Thousands of people are faced with medical issues that have effects on their breathing patterns during sleep. They are, however, not the only people whose breath changes during slumber; the breathing patterns of a normal person with no medical issues also changes while they sleep because the body has a lower rate of metabolism. Because of the lower rate of metabolism, there is less demand for the body to receive ventilation.
There are multiple changes that take place in the breath pattern during sleep including changes in the breath itself, the airway, and the muscles that make the respiratory system function. All of the changes that take place occur in different stages of sleep. Changes in the breath are less pronounced in the shallow stages of sleep, Non-REM sleep. In congruence, the more noticeable changes in the respiratory system take place during the deeper phases of sleep, Rapid Eye Movement, or REM sleep.
The breath undergoes many different changes during sleep. The breath becomes shallower during sleep. The shallowness of the breath gets more significant the deeper you go into the stages of sleep. During REM sleep, the tidal volume, or size of individual breaths, becomes quite variable with periods of very shallow breathing. For the most part, the rate of breath stays regular, but can become slightly varied during REM sleep. The respiratory center in the brain, the part of the brain that control breath, becomes less stimulated by changes in oxygen and carbon dioxide during sleep.
During REM sleep, the upper airway is also affected. In this stage of deep sleep, there is a loss of muscle tone in the upper airway muscles that can cause the airway to become more prone to collapsing. The collapsing of the airway results in additional resistance in the airflow going in and out of the lungs. The airflow in the body’s small airways is at its lowest level during sleep because natural rhythms of the body change blood hormone levels.
The muscles in our bodies that make up the diaphragm are our main muscles of ventilation. During Non-REM sleep, the accessory muscles of ventilation, which are located in the abdomen and chest, become much more involved in helping the diaphragm function. In opposition, during REM sleep, the activity and assistance of these muscles diminish. This is only an issue, however, for people who depend on their accessory muscles only for breath during sleep.
Other changes in the breath that take place during sleep are pretty standard. There is a small, but noticeable drop in lung volume during sleep. Also, blood flow in the lungs changes during sleep due to the effect of gravity on blood flow. When upright during the day, most of the blood flow goes to the lower parts of the lungs, or the base of the lungs. When lying on the back during sleep, more blood goes into the back of the lungs.