Spirometry for asthma: Bronchodilator response more reliable in the morning

If you suspect a patient has asthma, it's best to schedule a morning appointment, because spirometry with bronchodilator response measurement offers more representative results in the morning.Based on the normal opening hours of a pulmonary function laboratory, a study of 1,620 adults showed a greater proportion of patients responded positively to bronchodilators when spirometry was performed in the morning, compared with patients whose appointment was scheduled in the afternoon (28% vs. 23%).Most participants in this British study were referred for a diagnosis of asthma (n=944). The remainder were referred either for breathlessness of unknown cause, chronic cough, chronic obstructive pulmonary disease (COPD), rheumatoid or interstitial lung disease, bronchiectasis or vasculitis.From 8.30 a.m. onwards, every hour that elapsed reduced by 8% the chances of a positive response to the test, and therefore of the patient's lungs responding to treatment. This association was particularly strong for patients referred for asthma."The time of testing should be taken into account by clinicians when interpreting bronchodilator reactivity test results," said the authors of the study, published in Thorax. Ideally, the test would be performed at the same time of day for each patient."More reliable in winterThe researchers also observed variations in the seasonality of response to the test. Indeed, patients tested in winter were more likely to obtain a positive response to the bronchodilator, with 29% (n=113) of participants. In comparison, only 23% (n=83) achieved a positive response in spring. In summer and autumn, the proportion of patients with a positive response was slightly higher than in spring, but still lower than in winter (26% and 25% respectively).Asthma symptoms are known to vary according to the time of day, and are most severe at night, with bronchial hyper-reactivity peaking around 4 a.m. This nocturnal worsening of asthma would appear to be independent of sleep conditions or environmental effects, but rather linked to circadian rhythms. Studies have shown that a “clock protein” controls bronchial hyper-reactivity, and that inactivating this protein in mice cancels out the day-night effect on lung function.In addition to greater reliability, performing asthma diagnostic tests when patients are most symptomatic, i.e., in the morning, would offer a better representation of response to medication.To confirm these results, prospective studies will need to be carried out, including repeated measurements on the same individuals at different times of the day, the authors noted.You can read the study here in Thorax.

Spirometry for asthma: Bronchodilator response more reliable in the morning

Register for free access or login.

Related Topics

Business Topic