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Sleep is a chance for your heart to slow down, even though it has to keep working. Only a little larger than a fist, your heart works hard to pump about 2,000 gallons of blood each day. On average, your heart also "beats" (expands and contracts) 100,000 times a day.
I. Sleep and The Heart
The process of sleep is made up of the following two primary stages:
- Rapid-eye-movement (REM) sleep
- Non-REM sleep
When you first fall asleep you are in the non-REM stage. The non-REM stage of sleep is a time when your heart does not have to work so hard. About 80% of a full night's sleep is spent in this stage. During non-REM sleep, your heart rate, breathing and blood pressure all drop to levels below those that occur while you are awake.
REM is the stage of sleep when you have most of your dreams. It is only about 20% of your total sleep time. Your blood pressure and heart rate can go up and down during this stage. If you have a nightmare that wakes you up, you may find that your heart is racing.
When you wake up in the morning, your blood pressure and heart rate both go back up. It is time for you to be active again, and your heart has to get ready for a long day of work.
II. Sleep and Cardiovascular Disease
Sleep and sleep disorders both play a role in cardiovascular disease (CVD). The exact role that they play is still not quite clear. One thing that is certain is that there is a higher risk of sudden cardiac death in the first few hours after you wake up. This may be due to the amount of work your heart has to do when your body gets up and moving again. CVD is a leading cause of death in the U.S. It takes the life of nearly 2,600 Americans every day.
Common forms of CVD include the following:
- High blood pressure
- Coronary heart disease
- Heart attack
- Chest pain
- Congestive heart failure
- Congenital heart defects
People with obstructive sleep apnea (OSA) have been shown to have higher rates of coronary heart disease and strokes. People who have had a heart attack are more likely to have OSA than those without heart disease. It can be even harder for someone to fully recover from a heart attack if their OSA is not treated.
OSA is a sleep disorder that occurs when the tissue in the back of the throat blocks the airway. This is very common, because the muscles inside the throat relax as you sleep. You stop breathing, keeping the oxygen you need from getting to the lungs. When you stop breathing, your body wakes up. It happens so quickly, you aren't even aware of it. You can stop breathing hundreds of times in one night. Being treated for OSA reduces your risk of death due to CVD.
Sleep and High Blood Pressure (hypertension)
Several studies have shown that people with obstructive sleep apnea (OSA) are at a much greater risk of having high blood pressure. OSA causes your oxygen level to drop. Your heart beats faster due to the lack of oxygen. This causes your blood pressure to rise. Over time, this can lead to an ongoing increase in blood pressure. It is important to treat high blood pressure since it is a proven cause of other forms of cardiovascular disease. This includes heart attack, heart failure and stroke.
But treating high blood pressure may not be enough. When high blood pressure does not respond well to treatment, it is often due to the presence of untreated sleep apnea. Once the OSA is treated, then the high blood pressure tends to improve as well. It is vital for your doctor to determine if a sleep disorder such as OSA is a factor in your high blood pressure.
Sleep and Coronary Artery Disease
People with obstructive sleep apnea (OSA) have been shown to have higher rates of coronary artery disease (CAD). There are two main reasons why this may occur:
- OSA increases the risk for high blood pressure, which is a known cause of CAD.
- The events that occur during OSA can put great stress on the heart and worsen existing disease.
CAD limits the flow of blood due to narrow arteries. This prevents the right amount of oxygen from reaching the heart. Sleep apnea also causes the blood oxygen level to drop during pauses in breathing. This leads to a rise in the heart rate and blood pressure. An extra strain is put on the heart. The amount of oxygen sent to the heart decreases at the time when the heart needs more oxygen. Studies have shown that the presence of OSA increases the risk of death from CAD. But if the sleep apnea is treated, death due to CAD is reduced.
Sleep and Congestive Heart Failure
Damage to the heart that hurts its ability to pump blood is called congestive heart failure (CHF). Sleep disorders can be both a cause and an effect of CHF. The low oxygen levels and high blood pressure related to obstructive sleep apnea (OSA) can cause the kind of damage that leads to CHF. The heart muscle is unable to handle the stress caused by the OSA. People who have CHF from another cause will see it get worse if they then develop sleep apnea. If sleep apnea is treated, however, patients with CHF will see their heart function improve.
About 40% of people with CHF have a sleep disorder called central sleep apnea (CSA). CSA occurs when the brain fails to tell the lungs to breathe. As this signal is lost, the lungs do not take in the oxygen that your body needs. This happens most often as people are falling asleep. CSA also causes people to wake up many times in the night. When they wake up, their heart rate and blood pressure both rise.
The low levels of oxygen that result from CSA are very harmful. The result is that CSA may worsen heart failure. In return, the heart failure may promote CSA. This causes a horrible cycle of declining heart function. Properly treating the heart failure is the best way to prevent CSA. If CSA still develops, there are treatments that can be used to keep it from occurring.
Sleep and Stroke
A stroke damages the brain when the blood supply to the brain is cut off. This occurs when an artery that brings blood to the brain either clots or bursts. Brain cells can die if the flow of blood to the brain stops for longer than a few seconds. This can cause permanent brain damage. The part of the body controlled by that section of the brain will not be able to function normally. Strokes are the cause of one out of every 15 deaths in the U.S.
High blood pressure is the most common cause of a stroke. Obstructive sleep apnea (OSA) may indirectly lead to a stroke by causing a rise in blood pressure. Sleep apnea can also directly cause a stroke by reducing the blood flow to the brain. This occurs when the level of oxygen drops during pauses in breathing. It is also common for OSA to begin to occur after someone has had a stroke. This may hinder a person as he tries to recover from the stroke.
III. The Effects of Heart Disease on Sleep
Heart disease can affect your ability to sleep in subtle ways. People with congestive heart failure (CHF) often have a hard time falling asleep or staying asleep. This is due to the shortness of breath that is caused by CHF. This shortness of breath is often made worse when you lie down. The blood in your legs flows back into the heart. This can bring the heart more blood than it is able to pump.
People who have these symptoms may feel like they have insomnia. Doctors call these symptoms:
- Orthopnea (shortness of breath when lying down)
- Paroxysmal nocturnal dyspnea (waking up from sleep feeling short of breath)
Heart disease also causes people to worry about their health. They are often afraid that they might have a heart attack or stroke. This anxiety can make it very hard to sleep at night. Over time, this sleep problem can develop into chronic insomnia.
IV. Sleep and a Healthy Heart
There are many things you can do to keep your heart healthy. You should be sure to do the following:
- Eat a balanced diet
- Avoid being overweight
- Get plenty of exercise
- Watch out for and treat high blood pressure
- Get regular medical check-ups
Another thing you can do is to make sure that you get enough sleep to keep your body well rested. You can often sleep better by simply following the practices of good sleep hygiene. Sleep hygiene consists of basic habits and tips that help you develop a pattern of healthy sleep. See the Resources section of this site to find out how you can start down the path to better sleep.
Watch for signs that you may have a sleep disorder. Obstructive sleep apnea (OSA) is a sleep disorder that can put great stress on your heart. Men who are overweight and have large necks are most likely to have OSA.
Symptoms of OSA include the following:
- Loud snoring
- Gasping for breath or choking while asleep
- Trouble staying awake during the daytime
You may not be aware of these signs because they only occur while you are sleeping. Your breathing is normal when you are awake. Ask a bed partner or someone else who has observed your sleep to find out if you snore or stop breathing during your sleep.
Talk with your doctor about your risk of having a sleep disorder. This is very important if you already have high blood pressure or cardiovascular disease. People with congestive heart failure must be monitored for CSA and other sleep disorders. In contrast to OSA, people with heart failure and CSA are often thin and may not snore at all.
If your doctor thinks that you have a sleep disorder, he or she may suggest that you take a sleep study. This is called a polysomnogram. A sleep study is usually done overnight in a sleep center. It charts your brain waves, heart beat, and breathing as you sleep. It also records your eye and leg movements as well as muscle tension.
A sleep specialist will be able to see if there are any problems in the quality of your sleep. Your primary doctor is then given the results of the study. The two of you can decide on the best course of treatment. It is important to remember that sleep disorders are common and treatable. Treating your sleep disorder can help you have a healthier heart.