Complex flow in the proximal internal carotid artery challenges Doppler flow assumptions
Skye H T Ling1, Eudoxia Zafiris1, Jeremy N Cohen1
1Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, Ontario, Canada.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|June 24, 2026
Summary
Vector flow imaging (VFI) reveals complex internal carotid artery (ICA) blood flow persists further than 2 cm downstream of the carotid bifurcation. This highlights limitations of conventional Doppler ultrasound for accurate ICA flow estimation.
Area of Science:
- Cardiovascular Physiology
- Medical Imaging
- Ultrasound Technology
Background:
- Conventional duplex ultrasound measures internal carotid artery (ICA) blood velocity, assuming laminar flow for disease screening.
- Complex ICA geometry downstream of the carotid bifurcation creates turbulence and recirculation zones, violating laminar flow assumptions.
- Existing guidelines recommend flow measurement 2 cm distal to the bifurcation, potentially affected by non-laminar flow.
Purpose of the Study:
- To determine how far downstream of the carotid sinus complex multidirectional flow persists using vector flow imaging (VFI).
- To evaluate the validity of current guidelines recommending flow measurement 2 cm distal to the carotid bifurcation.
- To assess the impact of dynamic handgrip exercise (DHG) on ICA flow patterns.
Main Methods:
- Vector flow imaging (VFI) was performed on 16 healthy adults (8 females, 24 ± 3 yrs) at rest and during DHG (20% and 40% MVC).
- Multidirectional flow length (MDFL) was visually assessed to identify where flow returned to a laminar pattern.
- Conventional Doppler-derived ICA blood flow was measured across conditions for comparison.
Main Results:
- At rest, multidirectional flow persisted up to 2.45 ± 0.36 cm distal to the carotid sinus.
- MDFL did not change significantly at 20% MVC but decreased at 40% MVC (p < 0.01), indicating reduced flow complexity with higher exertion.
- Flow complexity increased at all locations during 20% MVC, and conventional Doppler measurements remained unchanged, revealing discrepancies.
Conclusions:
- Non-laminar flow patterns in the ICA extend beyond 2 cm distal to the carotid bifurcation, challenging current measurement guidelines.
- Conventional Doppler-derived ICA blood flow measurements may be inaccurate due to persistent turbulence and recirculation zones.
- It is recommended to measure ICA blood flow as distally as possible to minimize the influence of non-laminar flow on estimations.
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