A practical measure of the maximum ventilatory capacity in health and disease.

The assessment of disability in dust diseases of the lung presents a problem of great practical importance. Available evidence indicates that disturbance of the alveolar respiratory component of pulmonary function is of importance in producing disability only in such diseases as pulmonary sarcoidosis and berylliosis (Ferris, Affeldt, Kriete, and Whitten berger, 1951) where there is a lesion of the alveolar epithelium. Much further work remains to be done before the importance of disturbance of the mixing component of pulmonary function in producing disability can be evaluated. Evidence is now available, however, that the principal cause of disability in dust diseases of the lung is disturbance of the ventilatory function (Baldwin, Cournand, and Richards, 1949; Gilson and HughJones, 1953). This is also true of asthma and to a large extent of emphysema. This paper is concerned with the assessment of the maximum ventilatory capacity, and presents a method of measuring this aspect of pulmonary function which has been used during the past three years in an out-patient clinic, and which has been found simple and practical. The oldest objective method for assessing the ventilatory capacity of a subject is the simple vital capacity measurement. This, however, is a static measure of volume and is an imperfect and often misleading index of the ventilatory function (Gilson and Hugh-Jones, 1949). To detect changes in the ventilatory capacity of individual subjects from day to day, and to detect differences between individuals, it is essential to measure the maximum ventilatory capacity. Since the work of f-Hermannsen (1933) the measurement of the maximum breathing capacity (M.B.C.)-here termed the maximum voluntary ventilation (M.V.V.)-has been used extensively, and is now generally accepted as the best single index of the maximum ventilatory capacity (Gray, Barnum, Matheson, and Spies, 1950). However, in practice, the determination of the M.V.V. presents a number of difficulties. First, it has been found difficult or impossible in many cases to be certain that the patient is giving of his best in the M.V.V. test, especially when such issues as compensation are at stake, and the test may thus be partly a measure of his co-operation. Secondly, the measurement of the M.V.V. in practice is time-consuming and fatiguing both to the patient and to the observer. For these reasons attention has been devoted to finding a simpler measure of the maximum ventilatory capacity. It has been suggested (Kennedy, 1950) that a man's maximum voluntary ventilation or his maximum breathing capacity might be predictable from the analysis of his vital capacity tracings recorded on a fast-revolving kymograph. The remainder of this paper summarizes the development of this earlier work.