Is the structure of the vessel wall a generator of Spiral Flow? A Cadaveric histological study
In healthy individuals flow patterns in the arterial tree have a spiral vector (Spiral laminar flow, SLF) which is attributed to the eccentric myocardial action and the spiral nature of the aortic arch.Previous studies have shown that SLF is present within health and also within the arteries of patients with arteriovenous fistulas. This is disrupted through the swing segment yet is regenerated in the venous segment above this. This pattern is present in AVFs immediately post operatively and is a predictor of superior outcome.
This implies that veins are capable of generating spiral flow independently and that SLF may have physiological benefits.The aims of this study were to assess the anatomical ultra structure of artery and vein with particular reference to muscle fibre orientation as a potential generator of spiral flow.
Materials and Methods
Using preserved cadaveric post-mortem tissue brachial artery and cephalic vein structure was assessed using an established technique to analyse nuclear orientation. In brief sections were taken from vessels at two different angles allowing nuclear size to be assessed. By correlating nuclear length and the incident angle of the section the orientation of muscle fibres was determined allowing the 3 dimensional arrangements of muscle fibres to be assessed.
Using sectioning angles of 0˚and 20˚ randomly selected regions of tunica media within vessel sections were analysed. Maximum nuclear length was 18.26μm and 8.29μm at each angle respectively. This estimates an arterial smooth muscle pitch 6.04˚ to 6.28˚ of the muscular fibres using each section respectively. Within veins the angle estimates are more variable with multidirectional arrangement and the muscle angle pitch estimated at 1.4˚ to 9.3˚.
The obliquity of muscle fibres within the vessels is consistent with Doppler ultrasound findings of spiral laminar flow in both artery and vein. The central generation hypothesis of spiral flow is questioned by the clinical model of an AV fistula and this study supports the vessel wall as an independent peripheral generator of spiral laminar flow.