Gas Exchange

Gas Exchange explains how four processes—delivery of oxygen, excretion of carbon dioxide, matching of ventilation and perfusion, and diffusion—allow the respiratory system to maintain normal partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2) in the arterial blood. Partial pressure is important because O2 and CO2 molecules diffuse between alveolar gas and pulmonary capillary blood and between systemic capillary blood and the tissues along their partial pressure gradients, and diffusion continues until the partial pressures are equal. Ventilation is an essential part of gas exchange because it delivers O2, eliminates CO2, and determines ventilation–perfusion ratios. This chapter also explains how and why abnormalities in each of these processes may reduce PaO2, increase PaCO2, or both.