In individuals with airway hyperresponsiveness (AHR), the mean respiratory duty cycle (Ti/Ttot) resembled the assumed Ti/Ttot of 0.40 that is recommended when calculating methacholine challenge results, according to study results published in CHEST.

A total of 15 patients with AHR and 15 individuals without AHR were enrolled in the crossover study. During an exercise in which participants inhaled either room air or aerosolized solution an ultrasonic spirometer performed continuous measurement of the Ti/Ttot.

Each participant completed methacholine challenges, including 1 challenge using a continuous-output vibrating mesh nebulizer/ultrasonic spirometer and another using only the nebulizer. Room air and aerosolized saline were inhaled by each patient through the nebulizer/spirometer set-up to document baseline Ti/Ttot prior to the methacholine challenges.

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The mean Ti/Ttot was significantly lower in patients with AHR compared with patients without AHR during room air inhalation (0.392 vs 0.447, respectively; P <.001). In a similar fashion, the Ti/Ttot during saline inhalation was significantly lower in patients with AHR (0.389 vs 0.424, respectively; P =.040). While room air and saline Ti/Ttot were similar in patients with AHR (P =.675), they differed in patients without AHR (P =.022). In patients with AHR, there was no significant difference from the last methacholine dose Ti/Ttot and room air (P =.138) or saline Ti/Ttot (P =.095).

Study limitations included the small sample size, as well as the potential of the laboratory environment to influence the breathing rate and pattern of the patients.

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The researchers wrote that additional “studies may investigate the Ti/Ttot with greater induced bronchoconstriction in individuals with AHR or individuals who exhibit greater baseline bronchoconstriction such as those with chronic obstructive pulmonary disease.”

Disclosure: A study author declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Blais CM, Davis BE, Graham BL, Cockcroft DW. Respiratory duty cycles in individuals with and without airway hyperresponsiveness [published online September 19, 2019]. CHEST. doi:10.1016/j.chest.2019.09.005