Effect of neuromuscular blockade and assisted ventilation on breathing pattern, ventilation, and respiratory muscle function of anesthetized dogs.

8 healthy dogs were anesthetized with a continuous infusion of pentobarbital (1 mg/kg/h) and were weakened but not paralyzed by intravenous succinylcholine (1 mg/kg/h). They were then studied during alternating periods of spontaneous breathing and assisted ventilation (IPPB). After succinylcholine, there was a significant increase in PaCO2, no significant change in respiratory frequency, a significant decrease in tidal volume, no significant change in P100 and a significant decrease in peak diaphragm EMG. Comparing periods of IPPB with periods of spontaneous breathing, there was a decrease in PaCO2 to a mean approximating that before succinylcholine, an increase in tidal volume, no change in frequency, and significant decreases in P100 and diaphragm EMG. In three experiments in which PaCO2 was maintained constant during IPPB, IPPB again resulted in a decrease in EMG and P100. Assisted mechanical ventilation of partially paralyzed dogs resulted in a fall in PaCO2 and a decrease in respiratory center output as measured by diaphragm EMG and P100. The fall in PaCO2 could be ascribed to decreasing the limited muscular work of breathing even in the presence of normal mechanics. A major part of the changes in EMG and P100 could be ascribed to chages in chemoreceptor drive but alteration of other inputs which were not specifically indentified, such as lung reflexes and/or chest wall reflexes, must also have had an effect.