Acute changes of lung volumes and lung mechanics in asthma and in normal subjects.

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Abstract
Lung volumes, pulmonary mechanics and specific airway conductance (sGaw) were studied before and 15 min after administration of 200 .mu.g of aerosol salbutamol in 9 asthmatics undergoing mild spontaneous exacerbations of their disease and in 5 normal subjects. In addition, 3 of the normal subjects were studied after voluntarily breathing at high lung volumes for 1 min. The normal subjects and 4 of the asthmatics showed no overall changes in lung volumes or pressure-volume (PV) curves after salbutamol, even though airway dilatation was produced in the asthmatic subjects. In another 5 asthmatics, salbutamol induced a significant fall in the total lung capacity (TLC) in 3, and in the residual volume and functional residual capacity in all 5. There was a significant displacement of the PV curve downwards and to the right in all 5, with increased lung compliance (Cl stat) in 2. The fall in TLC could be accounted for by the increase in lung elasticity. There is reason to believe that this change in lung mechanics could be due to the reversal of asthma-induced stress relaxation. Sustained breathing at high lung volume is known to cause stress relaxation of the lung. This breathing pattern did not alter the PV curve or TLC in 2 of 3 normal subjects, which is consistent with stress relaxation being rapidly reversible. The other normal subject had an acute shift of the PV curve upwards and to the left after breathing at high lung volume. Stress relaxation is usually rapidly reversed but that in some individuals it may only be slowly reversed. This more persistent form of stress relaxation may contribute to the acute changes of TLC found in some asthmatics.