Doppler measurements of acceleration time (AT) in the pulmonary artery (PA) or right ventricular outflow tract have been used clinically to estimate PA pressure. We and others have previously shown that in the range of PA AT less than 100 ms, there is a linear inverse relationship between PA AT and (mean) PA pressure. However, previous studies relating PA AT and PA pressure have been performed primarily in patients without tachycardia. To determine the effect of acute changes in heart rate on PA AT, atrial pacing studies were performed in seven closed-chest pigs in the weight range of the normal human adult. medicine-against-diabetes.net
Material and Methods
Seven pigs weighing 45 to 79 kg were anesthetized with halothane after endotracheal intubation. An intra-arterial catheter was inserted to monitor systemic arterial pressure and a triple-lumen thermodilution catheter was used to measure right atrial and PA pressures and cardiac output. A pacing wire was inserted transvenously into the right atrium to pace the heart at rates from 100 to 140 beats/ min. Each pacing interval was maintained for at least five minutes to allow For stabilization of hemodynamic parameters. The following invasive hemodynamic measurements were made at baseline and at each pacing increment: systemic and pulmonary arterial pressures, stroke volume, and cardiac output.
Doppler echocardiographic studies were performed using a commercially available ultrasound instrument that combined a mechanical sector scanner for two-dimensional imaging with a spectrum analyzer-based pulsed Doppler velocimeter (Biosound Corp). Two-dimensional images recorded from a parasternal approach were used to locate the pulmonary artery in a short-axis view. The Doppler sample volume, a cylinder 10 mm long and approximately 4 mm in diameter, was positioned in the pulmonary artery to obtain pulsed Doppler recordings featuring the maximum PA flow velocity and the least spectral dispersion. The transducer was angulated until PA flow velocity recordings demonstrating these characteristics were obtained. A minimum of four beats was averaged to obtain the measurement for each heart rate. As previously described, peak flow velocity (PFV) was measured at the midpoint of the darkest portion of the spectrum at the time of the peak velocity (ie, peak modal velocity) (Fig 1). Acceleration time was measured from the onset of flow to the time of peak velocity. Ejection time (ET) was measured from the onset to the end of systolic flow. In addition, the ratio of acceleration time divided by ejection time (AT/ET ratio) was calculated.
Figure 1. Method of making measurements from pulsed Doppler flow velocity recordings in the pulmonary artery. Peak flow velocity (PFV) was measured in cm/s at midpoint of darkest portion of the spectrum at time of peak velocity, ie, peak modal velocity. Acceleration time (AT) was measured in ms from onset of flow to attainment of peak velocity. Ejection time (ET) was measured in ms from onset to end of systolic flow
Category: Pulmonary Artery
Tags: heart rate, porcine model, pulmonary artery