Small airway dysfunction is associated to excessive bronchoconstriction in asthmatic patients

BACKGROUND: We investigated whether a relationship between small airways dysfunction and bronchial hyperresponsiveness (BHR), expressed both in terms of ease of airway narrowing and of excessive bronchoconstriction, could be demonstrated in asthma. METHODS: 63 (36 F; mean age 42 yr ± 14) stable, mild-to-moderate asthmatic patients (FEV(1) 92% pred ±14; FEV(1)/FVC 75% ± 8) underwent the methacholine challenge test (MCT). The degree of BHR was expressed as PD(20) (in μg) and as ∆FVC%. Peripheral airway resistance was measured pre- and post-MCT by impulse oscillometry system (IOS) and expressed as R5-R20 (in kPa sL(−1)). RESULTS: All patients showed BHR to methacholine (PD(20) < 1600 μg) with a PD(20) geometric (95% CI) mean value of 181(132–249) μg and a ∆FVC% mean value of 13.6% ± 5.1, ranging 2.5 to 29.5%. 30 out of 63 patients had R5-R20 > 0.03 kPa sL(−1) (>upper normal limit) and showed ∆FVC%, but not PD(20) values significantly different from the 33 patients who had R5-R20 ≤ 0.03 kPa sL(−1) (15.8% ± 4.6 vs 11.5% ± 4.8, p < 0.01 and 156(96–254) μg vs 207 (134–322) μg, p = 0.382). In addition, ∆FVC% values were significantly related to the corresponding pre- (r = 0.451, p < 0.001) and post-MCT (r = 0.376, p < 0.01) R5-R20 values. CONCLUSIONS: Our results show that in asthmatic patients, small airway dysfunction, as assessed by IOS, is strictly associated to BHR, expressed as excessive bronchoconstriction, but not as ease of airway narrowing.