Right Atrial Pressure: Normal Range, Why Lower than Venous?

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what is the normal range of right atrial pressure? and why is it lower than venous pressure?

the order of the highest to lowest volume was venous, right atrial, and arterial, (in norma condition) why is this true?

trying to get the concept right!
 
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pharaoh said:
what is the normal range of right atrial pressure? and why is it lower than venous pressure?

The normal range is 0-5 mmHg (0-6.7 hPa). This is called the central venous pressure (CVP). This pressure needs to be lower than the peripheral venous pressure (PVP), to maintain venous blood return the heart. Right atrial (RA) volume is minimal at the beginning of ventricular systole, and then fills as the RA expands. The RA empties during ventricular diastole. At the end of this phase, the RA actively contracts (the P wave) giving the right ventricle (RV) an extra "shot" of blood and returns to its minimal volume. Because the RA is either filling by passive expansion or emptying into the RV, it maintains a lower pressure then the PVP which is not fully free flowing due to valves.

There are many abnormal situations where the CVP will increase; such as with left ventricular failure which elevates pulmonary blood pressure which in turn elevates RV and RA pressure. Pressure changes in the chest cavity can also affect CVP such as with air leakage from the lungs as result of injury or disease (emphysema with ruptured blebs).

I'm not sure what you mean regarding volumes. Total venous capacity can act as a kind of storage volume since veins are thin walled and can expand. However this is not a healthy situation since it can indicate heart failure or venous insufficiency due to incompetent venous valves among other things.
 
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By the way, your question isn't directly relavent to the Windkessel effect. This refers to the compliance of the aorta with the arterial pressure wave produced by the ejection volume from the left ventricle (LV). The measured systolic arterial blood pressure is largely a function of this. With atherosclerosis, the aorta stiffens and cannot absorb the pressure wave by expanding a bit. The result is that the pressure wave is less damped and carries though to the peripheral arteries where it manifests as elevated systolic blood pressure. This condition can also lead to LV enlargement and various degrees of heart failure due to increased arterial resistance. This will feed back to the RV and raise CVP. Is this what your asking? The most common cause of RV failure is LV failure and RV failure raises CVP. The failing heart will also be reflected in a rising diastolic arterial blood pressure.
 
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