ABSTRACT
Measurement of the lung's ability to transfer gas from the alveoli to the circulation is a fundamental respiratory function test, as it measures directly what the lung really does in life. Gas transfer indices provide a window on the blood-gas barrier and are relatively easy to measure in the lab. KCO is the primary measurement which is made of gas transfer. The alveolar volume is the volume of the lungs available for gas exchange, calculated by gas dilution using an inert gas in the test gas mixture. The physiology of pulmonary gas exchange is governed by Fick's law of passive diffusion. Because there are more physiological variables affecting the measurement of gas transfer than other lung function tests, results are subject to a wider range of normal variability than many other lung function tests. Pulmonary emphysema leads to destruction of alveolar septae, which reduces the surface area for gas exchange, but not the lung volume.
