Heart Failure: Compensation by the Heart and Body - Topic Overview
Heart failure means that your heart muscle doesn't pump as much blood as your body needs. Because your heart cannot pump well, your heart and your body try to make up for it. This is called compensation.
Your body has a remarkable ability to compensate for heart
failure. The body may do such a good job that many people don't feel symptoms in the earlier stages of heart failure. It is only when your
body isn't able to compensate enough that you will begin to experience
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Compensation may help your body adjust to the effects of
heart failure in the short term. But over time
it can make heart failure worse by further enlarging the heart and
reducing the pumping ability of the heart.
How does the body compensate?
With heart failure, the heart doesn't pump as well as it should. So your body doesn't get enough blood and oxygen. When this occurs, the body believes
that there isn't enough fluid inside its vessels. The body's hormone and
nervous systems try to make up for this by increasing blood
pressure, holding on to salt (sodium) and water in the body, and increasing
heart rate. These responses are the body's attempt to compensate for the poor
blood circulation and backup of blood.
The nervous system. If your body senses
that the brain and vital organs aren't receiving enough blood, the sympathetic nervous system starts working to get more blood to your brain and organs. This system
releases substances called
catecholamines into the bloodstream. These substances
cause the blood vessels to constrict and speed up the heart rate. At the same time, the arteries supplying the brain and vital organs
widen to carry the increased blood flow.
Hormone systems. When the body thinks it needs more
fluid in its blood vessels, it releases specific chemicals (renin, angiotensin,
and aldosterone) that cause the blood vessels to constrict. In addition, these
hormones cause the body to retain more sodium and water. This adds fluid to your circulatory system. This fluid becomes part of the blood
circulating throughout your system.
How does the heart compensate?
Your heart's goal in compensating for
heart failure is to maintain your cardiac output.
Cardiac output is the amount of blood your heart is able to pump in 1 minute.
The problem in heart failure is that the heart isn't pumping out enough blood
each time it beats (low stroke volume). To maintain your cardiac output, your
heart can try to:
Beat faster (increase your heart
Pump more blood with each beat (increase your stroke
How does the heart know to beat faster? Your
brain signals your heart to beat faster by sending messages to your heart's
electrical system, which controls the timing of your heartbeat. When your
cardiac output is low, your adrenal glands also release more norepinephrine
(adrenaline), which travels in the bloodstream and stimulates your heart to
beat faster. Although beating faster helps to maintain cardiac output as the
stroke volume falls, a faster heart rate can be counterproductive because it
allows less time for the ventricle to fill with blood after each heartbeat.
Also, a very fast heart rate can itself weaken the heart muscle over time.