Tuesday, August 24, 2010

How Our Heart Function

Please put your thinking the limit of two other points. We will try to make it as painless as possible. We also recommend that you become familiar with the physiology and pathophysiology points more than once because they are the basis of symptoms and treatment of congestive heart failure (CHF). Let ....

                                                   figure The Cardiac Cycle via xaraxone

Before going into details of how this works in the normal heart and no heart, you may be exposed to additional conditions. This will be repeated several times in terms of our discussion on the physiology and pathophysiology.

1. Cardiac output, the number of cc of blood the heart pumps through the body in minutes.
     --- Stroke volume - the amount of blood pumped by the heart with each heartbeat.

2. Heart rate, how many times a heart beats per minute.
    --- Withdrawal - refers to the inner strength to the heart muscle to contract and pump blood.

3. End-diastolic - the amount of blood in the left ventricle after cardiac relaxation phase (diastole)
   --- Consumption of myocardial oxygen (MVO2) the amount of oxygen required by the heart muscle to spasm.

4. Preload, the amount of blood in the ventricle of the heart, which remained over the previous contraction (diastolic end) and the amount of blood given to the ventricular venous system (superior vena cava is).
    --- Load - refers to the resistance of the meeting of the left ventricle as it tries to eject blood to the body.

5. Infusion, blood flow sufficient to target organs and many cells.
   --- Contraction, the heart contracts

6. Diastole when the heart rests between beats
    --- Venous return of blood to the heart brought on venous blood flow

The entire circulatory system is the provision of individual cells in each body a sufficient flow of blood (called perfusion), which gives them the nutrients and oxygen they need. When these cells have what they need to perform their normal functions. Thus, the kidneys, which means it can filter the waste. For the muscles, which means they can make a move. For the liver, which means that liver cells can soak drug metabolism in the body. The corresponding equivalent perfusate which reduces how much the heart can provide these cells. adequate cardiac output is necessary for infusion.

Cardiac output is the amount of blood pumped by the heart cc per minute. Determinants of cardiac output theheart rate (measured in beats per minute) and stroke volume (in cc of blood ejected with each heartbeat). The heart's ability to increase cardiac output is a very good thing. When you run a great distance, the muscle cells need more fuel than they are at rest. When the heart rate and increases with the amount of blood ejected with each heart beat (heart palpitations and stroke volume). This increased perfusion of muscle cells, and they are more oxygen, glucose and electrolytes. The increase in perfusion and allows them to get rid of carbon dioxide and other waste. Therefore, the muscles that run faster and stronger.

Several factors influence the cardiac output :
  • Preload
  • Load
  • Withdrawal muscle strength of each contraction of the heart
  • Heart rate, how many times a heart beats per minute
  • Scalability, the ability to stretch the muscles of the heart and return to normal
  • Synergy contraction, in a coordinated heartbeat.

To discuss more understandable than the preload and load:
Preload (End Diastolic Volume)
It is a process of priming the pump and for practical reasons, is composed mainly of blood, which veins between the left and right atrium (atrial fibrillation). Occurs in that split second when the heart does not beat what you know, is called diastole. We also call for the end-diastolic volume preload, as is the volume of blood in the ventricle of the heart at the end of diastole (just before systole). Technically, the preload is equal to venous return and left ventricular volume in the last contraction.

The volume increases preload brain. It is good to a point. This means that the quantity of blood from the posterior vena cava and the vena cava anterior to provide the right amount of blood the heart needs. This means a sufficient amount of blood comes from the lungs (pulmonary veins) to supply the left heart to the amount of oxygenated blood must be supplied by the organization.

In a normal resting state is constant preload. In the case of the beginning of the exercise you need to bring more blood to the muscles to their needs. venous system will bring more blood into the chambers of the heart during diastole (preload), so the heart can eject more blood with each beat (increased stroke volume). In addition, rapid heartbeat (tachycardia). Increase the volume of the brain and the heart increases cardiac output in the form above.

Increasing the preload increases afterload, which increases the volume chamber. Yes, now we'll talk about the afterload.

The charge refers to the resistance of the meeting of the left ventricle in trying to eject blood into the aorta, where agreements. Also refers to the resistance of the right of the meeting, since the blood flows into the lungs to get a fresh supply of oxygen. We return to this later, for the moment to think how, how much heart to pump against the pressure in the aorta to get blood moving.

vascular resistance is like a contraction or expansion of the artery as the blood flows through it. Blood pressure is a synonym for our discussion. You already know that the arteries constrict and expand continuously, all based on the needs of the organization in general and in particular they carry blood. To return to our scenario above the muscle, but an increase in cardiac output, cardiovascular system also causes the arteries (range) for the muscles, which also contributes to their infusion. This concept of blood pressure is very important that we include it in more detail.

Normal regulation of blood pressure involves many complex metabolic processes. Many body systems are affected, including the nervous system and kidneys, cardiovascular system and endocrine system. It is a very sophisticated system that can make changes minute in a rapid response to changing physiological needs.

It is part of our brain and spinal cord, which continuously monitors the normal physiological process that happens in the body. performs many functions, many of them critical to our survival that we are not even aware. A portion of our brain and spinal cord that is not the so-called autonomic nervous system (ANS). ANS that continuously monitors blood flow and blood pressure. It does this by controlling the pressure in structures called baroreceptors located near major blood vessels.

NSA when it detects drop in blood pressure, activates a complex set of physiological processes to maintain adequate blood pressure and thus the blood supply to vital organs like the brain and heart. YEARS said juxtaglomelular camera in the renal secretion of renin bloodstream.Renin transforms the relationship of angiotensin I to angiotensin angiotensin I circulates in the lungs, where inhibitors of the enzyme (ACE), it turns into angiotensin II, which led to a significantly increased constriction of blood vessels in the body in general. Angiotensin II increases the secretion of adrenal hormone aldosterone, which further increases the narrowing of the arteries (increased load) and increases venous stenosis (increase preload) and sodium and water retention increased ( increased preload). The end result is a narrowing or constriction of blood vessels in many other vital organs, which increases the blood pressure of critical organs like the heart and brain.

An Analogy Hose
By analogy, how to use his heart, like a snake and the blood vessels that irrigate the lawn with water. authority lawn look like the liver, as well as the individual blade of grass in the liver cells. When you turn the hose is only slightly lower pressure (low blood pressure) in the pipe, and you can not water your lawn well. Each blade of grass is not enough water, so there is inadequate perfusion. If you turn the faucet on the road increases the stroke volume leading to increased production incardiac. This increases blood pressure (high pressure) in the pipe, and all grass is enough water (better perfused). Kurek is the cardiac output, flow through a garden hose is your blood pressure, the amount of water every blade of grass receives an infusion.

In our analogy of a snake, it preloads the amount of city water supply to the stem (the water company is to make the venous blood to the heart). The load corresponds to how much force is necessary to obtain the appropriate amount of tap water to the lawn (adequate perfusion). When you change the pipes and connect the one that is smaller in diameter (an increase of vascular resistance), life is more necessary than tap water (more expense) to provide as much water your lawn (infusion appropriate). This means that tap water should do more work. If the valve is the heart, it means that more difficult to conclude that the blood to all cells in the body. A healthy heart is with this challenge, the heart is not sick.

So now, let's see what happens when all this was a complex physiological problem, a process that we call pathophysiology.
Pathophysiology of Heart Disease
There is a difference between heart disease and heart failure. In the heart of heart disease a kind of irregularity. If small enough, the heart is unable to provide adequate perfusion in the cells and there is no problem. In heart failure, the heart does not maintain adequate perfusion for the proper functioning of cells. Animals that are relatively inactive may be able to avert the effects of heart failure for the animals more active, because they do not challenge the cardiovascular system. But he has a bad side, because the symptoms of heart failure are finally visible to the owner, the disease is well entrenched and difficult to treat.

When the heart does not start (decrease in cardiac output) is the result of either 1) a reduction in stroke volume, or 2), abnormal heart rhythm:
  1. Stroke volume may decrease secondary to a reduction in preload (shock, dehydration, bleeding), low shrinkage (cardiomyopathy), increased afterload, or malfunction of the heart valves (endocardiosis, patent arterial cable) or the fluid around the heart (tamponade).
  2. Disorders of the heart are called cardiac arrhythmias, and this is due to problems with the electrical conduction system of the heart. The slowness of the heart (bradycardia), cardiac output will fall on the model has already been exposed to before. The high heart rate (tachycardia), cardiac output decreases because there is not enough time to fill the ventricles with blood during diastole. Therefore, if during the contraction of the heart is ejecting blood into the aorta, is throws less blood with each beat.

In both cases, heart failure is usually the result of the chronic process. This gives time to adjust to the body a small amount of inadequate perfusion in the early stages of heart failure. compensatory mechanisms are initiated to increase the blood supply to the cells. Initially, these compensatory changes work quite well. So good, in fact, they do not notice the first signs of heart failure in animals. Over time, however, in the heart is not out yet, and compensate for these changes will not work. In fact, become pests. That's when you start noticing the symptoms of heart failure.

In terms of units, insufficient blood supply to cells in heart failure mimics what happens when a healthy animal loses a significant amount of blood or passes in shock. The shock is the collapse of the cardiovascular system, resulting in blood flow decreased significantly in the cells. This can cause death if not treated quickly. A good example is the shock when the animal is struck by a car.

A number of compensatory measures are included in the composition of the animal with shock in terms of cardiovascular or circulatory. Insufficient volume of the circulatory system (preload) to maintain the heart. Therefore, the body activates compensatory measures to increase the blood pressure drops (by increasing vascular resistance) and depression increased cardiac output (by increasing contractility, increased heart rate and increased preload) to maintain perfusion of vital organs (brain and heart). While these measures may work adequately for a short period of adjustment shock, they are harmful if the shock lasts more than a few weeks, which is exactly what happens in heart disease. Unfortunately, the body reacts to all situations which reduces cardiac output in the same way a shock, even if it is heart failure, not a shock that causes poor blood flow to cells. Let countervailing measures and how they contribute to the cascading series of events leading cardiac congestive heart failure (CHF).

Heart does not lead to a weakening of the heart. The body responds first by increasing the heart rate and contractility and thus cardiac output, leading to an increase in the cell infusion. Autonomic nervous system also tightens selective peripheral arteries, which leads to increased blood pressure to vital organs, and yet, more than perfusion in their cells. This increases the blood pressure has increased the burden, putting further pressure on the heart is not as it tries to push the blood more resistance. Autonomic nervous system increases the pressure in the venous system, which brings more blood to the heart, increasing preload. Have you heard of any Section of Physiology, we are just a review.

How to increase the contractility of the heart is increased oxygen demand, which can lead to arrhythmias. If the arrhythmia is so serious, coordinated heartbeat is reduced and a further reduction in cardiac output occurs. This monitor the electrocardiogram (ECG).

Since redistribution of blood flow YEARS maintain cardiac output, heart and brain (as is the case in shock), away from peripheral vascular beds. This involves maintaining blood pressure at the appropriate level. It is the transfusion of blood in the internal organs and other important organs in the body, eventually leading to pale mucous membranes, slow capillary refill time, and cold extremities. Regarding implementation, the blood is diverted from the intestine, interfering with the absorption of food. If severe enough, can become an intestinal ulceration and bleeding begin.

Blood is diverted by the kidney, reducing its efficiency by reducing the glomerular filtration rate (GFR). The result is an accumulation of more sodium and water retention increased, leading to increased blood pressure and preload and load more. This causes the increase in the amount of waste that accumulated in the bloodstream. You can find more information about the waste on our kidneys.

As the volume (preload) is still growing, the pressure in the ventricle of the heart increases.If he will be in the left heart, the cons-pressure builds in the pulmonary veins, causing leakage through the walls of these vessels and the actual lung tissue (alveoli). The result is pulmonary edema which is an accumulation of fluid in the alveoli, the very area where the carbon dioxide and oxygen exchange. This fluid can significantly affect the exchange. the blood supply to the cells is unnecessary if the red blood cells that supply oxygen to these cells lack oxygen molecules in their use of the cells. Not only do we have a heart that is not enough infusion of cells with oxygen, we also have red cells that have problems finding fresh oxygen. This double whammy affects all organs, and even the heart. This results in a vicious circle develops where the body can not escape.

This is a severe pulmonary edema. This is the point of intersection of the lungs of a cat, who died of cardiomyopathy.

If the increase in preload occurs in the right heart, the pressure builds up in the veins, which provide two atria. From the back returns the blood from the inferior vena cava of the abdomen, increasing pressure to cause leakage of fluid from the inferior vena cava and in the abdomen. This is called ascites. Do ascites or pulmonary edema occurs depends on whether this problem occurs more in the left heart or the heart to the right. It can occur in both cores, as part of the liquid accumulated in the body cavities of many.

The increase in preload causes a significant increase in cardiac output to normal, but only a slight increase in stroke volume is not left to the heart. Thus, this smoothing mechanism has only a slightly positive effect on the blood supply to the cells. Conversely, a reduction in preload cause a significant decrease in cardiac output to normal, but only a slight reduction in stroke volume at heart.Therefore not a marked reduction in preload in the context of inadequate Cardiac resolve pulmonary edema or ascites, only a slight reduction in stroke volume. It is a great clinical importance. Some drugs that are used in heart has not taken advantage of their opportunities significantly lower preload, without affecting stroke volume. Until the final result of body cells infusion relatively satisfactory, but no pulmonary edema or ascites. Although the cells are not fully met, the animal feels much better, because it is less accumulation of fluid in the lungs and abdomen. In addition, less accumulation of fluid in the lungs of oxygen allows precise and exchange of carbon dioxide, which at least one physiological process is essential. We do not have an obvious problem with drugs that reduce, but at least make the animal feel much better, and better exchange of oxygen. This is huge for the animal or person who is literally drowning in the fluid in the lungs.

Other changes in compensation, which occurs when there is inadequate perfusion of cells is to increase the load. This occurs because the body tries to elevate blood pressure to critical organs like the heart and brain, which in theory gives them greater infusion of cells. As explained above, the body increases blood pressure by several mechanisms. Now you do not have the heart to pump against higher pressure (over load), which reduces the stroke volume and cardiac disorders. The load changes are more significant effect on stroke volume in the heart not the normal heart. Opportunity to improve cardiac output by reducing afterload (antihypertensives) is one of the main achievements in the treatment of cardiovascular diseases. We will discuss these drugs in the treatment section. These are the same drugs people use them to reduce blood pressure.

Many other changes occur heart failure progresses.We already know that the increase in heart rate increases cardiac output. It is good for blood cells, but becomes self limiting when the heart rate increased to a point (180-250 beats per minute for the dog) that is less time to fill the ventricles blood during diastole. This leads to insufficient blood is pumped by the heart during ventricular contraction. Increased heart rate increases oxygen consumption by the heart muscle leads to arrhythmias work because it becomes increasingly difficult. In addition, the heart muscle and requires an adequate blood supply to provide oxygen and nutrients, like all other cells in the body. The blood flow to the heart than during diastole, and heart rate, heart disease spend less time in diastole. The end result is that the heart does not even faster.

As the heart still heart still growing and the heart muscle receives less infusion. Finally got to the point where the normal heart rhythm coordinated electrical could more correctly, and cardiac arrhythmias occur. In this context arrhythmias can significantly reduce the stroke volume of the heart and can quickly spiral out of control. That's when the state is critical, generally see these animals in case of emergency.

Heart failure can also occur in conditions where the heart is the production of a normal cardiac output, but the metabolic needs of tissues will be increased. Diseases such as anemia hyperthyroidismor cats fall into this category. In this way, heart failure can occur under conditions where the strength of heart muscle appears normal, but the authorities must infusion is so big, healthy heart can not keep up with demand.

If the left heart is sick does not pump enough blood (decreased cardiac output) by the aorta to the division of cells. It is not enough blood ((poor perfusion) prevents these cells perform their normal function of the brain controls the infusion and to take action and sodium regulating hormones in combination with kidneys and lungs. This increases the pressure in the arterial system as a whole, and meets the needs of the cells temporarily providing greater blood flow (more blood flow). The blood pressure of more patients with left ventricle fills with blood more than usual (increased preload), causing it to expand and weaken it further. It also increases the pressure of the left ventricle must pump against (afterload increase) to get the blood into the aorta and into the cells. This adds Further work is already sick heart, a part of the problem even more. Finally, the blood presented to the left ventricle does not pump effectively, causing reflux (pressure) in the lungs. When the pressure reaches a certain point of the fluid in blood vessels in the lungs leaks, causing pulmonary edema. It is a congestive heart failure (CHF).

If the law becomes a disease of the heart, a similar set of physiological sequence occurs. higher blood pressure resulting from a cell to send an alarm signal for the results of the brain and more blood will be presented in the right heart (increased preload). Ultimately, the weakened heart can not be right to pump blood to the lungs more rapidly than the venous system shows him the blood. This causes the pressure build-cons in the venous system, especially the vena cava and other veins in the abdomen, and even the chest. When the pressure is high enough in the veins of the leak, leading to ascites and pulmonary effusion.

This problem can occur in both cores at the same time, causing even more problems.

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