Sensitivity of impulse oscillometry and spirometry in beta-blocker induced bronchoconstriction and beta-agonist bronchodilatation in asthma

BackgroundImpulse oscillometry (IOS) provides an alternative method of assessing pulmonary function to conventional spirometry.ObjectiveTo compare the sensitivities of IOS and spirometry in assessing bronchoconstriction to propranolol and bronchodilation with salbutamol.MethodsA post-hoc analysis of a randomized placebo-controlled crossover study was performed. Patients with mild-to-moderate persistent stable asthma taking 1,000 µg/day or less beclomethasone dipropionate equivalent received 10 or 20 mg of oral propranolol followed by histamine challenge, with recovery to nebulized salbutamol (5 mg). Spirometry and IOS were measured before and 2 hours after beta-blocker, post histamine, and 20 minutes post-salbutamol. Pre versus post percent change (95%CI) values were compared, and standardized response means (SRM) were calculated to assess the “signal to noise” of each test.ResultsThirteen participants (mean age, 34 years) completed the protocol. Eleven participants received 20 mg of propranolol; 2 received 10 mg, because this dose caused more than 10% decrease in forced expiratory volume in 1 second (FEV1) on the test-dose algorithm. All IOS indices (R5, R5-R20, AX, RF) showed significant worsening of airways resistance or reactance to propranolol. FEV1 but not FEF25-75 showed significant deterioration after beta-blocker (mean percent change, 4.6% and 6.2%). The magnitude of change was consistently higher for parameters of IOS, with the largest change being observed with R5 and RF (mean percent change, 30.8% and 39.4%). The SRMs for IOS outcomes were better than for spirometry. All measures of lung function showed significant bronchodilator response, with the best SRMs seen in R5 and RF.ConclusionIOS is a more sensitive response outcome than spirometry with respect to bronchoconstriction to oral propranolol and bronchodilatation after salbutamol in patients with mild to moderate asthma