Respiratory Duty Cycles in Individuals With and Without Airway Hyperresponsiveness

The respiratory duty cycle (T_i/T_tot) can influence bronchoprovocation test results and nebulized drug delivery. The T_i/T_tot has not yet been examined in individuals with airway hyperresponsiveness (AHR) in typical bronchoprovocation test conditions. This study investigated the mean T_i/T_tot in participants with and without AHR and whether the T_i/T_tot changes with increasing bronchoconstriction.

Fifteen participants with AHR and fifteen participants without AHR completed this randomized crossover study. An ultrasonic spirometer was used for continuous measurement of the T_i/T_tot 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 setup to record baseline T_i/T_tot data.

The mean T_i/T_tot findings [95% CIs] during room air inhalation were 0.392 [0.378-0.406] and 0.447 [0.426-0.468] in participants with and without AHR, respectively (P < .001). The mean T_i/T_tot during saline inhalation were 0.389 [0.373-0.405] and 0.424 [0.398-0.450] in participants with and without AHR (P = .040). The T_i/T_tot showed a nonsignificant downward trend with progressive methacholine-induced bronchoconstriction.

The mean T_i/T_tot in participants with AHR closely resembles the assumed T_i/T_tot of 0.40 recommended for standard use when calculating methacholine challenge results. Since the T_i/T_tot did not change significantly over the course of a methacholine challenge, the same T_i/T_tot can be used to calculate the dose of methacholine inhaled, regardless of the level of bronchoconstriction.

ClinicalTrials.gov; No.: NCT03505489; URL: www.clinicaltrials.gov.