Acute Phase Responses of Vasoactive Hormones to Non Pulsatile Systemic Circulation

Acute phase responses of vasoactive hormones to the rapid conversion of a systemic flow pattern from pulsatile or non pulsatile mode to the reverse were assessed in 20 goats weighing 45-69 kg. A total left heart bypass was instituted under general anesthesia, with pulsatile and non pulsatile pumps interposed in the circuit in parallel, and the systemic flow mode was rapidly and bidirectionally converted from the pulsatile mode or non pulsatile mode to the reverse. Vasoactive hormone levels and hemodynamics were evaluated before and after 5 min of conversion. No significant difference was observed between the modes either in blood flow or systemic vascular resistance, while the mean aortic pressure was significantly higher in the non pulsatile mode than the pulsatile mode (106.7 +/- 2.4 versus 99.9 +/- 3.5 mmHg). Among various vasoactive hormone levels evaluated, only norepinephrine showed a significant difference between the modes, where concentration in the non pulsatile mode was significantly higher than the pulsatile mode (391.0 +/- 60.7 versus 309.4 +/- 42.5 pg/ml). No correlation was found between the absolute values of mean aortic pressure and norepinephrine level, whereas a significant reciprocal correlation was detected between the magnitude of inter-mode differences in these two parameters. In conclusion, a non pulsatile systemic circulation does not exert significant influence on vasoactive hormone levels, except for slight increase in norepinephrine with a reciprocally correlated increase in mean aortic pressure. It is deduced that activity of the sympathetic nervous system represented by norepinephrine level is higher in the non pulsatile mode than the pulsatile mode, and the baroreceptor reflex functions in an acute phase after flow mode conversion.