Airway hyperresponsiveness to mannitol in relation to inspiratory and expiratory resistance in subjects with asthma, COPD, and healthy smokers.

Background: Airway hyperresponsiveness (AHR), a key feature of asthma, leads to airway narrowing in response to bronchoconstrictor stimuli. Notably, AHR is also observed in individuals with chronic obstructive pulmonary disease (COPD). The Mannitol challenge test is an indirect method to assess airway hyperresponsiveness.

Objective: The primary aim of this study was to explore airway hyperresponsiveness to mannitol in subjects with asthma and COPD regarding inspiratory and expiratory resistance and reactance. A secondary aim was to investigate fractional exhaled nitric oxide (FeNO), blood eosinophils, allergen sensitization, and symptom scores concerning airway hyperresponsiveness to mannitol.

Methods: The Mannitol challenge test was conducted on 292 subjects: 238 with asthma, 25 with COPD, 14 healthy smokers, and 15 healthy never-smokers. The response was assessed using both spirometry and respiratory oscillometry, with inspiratory and expiratory resistance and reactance measured separately.

Results: A positive mannitol test was confirmed in 84 (35%) subjects with asthma, 13 (52%) with COPD, and 7 (50%) of healthy smokers. Subjects with asthma who had a positive mannitol test had a higher inspiratory R5 and R19 at baseline, and also greater change in both inspiratory and expiratory R5, R5-R19, and X5 (but not R19), compared to asthma subjects with a negative test. A similar tendency was seen among subjects with COPD and healthy smokers. Subjects with asthma with a positive mannitol test had more symptoms than subjects with a negative test (median 21 versus 22; p = 0.036).

Conclusion: Inspiratory resistance, as measured by respiratory oscillometry, was shown to predict hyperresponsiveness to mannitol in asthma patients. Furthermore, respiratory oscillometry revealed a significant increase in resistance, primarily in the peripheral airways, following a mannitol challenge in these subjects. Integrating resistance and reactance measurements, along with traditional spirometry may offer a more comprehensive understanding of the hyperreactive airway response.