Alveoleluften

Alveoleluften refers to the air located in the alveolar spaces of the lungs, the site where gas exchange occurs between air and blood in the pulmonary capillaries. In this article the term is used to denote the alveolar air present during normal breathing, which differs from inspired air due to ongoing gas exchange and mixing with residual air in the alveoli.

In healthy adults at sea level, the alveolar oxygen partial pressure (PAO2) is about 100 mmHg and the alveolar carbon dioxide partial pressure (PACO2) about 40 mmHg. These values are determined by the balance between oxygen uptake and carbon dioxide removal, alveolar ventilation, and pulmonary blood flow. Humidified inspired air adds water vapor (PH2O ~47 mmHg), and the alveolar gas equation relates PAO2 to inspired oxygen: PAO2 ≈ PIO2 − (PACO2 / R), with PIO2 ≈ (Patm − PH2O) × FiO2 and the respiratory quotient R around 0.8.

Anatomically, the alveoli are tiny air sacs at the ends of the respiratory tree. Humans have roughly 480 million alveoli, providing a total surface area of about 70–100 square meters. The alveolar walls consist mainly of type I pneumocytes, with type II pneumocytes secreting surfactant to reduce surface tension. Alveolar macrophages patrol for debris and pathogens.

Functionally, alveoleluften is the medium through which oxygen diffuses into the blood and carbon dioxide diffuses out of it. Gas exchange efficiency depends on diffusion distance, membrane thickness, surface area, and ventilation-perfusion (V/Q) matching. Clinically, the alveolar–arterial gradient (A-a O2 gradient) measures gas exchange efficiency, and disorders such as COPD, edema, pneumonia, or fibrosis can alter alveolar gas composition. End-tidal CO2 is a noninvasive proxy for alveolar CO2 under some conditions.