Sleep apnea can have important effects on your overall health, including significant impacts on the function of your heart. Learn how untreated sleep apnea may affect your risk of heart failure and heart attack, exacerbate other risk factors like high blood pressure and diabetes, and about the role treatment may have in reversing these effects.
What Is Sleep Apnea?
Obstructive sleep apnea (OSA) occurs due to recurrent collapse of the upper airway during sleep. This may be partially (hypopnea) or completely (apnea), and results in fragmentation of sleep. These airway collapses last at least 10 seconds and are associated with drops in blood oxygen levels or arousals from sleep. This is very stressful on the heart.
Sleep apnea episodes may be associated with a spike in blood pressure and heart rate. In addition, there may be a burst of the stress hormone called cortisol. This may lead to other consequences, including higher blood pressure, hardening of the arteries due to low oxygen levels stressing the vessel walls (oxidative stress), and even insulin resistance and diabetes.
The severity of sleep apnea is classified by the number of events that are observed with a sleep study. This measure is sometimes called the apnea-hypopnea index (AHI). These classifications include:
- Mild – 5 to 15 events per hour
- Moderate – 15 to 30 events per hour
- Severe – More than 30 events per hour
In general, moderate to severe sleep apnea is more strongly correlated with the cardiovascular problems that can occur.
The Effects of Untreated Sleep Apnea
Beyond the nuisance symptoms of excessive daytime sleepiness, mood complaints, or problems with concentration or short-term memory, there can be other significant problems associated with untreated sleep apnea. There can also be unexpected signs. Some of the more serious health effects include:
High Blood Pressure (Hypertension)
Some of the largest population studies of sleep apnea demonstrate the fact that untreated sleep apnea increases blood pressure. The Wisconsin Cohort Study of 709 adults aged 30 to 65 showed that the risk of hypertension (with a reading of >140/90) doubles in mild, and triples in moderate, sleep apnea. The Sleep Heart Health Study of 6,132 adults aged 40 to 97 supported the association, suggesting that the risks increased 20 to 30 percent with sleep apnea.
People with blood pressure that is difficult to control with medications are extremely likely to have unrecognized sleep apnea. This is called refractory essential hypertension, and it usually involves persistent blood pressure elevation despite the use of 3 or more medications to lower it. An astounding 83% of people with this condition – and 95% of men! – have sleep apnea.
The good news is that the standard treatment of sleep apnea, continuous positive airway pressure (CPAP), can be effective in lowering blood pressure. Some studies suggest blood pressure can be reduced from 3.4 to 10 mm Hg. This is especially effective among those with severe OSA who are compliant to therapy.
Sleep apnea is correlated with insulin resistance and glucose intolerance, findings that are precursors to developing type 2 diabetes. This correlation exists independent of body mass index (BMI). This means that you can be of normal weight and sleep apnea may still increase your risk of developing diabetes.
The Sleep Heart Health Study shows that the incidence of diabetes doubles with sleep apnea, even if the AHI is in the mild range. It correlates with the degree of hypoxemia, meaning that if the sleep apnea drops your blood oxygen levels, you are more likely to develop diabetes.
The prevalence of diabetes is 15% in moderate to severe sleep apnea, according to the Wisconsin Sleep Cohort, compared to 3% in those with normal breathing in sleep.
The relationship between sleep apnea and diabetes may be due to the effects of sleep deprivation as well as the release of cortisol and catecholamines with the episodes of disrupted breathing.
CPAP has been shown to decrease a 3-month average of blood glucose called the hemoglobin A1c from 7.8% to 7.3% among patients with severe sleep apnea. Therefore, diabetics with sleep apnea may get better control of their sugars if they treat their disrupted breathing at night.
Coronary Artery Disease
Approximately 1 in 3 of those people with coronary artery disease have sleep apnea, with a large fraction not complaining of excessive daytime sleepiness. The blood vessels of the heart may become narrowed by plaques, leading to chest pain or even other consequences.
Sleep apnea may be additive or synergistic with other established risk factors for coronary artery disease. These factors include obesity, hypertension, smoking, hyperlipidemia, and others.
It is believed that the dips in blood oxygen levels associated with sleep apnea may stress the walls of the blood vessels. This may lead to dysfunction of the lining, or endothelium, and increase the plaques that narrow the passage through which blood is meant to pass.
Abnormal heart rhythms such as atrial fibrillation occur more frequently in those with untreated sleep apnea. In fact, the risk of atrial fibrillation doubles with sleep apnea, correlating with the severity of oxygen desaturation.
As atrial fibrillation can increase the risk of stroke or transient ischemic attacks (TIAs), the prevalence of sleep apnea is high in those who are admitted for these events. One study suggests that 95% of those with acute stroke or TIA had sleep apnea, with an AHI greater than 10. The Wisconsin Sleep Cohort study shows the risk of stroke is nearly 4 times as high when the AHI is greater than 20.
Due to the risk of other life-threatening rhythms with apnea events, the risk of sudden death increases overnight with sleep apnea.
Studies in the U.S. and Canada suggest 47 to 61 percent of patients with heart failure have moderate to severe sleep apnea. Mild pulmonary hypertension, a marker of heart failure, is common in sleep apnea. It may affect up to 20% of people with OSA and occurs due to low oxygen levels leading to constriction of the blood vessels within the lungs.
Treatment with CPAP or bilevel improves the function of the heart in those with heart failure. The volumes, pressures, and ejection fraction of the heart's ventricles can improve. This can improve long-term survival of those with heart failure.
Studies have demonstrated the association between OSA and ischemic heart disease, including heart attacks. This is likely related, in part, to the exacerbation of the other factors described above. Fortunately, treatment with CPAP has been associated with a reduction in these events.
How Treatment May Reduce Your Risks
Sleep apnea is a treatable condition. First, it must be recognized and then a sleep study will be arranged to determine the severity of the condition. Most people will be treated with continuous positive airway pressure. This can be well tolerated and accommodations can usually make it comfortable. There are other treatment options available as well, including the use of an oral appliance in mild to moderate OSA.
If you are concerned that you might have sleep apnea, start by speaking with your doctor. If you have developed health complications from the condition, the good news is that you can reduce your risk with treatment. You may even be able to reverse some of the effects of the condition. It is not too late to get the help you need to improve your sleep and your heart health.
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