exercise intensities, further establishing the utility of DCS.