Effects of an inhaled bronchodilator on gas distribution and over-all ventilatory efficiency in patients with chronic obstructive pulmonary disease

The effects of an inhaled bronchodilator on the distribution of inspired gas and over-all efficiency of ventilation were studied by the nitrogen washout technic in 16 patients with chronic obstructive pulmonary disease; three normal subjects and two patients with asymptomatic asthma (and normal spirometric values) were also studied. In normal and asthmatic subjects and in patients with chronic obstructive pulmonary disease and mild to moderate functional impairment, the nitrogen clearance did not vary significantly or showed changes suggesting less uniform gas distribution and reduced ventilatory efficiency. In most patients with advanced chronic obstructive pulmonary disease, the bronchodilator caused changes suggesting more uniform distribution of inspired gas and increased efficiency of ventilation. Multiple regression analysis showed that the behavior of the nitrogen clearance after treatment was also related to the response of the anatomic dead space. The effects of the bronchodilator varied with time. The results are consistent with the assumption that the changes in nitrogen clearance after bronchodilator therapy reflect the concourse of multiple factors, which may be expected to have favorable or unfavorable effects on the distribution of inspired gas and the efficiency of ventilation.