ANTIGEN-INDUCED BRONCHOSPASM IN CONSCIOUS SHEEP

In 10 conscious ewes with cutaneous sensitivity to Ascaris suum, measurements of pulmonary resistance (RL), static lung compliance (Cst), functional residual capacity (FRC), and arterial blood gas composition along with arterial plasma histamine concentration (H) were obtained before and after inhalation challenge with A. suum extract. Five animals showed no changes in respiratory mechanics after A. suum challenge; in these H did not change. The remaining 5 animals responded to A. suum challenge with bronchospasm reflected by the following maximum changes in mean values that were significant 15 and 30 min after beginning of challenge, respectively: RL 248%, FRC 126%, specific pulmonary conductance 33%, and arterial PO2 63% of base line. These parameters returned towards base line by 120 min. No changes occurred in Cst, arterial PCO2, and pH. Five minutes after beginning of A. suum challenge, mean H was increased to 423% of base line with a return to base line 10 min later. In the same 5 animals, no changes were observed in pulmonary function or H after inhalation of ragweed extract (control). These results suggest that antigen-induced bronchospasm in sensitized conscious sheep represents an anaphylactic airway response and shares distinct physiological features with human bronchial asthma including pulmonary hyperinflation.