Exercise and distribution of inspired gas in patients with obstructive pulmonary disease.

The effects of moderate exercise on the distribution of inspired gas and efficiency of ventilation were studied by the multibreath nitrogen washout method in three subjects with asymptomatic asthma and 11 patients with chronic obstructive pulmonary disease (COPD). The nitrogen washout curves were analyzed according to a lung model consisting of a poorly ventilated compartment (slow space) and one or more better ventilated compartments (intermediate and fast compartments). The overall efficiency of ventilation was also estimated by the lung clearance index (LCI). An increase in the ventilation of both well ventilated and poorly ventilated lung compartments was generally observed during exercise; however, the magnitude of the change in the ventilation of the slow compartment in response to exercise varied from subject to subject; the change was related to the degree of functional impairment, as expressed by current pulmonary function tests (spirometry, airway resistance, and arterial blood gas measurements). The magnitude of the change in the ventilation of the better ventilated lung compartments did not vary significantly with the degree of functional impairment. LCI showed no uniform changes with exercise. Our results indicate that in patients with obstructive lung disease the effect of exercise on the distribution of inspired gas tends to vary with the severity of the disease. The nitrogen washout data also suggest that in these patients the pattern of gas distribution during exercise is not compatible with a high level of ventilatory efficiency.