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

Abstract

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.

The use of colour Doppler imaging to determine the effects of administration of butorphanol, medetomidine and ketamine on indices of feline ocular impedance

“…PI, a parameter closely related to the RI, has also been shown in vitro to be related to vascular resistance (Legarth and Thorup 1989). PI, which decreases with distance from the heart, is equal to the difference between the peak systolic velocity and the minimum diastolic velocity divided by the mean velocity during the complete cardiac cycle (Gelatt-Nicholson et al 1999b).…”

Doppler estimation of zero flow pressure during changes in downstream pressure in a bench model of a circulation using pulsatile flow*

“…Physiologically, the factors that can affect the pulsatility of the flow velocity waveform are pulse rate, compliance and resistance of the distal vascular bed, the rheological properties of the blood, and the elasticity of the insonated part of the vessel [14][15][16][17]. Similar factors may also affect the arterial pressure waveform.…”

“…Changes in downstream pressure were mimicked by incorporating a collapsible segment into the insonated limb that could be subjected to external pressure in a controlled manner by changing the height of a water column around this segment. Thus, our model, like other described circulation models [15][16][17], was essentially a passive, non-autoregulating, simplistic system that assumed circulation through an organ to be linear and to pass through a single collapsible tube. We made no attempt to replicate the human circulation in terms of the elasticity and dimension of the vessels, the compliance of the system or the fluid dynamics of the circulating solution.…”

“…This limitation depends to a large extent on the question that the study seeks to answer and the appropriateness of the model for the purpose. Similar bench models have been used for validating Doppler indices [15][16][17]. For the present investigation, we required a model that was capable of generating 'realistic' pulsatile flow and simulating a controlled change in the downstream pressure.…”

Transcranial Doppler measurements in migraine and nitroglycerin headache

“…value that has been found to reflect the distensibility of the insonated vessel, and to be indicative of peripheral vascular resistance [14][15][16]. There is a paucity of published data on the PI in migraine.…”