Characteristics of Sympathetic Nerve Activity During Nonpulsatile Circulation

The autonomic nervous system plays an important role in circulatory control. However, the characteristics of sympathetic nerve activity (SNA) during nonpulsatile circulation, commonly applied to clinical cardiopulmonary bypass or circulatory assist, are not well understood. In this study, we examined the differences between renal SNA (RSNA) values in pulsatile and nonpulsatile systemic circulation in goats, whose heart rate and size are similar to those of humans. A 100% left heart bypass was instituted in two goats, weighing 60 and 66 kg, under general anesthesia. A pneumatic pulsatile pump and a centrifugal nonpulsatile pump were incorporated in parallel in the bypass circuit, so that the flow pattern was converted instantly. The pulse rate was set at 90 bpm during pulsatile circulation, irrespective of native heart rate, and the bypass flow rate was controlled to keep the mean aortic pressure constant. After depulsation, the pulse-synchronous discharges in RSNA disappeared and grouped discharges emerged irregularly instead, and mean RSNA increased. These results suggest that the vasotonus was changed by the loss of pulsatility in the systemic circulation during the immediate phase after depulsation.