Effect of phrenic nerve stimulation on neural transmission and diaphragmatic force generation in the dog

The effect of supramaximal bilateral phrenic nerve stimulation on neural transmission and diaphragmatic force generation was studied in anesthetized dogs. Different combinations of duty cycle and stimulation frequency were examined during intermittent stimulation (pacing) for 15 min. The effect of different stimulation frequencies was also examined during continuous stimulation for 60 sec. Force declined more with increasing stimulation frequency and duty cycle with intermittent stimulation, and with increasing stimulation frequency with continuous stimulation. Neural transmission decreased with increasing stimulation frequencies. The changes were always greater with continuous than with intermittent stimulation. We found no unique relationship between changes in neural transmission and changes in force generation, suggesting that if neural transmission failure is causally responsible for fatigue, it does so by a very complex mechanism.