Invited Commentary
Spiral Laminar Flow: a survey of a 3 dimensional arterial flow pattern in a group of volunteers
Mickaël OHANA1 MD, PhD; Sébastien GAERTNER2 MD, MSc; Nabil CHAKFE3 MD, PhD.
1. Department of Radiology, University Hospital of Strasbourg, Strasbourg, France.
2. Department of Vascular Medicine, University Hospital of Strasbourg, Strasbourg, France.
3. Department of Vascular Surgery and Kidney Transplantation, University Hospital of Strasbourg, Strasbourg, France,
In the paper “Spiral Laminar Flow: a survey of a 3 dimensional arterial flow pattern in a group of volunteers” [1], Dr Stonebridge and colleagueset al. bringbrought an update to a problem they raised 25 years ago2.. They initially suggested that blood-flow may propagate following a spiral pattern even in a normal setting, considering that it could be the consequence of the intrinsic helical shape of the heart and of the arterial tree anatomy. Following their initial publication on the constant presence of Spiral Laminar Flow (SLF) in the femoral arteries of 11 healthy subjects3, they used the same Doppler-based approach in 42 volunteers and found that SLF was indeed the predominant pattern in all but one person of this cohort.
Blood flow propagation in experimental conditions is described by most authors as following the Poiseuille law [4], by analogy with a pure liquid flowing steadily through a solid tube in concentric layers of increasing velocities, i.e. laminar pattern. However, once a sufficiently high-velocity rate is attained, these conditions are no longer met and blood flow ceased to be laminar to become turbulent. One can therefore understand that in a pathological setting (stenosis) or in particular anatomical landmarks (carotid bifurcation [5]), blood flow can significantly deviate from the classical laminar pattern. However, the description of a non-laminar flow in normal and relatively straight arteries such as those studied in the work of Stonebridge et al. is surprising and intriguing, as it has the courage to go in a different (complementary?) direction of traditional experimental and clinical observations.
The first reflex when facing disruptive results is to look for flaws in the techniques used to obtain them. We can acknowledge the authors an honest description of their study limitations, the two more obvious being the choice of their reference population which cannot be considered representative of normal, and the discrete methodology with analysis of separate anatomical landmarks without any information on potential transition zones. We can also cast some doubts regarding the true meaning of the “red/blue split” on transverse Doppler views, as exact axial cuts are tough to obtain and assess solely based on the Doppler color-transition, especially on small vessels, and that a slight angle deviation from this perfect plan could produce similar outcomes in a strictly laminar flow [6]. Moreover, it remains to prove that SLF exists in both resistive and visceral arteries, which have a different hemodynamic status. We can finally be surprised that the possibility of a SLF in straight arteries was never raised by early experimental and animal studies.
Yet, the demonstration made by Stonebridge et al. is precisely appealing since it pursue an innovative concept that was progressively built by its team upon 25 years, with at each publication additional points/concepts that strengthen the initial hypothesis. What could be the implications of knowing that blood flow follows predominantly a spiral pattern? It seems that it would be a marker of compensation or severity of a stenosis rather than an independent cardiovascular risk marker as suggested in [7]. Could it help in a better diagnosis and risk-stratification, as suggested in [7], or is it only a marker of compensation/severity of a stenosis? where absence of SLF is associated with a worse prognosis? Could its restoration be beneficial for the patient? The therapeutic management of the patient does not seem, to date, modulated by the presence of SLF or not. At the end of the day, only large outcome-based studies focusing on these points could definitely convince the reader of the importance of SLF.
1 Stonebridge PA, Suttie SA, Ross R, Dick J (2016) Spiral Laminar Flow: a survey of a 3 dimensional arterial flow pattern in a group of volunteers. Eur J Vasc Endovasc Surg 2016, in press
2. Stonebridge PA, Brophy CM. Spiral laminar flow in arteries? Lancet 1991; 338: 1360-1.
3. Stonebridge PA, Hoskins PR, Allan PL, Belch JF. Spiral laminar flow in vivo. Clin Sci (Lond) 1996; 91: 17-21.
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