Evidence of acinar airway involvement in asthma

We investigated acinar airway involvement in 20 patients with stable asthma , using the phase III slope analysis of the multiple breath N-2 washout pre viously applied in a group of patients with COPD (Am. J. Respir. Grit Care Med. 1998;157:1573-1577). This technique quantifies severity of conductive and acinar components of ventilation maldistribution separately, through in dices S-cond and S-acin, which increase when respective ventilation inhomog eneities increase. We also investigated the effect of salbutamol inhalation on S-cond and S-acin in patients with asthma and compared it with that obt ained in patients with COPD. Baseline measurements in the patients with ast hma show that (1) acinar ventilation inhomogeneity was indeed abnormal in p atients with asthma (S-acin = 0.195 +/- 0.026 L-1) despite the normal diffu sing capacity in this group; S-acin values were intermediate between those obtained in unaffected individuals and patients with COPD, and that (2) con ductive ventilation inhomogeneity was abnormal in the patients with asthma (S-cond = 0.076 +/- 0.006 L-1) but similar to that obtained in the patients with COPD. Measurements after salbutamol inhalations showed significant ch anges in S-cond and S-acin only in the patients with asthma (p < 0.001). Th is study primarily demonstrated significant, but partially reversible, acin ar airway impairment in patients with asthma, as compared with the more sev ere baseline acinar airway impairment in patients with COPD, which was not reversible after salbutamol inhalation.