Nitrogen and bolus closing volumes: the effect of beta-agonist bronchodilator aerosol

Studies of the effect of beta-agonist bronchodilators on closing volume in normal subjects have produced conflicting results. We studied the possibility that these differences might be due to the different methods of measuring closing volume. We measured closing volume by both the nitrogen washout and the bolus techniques in 19 healthy nonsmoking adults before and after inhalation of salbutamol aerosol. Prior to salbutamol, closing volume measured by the nitrogen method (N2 CV) was significantly smaller (p less than 0.02) than the closing volume measured by the bolus method (bolus CV). After salbutamol inhalation, N2 CV increased significantly (p less than 0.05); however, bolus CV did not change, so that following inhalation of salbutamol there was no significant difference between N2 CV and bolus CV. The increase in N2 CV after salbutamol inhalation was associated with an increase in the slope of phase IV (p less than 0.05). We suggest that beta-agonist bronchodilator aerosol has no effect on closing volume in normal individuals and the apparent increase in N2 CV after bronchodilator is probably an artefact.