A simple dosimeter for bronchial provocation testing using a solid-state electronic timing module

In conducting inhalational challenge tests of airway responsiveness to methacholine, we prefer to deliver the challenge aerosol intermittently, using a dosimeter that turns the nebulizer on for about 0.5 to 0.6 second to deliver each "puff." To avoid the considerable expense of commercially available dosimeters, we constructed our own electronically controlled device, which, in conjunction with a DeVilbiss Model 646 nebulizer, is easily calibrated and permits reproducible and precise timing of challenge puffs. The device was constructed of readily available components and cost us only $100. An experienced technician can use it to trigger on the nebulizer within 0.5 second of the start of inspiration, and in more than one year's experience we have found the system to be completely satisfactory and reliable.