Effects of increased skin blood flow on muscle oxygenation/deoxygenation: comparison of time-resolved and continuous-wave near-infrared spectroscopy signals.

PURPOSE

We quantified the contribution of skin blood flow (SkBF) to tissue oxygenation/deoxygenation of the flexor digitorum profundus muscle during cutaneous vasodilation.

METHODS

Time-resolved near-infrared spectroscopy (TRS-NIRS) was utilized to measure the potential influence of optical factors [mean optical pathlength (PL) and coefficients of absorption (μa) and reduced scattering ([Formula: see text])] on the NIRS-derived signals of eight male subjects.

RESULTS

The approximately threefold elevation of SkBF during 1 h whole-body heating (increased internal temperature ~0.9 °C) increased both μa and [Formula: see text] without changing PL. Assuming that the [Formula: see text] coefficient remained constant, i.e., as with continuous-wave (CW) NIRS, resulted in a significant increase in the apparent oxygenation [oxy(Hb + Mb), from 113 ± 13 μM (mean ± SD) for control to 126 ± 13 for the increased SkBF condition, P < 0.01]: this was in marked contrast to the unchanged TRS-derived values. The deoxygenation [deoxy(Hb + Mb)] also increased from control to elevated SkBF (CW-NIRS, from 39 ± 8 to 45 ± 7; TRS, from 38 ± 6 to 44 ± 7 μM; P < 0.01 for both), but less than that seen for oxy(Hb + Mb) and not different between TRS- and CW-NIRS. Further, and in contrast to oxy(Hb + Mb), temporal profiles of deoxy(Hb + Mb) measured by the two NIRS methods were not different.

CONCLUSIONS

These findings support use of either NIRS method to estimate local muscle fractional O2 extraction, but not oxygenation, when SkBF is increased at rest.