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Question: What is afterload?

What is preload and afterload?

Preload is the initial stretching of the cardiac myocytes (muscle cells) prior to contraction. It is related to ventricular filling. Afterload is the force or load against which the heart has to contract to eject the blood. Afterload is the ‘load’ to which the heart must pump against.

What causes increased afterload?

Afterload is increased when aortic pressure and systemic vascular resistance are increased, by aortic valve stenosis, and by ventricular dilation. When afterload increases, there is an increase in end-systolic volume and a decrease in stroke volume.

Is afterload the same as blood pressure?

Afterload is the pressure that the heart must work against to eject blood during systole (ventricular contraction). Afterload is proportional to the average arterial pressure.

What is afterload affected by?

Afterload is increased when aortic pressure and systemic vascular resistance are increased, by aortic valve stenosis, and by ventricular dilation. When afterload increases, there is an increase in end-systolic volume and a decrease in stroke volume.

What happens to preload and afterload in heart failure?

When the preload (EDV) and contractility are held constant, sequential increases (points 1, 2, 3) in arterial pressure (afterload) are associated with loops that have progressively lower stroke volumes and higher end-systolic volumes.

What happens during preload?

Preload is the force that stretches the cardiac muscle prior to contraction. This force is composed of the volume that fills the heart from venous return. Due to the molecular arrangement of actin and myosin in muscle, the more the incoming venous volume stretches the muscle, the further it will contract.

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What drugs reduce afterload?

1) Vasodilators – Drugs that decrease either preload or afterload. a) The major vasodilators used are ACE inhibitors and angiotensin II receptor antagonists, organic nitrates, hydralazine and nitroprusside.

Does increased afterload increase heart rate?

In isolated heart preparations, in which preload, inotropic state, and heart rate are controlled, increases in afterload cause reductions in left ventricular output (i.e., stroke volume; Fig. 24.5A).

Does afterload affect cardiac output?

Afterload. Afterload is the force against which the ventricles must act in order to eject blood, and is largely dependent on the arterial blood pressure and vascular tone. Similarly, reducing afterload can increase cardiac output, especially in conditions where contractility is impaired.

Why would you want to decrease afterload?

Compensatory increases in blood volume further increase preload and dilate the ventricle. Therefore, reducing afterload has been found to be very effective in the treatment of systolic dysfunction because it increases stroke volume and decreases preload (see figure), thereby improving ejection fraction.

What happens to afterload during exercise?

The increase in arterial pressure (increased ventricular afterload) that normally occurs during exercise tends to diminish the reduction in end-systolic volume; however, the large increase in inotropy is the dominate factor affecting end-systolic volume and stroke volume.

Does high blood pressure increase preload?

Increased aortic pressure, which increases the afterload on the ventricle, reduces stroke volume by increasing end-systolic volume, and leads to a secondary increase in ventricular preload.

How is heart afterload measured?

In the clinical setting, the most sensitive measure of afterload is systemic vascular resistance (SVR) for the left ventricle and pulmonary vascular pressure (PVR) for the right ventricle. Afterload has an inverse relationship to ventricular function.

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Why does afterload increase in cardiogenic shock?

One of the most significant concerns of an elevated arterial pressure is at the site of the aorta. If the overall pressure within the aorta is higher than normal, the ventricle must work harder to overcome the higher pressure to eject the blood, thus creating an increase in afterload.

Is preload the same as EDV?

Preload is related to the ventricular end-diastolic volume; a higher end-diastolic volume implies a higher preload. However, the relationship is not simple because of the restriction of the term preload to single myocytes.

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