Difference in the effect of pancuronium and vecuronium on baroreflex control of heart rate in humans

The effects of pancuronium and vecuronium, each in doses of 0.05 and 0.08 mg.kg(-1), on the baroreflex control of the heart rate were studied in 40 adult patients of either sex (21 men and 19 women) during stable nitrous oxide-oxygen-fentanyl anesthesia. The blood pressure was elevated by intravenous infusion of phenylephrine (4 micro g.kg(-1).min(-1)) for the pressor test, and lowered by a bolus injection of nitroglycerin (0.3-0.5 mg) for the depressor test. Baroreflex sensitivity was judged from the slope of the regression of the systolic blood pressure on the succeeding R-R intervals on the ECG. There was no significant difference between the baseline blood pressure at which both tests were carried out. Nitrous oxide-oxygen-fentanyl anesthesia alone suppressed the baroreflex sensitivity to a level which was at the lower limit of the physiological and non-anesthetized state. The 0.08 mg.kg(-1) dose of pancuronium significantly suppressed the reflex sensitivity in both the pressor and depressor tests. However, the 0.05 mg.kg(-1) dose of pancuronium and both doses of vecuronium did not cause any significant change in the test results.