Relation To Wall Tension
Regardless of site, blood pressure is related to the wall tension of the vessel according to the Young–Laplace equation (assuming that the thickness of the vessel wall is very small as compared to the diameter of the lumen):
where
- P is the blood pressure
- t is the wall thickness
- r is the inside radius of the cylinder.
- is the cylinder stress or "hoop stress".
For the thin-walled assumption to be valid the vessel must have a wall thickness of no more than about one-tenth (often cited as one twentieth) of its radius.
The cylinder stress, in turn, is the average force exerted circumferentially (perpendicular both to the axis and to the radius of the object) in the cylinder wall, and can be described as:
where:
- F is the force exerted circumferentially on an area of the cylinder wall that has the following two lengths as sides:
- t is the radial thickness of the cylinder
- l is the axial length of the cylinder
Read more about this topic: Blood Pressure
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