Blood Flow: Laminar vs Turbulent

is the quantity of blood that passes a given point in circulation in a unit time.
e.g. renal blood flow is about 1000 ml/min.
In adults total blood flow through the entire systemic circulation is about 5000 ml/min under resting conditions.

occurs when blood flows...
- at a steady rate.
- through a long and smooth blood vessel.
is silent.
Blood flows in streamlines.

A layer of blood close to the vessel wall is almost stagnant due to cohesive forces between the inner surface of vessel wall and blood.

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Inner concentric cylindrical layer of blood slips over this outer layer → moves faster than the first layer

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The third layer slips over the second one → its velocity is even higher

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Thus the velocity of blood layers increases as we go from wall to the center of the vessel.

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The resultant velocity profile is a bullet-like parabola with the maximum velocity at the center.

occurs when...
- blood flow is very high.
- there is an obstruction in the vessel.
- the blood makes a sharp turn.
- the blood flows over a rough surface.
Blood flows in all directions, usually forming whorls and continuously mixing within the vessel.
Increases resistance to blood flow.
Can be auscultated as murmers e.g.
- Korotokoff sound during measuring blood pressure
- Murmers of stenosis, shunt, cardaic valvular lesions etc.
Very intense turbulance can be felt with touch as thrills.

d = diameter of the blood vessel. Large diameter tends to cause turbulence. In smaller vessels, blood flow is almost always laminar.
v = velocity of blood. High velocity tends to cause turbulence e.g. high cardiac output.
ρ = density of blood. High density tends to cause turbulence.
η = viscocity of blood. High viscocity tends to cause laminar flow.

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