Determining Factors of Tissue O₂ Uptake

Abstract

The factors which affect O₂ uptake by whole the body or by organs such as skeletal muscles have been extensively studied. Some of these studies have shown that O₂ uptake (VO₂) may be altered by changes in blood flow (Q) [1, 2], arterial oxygen tension (PaO₂) [1,2], other blood gas parameters (O₂ capacity [3], O₂ hemoglobin affinity [4–7], or by saturation of the mitochondrial ATP-generating capacity [8]. However, in normal conditions, when O₂ demand is low, it is generally admitted that O₂ uptake is independent of these parameters [2]. More generally, O₂ uptake is independent of O₂ delivery until very low levels of O₂ delivery are reached [9-11]. When O₂ demand is high, tissue O₂ uptake becomes O₂ delivery-limited over a wider range. Recently, some experimental data in canine skeletal muscle have demonstrated that in situations of high O₂ demand, O₂ uptake can be limited not only by O₂ delivery but also by O₂ diffusion [12, 13]. In addition, certain pathological states such as adult respiratory distress syndrome and sepsis have been found to alter drastically the relationships between O₂ delivery and O₂ uptake [14–16].