Sleep is a time of rest for the entire body. Even the heart, which works day and night, naturally slows down during sleep.
That’s why unhealthy heart function (caused by conditions such as heart disease) can deprive the body of restful sleep. Yet, the relationship between heart function and sleep works both ways. For instance, sleep related breathing disorders have been shown to play a major role in causing several types of heart and blood vessel disease.
There are two distinct types of sleep:
Typically, when you fall asleep you begin in non-REM sleep and spend about 80% of the night in this type of sleep. During non-REM sleep your heart rate, breathing and blood pressure all drop to levels below those occurring while you are awake.
During REM sleep – approximately 20% of your time asleep – both your blood pressure and heart rate can fluctuate. Any time you wake up from sleep (even briefly), your heart rate and blood pressure climb and your heart must work harder. When you wake up in the morning, your blood pressure and heart rate both go up and then stay at a higher level throughout the day.
“Treating certain sleep-related breathing disorders may actually decrease a person’s chances of developing certain cardiovascular diseases”.
Although all aspects of the relationship are not clear, there is definitely a direct connection among sleep, sleep disorders and heart disease.
Several studies have shown a link between hypertension and the presence of a disorder of abnormal breathing during sleep called obstructive sleep apnoea (OSA). Not only is hypertension common in those with OSA, but evidence suggests that OSA can lead directly to the development of hypertension.
People with OSA have repeated interruptions in breathing during sleep, caused by the main breathing passage in the back of the throat closing or becoming too narrow. Every time this passage is blocked, breathing stops and oxygen is used up. After a while (usually 10 – 20 seconds, although up to one minutes is not unusual) the breathing difficulty causes a brief awakening, often so short that the person is unaware of any interruption in sleep. The awakening relieves the blockage in the breathing passage and normal breathing resumes, at least until the person falls back asleep, when the entire process can repeat (often hundreds of times per night). The drop in oxygen level from not breathing and the increase in heart rate and blood pressure caused by waking up, puts stress on the heart. These nightly increases in blood pressure eventually lead to permanent increases in blood pressure, even during the day.
It is important to treat hypertension since it is a known risk factor for the development of other forms of cardiovascular disease such as heart attack, heart failure and strokes. But treating hypertension may not be enough if the key reason for a person’s high blood pressure is an unrecognised sleep disorder like OSA.
Hypertension medications, for instance, may not work well if OSA remains untreated. Many people who have difficult cases of hypertension are later found to have untreated OSA and treatment of the OSA can improve hypertension.
For this reason, it is important for your healthcare professional to investigate all the possible causes of your hypertension, including sleep disorders like OSA.
There is a direct association between sleep-related breathing disorders and cardiovascular disease. People with OSA, for example, have been known to have higher rates of coronary artery disease (CAD). There are several reasons why this may occur:
In people with CAS the flow of blood, which carries oxygen to the heart, is limited (due to narrowed arteries). So, if they experience OSA, their blood oxygen levels drop and their heart rate and blood pressure rise, increasing the work required of the heart.
As a result, the amount of oxygen supplied to their heart decreases just as there is demanding more oxygen. Several research studies have shown changes indicating ischemia, or lack of blood flow, on electrocardiogram during apnoeas in people with CAD. However, if recognized, treatment of OSA reduces death due to CAD.
Congestive heart failure occurs when the heart is damaged so much that it is unable to pump blood effectively. Disorders of sleep and breathing can cause heart failure and develop as a result of heart failure.
Studies have shown that OSA is a significant risk factor for the development of congestive heart failure. In addition, people who have heart failure from another condition, such as coronary artery disease or hypertension, risk worsening their congestive heart failure if they develop OSA. The heart muscle, already in a weakened state, is unable to handle the additional stress caused by the OSA. However, treating OSA can improve heart function in patients with congestive heart failure.
About 40% of people with congestive heart failure also have a sleep-related breathing disorder called central sleep apnoea (CSA). In CSA there are repetitive episodes of interruptions in breathing during sleep, just like in OSA.
However, in CSA the breathing passage remains open but the person stops making efforts to breathe. Frequent awakenings and drops in the level of oxygen in the blood also occur in CSA. The awakenings increase heart rate and blood pressure, which can worsen heart failure, in turn leading to more CSA and causing a vicious cycle that decreases heart function.
The first approach to treating CSA is to prevent it by treating the heart failure as thoroughly as possible. If CSA is still present, treatments are available to correct the CSA. Treatment of CSA can improve heart function as well as improve sleep quality.
During a stroke, the brain is damaged when the supply of blood and oxygen is reduced or cut off. Hypertension is the most common cause of stroke, and, as stated above, OSA can lead to the development of hypertension. In addition, OSA may cause strokes directly since blood flow to the brain is reduced and the level of oxygen drops during apnoeas.
Abnormal breathing patterns during sleep, especially OSA, are also more common immediately following a stroke. Other effects of OSA, such as excessive sleepiness from disrupted sleep and impaired thinking, may hamper a person’s recovery from a stroke.
As outlined above, sleep-related breathing disorders can directly cause heart disease. Yet, there are effects of heart disease on sleep that, though more subtle, are also important to address.
For instance, patients with congestive heart failure often report difficulty falling asleep or staying asleep because of the shortness of breath that often accompanies heart failure. This shortness of breath is often worse when the patient lies down because blood in the legs flows back into the heart and can overwhelm its ability to pump. Doctors call these symptoms orthopnea (shortness of breath when lying down) and paroxysmal nocturnal dyspnea (waking up from sleep short of breath). The patients who experience these symptoms may feel like they have insomnia since their sleep is interrupted.
In addition to experiencing these complications from heart disease, patients often worry about the long term consequences of a heart attack or chronic heart disease. Such anxiety, by itself, can lead to the development of chronic insomnia.
Taking into consideration all of these plus the direct relationship of numerous heart conditions with sleep-related breathing disorders, it is clear that people with heart conditions need to take special care and seek medical attention in order to ensure their ability to sleep well.
Many things can be done to maintain a healthy heart:
If you have any kind of heart condition, it is I especially important to watch for signs that you may have a sleep related breathing disorder, such as OSA, which could stress your heart. People with OSA are often overweight and experience loud snoring, as well as trouble staying awake during the daytime.
If you already have hypertension or cardiovascular disease (coronary artery disease, angina pectoris, stroke), talk with your healthcare professional about whether or not you may have a sleep and breathing disorder, such as OSA or CSA.
It is also important that patients with congestive heart failure be monitored for CSA and other sleep disorders at a Sleep Disorders Centre. In contrast to people with OSA, those with heart failure and CSA are commonly thin and may not snore at all.