Effects of caffeine on diaphragmatic contractility and fatigue.

The effects of caffeine on diaphragmatic contractility and fatigue was investigated in 21 dogs. Diaphragmatic contractility was assessed by measuring transdiaphragmatic pressure (Pdi) during supermaximal stimulation of the phrenic nerves at different frequencies, and Pdi was measured with a pair of balloons. In protocol 1, the effect of caffeine on contractility of non-fatigued diaphragm was studied in 7 dogs. Caffeine infusion increased Pdi significantly at all frequencies of stimulation. In protocol 2, diaphragmatic fatigue was induced by electrophrenic stimulation (30 Hz, duty cycle 1.0, 30 minutes). The recovery profile after fatigue run was observed in 5 dogs. In another group of 9 dogs, caffeine was infused during stable fatigue period and Pdi increased significantly at all frequencies of stimulation after caffeine infusion. The increase in Pdi was not due to changes in cardiac output or lung mechanics (Cdyn and Rtot), neither of which changed significantly after caffeine infusion. We conclude that caffeine improves muscle contractility both in non-fatigued and fatigued diaphragm in dogs.