HEMODYNAMICS AGAIN

[sathyasai baba]

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QUOTE FROM LINDA
"Mean pressure in the aorta is high, averaging 100 mm Hg . This high mean arterial pressure is a result of two factors: the large volume of blood pumped from the left ventricle into the aorta (cardiac output) and the low compliance of the arterial wall. (Recall that a given volume causes greater pressure when compliance of the vessel is low.) The pressure remains high in the large arteries, which branch off the aorta, because of the high elastic recoil of the arterial walls. Thus, little energy is lost as blood flows from the aorta through the arterial tree."

Doesn't elasticity provide more compliance?
it says low compliance of arterial wall & also high elastic recoil.
can someone clarify please.

 

[Frazier]

QUOTE FROM LINDA
"Mean pressure in the aorta is high, averaging 100 mm Hg . This high mean arterial pressure is a result of two factors: the large volume of blood pumped from the left ventricle into the aorta (cardiac output) and the low compliance of the arterial wall. (Recall that a given volume causes greater pressure when compliance of the vessel is low.) The pressure remains high in the large arteries, which branch off the aorta, because of the high elastic recoil of the arterial walls. Thus, little energy is lost as blood flows from the aorta through the arterial tree."

Doesn't elasticity provide more compliance?
it says low compliance of arterial wall & also high elastic recoil.
can someone clarify please.

They can be thought of separately.

Aortic elasticity offers a route to turn the KE (of ventricular contraction) into PE (stretch) back into KE (recoil upon diastole).

Compliance is a characteristic of a material to distend and refrain from returning to its original shape (ie high compliance=resist recoil).

So essentially it says that the aorta is prone to snap back (recoil due to high elasticity) and furthermore not fight that recoil (low compliance).

 

[SBR249]

I'm not a fan of how elasticity is treated here as in material science, the concept is a rather complex multi-parameter property of materials. However, I think I can give it a shot.

So the implicit assumption here is that under conditions where the amount of deformation is equal, the stiffer material will require a greater pressure to achieve the same amount of deformation compared to a more compliant material. Assuming elastic deformation only (meaning non-permanent deformation where the material returns to its original shape) and according to Newton's third law, both materials will exert the same amount of pressure back onto the material it is in contact with (the elastic recoil pressure). However, the compliant material will exert less pressure back (less elastic recoil) because it initially took less pressure to cause it to elastically deform.

A good physical example is this. If you have a stiff rubber band and a soft rubber band, it takes more force to stretch the stiff one to the same extent as the soft one. In the same token, if you stretched both to the same extent, the stiffer one will give you much more recoil because it stored more energy during the stretching (because you had to use more force to stretch it).

Thus elastic recoil is proportional to stiffness and inversely proportional to compliance.

 

[sathyasai baba]

thanks for sparing your time ,doubt clarified.
many thanks