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### Course: Health and medicine>Unit 2

Some say Preload = End-Diastolic Pressure, others say Preload = End-Diastolic Volume, so which one is it? Watch and find out! Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.

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• Doesn't the wall stress calculation assume no compliance or elastance?
• Compliance is V/P and Elastance is P/V. You can rearrange Laplace's equation to include those terms if you would like.
• Why is everything just to do with the left ventricle?
• The left ventricle circulates blood to the entire body, which means that it experiences significantly more resistance than the right ventricle, which circulates blood only to the pulmonary system. Although pulmonary hypertension exists, it is much less common than systemic hypertension.
• At you use R_TOT in the wall stress equation. I believe that should be the internal radius as the pressure is only acting over the inside of the heart? I believe the derivation of this equation more generally uses for pressure vessels supports this. Unfortunately I cant type the derivation here very easily, but here on wikipedia it describes the equation.
http://en.wikipedia.org/wiki/Pressure_vessel
Refer to 'Stress in thin walled pressure vessels'

I have posted the same question on the next video where R_TOT is used again.
Cheers
• is it safe to say, in simpler terms, that preload is the amount of stretching the ventricles experience when they receive blood from the atria?
• yes, preload depends directly on venous return. But it can change depending on factors affected by physiologic demand, it inst constant. Greater preload means greater pressure in isometric contraction of the ventricle. See Frank-Starling law for more info.
(1 vote)
• Is preload of the right ventricle same as the preload of the left ventricle?
• No, it would not be. Since preload is affected by wall stress and thickness, the right ventricle preload would have different values from the left, because the left ventricle has significantly more muscle.
• My textbook (Rhoades&Bell 4th int. ed. page 217) used the concept of vascular capacitance and compliance, but explains nothing of elastance.

Is elastance (=EDP/EDV) simply the reciprocal of vascular capacitance (=EDV/transmural pressure)?
• what is extracorporeal circulation?
• extra corporeal circulation is when the blood is taken away from the body's circulation and then it returned. So it is circulating trough an artificial system outside the body.A good example of this is dialysis, When a patient is receiving dialysis the blood gets removed; It passes trough a filter and the it gets returned to the body. Or like when you donate platelets and they return your blood the needles and tubes that pass trough the machine are the extra corporeal circuit.
• Is this measured at the ventricle or atria? I know that you could specifically specify in conversation. But when people say preload by its self as pertaining to the whole heart. is there a convention in which we should think about it? I think it would be safe to assume it is measured at the left ventricle when not specified. Is this correct?
(1 vote)
• Although preload can be measured in all four chambers, it is typically measured in the ventricles and yes, the left ventricle is typically what people are referring to. Clarify if you can, though.