Effect of aerosol propellants and surfactants on airway resistance

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Abstract
The effects on the airways of inhalation of the vehicles used in two commercial pressurized bronchodilator aerosols were studied in 20 normal and seven asthmatic subjects. Changes in bronchial calibre due to bronchoconstriction were measured as changes in airway resistance using a constant volume whole body plethysmograph, and results were expressed as changes in the ratio Airway conductance/Thoracic gas volume (=specific airway conductance). The aerosols caused very slight bronchoconstriction in the normal subjects, with a mean decrease of 5·3% in specific airway conductance after inhalation of a spray containing sorbitol trioleate as a surface tension lowering agent, and of 9·7% after inhalation of a spray containing lecithin. This effect was prevented by prior inhalation of atropine methonitrate, and its mechanism was therefore probably a vagally mediated reflex. The bronchoconstriction was also reversed by the addition of isoprenaline to the aerosol. The asthmatic subjects showed larger mean reductions in specific airway conductance of 13% and 21% after sorbitol and lecithin respectively: the response was again prevented by atropine. We conclude that, although the aerosol vehicles cause slight bronchoconstriction, this is unlikely to be a clinical danger since it is insufficient to cause symptoms of wheezing, and is less than that caused by inhalation of a single cigarette. Moreover, the constriction is regularly converted to dilatation in both normal and asthmatic subjects by the addition of atropine or isoprenaline to the aerosol.