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Posts Tagged ‘diastolic run off in aortic regurgitation’

We know aortic regurgitation causes  a deluge of   hugely popular peripheral signs of aortic run off  , which are taught  right from 2nd year medical school.

aortic runoof

When the aorta  leaks it reflects in the entire vascular tree .How is that a  leak in the remote aortic valve cause a quincke’s to and fro pulsations in the finger pulp ?

aortic-insufficiency

Is the blood in the finger  trying to follow  the regurgitant  jet  that  go back into left ventricle ? Does the to and fro murmur of  Duroziez over the  femoral artery imply  there is reversal of  blood flow in femoral artery ?

Things are  little complex than it appears

It is true the initiating event of collapsing pulse is the regurgitant jet , however the mechanism that amplifies and sustains it , lies in the altered peripheral hemodynamics.

The systemic arteriolar resistance is  dramatically low in chronic  severe AR  by a reflex phenomenon ,  as cardiac out put is increased and vascular tree adopt to it. So, with each  beat when blood is ejected two things happen in diastole .While a small fraction runs back into LV , the rest of  blood runs off , as if it goes in a free way  making all peripheral pulses dynamic , bounding and collapsible.

Hence as the name suggest all the peripheral signs of AR  are due to the peripheral mechanisms rather than primary event of aortic run off  into left ventricle.

Why carotid pulse does not show the collapsible nature of  pulse in AR  ?

If aortic leak into LV  is the dominant mechanism ,  carotid  artery should obviously manifest a collapse ,but it doesn’t  ,as carotid has no direct continuity with the  peripheral low resistance circuit

What is the hemo-dynamic  correlates of    descending  aortic flow reversal  in  severe AR ?

The central vascular tree  manifest  some  reversal till the regurgitant  velocity fades off . This can occur in severe AR, extending into certain length of aorta. This can be picked up by Doppler probe. Please realise  it is only  the wave form that get reversed  not the actual blood stream.( The momentum gained in systole  continues to push forward in-spite of the pulling back forces of regurgitation)

Why peripheral signs are  absent in acute AR ?

Acute AR even if it’s  significant does not cause a collapsing  pulse because it takes time for the peripheral vascular tree to go for vasodilatory mode.Further ,LV is also less compliant keeping the LVEDP high and regurgitant fraction low.

Summary

Answering  the title question ,the mechanism of  Aortic run off  in AR is both central and peripheral.  However  clinical  signs are largely due to high cardiac out put and the resultant   adaptive  response  of the  vascular tree due to low  systemic   vascular  resistance  triggered by  reflex  dilatation of small arterioles of the  peripheral vascular bed.

 

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