Relation of airway responsiveness to salbutamol and to methacholine in smokers

Airway hyperresponsiveness (AHR), the most characteristic feature of asthma, is reported in COPD patients and smokers. There are controversies, however, regarding airway responsiveness to b-adrenergic agonists in asthma as well as COPD and smokers. After our previous studies had shown AHR to b-agonists in asthmatic patients, we examined airway responsiveness to salbutamol and its relationship to responsiveness to methachline in smokers.

The threshold concentrations of inhaled salbutamol or methacholine required for a 20% change in forced expiratory flow in 1 sec (FEV1), recorded as PC20, or a 35% change in specific airway conductance (sGaw), recorded as PC35, was measured in 14 nonsmoker and 14 smokers.

Airway responsiveness to salbutamol was greater in smokers (PC20=66.85, PC35=22.74 mg/l) than in nonsmokers (PC20=241.42, PC35 =88.72 mg/l, p<0.001 for both). Airway responsiveness to methacholine was also significantly greater in smokers (PC20= 1.34 and PC(35)=1.01 g/l) than nonsmokers (PC20=5.66 and PC35=4.63 g/l, P<0.001 for both cases). There were significant correlations between FEV(1)with both PC20 salbutamol (r=0.577, p<0.001) and PC20 methacholine (r=0.638), (p<0.001 for both cases). The correlations between airway responsiveness to salbutamol with responsiveness to methacholine using both PC(20) (r=0.819) and PC(35) (r=0.783) were also statistically significant (p<0.001 for both cases). The slopes of the concentration-response curves of both agents were significantly greater in smokers than nonsmoker (P<0.001 for all cases).

These results showed increased sensitivity of smokers' airways to salbutamol, which correlates closely to airway responsiveness to methacholine.