Sleep Apnea
Sleep apnea is a periodic upper airway closure (obstructive sleep apnea, OSA) or periodic absence of nerve impulses to breathe (central sleep apnea, CSA), which can occur from five to 200 times an hour, most commonly during REM sleep, but possible in other stages, too. This sometimes causes severe oxygen deprivation, circulatory changes and heart stress along with changes in heart rates. The actual rate depends on factors such as previous MI, cardiac medications, continuous positive airway pressure therapy (CPAP) for OSA, oxygen administration and many others. No "normal" sleeping heart rate can be predicted in sleep apnea patients.