How Do Hypertension Increases Afterload .

Why decreasing in preload and afterload can increase cardiac output?

Decreasing preload is not usually good for increasing cardiac output which is the volume of blood ejected from the left ventricle supplying blood to the brain and the body. Preload refers to how much blood enters the heart and stretches the heart muscle cells which then contract (squeeze). The more the sarcomeres (the functional units of the heart muscle cells) are stretched, the stronger the contraction which in turn increases the amount of blood pushed forward. This is known as the stroke volume. Things which decrease preload include shock, hypotension and tamponade (fluid build-up in the sac surrounding the heart). The heart rate (HR) compensates by speeding up. Adding IV fluids to increase fluid volume or in the case of tamponade removing the fluid from around the heart will increase (a good thing) preload.Now, this is in a healthy myocardium (or heart muscle). In an enlarged heart (also known as heart failure or cardiomyopathy) decreasing preload may be necessary because the heart muscle cells are already stretched out and are not as effective. This is why heart patients are sometimes told to decrease their salt intake which pulls additional fluid (water) into the circulatory system. So in this case, yes, decreased preload is helpful.Afterload refers to the resistance the left ventricle encounters when trying to move the blood into the circulatory system. Conditions such as hardened and/or narrowed arteries (atherosclerosis) make it harder for the heart to eject the blood from the left ventricle and consequently less blood will be put into circulation. Hence, stroke volume is decreased. This is known as the ejection fraction (EF) which is normally only 2/3’s of the amount of blood in the left ventricle so 55% to 70% EF is considered normal or healthy. In a sick heart the EF decreases significantly so decreasing afterload certainly will help. Many times the use of anti-hypertensive drugs (blood pressure pills) will be utilized to achieve this.A helpful equation can illustrate this:Cardiac output = stroke volume x heart rateThis is a fairly simplistic explanation but I hope your question is adequately answered and that you have a better understanding of the terminology used when discussing this topic.

How can vasoconstriction increase blood pressure but decrease blood flow?

This is the most easy explanation I can give to you (I have a very limited knowledge): If you put the thumb in the distal extreme of the hose, you are actually incrementing the pressure, creating a "vasoconstriction", and simultaneously decreasing the water flow by reducing the area in the distal extreme of the hose. If you put the thumb off, the water flow it is going to be more, but the pressure low.    In head trauma and stroke, the cerebral circulation, sometimes responds as the hose of the example. Cerebral vasoconstriction increase pressure to increase perfussion, but with a cost: it is going to decrease the blood flow.Below it is a old but very  reference to the journal of neurosurgery to understand better the importance of vasoconstriction in head trauma and stroke.  The hose photo it is not mine. it is a google photo. and...I apologize for my syntaxis. I hope you find the answer useful.    Journal of NeurosurgeryAugust 1997 / Vol. 87 / No. 2 / Pages 221-233CLINICAL ARTICLESHemodynamically significant cerebral vasospasm and outcome after head injury: a prospective study.

How is high blood pressure related to left ventricular hypertrophy?

Muscles grow in response to increased workload. The increased pressure against the walls of the left ventricle causes the myocardium to swell in size, decreasing the diameter of the chamber and it’s ability to squeeze blood into the body effectively. This can potentially lead to congestive heart failure as the ejection fraction decreases.Here’s a picture of the decreased chamber space due to the hypertrophy of the myocardium (the thick read area).

What is left ventricular hypertrophy, and how does this happen?

Thanks for the A2A.Left ventricular hypertrophy (LVH) is thickening of the heart muscle of the left ventricle of the heart, that is, left-sided ventricular hypertrophy.The causes are well clear:While ventricular hypertrophy occurs naturally as a reaction to aerobic exercise and strength training, it is most frequently referred to as a pathological reaction to cardiovascular disease, or high blood pressure. It is one aspect of ventricular remodeling.While LVH itself is not a disease, it is usually a marker for disease involving the heart. Disease processes that can cause LVH include any disease that increases the afterload that the heart has to contract against, and some primary diseases of the muscle of the heart.Causes of increased afterload that can cause LVH include aortic stenosis, aortic insufficiency and hypertension. Primary disease of the muscle of the heart that cause LVH are known as hypertrophic cardiomyopathies, which can lead into heart failure.Long-standing mitral insufficiency also leads to LVH as a compensatory mechanism.Basics but it would answer your question.Hope this helps.Best of Luck.