Limitations of oxygen transport to the cell

Summary

Perhaps the major points to be made from this review are the following:

• 1. Transport of O₂ from the environment to the mitochondrion is accomplished in a well-described but not yet well-understood sequence of diffusive and convective steps that are highly interactive and thus integrative in their outcome.

• 2. Thus, under conditions of O₂-supply limitation of$\dot V_{O_2 \max }$ in strenuous exercise in health,all transport steps affect the value of$\dot V_{O_2 \max }$ reached, but the sensitivity of$\dot V_{O_2 \max }$ (to changes in any step) is not the same for each step, and moreover, will vary with the quantitative conditions. It is time to abandon the very concept of a single limiting factor to$\dot V_{O_2 \max }$.

• 3. O₂ supply limitation of$\dot V_{O_2 }$ is seen under two very different conditions that in fact are at the opposite ends of the spectrum of metabolic scope:$\dot V_{O_2 \max }$ in strenuous exercise in health and basal$\dot V_{O_2 }$ in severe disease. Analysis of the latter using lessons learned from the former may be valuable.

• 4. We are currently greatly limited in our understanding of supply limitation in disease, mostly because of unavailability of methods to assess organ-specific cellular metabolism and its relation to O₂ supply in patients, essentially noninvasively — a research direction that needs much support.