Sleep apnea, which is thought to affect up to 1 in 4 adults, occurs when we briefly stop breathing while asleep. The brain senses the decrease in blood oxygen levels that occurs during the interruption and wakes us up so we’ll take a breath. Some of the most common daytime symptoms of sleep apnea are fatigue, mood changes and difficulty concentrating. This is because the sleep-wake-sleep cycles prevent us from entering the deeper stages of sleeping that make us feel well-rested.
In addition to causing fatigue, sleep apnea isn’t good for our cardiovascular system. When oxygen in our blood decreases, our immune system activates and inflammation can occur throughout our body. Repeated exposure to inflammation causes our blood vessels to adapt to this change (called remodeling), which leads to high blood pressure.
The heart muscle is also strained when oxygen is low because it must work harder to pump blood around the body. This increases the risk of heart attack and other cardiac issues, particularly for people who already have other health conditions, such as heart disease. One of the best nonsurgical treatments for obstructive sleep apnea is a continuous positive airway pressure (CPAP) machine, which delivers air pressure through a mask to keep airways open while sleeping.
When we see a disease or disorder in humans, scientists can sometimes look to nature and ask whether there’s an animal that experiences the same thing without the negative health effects we see in people. This can be helpful to understand a disease and create potential therapies.
Elephant seals, which live along the Pacific Coast of North America and in the Antarctic, also experience sleep apnea. Researchers noticed that the seals would sometimes hold their breath while asleep on the beach. The seals would hold their breath for about 10 minutes, breathe continuously for two to three minutes and hold their breath again. When scientists looked at what other physiological changes occurred during seal sleep apnea, they found that sleeping seals have decreases in blood oxygen levels just like people. However, the seals keep their heart rates low during apnea and don’t seem to suffer from systemic inflammation as we do. As a result, seals with sleep apnea don’t put stress on their cardiovascular system.
If scientists can understand what factors allow seals to escape the inflammation that goes along with sleep apnea in people, they may be able to develop treatment for inflammatory disorders that strain the cardiovascular system, including sleep apnea.
Kaitlin Allen is a PhD student in the Department of Integrative Biology at the University of California, Berkeley. She works in the Vázquez-Medina lab, where she studies diving physiology and hypoxia tolerance in northern elephant seals.