Abstract
We used near-infrared spectroscopy (NIRS) to measure the regional distribution of blood flow 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 acute hypoxia (FIO2=0.12). From each of six optodes on the skin over the upper, middle and lower vastus lateralis, we recorded: a) indocyanine green dye (ICG) inflow after intravenous injection to measure blood flow (Q), and b) fractional tissue O2 saturation (StO2). Varying both exercise intensity and FIO2 provided a (directly measured) femoral venous O2 saturation (SfvO2) range of about 10 to 70%, and a correspondingly wide range in StO2. A linear relationship was found between mean Q-weighted StO2 over the 6 optodes and SfvO2 in each subject. We used this relationship to compute local muscle venous blood O2 saturation from StO2 recorded at each optode, from which local VO2/Q ratios could be calculated by the Fick principle. Multiplying regional VO2/Q by Q yielded the corresponding local VO2. Assuming that the six optodes adequately surveyed the extent of heterogeneity, which must be tested in the future, relative dispersion of both Q and VO2 was about 0.5 under all conditions, while that for VO2/Q was minimal (only about 0.1), indicating in fit young subjects: a) a strong capacity to regulate blood flow according to regional metabolic need from rest to heavy exercise in both normoxia and hypoxia, and b) a likely minimal impact of heterogeneity on muscle O2 availability. Future application of this novel approach should clarify the extent and importance of heterogeneity in muscle of patients with chronic lung diseases.
- © 2014 ERS