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Diffusive resistance to O2 transport in muscle
1Division of Physiology, Department of Medicine, University of California, San Diego, La Jolla, CA 92093-0623, USA.
Acta Physiologica Scandinavica
|April 12, 2000
Summary
Oxygen transport to muscle mitochondria is limited by diffusion, impacting maximal oxygen uptake (VO2max). Capillary structure and hemoglobin levels, not fiber size, constrain this vital process.
Area of Science:
- Exercise Physiology
- Muscle Metabolism
- Cardiovascular Physiology
Background:
- August Krogh's 20th-century work established O2 diffusion from red blood cells to mitochondria.
- The precise role of diffusion in maximal oxygen flux remains debated.
Purpose of the Study:
- To review evidence on the limitations of O2 diffusion in muscle.
- To assess the impact of diffusion limitations on maximal oxygen consumption (VO2max).
Main Methods:
- Review of existing physiological data.
- Analysis of factors influencing diffusional conductance in muscle.
Main Results:
- Maximal O2 diffusion is limited by capillary structure and blood hemoglobin concentration.
- Diffusional conductance is independent of muscle fiber size.
- Limited diffusion constrains O2 unloading and VO2max, particularly in trained individuals.
Conclusions:
- O2 transport from microvasculature to mitochondria faces significant diffusion limits.
- These limits substantially affect maximal VO2, comparable to blood flow limitations.
- Further research is needed to assess O2 unloading impairments due to perfusion/metabolism heterogeneity.