Heart Failure: Compensation by the Heart and Body - Topic Overview
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 rate).
- Pump more blood with each beat (increase your stroke volume).
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.
How does the heart increase its stroke volume? To increase its stroke volume, your heart can try to:
Get more blood into your heart. If your left ventricle isn't doing a good job pumping blood out, your heart can try to compensate by allowing more blood to fill the ventricle before it pumps by expanding its size (dilating) to increase its volume. This form of compensation may be helpful at first, but as the heart gets bigger and bigger, there is more and more tension on the walls of the heart to pump out the blood inside it. This increases the strain on the heart, making its function worse over time.
Pump harder. Your heart can pump harder by developing stronger, thicker muscle. This thickening of your heart muscle is called hypertrophy, and it can help your heart pump more forcefully and increase your stroke volume. But hypertrophy of the heart muscle increases the heart's need for oxygen and other nutrients. These requirements can eventually outstrip the blood supply to the heart, leading to further weakening of the heart muscle. In addition, hypertrophy of the walls of the heart can make diastolic function worse by impairing the ability of the heart to relax properly. This limits the heart's ability to fill with blood, which can also further reduce cardiac output.