The maximum breathing capacity test.

Since the introduction of this test by Hermannsen (1933), the measurement of maximum breathing capacity (M.B.C.) on different groups of subjects has been reported on several occasions (for example, Gray and Green, 1945; Baldwin, Cournand, and Richards, 1948; Wright, Yee, Filley, and Stranahan, 1949; and Gilson and Hugh-Jones, 1949). Most investigators have performed this test with a spirometer, such as is used for metabolic rate determinations, from which the non-return valves and carbon dioxide absorbing canister have been removed. The instructions issued to the subjects have varied. Baldwin instructed his subjects to "breathe as quickly and as deeply as possible: the accent on speed." The instructions given by Gray and Green are too lengthy and complicated for general use. Gilson and Hugh-Jones instructed the subjects to breathe " as deep as you can, as fast as you can." They modified these instructions to some extent by exhorting the subjects, during the first few moments of the test, to make greater efforts to increase the depth of breathing, or the rate, or both the rate and the depth as deemed necessary by an experienced observer who knew the conditions of breathing likely to give the highest value. In the course of a pilot experiment it was noted that subjects chose widely varying respiration rates when told to " breathe as deep as you can, as fast as you can." Not only was there a wide variation in the rate chosen by different subjects, but the same subject chose different rates at successive attempts. It was also noticed that, if the rate chosen was above approximately 55 respirations per minute (R.P.M.), so violent were the movements of the water in the spirometer that often it was aspirated into the connecting tubes and no observations were possible. We have therefore investigated the maximum ventilatory capacity (M.V.C.), at controlled rates of breathing, of a group of medical students and laboratory workers whose ages ranged from 19 to 32 years. We use the term maximum ventilatory capacity when we refer to the maximum number of litres per minute that a subject can breathe at a controlled rate of respiration.