Steal phenomenon in radiocephalic arteriovenous fistula. In vitro haemodynamic and electrical resistance simulation studies.
OBJECTIVE
steal phenomenon following an arteriovenous fistula (AVF) creation is characterised by retrograde flow in the artery segment distal to the anastomosis and occurs in the majority of patients with radiocephalic AVF although this rarely leads to distal ischaemia. To investigate the local haemodynamics after the creation of an AVF, a simple electrical resistance model which assumes time-independent flow was used. The applicability of this model to pulsatile flow conditions was verified using an in vitro flow circuit. The effects of stenoses in various artery segments were also investigated.


METHODS
the electrical analogue model consists of a pressure source, constant resistances that represent the resistance to flow of various arterial segments and the fistula. The stenosis was modelled by a resistor and a non-linear term is simulated by a current-controlled voltage source. In vitro experiments were performed in pulsatile and steady flow and the results were compared with electrical simulations. The effects of fistula flow and the presence and severity of a stenosis on flow distribution, particularly the direction of flow in the distal radial artery and flow into the hand were assessed.


RESULTS
steady and pulsatile time-averaged flows measured in vitro compared well with the results of electrical circuit simulations for cases without a stenosis. When a stenosis was present comparisons were made only in steady flow and these show good agreement for stenoses of 75% area reduction. The direction of flow in the distal radial artery was antegrade (towards the hand) at low fistula flow and became retrograde as fistula flow increased. The presence of a severe stenosis in the brachial artery was found to have the strongest influence on flow to the hand.


CONCLUSIONS
an electrical resistance model of a radiocephalic AVF has been validated with an in vitro pulsatile flow circuit. One of the benefits of this model is that it can be easily analysed using standard circuit simulation software. The model also provide insights into the possible haemodynamics consequences of creating an AVF with or without the presence of a stenosis in the arterial segments.
Ramuzat
A
A
Department of Clinical Engineering, University of Liverpool, UK.
How
T V
TV
Bakran
A
A
D001164:Arteriovenous Fistula / Q000503:physiopathology*; D001166:Arteriovenous Shunt, Surgical; D001783:Blood Flow Velocity / Q000502:physiology; D001808:Blood Vessels / Q000502:physiology*; D017097:Electric Impedance; D005542:Forearm / Q000098:blood supply* / Q000601:surgery; D006801:Humans; D066298:In Vitro Techniques; D007511:Ischemia / Q000503:physiopathology*; D008953:Models, Anatomic; D011673:Pulsatile Flow / Q000502:physiology; D017534:Radial Artery / Q000502:physiology / Q000601:surgery; D012039:Regional Blood Flow / Q000502:physiology; D014655:Vascular Resistance / Q000502:physiology