Systemic Oxygen Transport with Rest, Exercise, and Hypoxia: A Comparison of Humans, Rats, and Mice

Area of Science:

• Physiology
• Comparative Physiology
• Exercise Physiology

Background:

• Understanding systemic oxygen (O2) transport is crucial for comparative physiology.
• Rodent models are frequently used to study O2 transport, but their applicability to humans requires careful evaluation.
• Key O2 transport components include ventilation, diffusion, and circulation.

Purpose of the Study:

• To compare and contrast systemic O2 transport characteristics in humans, rats, and mice.
• To identify conditions under which rodent O2 transport findings can be extrapolated to human responses.
• To analyze O2 transport as a system of linked conductances.

Main Methods:

• Analysis of systemic O2 transport as four linked conductances: ventilation, alveolo-capillary diffusion, circulatory convection, and tissue capillary-cell diffusion.
• Comparison of available data across species at rest and during exercise, in normoxia and hypoxia.
• Identification of data gaps, particularly for mice.

Main Results:

• Mechanisms of O2 transport are similar across species, but quantitative differences are significant.
• Abundant data exist for resting conditions, but information on pulmonary gas exchange, circulatory convection, and tissue diffusion is scarce in mice.
• Resting alveolar and blood O2 partial pressures (PO2) are similar across species in normoxia.
• Rats exhibit a greater ventilatory response and maintain blood PO2 closer to resting values during hypoxia and exercise compared to humans, suggesting higher gas exchange efficacy.

Conclusions:

• While O2 transport mechanisms are conserved, quantitative differences necessitate caution when applying rodent findings to humans.
• Significant data gaps exist for mice, particularly concerning circulatory and tissue O2 transport.
• Rats demonstrate enhanced gas exchange efficacy under hypoxic and exercise conditions compared to humans, primarily due to a more robust ventilatory response.