Written by: Madison Estrella
Medically reviewed by: Rob Philibert MD PhD
Sleep is necessary for our everyday function, but conditions like sleep apnea can disrupt our normal sleep patterns. These disruptions may have adverse implications on our cardiovascular system.
What is Sleep Apnea?
Sleep apnea is a potentially life-threatening disorder in which a person’s breathing repeatedly stops during their sleep. It is a fairly common condition that occurs more frequently in men, especially in black and Hispanic men, than in women. Although sleep apnea can occur in people of all ages, it is most common in people between the ages of 30 to 70 years old.[1]
There are three types of sleep apnea: obstructive, central and mixed sleep apnea. Among these three types, obstructive sleep apnea (OSA) is the most common. It occurs when the soft tissue that supports the muscles of the airway temporarily relaxes, blocking airflow. Central sleep apnea, on the other hand, occurs when the brain fails to send proper signals to the muscles controlling breathing. Mixed sleep apnea is a combination of the two.
There are several signs of sleep apnea– some of which include:
- Loud snoring
- Pausing in breathing while sleeping
- Excessive daytime sleepiness (hypersomnia)
- Choking or gasping in sleep that wakes you up
Talk to your doctor if you have any symptoms of sleep apnea. A proper diagnosis can only be given following an observed sleep study.
Shared Risk Factors Between Sleep Apnea and Heart Disease
The relationship between sleep apnea and heart disease can be exacerbated by their shared risk factors such as obesity, hypertension and metabolic syndrome.
1) Obesity
According to the CDC, 42.5% of Americans are obese [2]. Obesity can increase one’s risk for several conditions, but it can especially heighten one’s chances of developing heart disease and/or sleep apnea. In fact, it is believed that as much as 45% of the obese population have some form of OSA [3].Obesity increases one’s risk of OSA due to the presence of excess soft tissue lining the airway, which increases the chances of temporary obstruction during sleep.
As mentioned in a previous blog post, obesity is also associated with diabetes, increased blood pressure, enlargement of the heart and high blood lipid levels, which may be deposited in the arteries. All of these factors associated with obesity are independent risk factors for cardiovascular disease.
2) Hypertension
Hypertension (high blood pressure) is inextricably linked to heart disease and sleep apnea. According to a study in the American Journal of Medicine, 40% of patients with sleep apnea suffer from hypertension, whereas 30% of hypertensive patients have occult sleep apnea [5].
The excess pressure on the arterial walls can increase one’s risk for heart disease by narrowing the blood vessel walls over time. This can force the heart to have to work even harder to pump a sufficient amount of blood throughout the body. As for the relationship between sleep apnea and hypertension, many scholars believe that sleep apnea may cause high blood pressure. This relationship will be explored shortly.
3) Metabolic Syndrome
Metabolic syndrome refers to a group of conditions that increase the risk for heart disease, stroke and diabetes. These conditions include high blood pressure, insulin resistance, excess body fat around the waist and high cholesterol levels. Each of these components are independently associated with sleep apnea and heart disease, but the relationship between metabolic syndrome, sleep apnea and heart disease are still being investigated.
The Relationship Between Sleep Apnea and Heart Disease
Not only do sleep apnea and heart disease have similar risk factors, but sleep apnea can increase one’s risk for heart disease. When left untreated, sleep apnea has been found to be associated with adverse cardiac outcomes such as high blood pressure, arrhythmia, stroke and coronary heart disease. [1] In fact, a study by Dr. Eyal Shahar and colleagues found that obstructive sleep apnea increases risk of heart failure by 140%, stroke by 60%, and coronary heart disease by 30%.[6] Moreover, obstructive sleep apnea can also worsen heart problems in patients with existing heart disease.
There are several studies exploring the relationship between obstructive sleep apnea and heart disease. One major focal point is that endothelial (cells living blood vessels) dysfunction is especially common in patients with OSA. This dysfunction has been closely linked to inflammation and abnormal levels of vasoactive second messengers, which can contribute to the onset of cardiovascular disease.
A study by Dr. Lena Lavie of the Israel Institute of Technology examined how sleep apnea triggers oxidative stress. They found that repeated closure of the airway in sleep apnea patients can lead to acute hypoxia (oxygen deprivation of cells). As a result, oxygen reactive species are produced. These harmful molecules can activate signal transduction pathways that encode proteins responsible for adapting to hypoxia, such as those that elicit the inflammatory response. Unwarranted inflammation can be concerning as it may damage endothelial cells of blood vessels. This inflammation is also associated with atherosclerosis (the buildup of plaque in the arteries).[7]
The Sleep Foundation is an organization that compiles comprehensive, research-based information on the important role of sleep in health. Their team found that sleep apnea may trigger hypertension by activating the sympathetic nervous system. As obstruction of airflow through the airway leads to the decrease in blood oxygen levels, chemoreceptors activate the sympathetic nervous system. The nervous system responds by constricting blood vessels and increasing heart rate. Continuous stimulation of this response can lead to hypertension and long-term problems with blood pressure.[9]
Treating Sleep Apnea Improves Cardiovascular Function
OSA can be treated using a mechanical device called a continuous positive airway pressure device (CPAP). This machine is attached to a mask that provides air through the nose and mouth in a way that prevents the airway from closing. This treatment of sleep apnea not only improves one’s ability to get a good night’s sleep, but it can also prevent and/or improve heart problems associated with OSA. For instance, some studies found that OSA patients using CPAP have seen improved blood oxygen levels, reduced systolic pressure and corrected arrhythmias (irregular heart rhythm).[10]
Based on these and other findings, it is clear that cardiac outcomes can be improved by understanding how sleep disorders impact the cardiovascular system. There is a strong relationship between cardiovascular disease and sleep apnea. As a result, the treatment of heart disease and sleep apnea requires more holistic care. For many patients, sleeping well may be the first step to better heart health.
References:
- What is Sleep Apnea? American Sleep Apnea Association. (2021, January 11). https://www.sleepapnea.org/learn/sleep-apnea/.
- Centers for Disease Control and Prevention. (2021, March 1). Overweight Prevalence. Centers for Disease Control and Prevention. https://www.cdc.gov/nchs/fastats/obesity-overweight.htm.
- Romero-Corral, A., Caples, S. M., Lopez-Jimenez, F., & Somers, V. K. (2010). Interactions Between Obesity and Obstructive Sleep Apnea. Chest, 137(3), 711–719. https://doi.org/10.1378/chest.09-0360
- Makinodan, K., Yoshikawa, M., Fukuoka, A., Tamaki, S., Koyama, N., Yamauchi, M., Tomoda, K., Hamada, K., & Kimura, H. (2008). Effect of Serum Leptin Levels on Hypercapnic Ventilatory Response in Obstructive Sleep Apnea. Respiration, 75(3), 257–264. https://doi.org/10.1159/000112471
- Fletcher, E. C. (1995). The relationship between systemic hypertension and obstructive sleep apnea: Facts and theory. The American Journal of Medicine, 98(2), 118–128. https://doi.org/10.1016/s0002-9343(99)80395-7
- Shahar, E., Whitney, C., Redline, S., Lee, E., Newman, A., Javier Nieto, F., O’Connor, G., Boland, L. , Schwartz, J., & Samet, J. (2001). Sleep-disordered Breathing and Cardiovascular Disease. American Journal of Respiratory and Critical Care Medicine, 163(1), 19–25. https://doi.org/10.1164/ajrccm.163.1.2001008
- Lavie, L. (2003). Obstructive sleep apnoea syndrome – an oxidative stress disorder. Sleep Medicine Reviews, 7(1), 35–51. https://doi.org/10.1053/smrv.2002.0261
- Jean-Louis, G., Zizi, F., Clark, L. T., Brown, C. D., & McFarlane, S. I. (2008). Obstructive Sleep Apnea and Cardiovascular Disease: Role of the Metabolic Syndrome and Its Components. Journal of Clinical Sleep Medicine, 04(03), 261–272. https://doi.org/10.5664/jcsm.27191
- Is Sleep Apnea Connected to Heart Disease? Sleep Foundation. (2021, February 5). https://www.sleepfoundation.org/sleep-apnea/sleep-apnea-linked-heart-disease.
- Drager, L. F., McEvoy, R. D., Barbe, F., Lorenzi-Filho, G., & Redline, S. (2017). Sleep Apnea and Cardiovascular Disease. Circulation, 136(19), 1840–1850. https://doi.org/10.1161/circulationaha.117.029400