Characteristics of Doppler blood-velocity waveforms in a cardiovascular in vitro model. II. The influence of peripheral resistance, perfusion pressure and blood flow.

A cardiovascular in vitro model was used to examine the influence of peripheral resistance on the Doppler blood-velocity waveforms. In the study the velocity indices were determined as a function of peripheral resistance either with the flow kept constant (the perfusion pressure varied) or with the pressure constant (the flow varied). The peak velocity (Vpeak) is normally accepted as a simple expression of the stroke volume. However, in this study Vpeak did increase with resistance when the stroke volume was constant. Rising slope (RS) is said to correlate with heart contractility, but in this study such a relation was not found. Pulsatility index (PI) and A/B ratio (A/B) are normally considered to reflect peripheral resistance. PI was found to be a flow- and pressure-independent proportional expression of peripheral resistance. A/B also increased with resistance but this relationship is more uncertain. The results of this in vitro study support the clinical use of PI as a flow- and pressure-independent estimate of peripheral resistance. The relation of RS and Vpeak to heart contractility and stroke volume, respectively, is found to be dependent also on resistance, blood flow, and pressure.