Editing Rapid eye movement sleep (section)

=== Circulation, respiration, and thermoregulation ===

Generally speaking, the body suspends [[homeostasis]] during paradoxical sleep. [[Heart rate]], cardiac pressure, [[cardiac output]], [[Blood pressure|arterial pressure]], and [[respiratory rate|breathing rate]] quickly become irregular when the body moves into REM sleep.<ref name = "Parmeggiani_2011" />{{rp|12–15}} In general, respiratory reflexes such as response to [[Hypoxia (medical)|hypoxia]] diminish. Overall, the brain exerts less control over breathing; electrical stimulation of respiration-linked brain areas does not influence the lungs, as it does during non-REM sleep and in waking.<ref name = "Parmeggiani_2011" />{{rp|35–15}}

[[Erection]]s of the [[penis]] ([[nocturnal penile tumescence]] or NPT) normally accompany REM sleep in rats and humans.<ref name = "Jouvet_1999">{{cite book | vauthors = [[Michel Jouvet|Jouvet M]] | date = 1999 | title = The Paradox of Sleep: The Story of Dreaming | translator-last1= Garey |translator-first1= Laurence | name-list-style = vanc | location = Cambridge | publisher = MIT Press | isbn = 0-262-10080-0 }}</ref>{{rp|169–173}} If a male has [[erectile dysfunction]] (ED) while awake, but has NPT episodes during REM, it would suggest that the ED is from a psychological rather than a physiological cause. In females, erection of the [[clitoris]] ([[nocturnal clitoral tumescence]] or NCT) causes enlargement, with accompanying vaginal blood flow and transudation (i.e. lubrication). During a normal night of sleep, the penis and clitoris may be erect for a total time of from one hour to as long as three and a half hours during REM.<ref>{{cite journal | vauthors = Brown RE, Basheer R, McKenna JT, Strecker RE, McCarley RW | title = Control of sleep and wakefulness | journal = Physiological Reviews | volume = 92 | issue = 3 | pages = 1087–1187 (1127) | date = July 2012 | pmid = 22811426 | pmc = 3621793 | doi = 10.1152/physrev.00032.2011 }}</ref>

Body temperature is not well regulated during REM sleep, and thus organisms become more sensitive to temperatures outside their [[thermoneutral zone]]. Cats and other small furry mammals will [[shiver]] and [[tachypnea|breathe faster]] to regulate temperature during NREMS—but not during REMS.<ref name = "Parmeggiani_2011" />{{rp|12–13}} With the loss of muscle tone, animals lose the ability to regulate temperature through body movement. (However, even cats with pontine lesions preventing muscle atonia during REM did not regulate their temperature by shivering.)<ref name = "Parmeggiani_2011" />{{rp|51–52}} Neurons that typically activate in response to cold temperatures—triggers for neural thermoregulation—simply do not fire during REM sleep, as they do in NREM sleep and waking.<ref name = "Parmeggiani_2011" />{{rp|51–52}}

Consequently, hot or cold environmental temperatures can reduce the proportion of REM sleep, as well as amount of total sleep.<ref>{{cite book | vauthors = Szymusiak R, Alam MN, McGinty D | date = 1999 | chapter = Thermoregulatory Control of the NonREM-REM Sleep Cycle | title = Rapid Eye Movement Sleep | publisher = CRC Press | veditors = Mallick BN, Inoué S | isbn = 978-0-8247-0322-6 }}</ref><ref name = "Parmeggiani_2011" />{{rp|57–59}} In other words, if at the end of a phase of deep sleep, the organism's thermal indicators fall outside of a certain range, it will not enter paradoxical sleep lest deregulation allow temperature to drift further from the desirable value.<ref name = "Parmeggiani_2011" />{{rp|45}} This mechanism can be 'fooled' by artificially warming the brain.<ref name = "Parmeggiani_2011" />{{rp|61}}