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Fluid Dynamics and Aneuryisms.

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  • 23-12-2011 3:51pm
    #1
    sinead1992
    Closed Accounts Posts: 3 ✭


    Could anyone help me out with this, it is for an exam :

    Using the principles of fluid dynamics, explain why the diameter of aneurysms in blood vessels always increase with time.


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    #2
    krd
    Banned (with Prison Access) Posts: 3,455 ✭✭✭krd


    I think it's because the wall of blood vessel at the point of the aneurysm is weaker. The blood pressure throughout the blood vessel should be constant (or the relationship between the diameter of the healthy blood vessel, and blood pressure, and the bulge diameter and blood pressure in the bulge, should be constant). The weaker wall will expand, until it's giving back the same force as the stronger walls.

    It think it's as much to do with elasticity as fluid dynamics. The weak walls of the bulge are trying to push back to equalise with the flow and pressure from the healthy parts of the blood vessel - the bulge walls bulge because the tissue is weaker.

    I've forgotten all my fluid dynamics, and all the equations. Same with anything I learned about elasticity.

    I think Volumeofhealthbloodvessel X HealthyBVPressure = VolumeofBulge X BulgePressure


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    #3
    Delphi91
    Registered Users Posts: 1,501 ✭✭✭Delphi91


    sinead1992 wrote: »
    Could anyone help me out with this, it is for an exam :

    Using the principles of fluid dynamics, explain why the diameter of aneurysms in blood vessels always increase with time.

    Speaking as someone who's come out the other side of a burst aneurysm, let me suggest a possible answer.....

    An aneurysm occurs where the walls of the blood vessel are weak. Therefore the pressure exerted by the blood in the vessel will push out the weak spot a little. That will result in a slight widening of the blood vessel and consequential slowing of the blood in that area. Slower moving liquid exerts more pressure, thereby pushing out the bulge a little more. This widens the diameter a little more, slowing the blood a little more and increasing the pressure, etc, etc. This cycle continues and can be catastrophic if it happens undetected. Aneurysms can be kept under control by taking medication which keeps the blood pressure low (or at least prevents it from rising).


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    #4
    sinead1992
    Closed Accounts Posts: 3 ✭sinead1992


    Guys thanks so much for your replies as I'm finding physiology very difficult. But this has helped with one question anyway! Delphi91 I think that is the answer my examiner is looking for.


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    #5
    opinion guy
    Closed Accounts Posts: 11,001 ✭✭✭✭opinion guy


    sinead I hope I'm not too late butfor what its worth - the guys answers are heading in the right area here but I think your examiners are looking for something more specific - the Law of Laplace

    http://emedicine.medscape.com/article/424904-overview#a0104
    medscape wrote:
    Hemodynamically, the coupling of aneurysmal dilation and increased wall stress is defined by the law of Laplace. Specifically, the law of Laplace states that the (arterial) wall tension is proportional to the pressure times the radius of the arterial conduit (T = P x R). As diameter increases, wall tension increases, which contributes to increasing diameter. As tension increases, risk of rupture increases. Increased pressure (systemic hypertension) and increased aneurysm size aggravate wall tension and therefore increase the risk of rupture.


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