Response Localization of the Pharmacological Agents Histamine and Salbutamol Along the Respiratory System by Forced Oscillations in Asthmatic Subjects

The bronchodilating effect of 1 mg and 0.4 mg salbutamol on the impedance of the respiratory system was studied in 25 asthmatic subjects after histamine-induced bronchoconstriction. Histamine caused an increase of respiratory resistance (R_rs) at lower frequencies and a frequency dependence of R_rs. Respiratory reactance (X_rs) decreased at all frequencies after histamine challenge. These changes can be explained by peripheral airway obstruction. Impedance measurements performed 5 min after inhalation of 1 mg and 0.4 mg salbutamol showed a decrease of R_rs values at lower frequencies, a disappearance of the frequency dependence of R_rs, and a significant increase of X_rs values. No significant differences in absolute changes of R_rs and X_rs are observed between the salbutamol regimens. These changes after inhalation of salbutamol can be explained by supposing a predominant action on the peripheral airways.