Is there a competition for oxygen availability between respiratory and limb muscles?

Area of Science:

• Exercise Physiology
• Altitude Physiology
• Muscle Metabolism

Background:

• During strenuous exercise, muscles require more oxygen.
• Hypoxia, or low oxygen levels, may alter blood flow distribution.
• It is hypothesized that blood flow may shift from peripheral to respiratory muscles during heavy exercise in hypoxic conditions.

Purpose of the Study:

• To investigate if hypoxia causes blood flow redistribution from limb to respiratory muscles during heavy exercise.
• To test the hypothesis that oxygen competition between muscles favors respiratory muscles.

Main Methods:

• Non-invasive near-infrared spectroscopy (NIRS) monitored regional tissue oxygen saturation (rSO2) and tissue hemoglobin concentration ([Hbt]).
• Measurements were taken on intercostal (respiratory) and vastus medialis (limb) muscles in lowlanders and highlanders at sea level and 4350m altitude.
• Subjects underwent incremental exercise tests.

Main Results:

• At altitude, both intercostal and vastus medialis rSO2 were lower and decreased similarly during exercise.
• Tissue hemoglobin concentration increased in both muscle groups during exercise.
• Maximal exercise in hypoxia did not change the oxygen saturation or hemoglobin kinetics in peripheral muscles.

Conclusions:

• The study's findings do not support the hypothesis of blood flow redistribution from peripheral to respiratory muscles during heavy exercise in hypoxia.
• Oxygen demand competition does not appear to favor respiratory muscles in terms of blood flow allocation under these conditions.