Lung volume changes in asthma measured concurrently by two methods.

Serial measurements of functional residual capacity and total lung capacity were made by body plethysmography and by a helium dilution method in 8 patients during recovery from episodes of severe asthma and in 7 normal subjects. In the patients, plethysmography yielded significantly larger values of functional residual capacity and total lung capacity than did the dilution method; the differences were greatest when the asthma was most severe and decreased during clinical recovery. The two methods gave similar results in 5 of the 7 normal subjects. Serial plethysmographic studies showed that functional residual capacity increased during severe asthma in all patients, although this was revealed by helium dilution in only 5 of them. Plethysmographic total lung capacity increased in 7 of 8 patients during severe asthma, although this was revealed by helium dilution in only 3 of them. Plethysmographic measurements of lung volumes thus indicated a more uniform response to the presence of severe asthma than did ...