Abstract

The dynamic and static lung volumes, arterial blood-gas tensions, and single-breath carbonmonoxide transfer factor have been compared in 72 asthmatic and 45 bronchitic patients with airways obstruction of comparable severity to determine which measurements might be used to discriminate between the two diseases. The forced vital capacity, total lung capacity, arterial carbon-dioxide tension, and transfer factor were useful in this respect. Thus, in a patient with airways obstruction the finding of a low% predicted FVC (<70) and a low% predicted Dlco (<50) with a relatively normal% predicted TLC and a raised Paco₂ is strongly suggestive of chronic obstructive bronchitis, whereas the finding of a relatively normal% predicted FVC and a high% predicted TLC (>115) with a nearly normal Dlco and a normal or low Paco₂ is most compatible with a diagnosis of bronchial asthma.