Clinical and functional responses to salbutamol inhaled via different devices in asthmatic patients with induced bronchoconstriction

Abstract

Aims: This study aimed at evaluating changes in airway patency, lung volumes and perception of breathing discomfort intensity following salbutamol administration via the Diskus dry-powder inhaler (DPI) or a pressurized metered-dose inhaler with the Volumatic valved holding chamber (pMDI + Volumatic) in asthmatic patients with methacholine-induced bronchoconstriction.

Methods: On six different study days, 18 patients inhaled methacholine until forced expiratory volume in 1 s (FEV(1)) decreased by approximately 35% of baseline. Following placebo, 200 and 400 microg of salbutamol through the pMDI + Volumatic or the Diskus, changes in FEV(1), volume-adjusted mean forced expiratory flow from 25 to 75% of the forced vital capacity (isoFEF(25-75)), lung volumes and breathing discomfort intensity, assessed by visual analogue scale (VAS) score, were repeatedly measured over a 60-min observation period.

Results: Induced bronchoconstriction was accompanied by obvious reductions in lung volumes and increases in VAS score. After salbutamol administration, FEV(1) and VAS score changes were similar in all experimental conditions. However, following 400 microg salbutamol via pMDI + Volumatic, isoFEF(25-75) values increased up to 4.48 l s(-1) (95% confidence interval 4.06, 4.90), a significantly (P < 0.01) higher value than those attained in all other experimental conditions. Independently of the salbutamol dose, lung volumes rose to significantly (P < 0.01) higher levels in pMDI + Volumatic than in Diskus trials. The low salbutamol dose via the pMDI + Volumatic and the high dose via the DPI increased isoFEF(25-75) and lung volumes to similar extents.

Conclusions: Salbutamol via the pMDI + Volumatic provides greater isoFEF(25-75) and lung volume increases in asthmatic patients with induced bronchoconstriction; salbutamol-induced changes in VAS scores poorly reflect those in small airway patency. The lack of differences in FEV(1) increases observed after 200 and 400 microg salbutamol may reflect attainment of the flat portion of the dose-response curve using either device.

Figure 1

The panels depict the 60-min time course of mean (18 patients) values of forced expiratory volume in 1 s (FEV₁), volume-adjusted mean forced expiratory flow from 25 to 75% of the forced vital capacity (isoFEF₂₅₋₇₅), visual analogue scale (VAS) scores, vital capacity (VC), inspiratory capacity (IC) and expiratory reserve volume (ERV) obtained at baseline (b), at maximum bronchoconstriction (bc), and following administration of placebo (mean values of two different preparations, X symbols), 200 (empty symbols) and 400 (filled symbols) µg of salbutamol through the pressurized metered dose inhaler with the Volumatic valved-holding chamber (circles) and the Diskus inhaler (triangles). *P < 0.01 compared values recorded at 60th min with the corresponding values recorded in baseline condition