Effects of aminophylline and terbutaline sulfate on the contractility of feline diaphragm.

1. The effect of aminophylline and terbutaline sulfate, separately and in combination, on the contractility of the feline diaphragm was investigated. 2. Diaphragmatic contractility increased significantly (P less than 0.05) to 28.3% above control level as long as theophylline plasma levels were maintained between 10-20 mg/l (mean 13.9 +/- 0.8 mg/l). 3. Diaphragmatic contractility showed a significant (P less than 0.05) 41.5% increase after i.v. administration of terbutaline sulfate as a maintenance dose of 1.4 micrograms/kg-hr, and the increase leveled off after 180 min. 4. Administering the two drugs in combination showed a significant (P less than 0.05) 27.3% increase which suggests a non-synergistic effect of aminophylline and terbutaline sulfate on diaphragmatic contractility. 5. By enhancing the contractility of the diaphragm, aminophylline and terbutaline sulfate may improve the clinical status of patients with airway obstructive diseases and help in preventing respiratory muscle fatigue.