Gas Exchange in the Lung

Gas exchange in the lung depends on tidal breathing, which brings new oxygen to and removes carbon dioxide from alveolar gas. This maintains alveolar partial pressures that promote passive diffusion to add oxygen and remove carbon dioxide from blood in alveolar capillaries. In a lung model without ventilation and perfusion (V-A /Q) mismatch, alveolar partial pressures of oxygen and carbon dioxide are primarily determined by inspiratory pressures and alveolar ventilation. Regions with shunt or low V-A /Q ratios worsen arterial oxygenation while alveolar dead space and high V-A /Q lung units lessen CO2 elimination efficiency. Although less common, diffusion limitation might cause hypoxemia in some situations. This review covers the principles of lung gas exchange and therefore mechanisms of hypoxemia or hypercapnia. In addition, we discuss different metrics that quantify the deviation from ideal gas exchange.

Automated summary

Gas exchange in the lung is crucial for maintaining normal respiration. Tidal breathing allows fresh oxygen to enter the alveoli and removes waste carbon dioxide. The pressures of oxygen and carbon dioxide in the alveoli affect the concentrations of these gases in the blood. Factors such as ventilation-perfusion mismatch, shunt, dead spaces, and imbalanced lung unit ratios can lead to abnormal oxygenation and carbon dioxide elimination. Understanding the principles of lung gas exchange and using appropriate metrics for assessment are important for studying respiratory disorders.