Absence of habituation of airway dilation following lung inflation

In order to test the possibility that airway dilation following lung inflation (ADFLI) could exhibit habituation, partial and complete maximum expiratory flow-volume curves were obtained in 12 healthy individuals before and after inhaling methacholine aerosol in a dose that reduced in each individual the partial expiratory flows to approximately 50% of baseline values. Following methacholine inhalation, the difference in flows between complete and partial flow-volume curves at 40% VC was 64 +/- 22% (mean +/- SD) of partial curves after a single full lung inflation and 79 +/- 36% after 12 consecutive full inflations (p = NS). The absence of demonstrable habituation (tachyphylaxis) of ADFLI makes it unlike that ADFLI is due to a release of mediators and supports the view that it may be due to the intrinsic properties of the airway smooth muscle.