Respiratory mechanics in airways obstruction associated with inspiratory dyspnoea

airways obstruction associated with inspiratory dyspnoea. Inspiratory muscle strength and the flow and elastic pressure opposing inspiration were measured in seven patients with severe airways obstruction who found inspiration difficult at rest. A comparison was made ofmeasure-ments obtained from seven normal subjects and five patients with airways obstruction not ex-periencing inspiratory dyspnoea at rest. Measurements were also obtained when inspiratory dyspnoea was induced in the normal subjects by adding an inspiratory resistance or by volun-tarily increasing lung volume. Compared with the controls the inspiratory muscle strength ofthe patients was reduced but was not significantly less than that of the patients without inspiratory dyspnoea. The pressure required to produce inspiratory flow was significantly greater when inspiratory dyspnoea was present (p=0-01). However, there was considerable overlap in the pressures of those with and without inspiratory dyspnoea. A better relationship was obtained when muscle strength was considered. The ratio of inspiratory muscle strength to the pressure required to produce flow was 0 24±0 07 (mean ±SD) in patients with inspiratory dyspnoea, 0-10+0-03 in patients without inspiratory dyspnoea, and 0-033+0-019 in normal subjects. There was no overlap between the two patient groups. The ratios of the normal subjects wer