Effects of dobutamine on the fatigued diaphragm: A comparison with dopamine.

We examined the effects of dopamine (DOA) 10 μg·kg(-1)·min(-1) I.V. and dobutamine (DOB) 10 μg·kg(-1). min(-1) I.V. on the contractility of the fatigued diaphragm in 26 anesthetized, mechanically ventilated dogs. Animals were divided into two groups of 13 each: the DOA and DOB groups. Diaphragmatic fatigue was induced by intermittent supramaximal bilateral electrophrenic stimulation at a frequency of 20 Hz applied for 30 min. Diaphragmatic contractility was assessed from changes in transdiaphragmatic pressure (Pdi). After diaphragmatic fatigue, Pdi at low-frequency (20 Hz) stimulation decreased significantly compared with the prefatigue value (P<0.05), whereas no change in Pdi was observed at high-frequency (100 Hz) stimulation. In the fatigued diaphragm, Pdi at both stimuli increased with an infusion of either DOA (P<0.05) or DOB (P<0.05). The increase of Pdi at 20 Hz stimulation was significantly larger in the DOB group compared with that of the DOA group (P<0.05). In each group, Pdi at both stimuli decreased after the cessation of administration. The integrated diaphragmatic electric activity (Edi) in the two groups did not change at any frequency of stimulation throughout the study. We conclude that DOB in comparison with DOA is more effective in improving the contractility of the fatigued diaphragm.