Haemodynamics and vasoactive agents: the haemodynamic effects of vasoactive agents in rats with chronic arteriovenous fistula

Guo, Liang (2006) Haemodynamics and vasoactive agents: the haemodynamic effects of vasoactive agents in rats with chronic arteriovenous fistula. Masters thesis, Memorial University of Newfoundland.

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Abstract

An arteriovenous fistula is an abnormal direct passage between an artery and a vein. The existence of an arteriovenous fistula generates a high output low total peripheral resistance state that resembles the hyper-haemodynamic condition of several diseases such as vascular injury, congenital malformation, chronic severe anemia, severe hepatic or renal disorders, and septic shock. In the present study, we investigated the haemodynamic changes in rats with chronic arteriovenous fistulae and the haemodynamic effects of noradrenaline, arginine vasopressin, and sodium nitroprusside in this model. -- Creation of a chronic fistula between abdominal aorta and inferior vena cava increased cardiac output compared to sham-operated rats. The haemodynamic factors when compared to respective values in sham-operated rats changed in the following ways: 1) total peripheral resistance and resistance to venous return decreased; 2) heart rate and cardiac contractility based on dP/dt values recorded remained stable at the baseline level; and 3) blood volume and mean circulatory filling pressure increased. The augmentation of total blood volume, mean circulatory filling pressure and reduction in vascular resistance together contributed to the increase in cardiac output. -- Noradrenaline infusion did not change the cardiac index in rats with chronic arteriovenous fistulae. Administration of noradrenaline 1) increased total peripheral resistance and resistance to venous return; 2) increased heart rate and cardiac contractility based on dP/dt values recorded; and 3) did not change total blood volume but increased mean circulatory filling pressure. The positive effects of noradrenaline on heart rate, cardiac contractility, and total body venous tone tended to increase cardiac index. However, the increase of cardiac index was prevented due to the increase in total peripheral resistance and resistance to venous return. -- Administration of arginine vasopressin did not change the cardiac index in rats with chronic arteriovenous fistulae. Upon arginine vasopressin infusion, 1) total peripheral resistance and resistance to venous return increased; 2) heart rate did not change while cardiac contractility increased based on dP/dt value recorded; and 3) total blood volume and mean circulatory filling pressure increased. Unlike its actions in the intact animal, administration of arginine vasopressin ·in rats with chronic arteriovenous fistulae reversed the preload-afterload mismatch by increasing mean circulatory filling pressure and total blood volume with little effect on resistance to venous return. Therefore, cardiac index did not fall despite of elevation of the afterload. -- Administration of sodium nitroprusside had limited effects on cardiac index in rats with chronic arteriovenous fistula. The circulatory parameters altered in the following manner: 1) total peripheral resistance and resistance to venous return remained at the baseline level; 2) heart rate did not change while cardiac contractility decreased at the highest dose based on dP/dt value recorded; and 3) total blood volume and mean circulatory filling pressure was kept unchanged. Due to the special condition in our experimental model such as low vascular resistance and maximal vasodilation, administration of sodium nitroprusside had limited haemodynamic effects.

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