Saturday, May 12, 2012
Sleep apnea is the periodic suspension of breathing during sleep. There are two general kinds of sleep apnea. Central sleep apnea is mainly caused by a decrease in neural output from the respiratory center in the medulla to the phrenic motor nerve output to the diaphragm. Obstructive sleep apnea is due to increased airway resistance because of narrowing or collapse of the upper airways (primarily pharynx) during inspiration. Obstructive sleep apnea may occur in as much as 4 percent of the adult population and with a greater frequency in the elderly and in men. Significant snoring may be an early sign of the eventual development of obstructive sleep apnea. Obesity is clearly a contributing factor because the excess fat in the neck decreases the caliber of the upper airways. A decrease in the activity of the upper airway dilating muscles during sleep (particularly REM sleep) also contributes to airway collapse. Finally, anatomical narrowing and increased compliance of the upper airways also contributes to periodic inspiratory obstruction during sleep.