During the most peaceful sleep, some people snore terribly loudly, ruining the chances of sleeping for anyone who shares their room. But even those who do not snore breathe more loudly when they doze than when they are awake. Why do people breathe so loudly when they sleep?
The sound made when you breathe – whether awake or asleep – is caused by the vibration of air moving through the breathing tube, said Dr. Timothy Morgenthaler, a pulmonologist and sleep medicine specialist at the Mayo Clinic in Minnesota. The volume of breathing sounds depends on how narrow the breathing tube is and how fast air passes through it. “You can almost see it as a musical instrument,” he said.
When you inhale, the rapid movement of air flowing into the upper airways – the part of the respiratory system that extends from the mouth to the larynx – decreases pressure throughout the respiratory tract, also known as the airway. This change in pressure can collapse the upper airways, which obstructs breathing. A reflex in the upper airways prevents this collapse and keeps the tubes open when you are awake. “Because it is open, the flow through the airways is not turbulent, so the air moves without much sound,” Morgenthaler told Live Science. But when you are sleeping, that reflection is not so strong. The upper airways tend to partially collapse and breathing becomes more noisy.
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Sleep, especially during rapid eye movement (REM), also leads to decreased muscle tone around the airways, added Morgenthaler. In other words, the muscles that support the airways relax, allowing the breathing tube to contract. When the airway gets narrower, the speed of the air moving through it increases. The air vibrates more and creates more sound.
Narrowness also means that your breathing becomes rapid and shallow. An average person breathes about 14 times a minute when he is awake and 15 or 16 while sleeping, said Morgenthaler. Although you breathe more frequently while sleeping, you actually inhale less oxygen and expel less carbon dioxide because your body’s need for ventilation is not as high as when you are awake. “We are not expecting to go out and run or chase an animal or harvest crops,” he said.
If a person’s breathing tube becomes particularly narrow, they can begin to snore. This usually happens when the airways reach the diameter of a McDonald’s straw, which is slightly wider than regular straws, said Morgenthaler. When it is so small, not only does the air within the airways vibrate, but also the tissues in the area, causing snoring.
If a person’s airways narrow further during sleep, they can develop obstructive sleep apnea. The airways can become so narrow that it is impossible to breathe and the person wakes up with shortness of breath. Even in people without sleep apnea, the airways can narrow as much as four times an hour. When it occurs more often, it becomes obstructive sleep apnea. Weight loss is often an effective treatment because excess fat around the airways can obstruct breathing. Morgenthaler also recommended skipping alcohol close to bedtime because it makes the muscles around you relax. If that doesn’t help, the person may need a machine such as continuous positive airway pressure (CPAP) to keep the airway open during sleep, he said.
Originally published in Living Science.