Diffusing capacity represents a measure of how efficiently can carbon dioxide and oxygen can get diffused between the lungs and the blood. It is often used for testing the diagnosis of COPD and other lung diseases for monitoring and treating. Diffusing capacity can be reduced in multiple ways, and healthcare providers usually employ the measure in combination with other function tests to determine the extent of either obstructive or restrictive lung conditions.
According to Fick’s Law, the rate of gas diffusion across a membrane is pre-determined by the chemical structure of the membrane itself, its surface area, thickness, and the partial pressure gradient of the gas across the membrane. Therefore, the law implies a qualitative relationship between the diffusion of gas and the particular chemical properties of the membrane. Due to the fact that all variables described by Fick’s Law cannot be measured directly, the indicator of diffusion capacity is used as an empirically measurable identifies that combines the influence of the variables.
In lung disease, the qualities of the alveolar membranes change, leading to them becoming thicker. This decreases diffusing capacity, leading to difficulties in breathing. The thickening of the membrane occurs in such conditions as sarcoidosis and pulmonary fibrosis. Also, diffusing capacity can be low if there is less surface area available for the transferring of carbon dioxide and oxygen, which is a characteristic of COPD.