[Action of aminophylline on the strength of contraction of the diaphragm in patients with chronic obstructive respiratory insufficiency].

The effect of a sustained-release aminophylline preparation on diaphragmatic contractility was investigated in patients with stable chronic obstructive lung disease (FEV1 = 22.6% of predicted value). Ten such patients were tested before (control) and after a week's course of oral aminophylline. Diaphragmatic contractility was evaluated by measuring the transdiaphragmatic pressure generated at residual functional capacity by bilateral electrical stimulation of the phrenic nerves. The nerves were stimulated supramaximally at 1 Hz, using needle electrodes. Plasma aminophylline levels (12.5 +/- 0.9 mg/l) were within therapeutic range in all patients. After treatment with aminophylline, for each stimulation the transdiaphragmatic pressure increased significantly from 14 +/- 1.3 to 17 +/- 1.3 cm H2O (+21%; P less than 0.005). These results confirm that aminophylline increases the force of contraction of the diaphragmatic fibres electively tested by the technique used. Long-term treatment with theophylline in therapeutic doses may be of interest in such patients, as it might improve their diaphragmatic contractility and result in better control of both respiratory muscle fatigue and episodes of acute respiratory failure.