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.
History
The syndrome was first extensively noted by Robert Foster Kennedy in 1911, an Irish neurologist, who spent most of his career working in the United States of America. However, the first mention of the syndrome came from a William Gowers in 1893. Schultz–Zehden described the symptoms again in 1905. A later description was written by Wilhelm Uhthoff in 1915. References


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