Respiratory cycle time duration during exercise in patients with chronic obstructive lung disease.

Respiratory cycle time components during rest and graded exercise were measured in 18 patients with chronic obstructive lung disease, and compared with controls matched for sex and age. For a given exercise level (50 W) increased minute ventilation was present in the patients. This was due to shorter cycle time. Both inspiratory and expiratory time shortened to the same degree rendering the ratio inspiratory time/total respiratory cycle time similar in the two groups. At maximal exercise total respiratory cycle time and inspiratory time was shorter in the patients than in the control group, but the ratio between them was still similar. However, for a given total cycle time during maximal exercise inspiratory time was shorter. Inspiratory time and the ratio inspiratory time/total cycle time as measured during 50 W exercise, were positively correlated with the patient's exercise capacity, but not of sufficient accuracy for useful prediction of the latter. The difference in concomitant variation of tidal volume and inspiratory time during exercise ventilation between the patients and the control subjects seemed satisfactorily explained by the different lung volumes at which the two groups were breathing.