Bronchodilator response in pulmonary disease at two different states of respiratory mechanics

It would be convenient to be able to measure airway responsiveness to bronchodilator drugs with a sequential use of oscilloresistometry and spirometry, which may allow the comparison of the response to bronchodilator at two different states of respiratory mechanics i.e. resting tidal breathing at functional residual capacity (FRC) versus forced expiratory manoeuvre from total lung capacity to residual volume. The evaluation of airway resistance and forced expiratory volume at 1 s (FEV₁) may thus assist in the interpretation of bronchial responsiveness tests (BRT) to pick up responders among non-responders to administered bronchodilator. Such a concept was verified in 54 patients with respiratory disease before and 10 min after inhalation of 200 μg of salbutamol. Within 10 min following salbutamol challenge the increase for forced vital capacity (FVC), FEV₁and peak expiratory flow rate (PEFR) was 23, 27 and 39% in 27 asthmatic patients of group A (p < 0.005). On the other hand, 27 patients with chronic obstructive pulmonary disease in group B did not show any significant change in FEV₁and PEFR (p >0.05). However, they showed a decrease in airway resistance of 30% (p < 0.005) during normal tidal breathing at FRC. Twenty-two normal controls in group C showed values of airway resistance and expiratory flow rates to be within the normal range and the response to administered salbutamol inhalation was not significant (p >0.05). It may be concluded that the airway responsiveness to bronchodilators using only FEV₁as an index of BRT should be interpreted with caution in non-responders because they may not be able to tolerate the mechanical challenge in the form of an FCV manoeuvre but show a significant decrease in airway resistance during resting tidal breathing at FRC.