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 (FEV1 92% pred ±14; FEV1/FVC 75% ± 8) underwent the methacholine challenge test (MCT). The degree of BHR was expressed as PD20 (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 (PD20 < 1600 μg) with a PD20 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 PD20 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.