Luftutbytet

Luftutbytet, or gas exchange, refers to the transfer of oxygen from inhaled air into the blood and the removal of carbon dioxide from the blood into the lungs for exhalation. In humans, this exchange occurs mainly in the lungs, across the alveolar-capillary membrane.

The mechanism relies on diffusion driven by differences in gas partial pressures between the alveolar air and the blood in surrounding capillaries. Oxygen moves from alveolar air (high PO2) into blood (low PO2), while carbon dioxide moves from blood (high PCO2) into alveolar air (low PCO2). The rate of transfer depends on surface area, membrane thickness, diffusion distance, and the matching of ventilation (airflow) and perfusion (blood flow). The alveolar membrane consists of alveolar epithelium, a shared basement membrane, and capillary endothelium, with pulmonary surfactant reducing surface tension and aiding gas diffusion.

Regulation and assessment focus on ventilation-perfusion matching, ensuring adequate air reaches the alveoli and sufficient blood is available for gas transfer. Clinical evaluation uses arterial blood gas analysis, pulse oximetry to monitor oxygen saturation, and diffusion capacity testing (DLCO) to quantify gas transfer efficiency. Conditions such as pneumonia, pulmonary edema, interstitial fibrosis, chronic obstructive pulmonary disease, or acute respiratory distress syndrome can impair luftutbytet and lead to hypoxemia or hypercapnia.

Physiological importance lies in supplying oxygen for cellular respiration and removing metabolic carbon dioxide. Variations occur during high altitude, exercise, or changes in cardiovascular status, where adjustments in ventilation and perfusion help maintain adequate oxygen delivery. Disruptions to luftutbytet are central to many respiratory diseases and are a primary target for diagnostic and therapeutic strategies.