Adaptation to Nonpulsatile Mechanical Circulation : Should We Pulse in Mechanical Circulation?

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Responses of arterial baroreceptor afferent (ABA) activity to nonpulsatile systemic circulation was directly measured.Electrodes were placed on the left aortic depressor nerve (ADN) to measure the ABA activity in twenty-seven anesthetized rabbits. Total left heart bypass (TLHB) was conducted to obtain the nonpulsatile systemic flow. (Exp.1) To evaluate the influence of circuit priming fluid, before the starting partial left heart bypass (PLHB), before the starting TLHB after the starting PLHB and 5 min after the starting TLHB,spike counts of ADN activity were measured in the 7 animals maintaining mean aortic pressure (MAP) changes. There were no significant difference between before and after the starting PLHB.(Exp.2) To evaluate the adaptation of ABA activity to nonpulsatile flow, the spike counts of ADN activity were collected before and 5,20,30,40,50 and 60 min after the starting TLHB in the other 10 animals maintaining MAP changes. The ADN activity at 5 min after significantly increased from control (before TLHB). The activity at 30 min after significantly decreased and that level was persisted at 60 minutes after. (Exp.3) To evaluate the response of ABA activity to aortic pressure (AoP) changes, the spike counts of ADN activity were measured before, 5 and 30 min after the starting TLHB in the other 10 animals when MAP was risen and fallen by 20 mmHg. There were no significant difference when MAP was fallen. But there were significant difference when MAP was risen, percent changes in ADN activities at 5 and 30 min after the initiation of TLHB significantly less than before TLHB.It appears that ABA activity is activated immediately after starting nonpulsatile flow, but acute adaptation of ABA activity occurs 30 min after. Also the changes of ABA activity against increase of AoP are depressed under the nonpulsatile systemic flow condition.