Get the most up to date information about the sleep apnea and blood pressure connection from a sleep doctor's perspective.
Sleep Apnea and Blood Pressure: the Whole Story
Are sleep apnea and high blood pressure related? Can obstructive sleep apnea cause hypertension? Do people with sleep apnea have improvement in their blood if they use continuous positive airway pressure (CPAP)? Read on to find the answers to these questions and more.
In order to explain the high blood pressure and sleep apnea connection, let's first define a few key concepts.
What Is Hypertension?
The technical medical term for high blood pressure is hypertension - often abbreviated by doctors as "HTN." High blood pressure is defined when the systolic (the top number) and/or diastolic (the bottom number) are consistently elevated on multiple readings. Note: pulmonary hypertension is a different medical disorder; a separate article is needed to discuss the sleep apnea and pulmonary hypertension connection. Normal blood pressure is <120/80. The following blood pressure chart describes the criteria for prehypertension and hypertension:
What Is Sleep Apnea?
In this article, we will be talking about obstructive sleep apnea (OSA), the most common form of sleep apnea and the type that is most associated with cardiovascular diseases, such as hypertension and heart disease. OSA is a sleep disorder that is caused by abnormal breathing during sleep with repetitive episodes of partial or full throat closure and requires a sleep apnea test for diagnosis. Patients with OSA usually have chronic, loud snoring. The sleep study can be a home sleep apnea test (also called a home sleep study) or an in-lab study. A sleep doctor reviews the sleep test data and determines whether you have sleep apnea.
A Dysfunctional Relationship: the OSA & Hypertension Connection
Multiple research studies show that patients with OSA are more likely to have hypertension, independent of other risk factors like weight. Sleep apnea seems to be more associated with isolated diastolic or combined systolic/diastolic hypertension than isolated systolic HTN. Those with mild sleep apnea, an apnea-hypopnea index (AHI) between 5-15 (in other words, an average of 5-15 abnormal breathing events per hour), are twice as likely to get hypertension. People with moderate sleep apnea, defined as an AHI between 15 and 30, are three times as likely to develop high blood pressure. This trend supports what doctors call a "dose-response curve" in the relationship between OSA and high blood pressure: the worse the sleep apnea, the more likely people are to have high blood pressure. This sort of relationship is the best evidence that two separate medical conditions are truly linked.
Stressed Out: How Sleep Apnea Causes High Blood Pressure
Your body undergoes a great deal of stress during each abnormal breathing event. This triggers something called your "sympathetic nervous system" to kick in. This is also called the "fight or flight response," which causes a number of negative physiological things to occur inside your body, including a spike in blood pressure and a drop in your oxygen level. Studies that have measured blood pressure directly through a catheter implanted in an arm artery showed systolic blood pressure rising well into the 190s during abnormal obstructive breathing events.
Normally, blood pressure drops during sleep, a phenomenon called "nocturnal dipping." This trend is depicted below. Notice the relatively low blood pressure during sleep:
Initially, sleep apnea causes the loss of the normal dipping blood pressure pattern as seen in the following graph:
The mechanism by which sleep apnea causes hypertension is believed to be a result of the pathophysiology (negative physiological changes in the body) of continuous stress to the body when it should be recovering during sleep.
Over time, if OSA is left untreated, "diurnal" (daytime) blood pressure starts to become elevated, leading to hypertension. The first sign of this is often higher blood pressure readings in the morning.
Blood Pressure and Sleep Apnea: Special Cases
Sleep Apnea and Resistant Hypertension
Resistant hypertension is high blood pressure that is not under good control despite use of three different blood pressure medications. Sleep apnea is very common in patients with resistant hypertension. Studies have shown that up to 85% of patients with resistant hypertension have OSA. If you have been diagnosed with resistant hypertension, you should have a sleep apnea study.
"Secondary causes of hypertension" refers to high blood pressure that is the result of another medical problem. Sleep apnea is one of the more common causes of secondary hypertension. Here is the entire list:
- sleep apnea
- renal artery stenosis
- primary aldosteronism
- chronic kidney disease
- Cushing's syndrome
- aortic coarctation
If you've been diagnosed with high blood pressure at a young age and you are otherwise healthy, it is particularly important to have a sleep study test to rule out obstructive sleep apnea as the primary cause of your hypertension.
Sleep Apnea Treatment: Blood Pressure Effects
The gold standard sleep apnea treatment is the CPAP machine (pictured above), or its cousin, the BiPAP machine, depending on your particular sleep breathing problem. How does using CPAP impact blood pressure? Important research still needs to be done in this area, but there is strong evidence that CPAP does reduce blood pressure. Regular use of CPAP has been associated with a small but significant decrease in blood pressure of about 3 mm Hg. While 3 mmHg doesn't sound like a huge improvement, this degree of blood pressure drop has been found to reduce the long-term risk of heart attack, stroke and heart failure. Additionally, if you have resistant hypertension and sleep apnea, the consensus is that, over time, you probably will have difficulty controlling your blood pressure until you address your sleep apnea. How amazing would it be to be able to treat high blood pressure without having to take any medications and deal with all of their side effects? If you have secondary hypertension due to sleep apnea, then a CPAP machine might be the only treatment that you need to achieve normal blood pressure.
Do CPAP Alternatives Help Blood Pressure?
Of all sleep apnea treatments, CPAP has the strongest evidence of benefiting blood pressure. One study compared treating sleep apnea with CPAP versus oxygen and found that CPAP was far superior to oxygen in improving blood pressure. This makes sense because we think the blood pressure/sleep apnea link is due to the repetitive "fight or flight" response kicking in during sleep, and not the oxygen dips that are also caused by sleep apnea. CPAP actually keeps the throat from closing up and prevents the fight or flight responses in the first place. Limited research has been done looking at CPAP alternatives like oral appliances for sleep apnea, but the results suggest that use of oral appliances may have blood pressure benefits similar to CPAP treatment.
The Bottom Line for Your Health:
- Sleep apnea is very closely associated with high blood pressure.
- In some patients, sleep apnea may be a major contributor to or the cause of hypertension.
- Sleep apnea first leads to loss of the normal blood pressure dip during sleep, which over time progresses into daytime high blood pressure.
- If your high blood pressure is difficult to treat, you should undergo sleep apnea testing.
- If you have sleep apnea and don't treat it, your blood pressure is likely to get worse over time.
- A CPAP or BiPAP machine is the best option for treating sleep apnea in patients with high blood pressure.
- Treating sleep apnea with a CPAP machine lowers blood pressure and helps heart health by preventing cardiovascular disease like heart attack, stroke, and heart failure.
Please share this article with your friends and loved ones who have blood pressure issues!
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Joseph Krainin, M.D., FAASM is the founder of Singular Sleep, the world's first online sleep center. He is a Fellow of the American Academy of Sleep Medicine and board certified in both sleep medicine and neurology. He has been practicing medicine for over 10 years.