Evaluation of Blood Flow Velocity Waveform in an Animal Model

Blood flow velocity waveforms in the abdominal aorta of three anesthetized pigs were recorded by a combined 3.5-MHz real-time and 2-MHz pulsed-Doppler ultrasound. The flow velocity waveforms were analyzed for pulsatility index, systolic to diastolic ratio, rising slope, descending slope, and the minimum diastolic velocity, and then were compared with volume blood flow measured by electromagnetic flow-meter (Q), mean arterial pressure (MAP), and total peripheral resistance (TPR). Total peripheral resistance was calculated according to the formula TPR = MAP/Q. A total of 111 recordings were performed over a range of heart rate: 90–250 beats/min, of Q: 65–1318 mL/min, of MAP: 72–165 mmHg and of total peripheral resistance 0.10–2.17 mmHg × min/mL. A significant positive correlation was found between pulsatility index and total peripheral resistance (correlation coefficient r ranging 0.64–0.87) and between systolic to diastolic ratio and total peripheral resistance (r: 0.59–0.83). The minimum diastolic velocity showed a negative correlation to TPR (r: -0.68 – -0.76). The pulsatility index was dependent on the heart rate, mean arterial pressure and rising slope; however, the relations were not consistent in all experiments. The results indicate that the pulsatility index is a good indicator of the flow velocity waveform changes depending on changes in the peripheral vascular resistance, and that the relationship between the total peripheral resistance and pulsatility index is linear. The systolic to diastolic ratio proved to be comparable even though it is somewhat less effective in performance than the pulsatility index.