Fig. 4.

Relationship between oxygen delivery (DO₂) and oxygen consumption (VO₂). DO₂ is a product of blood flow and arterial oxygen content (CaO₂). The driving force for oxygen from alveoli to mitochondria is the partial pressure of oxygen (PO₂). Increased mitochondrial PO₂ can lead to formation of reactive oxygen species (ROS). When DO₂ decreases below a critical point, VO₂ becomes dependent on delivery. Hypoxemia leads to hypoxic pulmonary vasoconstriction, anaerobic metabolism, and lactic acidosis. Persistent hypoxemia can result in cell death.