Fig. 4

Relationship between PO₂ and the rate of oxygen usage by the cells at different concentrations of intracellular adenosine diphosphate (ADP). As long as intracellular PO₂ remains above 1 mmHg, the rate of oxygen usage remains constant, depending on the ADP concentration. (Reuse from Guyton and Hall Textbook of Medical Physiology 14th ed. with permission from Elsevier B.V.)