Respiratory duty cycles in individuals with and without airway hyperresponsiveness

Abstract Background The respiratory duty cycle (Ti/Ttot) can influence bronchoprovocation test results and nebulized drug delivery. The Ti/Ttot has not yet been examined in individuals with airway hyperresponsiveness (AHR) in typical bronchoprovocation test conditions. This study investigated the mean Ti/Ttot in participants with and without AHR and whether the Ti/Ttot changes with increasing bronchoconstriction. Methods Fifteen participants with AHR and fifteen participants without AHR completed this randomized crossover study. An ultrasonic spirometer was used for continuous measurement of the Ti/Ttot as participants inhaled room air or aerosolized solution. Each participant completed two methacholine challenges, one using a continuous-output vibrating mesh nebulizer/ultrasonic spirometer and one with the nebulizer only. Prior to each methacholine challenge, participants inhaled room air and aerosolized saline through the nebulizer/spirometer set-up to record baseline Ti/Ttot data. Results The mean Ti/Ttot +/- standard deviation during room air inhalation were 0.392 +/-0.043 and 0.447 +/-0.056 in participants with and without AHR, respectively (p Conclusions The mean Ti/Ttot in participants with AHR closely resemble the assumed Ti/Ttot of 0.40 recommended for standard use when calculating methacholine challenge results. Since the Ti/Ttot does not change significantly over the course of a methacholine challenge, the same Ti/Ttot can be used to calculate the dose of methacholine inhaled, regardless of the level of bronchoconstriction.