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Blood Flow Patterns

For medical students2 min readUpdated 2026-10-10

In the circulatory system, fluid may move in orderly layers or mix with the formation of vortices. The nature of movement depends on the properties of the vessels and physical parameters of the blood, and the transition between patterns is predicted by a special physical criterion.

Laminar flowFluid moves in parallel, non-mixing layers.

TurbulenceLayers mix, and multiple vortices arise.

Flow boundaryDetermined by the Reynolds number (transition range 2000–3000).

Cost of vorticesTurbulent flow requires additional energy expenditure from the heart.

Evolution of Blood Flow from the Heart to the Periphery

The movement of blood through the vascular bed is heterogeneous and changes with distance from the heart. During the cardiac cycle, pressure experiences significant fluctuations, but they gradually attenuate. The prominent elasticity of the walls of the aorta and large conduit arteries plays the major role in this smoothing.

Depending on the caliber of the vessel, the flow pattern changes drastically:

Aorta and large arteries: blood flow has a pronounced pulsatile character; blood moves forward in separate pulses, synchronous with cardiac contractions.
Arterioles and capillaries: pulsations are completely damped, and blood flow becomes entirely continuous, which is critically important for adequate transcapillary exchange.

Two Fluid Flow Patterns

Hemodynamics describes two fundamentally different patterns of blood movement through vessels: laminar and turbulent. The transition between them is directly related to changes in fluid velocity.

Laminar flow. This is strictly orderly movement. Blood moves in regular layers that slide parallel to the direction of flow (the so-called axial flow). The layers do not intersect or mix with each other.
Turbulent flow. This occurs with a significant increase in movement velocity. Orderliness is completely destroyed: intensive mixing of absolutely all fluid layers occurs, accompanied by the formation of numerous vortices.

Reynolds Number ($NR$)

To predict the pattern in which blood will flow in a particular vessel, a mathematical criterion is used — the Reynolds number ($NR$). It is calculated by the following formula:

$NR = (\rho \cdot D \cdot v) / \eta$

Where:

$\rho$ (rho) is the fluid density;
$D$ is the diameter of the blood vessel (tube);
$v$ is the average flow velocity;
$\eta$ (eta) is the fluid viscosity.

Evaluating the resulting value allows precise determination of the pattern:

If $NR < 2000$, the flow is guaranteed to remain laminar.
If $NR > 3000$, the flow transitions to turbulent.

Factors Causing Turbulence

Vortices in blood flow do not appear randomly. Turbulence occurs when certain physical and anatomical conditions coincide. Factors provoking the breakdown of laminar flow include:

Decreased blood viscosity.
Increased flow velocity.
Large blood vessel diameter.
High fluid density.
Presence of irregularities on the inner vascular walls.

Shear thinning plays a special role. The essence of this phenomenon is that with a significant increase in blood flow velocity, one fluid layer begins to actively shear relative to another. This physical interaction leads to an actual decrease in blood viscosity, which, according to the Reynolds formula, additionally increases the risk of turbulence development.

Physiological Significance of Turbulence

Turbulent flow is not always a pathology; it has distinct localization and conditions of occurrence in a healthy body.

Initially, vortex flows normally exist at the moment a portion of blood is ejected from the left ventricle into the aorta. Turbulence also naturally occurs at vascular branching sites (bifurcations), where flow geometry is disrupted. In other arteries, flow may temporarily become turbulent with a sharp increase in blood flow velocity—for example, during intense physical exertion.

The main physiological consequence of turbulence is energetic. Such flow requires additional energy expenditure to propel blood through the vascular bed. Consequently, this creates substantial additional workload on the pumping function of the heart.

Mnemonic

To remember the factors of turbulence, look at the Reynolds formula: everything in the numerator (density, diameter, velocity), when increased, causes vortices. Conversely, what is in the denominator (viscosity), when increased, maintains laminar flow.

Frequently asked questions

What velocity profile of layer distribution is characteristic of laminar blood flow?

Laminar blood flow is characterized by orderly movement: blood moves in layers parallel to the direction of flow, forming an axial flow. A parabolic flow profile is described in microvessels: due to transverse pressure differences, formed elements shift from the periphery to the center. As a result, the movement velocity of cells through the capillary is higher than the velocity of whole blood; the phenomenon of decreased blood viscosity in microvessels is associated with this.

In which cardiovascular pathologies does turbulent blood flow occur?

Turbulent blood flow is described in the following cardiovascular pathologies:

Renal artery stenosis — blood flow turbulence is detected distal to the stenosis;
Acute mitral regurgitation — the retrograde jet from the left ventricle into the left atrium appears dark on cine-MRI due to turbulent flow.

Sources also indicate that vortices initially exist during the ejection of blood from the ventricle into the aorta and at vascular bifurcation sites; in arteries, flow can become turbulent with increased blood flow velocity, such as during physical exertion.

Why is blood flow continuous in capillaries but pulsatile in the aorta?

In the aorta, blood moves in discrete pulses due to rhythmic cardiac outputs. As it moves toward the periphery, these pressure fluctuations are completely smoothed out thanks to the high elasticity of the walls of conduit vessels.

What is the shear thinning phenomenon?

This is the phenomenon of decreasing blood viscosity with increased blood flow velocity. It occurs because at high velocity, fluid layers begin to actively shear past each other.

Where can turbulent blood flow normally be found?

In a healthy body, vortices are formed when blood is ejected from the ventricle into the aorta, as well as at sites of vascular bifurcations (branching). In other arteries, they may appear during heavy physical exertion due to increased flow velocity.

Go deeper

Mechanisms of arterial blood pressure pulse damping
Influence of vascular wall irregularities on hemodynamics
Hemodynamics at blood vessel bifurcations
Myocardial energy expenditure in overcoming turbulence