This test provides information about the rate of oxygen transfer from the lung to the pulmonary capillary bed. This transfer occurs by a process of passive diffusion and is documented by using carbon monoxide, which is transferred by the same path, by binding with hemoglobin.
Gas exchange in the lungs across alveolar- capillary interface depends on its structural and functional properties.
Lung gas volume; path length for diffusion in gas phase; thickness & area of the alveolar capillary membrane; effects of airway closure; and blood volume of the capillaries that are supplying the ventilated alveoli.
Absolute levels of ventilation & perfusion; their distribution relative to each other; alveolar gas composition; membrane diffusion characteristics; hemoglobin (Hb) concentration & its binding properties in alveolar capillaries; and gas tensions in blood where gas exchange is taking place.