Changes in aortic blood pressure and cardiac output curves as induced by stenosis of the descending thoracic aorta.

In 9 anaesthetized open chest rabbits cardiac output and aortic blood pressure were recorded. Cardiac output was obtained by means of an electromagnetic blood flow transducer placed around the ascending aorta. When a 10 sec stenosis of the descending thoracic aorta was produced, an increase of mean, systolic, diastolic and pulse pressure was observed above the stenosis, with a remarkable delay of the peak systolic pressure with respect to the peak velocity of ventricular ejection. Moreover, it is note worthy that during the stenosis the deceleration phase of the ventricular ejection showed a slackening which was responsible for a longer ejection time. Owing to such a longer ejection time, in 4 experiments stroke volume and cardiac output increased above the control in spite of a high aortic impedance. It is probably that the changes observed in the contour of the ventricular ejection curve, depend on modifications of the gradient between left ventricle and aortic blood pressure as well as on the combined effects of the Starling's law and of the afterload.

Vectorcardiographic analysis of prefibrillatory ventricular tachycardia in the rabbit.

In 10 urethan anaesthetized rabbits, VCG of acontine induced VT was studied. At the beginning of VT, both QRS and T loops arise and end regularly at the e point. Then, QRS loop opens and its end moves outside the E point, as a result of changes in ST segment. Later on, when ST segment disappears completely owing to an initial overlapping of the depolarization and repolarization processes, no arrest of the trace is observed between QRS and T loops. Lastly, immediately before the appearance of ventricular fibrillation, a progressive increase of the rate of VT above 400/min produces a fusion between the end of the T and the initial part ofn the next QRS loop. At this stage, no E point can be recognize. The results suggest that the transformation of VT into VF occurs through a delay and an overlapping of the depolarization-repolarization sequence.