Characteristics of Doppler blood-velocity waveforms in a cardiovascular in vitro model. I. The model and the influence of pulse rate

Abstract

In order to study the indices describing the flow-velocity curves a cardiovascular in vitro model has been constructed. The model consists of two parts: (i) A heart simulator producing controllable cardiac output, pulse rate and pressure variations, (ii) a circulatory system made of elastic butyl rubber tubes with adjustable peripheral resistance bed.

The flow-velocity curves were obtained by a Doppler velocity meter as a function of the pulse rate (PR) when pressure, volumetric flow, and peripheral resistances were constant.

The four evaluated indices, pulsatility index (PI), peak velocity (V_peak), rising slope (RS) and A/B ratio (A/B i.e. maximum/minimum velocity ratio) all showed significant correlation with pulse rate. PI, A/B and V_peak showed a marked increase at low pulse rate and the inverse relation between these indices and pulse rate were best described by power functions, whereas RS was found to be inversely proportional to pulse rate.

The results are in good agreement with the few existing clinical observations, and we suggest that the relations described are taken into consideration in the clinical interpretation of blood velocity indices.

Key Words:

• A/B ratio
• blood flow velocity
• circulation models
• Doppler
• heart rate
• pulsatility index