120-Day study of cardiac output in unanesthetized rats

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Abstract
The technique of permanent cannulation of the aorta and right atrium which permits the simultaneous sampling of arterial and venous blood in unanesthetized small laboratory animals was modified so that the venous cannula is inserted in the right ventricle and the patency of the cannulas increased to well over 100 days. After cannulation rats were used for cardiac output determinations (Fick principle). The animals were unanesthetized and unrestrained. Oxygen consumption, oxygen contents of the blood, and cardiac output were determined seven times in 98 adult male rats during a period of 120 days. The mean value of the cardiac index was 286 ± 25 ml/min kg, remaining unchanged during a period in which the body weight of the animals increased from 300 to 500 g. The results indicate that the technique of permanent cannulation of the aorta and the right ventricle offers a reliable and reproducible method for cardiac output determinations in unanesthetized and unrestrained rats during a period of several months after the cannulation.