Effect of Theophylline on Respiratory Muscle Function

¹ From the Critical Care Medicine Division, Hôpital Beaujon, Clichy, Paris and Royal Victoria Hospital, McGill University, Montreal, Canada

Theophylline improves diaphragmatic contractility of the respiratory muscles both in isolated muscle preparations, as well as in animals and normal human beings. Furthermore, theophylline restores diaphragmatic fatigue and prevents fatigue of the diaphragm when given prophylactically. Finally, it was recently shown that theophylline improves diaphragmatic function in COPD patients, all of whom were CO₂ retainers (PaCO₂ 53 ± 3 mm Hg) and hypoxemic (PaO₂ 57 ± 8 mm Hg). Patients improved transdiaphragmatic pressure and were less susceptible to fatigue. Presently the mechanisms of action of theophylline regarding its effects on diaphragmatic function are not fully elucidated. Experimental evidence, however, suggests that theophylline may have an effect on transmembrane calcium movements by blocking adenosine receptors.