Normal standards for lung volumes, intrapulmonary gas-mixing, and maximum breathing capacity.

An objective assessment of respiratory function is important in the diagnosis and management of patients complaining of dyspnoea or suffering from disease involving the lungs. There are four main subdivisions, excluding blood composition, of the respiratory gas exchange process (ventilatory, distributive, diffusional, and circu!atory), which are disturbed in various proportions in different diseases; therefore no single test of respiratory function can be adequate in all cases (Comroe, 1951 ; Gilson and Oldham, 1952). The ventilatory and distributive (intrapulmonary gas mixing) aspects of respiratory efficiency are commonly studied by measuring the total lung capacity (T.L.C.) and its subdivisions, the maximum breathing capacity (M.B.C.), the timed vital capacity (T.V.C.), and some form of "mixing efficiency" test. It is perhaps rather generally assumed that reasonably adequate information is already available concerning these tests, which have been in