Lung Function Tests

Abstract

Lung function tests are of value in defining disease quantitatively from a functional aspect and in monitoring effects of treatment, and they are becoming increasingly useful in the detection of industrial lung diseases and in monitoring the physiology of ageing. The main function of the lungs is to exchange carbon dioxide and oxygen with pulmonary capillary blood. This requires an efficient set of bellows, conducting airways and gas exchange mechanisms. Tests of lung function in routine use include the following:

• 1. The volume of gas in the lungs and its various subdivisions (static lung volumes)

• 2. The ability of the lungs to conduct gas out of the chest as rapidly as possible (the forced expiratory manoeuvre).

• 3. The ability of the lungs to transfer carbon monoxide (CO) from outside the body into the pulmonary capillary blood (the CO transfer test).

• 4. The ability of the lungs to maintain normal levels of Paco₂, Pao₂ and (H⁺) (see Chapter 5).