Sleep Apnea Health Article

Central sleep apnea

In central sleep apnea, the airway remains open, but the nerve signals controlling the respiratory muscles are not regulated properly. This can cause wide fluctuations in the level of carbon dioxide (CO₂) in the blood. Normal activity in the body produces CO₂, which is brought by the blood to the lungs for exhalation. When the blood level of CO₂ rises, brain centers respond by increasing the rate of respiration, clearing the CO₂. As blood levels fall again, respiration slows down. Normally, this interaction of CO₂ and breathing rate maintains the CO₂ level within very narrow limits. CSA can occur when the regulation system becomes insensitive to CO₂ levels, allowing wide fluctuations in both CO₂ levels and breathing rates. High CO₂ levels cause very rapid breathing (hyperventilation), which then lowers CO₂ so much that breathing becomes very slow or even stops. CSA occurs during sleep because when a person is awake, breathing is usually stimulated by other signals, including conscious awareness of breathing rate.

A combination of the two forms is also possible, and is called "mixed sleep apnea." Mixed sleep apnea episodes usually begin with a reduced central respiratory drive, followed by obstruction.

OSA and CSA cause similar symptoms. The most common symptoms are:

• daytime sleepiness
• morning headaches
• a feeling that sleep is not restful
• disorientation upon waking

Sleepiness is caused not only by the frequent interruption of sleep, but by the inability to enter long periods of deep sleep, during which the body performs numerous restorative functions. OSA is one of the leading causes of daytime sleepiness, and is a major risk factor for motor vehicle accidents. Headaches and disorientation are caused by low oxygen levels during sleep, from the lack of regular breathing.

Other symptoms of sleep apnea may include sexual dysfunction, loss of concentration, memory loss, intellectual impairment, and behavioral changes including anxiety and depression.

Sleep apnea can also cause serious changes in the cardiovascular system. Daytime hypertension (high blood pressure) is common. An increase in the number of red blood cells (polycythemia) is possible, as is an enlarged left ventricle of the heart (cor pulmonale), and left ventricular failure. In some people, sleep apnea causes life-threatening changes in the rhythm of the heart, including heartbeat slowing (bradycardia), racing (tachycardia), and other types of "arrhythmias." Sudden death may occur from such arrhythmias. Patients with the Pickwickian syndrome (named after a Charles Dickens character) are obese and sleepy, with right heart failure, pulmonary hypertension, and chronic daytime low blood oxygen (hypoxemia) and increased blood CO₂ (hypercapnia).