Central sleep apnea (CSA) or central sleep apnea syndrome (CSAS) is a  sleep-related disorder in which the effort to breathe is diminished or absent, typically for 10 to 30 seconds either intermittently or in cycles, and is usually associated with a reduction in blood oxygen saturation. CSA is usually due to an instability in the bodys feedback mechanisms that  control respiration. Central sleep apnea can also be an indicator of Arnold–Chiari malformation. Signs and symptoms
In a healthy person during sleep, breathing is regular so oxygen levels and carbon dioxide levels in the bloodstream stay fairly constant:  After exhalation, the blood level of oxygen decreases and that of carbon dioxide increases. Exchange of gases with a lungful of fresh air is necessary to replenish oxygen and rid the bloodstream of built-up carbon dioxide. Oxygen and carbon dioxide receptors in the body (called chemoreceptors) send nerve impulses to the brain, which then signals for reflexive opening of the larynx (enlarging the opening between the vocal cords) and movements of the rib cage muscles and diaphragm. These muscles expand the thorax (chest cavity) so that a partial vacuum is made within the lungs and air rushes in to fill it.
Criteria
CSA is divided in 6 categories, Primary CSA, Cheyne–Stokes respiration, High-altitude periodic breathing, CSA due to a medical condition without CSB, Central sleep apnea due to a medication or substance and Treatment Emergent Central Apnea (also called Complex Sleep Apnea). The following symptoms are present in the Primary CSA: excessive daytime sleepiness, frequent arousals and awakenings during sleep or insomnia complaints, awakening short of breath, snoring, witness apneas. His polysomnography shows ≥5 central apneas and/or central hypopneas per hour of sleep, representing at least 50% of total respiratory events in the apnea-hypopnea index. CSA with Cheyne-Stokes breathing is characterized by at least one of the criteria of Primary CSA or the presence of atrial fibrillation/flutter, CHF, or a neurologic disorder. His polysomnography looks like the Primary CSA polysomnography with the addition of a ventilatory pattern compatible with CSB. High-Altitude Periodic Breathing requires that the patient has recently been at least 2500 meters. In the CSA due to a medication or substance, opioid or respiratory depressants must had been taken. For the CSA due to a medical condition without CSB, the criteria are the same as Primary CSA, but the symptoms are caused by a disease. In the Treatment Emergent Central Apnea, there was firstly some obstructive respiratory events but after their disappearance, the CSA has appeared.