THE EFFECT OF AMINOPHYLLINE ON INSPIRATORY MUSCLE CONTRACTILITY

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Abstract
Effects of aminophylline on diaphragmatic muscle contractility were studied in 8 dogs. Relationships of the electromyographic signal from the diaphragm and the pressures developed by this muscle were compared before and after the administration of aminophylline in doses of 6, 20, 40, 80 and 120 mg/kg. Measurements were made during occluded inspiratory efforts at functional residual capacity. In a 2nd group of 4 dogs, the relationships were compared while the rib cage expansion was limited by a plaster cast. In a 3rd group of 4 dogs, after the diaphragm had been paralyzed by phrenicotomy, the relationship of pleural pressure to the electromyographic signal of the intercostal muscles was assessed before and after administration of aminophylline. In all cases, aminophylline progressively shifted the electromyographic pressure relationship up and to the left. This effect became significant (P < 0.01) at a dose of 20 mg/kg, reached a peak at 80 mg/kg, and then declined at a dose of 120 mg/kg. The amount producing blood concentrations closest to the human therapeutic blood concentration was 20 mg/kg. The peak increase in pressures compared to control values were 58% in the 1st group, 27% in the 2nd group and 52% in the 3rd group (P < 0.01). Aminophylline increases respiratory muscle contractility in a dose-related manner. This may have important therapeutic and pathophysiologic implications.