Comparison of active and passive manoeuvres on the pattern of airway closure in man.

The effect of active and passive manoeuvres on closing volume was studied in conscious subjects. There were no significant differences in closing volume in nine of 10 non-smokers. There was a significantly greater closing volume with the passive manoeuvre (airway pressure +3 kPa to --2 kPa) in seven of nine smokers and one non-smoker with evidence of mild obstructive airway disease. The sensitivity of the closing volume to airway pressure could not be reproduced in three non-smokers exposed to a histamine aerosol. In two of three smokers the effect of airway pressure on closing volume was abolished by salbutamol. The results suggest that subjects with irritable airways may show an increase in closing volume with a change in airway pressure.