Finally, it should be noted that although PA acceleration time is useful for the evaluation of pulmonary hypertension, this Doppler measurement is affected not only by PA pressure, but also by pulmonary blood flow and pathologic changes in the pulmonary vascular bed. For example, patients with an atrial septal defect who exhibit high PA pressure associated with high pulmonary blood flow may have a PA acceleration time in the normal range (>120 ms). Clearly, pulmonary artery resistance is an important factor influencing the PA acceleration time. It has also been noted that in patients with severe pulmonary hypertension, the PA ejection time may shorten greatly, tending to normalize the PA AT/ET ratio. In these cases, it may be helpful to examine the ratio of right ventricular preejection period to ejection time, which becomes significantly increased.
When estimating PA pressures in tachycardic states using Doppler PA flow velocity measurements, the PA AT/ET ratio may be a more useful measurement than PA acceleration time. In the presence of tachycardia, the diagnosis of pulmonary hypertension should be strongly considered when the ratio of PA AT/ET falls 2 SD below the mean noted for normal PA pressure in our study—ie, below 0.30. alta white teeth whitening
Studies are currently in progress in a porcine model to document the relative effects of tachycardia and acute pulmonary hypertension in producing shortening of the Doppler PA acceleration time. It might also be useful to assess whether there is significant variation in PA acceleration time over heart rates ranging from 60 to 100 beats/min in cases of both normal and elevated PA pressure. Finally, it should be emphasized that in this study, the effects of acute changes in heart rate on PA acceleration time were evaluated in an animal model. Acute Doppler measurements of acceleration time and ejection time may differ from those detected in patients with chronic pulmonary hypertension. Nonetheless, this study emphasizes the importance of correcting the PA acceleration time for another time-based measurement such as ejection time.
Category: Pulmonary Artery
Tags: heart rate, porcine model, pulmonary artery