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 stimul ation of the phrenic nerves at different frequencies, and Pdi was meas ured with a pair of balloons. In protocol 1, the effect of caffeine on contractility of non-fatigued diaphragm was studied in 7 dogs. Caffei ne infusion increased Pdi significantly at all freqencies of stimulati on. 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 s ignificantly at all freqencies 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 afte r caffeine infusion. We conclude that caffeine improves muscle contrac tility both in non-fatigued and fatigued diaphragm in dogs.