Velocity distribution in the ascending aorta in pigs during chronotropic and inotropic stimulation

The influence of heart rate, stroke volume and myocardial contractility on temporal and spatial velocity distribution in the ascending aorta was investigated in 10 pigs. A pulsed Doppler ultrasound technique with intraluminal probe and a single crystal connected to a position-sensitive device was used to measure blood velocity. After baseline registration, the heart rate was increased in two discrete steps of 20 beats/min by right atrial pacing. Isoproterenol infusion was given to increase contractility. Finally, without isoproterenol, the heart rate was again raised to the values found during inotropic stimulation. The first three measuring situations did not differ haemodynamically, apart from increased heart rate and reduced stroke volume. Increased heart rates were not associated with significant change in the parameters for skewness of velocity distribution (peak systolic slope and ratio, maximum skewness slope and ratio). During inotropic stimulation the peak left ventricular dP/dt, aortic systolic pressure, cardiac output and stroke volume were greater than at comparable paced heart rate, and the peak systolic slope of velocity distribution was significantly increased. Velocity distribution in the ascending aorta thus was not altered by increased heart rate alone, whereas skewness of distribution was enhanced by increased inotropic drive of the myocardium and the concomitant central and peripheral vascular changes.