| Popis: |
Heterogeneity in the distribution of both blood flow (Q) and O2consumption (VO2) has not been assessed by near-infrared spectroscopy in exercising normal human muscle. We used near-infrared spectroscopy to measure the regional distribution of Q and VO2 in six trained cyclists at rest and during constant-load exercise (unloaded pedaling, 20%, 50%, and 80% of peak Watts) in both normoxia and hypoxia (inspired O2 fraction = 0.12). Over six optodes over the upper, middle, and lower vastus lateralis, we recorded 1) indocyanine green dye inflow after intravenous injection to measure Q; and 2) fractional tissue O2 saturation (StiO2) to estimate local VO2-to-Q ratios (VO2/Q). Varying both exercise intensity and inspired O2 fraction provided a (directly measured) femoral venous O2 saturation range from about 10 to 70%, and a correspondingly wide range in StiO2. Mean Q-weighted StiO2 over the six optodes related linearly to femoral venous O2 saturation in each subject. We used this relationship to compute local muscle venous blood O2 saturation from StiO2recorded at each optode, from which local VO2/Q could be calculated by the Fick principle. Multiplying regional VO2/Q by Q yielded the corresponding local VO2. While six optodes along only in one muscle may not fully capture the extent of heterogeneity, relative dispersion of both Q and VO2 was ∼0.4 under all conditions, while that for VO2/Q was minimal (only ∼0.1), indicating in fit young subjects 1) a strong capacity to regulate Q according to regional metabolic need; and 2) a likely minimal impact of heterogeneity on muscle O2availability. Copyright © 2015 the American Physiological Society. |
