asaaal
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can someone please explain why peripheral venodiltion reduces preload?

why does peripheral arterial and arteriolar dilation reduce after load?

thank you in advance, sorry if its a silly question.
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Dynamo123
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(Original post by asaaal)
can someone please explain why peripheral venodiltion reduces preload?

why does peripheral arterial and arteriolar dilation reduce after load?

thank you in advance, sorry if its a silly question.
Well, to understand this, just think what preload and afterload are. Afterload, although considered to a pressure, is often interpreted as the systemic resistance to blood flow. When your vessels, especially the arteries and arterioles are dilated, blood can move with greater ease and the resistance is diminished. This reduces afterload.
Preload can be considered roughly as the amount of blood returning to the RA. This amount of blood, within physiological limits, is equivalent to your cardiac output. When veins are dilated, they serve as reservoirs to "dam" or pool blood. As a result, the total amount of blood returning to the heart, or the preload is reduced.
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asaaal
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(Original post by Dynamo123)
Well, to understand this, just think what preload and afterload are. Afterload, although considered to a pressure, is often interpreted as the systemic resistance to blood flow. When your vessels, especially the arteries and arterioles are dilated, blood can move with greater ease and the resistance is diminished. This reduces afterload.
Preload can be considered roughly as the amount of blood returning to the RA. This amount of blood, within physiological limits, is equivalent to your cardiac output. When veins are dilated, they serve as reservoirs to "dam" or pool blood. As a result, the total amount of blood returning to the heart, or the preload is reduced.
thats very useful thank you !
How does low preload/afterload effect oxygen demand?
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Asklepios
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(Original post by asaaal)
thats very useful thank you !
How does low preload/afterload effect oxygen demand?
Afterload - if there is greater systemic resistance to blood flow, meaning that the heart has to work against a greater pressure, will it need more or less oxygen?

Preload - if there is more blood in the heart at the end of diastole so greater stress on the ventricular walls, will the heart have to work harder or not? And what does this mean for oxygen demand?


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Dynamo123
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(Original post by asaaal)
thats very useful thank you !
How does low preload/afterload effect oxygen demand?
Asklepois is right. You must first consider where you are considering oxygen demand to be affected; in the coronary circulation or in the general systemic circulation.
Afterwards, think about it. If your afterload, which is the resistance, is low, the heart won't have to work against a greater resistance. Consequently, it will need less oxygen. and we know that peripheral vasodllation, which decreases afterload is associated as a compensatory response to low oxygen supply to tissues.

If the preload is less, less blood is returning to heart and consequently the End diastolic volume will be less. Although Asklepois's proposition of a low pressure leading to low oxygen demand in case of reduced preload is true, the effects on other tissues will hardly be the same. A reduced preload will mean a decreased stroke volume and a decreased cardiac output, leading to less supply of oxygenated blood to the tissues and increasing the tissue demand. The effects of this on the heart muscle itself won't be appreciable, because normally the heart receives oxygenated blood before any other tissues have been supplied.
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