Standards and significance for three tests of the distribution of ventilation: The time to equilibration, the forced equilibrating expiration and the fowler single breath test: Normal subjects

Abstract

Three tests of the distribution of ventilation are performed in our laboratory during the closed circuit equilibration with oxygen of a patient who has previously breathed air. The forced equilibrating expiration (FEE) is the procedure designed to test for a new type of distribution abnormality, not previously distinguished from the others, namely, the presence of inelastic sacs or bullae open to the bronchi. Such bullae would presumably not be ventilated while held open at volumes above the end-tidal, yet would empty during forced expirations below the end-tidal volume. The Fowler single breath test examines the distribution of ventilation within a single expiration due to the differences in time constants, differences in percentage elastance and differences in the per cent dead space among the alveoli. The time to equilibrium (TTE), like other qualitative tests of the efficiency of washout during a series of breaths, examines for all of these types of unevenness and even for unevenness due to alveoli that open during forced inspiration but that close early as inspiration is reduced. By examining 115 normal subjects, standards delimiting the range of normal were found for the FEE, the TTE and for some modifications of the single breath test. Even in normal subjects, about a third of variance in the TTE may be accounted for by the variation in the other two tests, distributed about equally between them.