Measuring lung volumes in advanced asbestosis: comparability of plethysmographic and radiographic versus helium rebreathing and single breath methods.

Total lung capacity was measured in 16 workers with pulmonary asbestosis using four standard methods: body plethysmography, radiographic lung area, helium dilution by multiple breath and by single breath (alveolar volume). All men had irregular opacities of ILO profusion category 2/1 or greater and four had pleural plaques in addition. The radiographic and plethysmographic methods produced virtually identical mean values for TLC of 7.52 l and 7.64 l and for RV of 4.06 l and 4.32 l and all values were larger than those by helium dilution. The closed circuit helium dilution method systematically underestimated TLC with a mean of 5.89 l as did single breath helium dilution with a mean of 6.39 l. These men had a larger mean RV/TLC, measuring 56.9% by body plethysmography and 54.6% by X-ray area than by the rebreathing dilutional method which was 43.8%. Air trapping within a normal TLC which characterizes asbestosis is revealed by radiographic and plethysmographic methods but concealed by gas dilution methods. Use of the latter is at least partly responsible for the impression that asbestosis is a 'restrictive disease'.