What is Congestive Heart Failure (CHF)?
How common is CHF
How serious is CHF
What are the causes of CHF?
What are the symptoms or complaints of CHF?
How does the body respond to CHF?
What is Diastolic heart failure?
How is CHF diagnosed?
How is CHF treated?
How does the body respond to CHF? When the body perceives a decrease in the pumping ability or output of the heart, specific reflexes are triggered to allow it to cope with this problem. God equipped us with these reflexes to help survive injury and blood loss until our heart has had a chance to recover. These reflexes were not designed as a long term measure to support a very sick heart. It is very important to remember this concept!.
With blood loss, the heart is forced to work with a smaller volume of circulating blood. This smaller volume results in decreased filling of the heart. The heart muscle is composed of units known as actin and myosin. These units serve as the contracting mechanism of the heart, very similar in its action to spring devices that are used in a gym.
In the example shown above, the spring would be expected to contract more vigorously if it was stretched a little more. Conversely, the spring would have a weaker recoil or contraction if it was stretched less. In medical terms, this is known as Frank-Starling's mechanism (more about this later).
Therefore, it comes as no surprise that decreased filling of the heart would be expected to cause a reduction in the pumping ability of the heart. If the body suffered from an excessive reduction in the circulating volume (as with severe blood loss or even with marked dehydration), the output of the heart would be reduced so drastically that it would not be able to maintain the blood pressure of a patient. This would cause a very low blood pressure or even result in shock.
The output of the heart can also be reduced when its muscle is weakened or failing. As less blood is pushed out, more blood is left behind. The body compensates for the reduced output by trying to increase its filling.
First, the veins that return blood to the heart is constricted or reduced in caliber (as shown above). This shunts more blood to the heart.
Secondly, the kidney releases chemical substances that causes the body to retain sodium and water. This in turn increases the volume of circulating blood.
Both of these mechanisms cause the heart to dilate or enlarge in an attempt to take advantage of Frank-Starling's law (exercise spring example)..
However, the Frank-Starling's law also points out that increased stretch of the elastic heart muscle increases its recoil within set limits. If these limits are exceeded (when the elastic heart muscle strips are stretched beyond a certain point), the heart muscle looses its recoil or elasticity. You can compare this to an exercise spring (above) that has been stretched too far and now cannot "spring back" like it used to.
Increased filling of the failing heart with associated decreased emptying causes "back-pressure" or congestion of all the parts of the body that have to return blood to it. This causes fluid build up and swelling of the feet, ankles, legs, liver, lungs, etc., as previously discussed.
If the body's need for nutrients cannot be met by the struggling heart, the system now calls upon another emergency measure which is a ration system. Blood supply to the brain and vital organs are given the highest priority, while supply to relatively less important parts of the body (skin, muscles of the arms and legs, etc.) is drastically reduced. This is made possible by selective constriction (contraction) of the arteries that supply blood to the less vital organs, while the arteries to the brain, etc. are left wide open.
This is shown in the example (above), where the failing heart is represented by a pump and different parts of the body are depicted by the colored balloons. The clothes pins show how the tube (arteries) to the skin and muscle is clamped down (two pins) to a greater degree than the tube to the brain (no pins) and other parts of the body (one pin). The clamping down (clothes pin effect along the entire length of the affected artery) is induced by the release of chemical substances such as angiotensin converting enzyme (ACE) and catecholamines (adrenaline and similar chemicals).
The above stop gap rationing system ensures adequate blood supply to the brain by reducing supply to parts of the body that have less or intermediate importance. However, the constriction or clamping down of the arteries creates a new problem by increasing the resistance against which the failing heart has to pump against. This load makes the heart fail even further.
In summary, all the above mechanisms serve as a safety back-up systems that can temporarily increase the output of the heart. If the heart does not recover, or if it continues to weaken, all of these mechanisms turn into a self-destruct mechanism. The fittest survive, while others need medications to counteract the above reflexes. Remember that these measures were designed to combat a low output of a normal heart (as caused by blood loss during an accident) and can only temporarily help a failing heart.