Study of ventricular assisted circulation aiming at new physiological control

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We have conducted studies concerning physiological reactions to a long-term left heart assist with pulsatile or continuous left ventricular assist device, mainly by the use of animal experiments. We evaluated the cerebral circulatory metabolism and pathological changes of the central nervous system and its arteries under the circulation of a long-term left heart assist with pulsatile or continuous left ventricular assist device. The cerebral circulatory metabolism was not affected, and there were not observed remarkable pathological changes in the central nervous system and its arteries. As for autonomic nervous system, we investigated changes of heart rate variability (HRV) during long-term pulsatile and continuous flow left heart bypass in an animal study and found that a long-term left heart bypass exerts a different influence on HRV between pulsatile and continuous flow left heart bypass. The powers of the low frequency band (0.04-0.15 Hz; LF) and those of the high frequency band ( … More 0.15-0.40 Hz; HF) showed an increasing tendency during continuous flow left heart bypass, indicating an increase of cardiac vagal activity. During continuous flow left heart bypass, bradycardia phenomena, supposed to be caused by an increase of cardiac vagal activity, were often observed in animals with otherwise stable conditions. We also evaluated and found that there was no significant difference in plasma catecholamine level between the conditions under chronic pulsatile and continuous flow left heart bypass. Concerning systemic vascular resistance, we examined the constrictive function of the vascular system using vascular a-1 receptor agonist phenylephrine or norepinephrine administration. Prolonged continuous flow left heart bypass caused a significant decrease in systemic vascular resistance response to phenylephrine and norepinephrine, indicating a decrease of vasoconstrictive function although no remarkable change was not observed in systemic vascular resistance and its response during under prolonged pulsatile left heart bypass. Alternatively, systemic vascular resistance response to nitroglycerin injection showed no significant changes during pulsatile and continuous flow left heart bypass. Baroreceptor sensitivity was evaluated and it did not change significantly. We evaluated changes in circadian rhythm during prolonged pulsatile and continuous flow left heart bypass focusing on hormonal factors, body temperature, and aortic pressure. The circadian rhythm of melatonin and body temperature was not affected, while it was modified in the variations of hemodynamics-responsive renin and aortic pressure. Less