View source for Apnea

{{Short description|Suspension of breathing}}
{{About||the underwater sport|Freediving|the songs|Apnea (Ricardo Arjona song)|and|Apnea (Emma Marrone song)}}
{{Use dmy dates|date=September 2020}}
{{Use American English|date=September 2024}}
{{Infobox medical condition (new)    
| name            = Apnea    
| synonyms        = Apnoea
| image           = Snoring under severe sleep apnoea - 1741-7015-9-17.oga    
| caption         = A 32 second breathing pause in a [[sleep apnea]] patient   
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| field           = [[Pulmonology]], [[pediatrics]]  
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'''Apnea''' (also spelled '''apnoea''' in  [[British English]])<ref>{{cite web |url=https://www.nhs.uk/conditions/sleep-apnoea/ |title=Sleep apnoea |website=nhs.uk |date=15 August 2019 |access-date=2020-04-21 |archive-date=26 April 2020 |archive-url=https://web.archive.org/web/20200426043733/https://www.nhs.uk/conditions/sleep-apnoea/ |url-status=live }}</ref> is the temporary cessation of [[breathing]]. During apnea, there is no movement of the [[muscle]]s of [[inhalation]],{{citation needed|date=April 2021}} and the volume of the [[lung]]s initially remains unchanged. Depending on how blocked the [[airway]]s are ([[wikt:patency|patency]]), there may or may not be a flow of [[gas]] between the lungs and the environment. If there is sufficient flow, [[gas exchange]] within the lungs and [[cellular respiration]] would not be severely affected. Voluntarily doing this is called '''holding one's breath'''.
Apnea may first be diagnosed in childhood, and it is recommended to consult an ENT specialist, allergist or sleep physician to discuss symptoms when noticed; malformation and/or malfunctioning of the upper airways may be observed by an orthodontist.<ref>{{Cite web|date=2021-06-07|title=Sleep apnoea and orthodontics|url=https://orthodonticsaustralia.org.au/sleep-apnoea-and-orthodontics/|access-date=2022-02-28|website=Orthodontics Australia|language=en-AU|archive-date=22 March 2021|archive-url=https://web.archive.org/web/20210322183238/https://orthodonticsaustralia.org.au/sleep-apnoea-and-orthodontics/|url-status=live}}</ref>

==Cause==
Apnea can be involuntary—for example, [[drug]]-induced (such as by [[opiate]] toxicity), mechanically / physiologically induced (for example, by [[strangulation]] or [[choking]]), or a consequence of neurological disease or [[Physical trauma|trauma]]. During sleep, people with severe [[sleep apnea]] can have over thirty episodes of intermittent apnea per hour every night.<ref>{{cite web |title=The Dangers of Uncontrolled Sleep Apnea |url=https://www.hopkinsmedicine.org/health/wellness-and-prevention/the-dangers-of-uncontrolled-sleep-apnea |website=www.hopkinsmedicine.org |access-date=28 April 2022 |language=en |date=10 March 2022 |archive-date=28 April 2022 |archive-url=https://web.archive.org/web/20220428204813/https://www.hopkinsmedicine.org/health/wellness-and-prevention/the-dangers-of-uncontrolled-sleep-apnea |url-status=live }}</ref>

Apnea can also be observed during periods of heightened [[emotion]], such as during [[crying]] or accompanied by the [[Valsalva maneuver]] when a person [[laughs]]. Apnea is a common feature of sobbing while crying, characterized by slow but deep and erratic breathing followed by brief periods of breath holding.

Another example of apnea are [[breath-holding spell]]s; these are sometimes emotional in cause and are usually observed in children as a result of frustration, emotional stress and other psychological extremes.

Voluntary apnea can be achieved by closing the [[vocal cords]], simultaneously keeping the mouth closed and blocking the [[nasal vestibule]], or constantly activating expiratory muscles, not allowing any inspiration.

==Complications==
Under normal conditions, [[human]]s cannot store much [[oxygen]] in the body. Prolonged apnea leads to severe lack of oxygen in the [[circulatory system|blood circulation]], leading to dysfunction of [[Organ system|organ systems]]. Permanent [[brain damage]] can occur after as little as three minutes and [[death]] will inevitably ensue after a few more minutes unless ventilation is restored. However, under special circumstances such as [[hypothermia]], [[hyperbaric oxygenation]], [[#Apneic oxygenation|apneic oxygenation]] (see below), or [[extracorporeal membrane oxygenation]], much longer periods of apnea may be tolerated without severe detrimental consequences.

Untrained humans usually cannot sustain voluntary apnea for more than one or two minutes, since the urge to breathe becomes unbearable.{{Citation needed|date=February 2011}} The reason for the time limit of voluntary apnea is that the rate of breathing and the volume of each breath are tightly regulated to maintain constant values of [[carbon dioxide|CO<sub>2</sub>]] tension and [[pH]] of the [[blood]] more than oxygen levels. In apnea, CO<sub>2</sub> is not removed through the lungs and accumulates in the blood. The consequent rise in CO<sub>2</sub> tension and drop in pH result in stimulation of the respiratory centre in the brain which eventually cannot be overcome voluntarily. The accumulation of carbon dioxide in the lungs will eventually irritate and trigger impulses from the respiratory center part of the brain and the [[phrenic nerve]]. Rising levels of carbon dioxide signal the body to breathe and resume unconscious respiration forcibly. The lungs start to feel as if they are burning, and the signals the body receives from the brain when CO<sub>2</sub> levels are too high include strong, painful, and involuntary contractions or spasms of the diaphragm and the muscles in between the ribs. At some point, the spasms become so frequent, intense and unbearable that continued holding of the breath is nearly impossible.{{Citation needed|date=February 2021}}

When a person is immersed in water, physiological changes due to the mammalian [[diving reflex]] enable somewhat longer tolerance of apnea even in untrained persons as breathing is not possible underwater. Tolerance can in addition be trained. The ancient technique of [[free-diving]] requires breath-holding, and world-class free-divers can hold their breath underwater up to depths of {{convert|214|metres}} and for more than four minutes.<ref>{{cite web|url=http://www.divemagazine.co.uk/news/article.asp?uan%3D3745 |title=Where is it |access-date=2008-03-02 |url-status=dead |archive-url=https://web.archive.org/web/20080927221313/http://www.divemagazine.co.uk/news/article.asp?uan=3745 |archive-date=27 September 2008}} for 214-metre diving record</ref> Apneists, in this context, are people who can hold their breath for a long time.

==Hyperventilation==
Voluntary [[hyperventilation]] before beginning voluntary apnea is commonly believed to allow the person involved to safely hold their breath for a longer period. In reality, it will give the impression that one does not need to breathe, while the body is actually experiencing a blood-oxygen level that would normally, and indirectly, invoke a strong [[dyspnea]] and eventually involuntary breathing. Some have incorrectly attributed the effect of hyperventilation to increased oxygen in the blood, not realizing that it is actually due to a decrease in {{CO2}} in the blood and lungs. Blood leaving the lungs is normally fully saturated with oxygen, so hyperventilation of normal air cannot increase the amount of oxygen available, as oxygen in blood is the direct factor. Lowering the {{CO2}} concentration increases the pH of the blood, thus increasing the time before blood becomes acidic enough so the respiratory center becomes stimulated, as described above. While hyperventilation will yield slightly longer breath-holding times, any small time increase is at the expense of possible [[Hypoxia (medicine)|hypoxia]], though it might not be felt as easily.<ref>{{cite journal |last=Given |first=Mac F. |title=The Effect of Hyperventilation on the Ability to Hold One's Breath: Testing the Influence of Beliefs versus Physiology |journal=The American Biology Teacher |date=1 April 1997 |volume=59 |issue=4 |pages=229–231 |doi=10.2307/4450291|jstor=4450291 }}</ref> One using this method can suddenly lose consciousness unnoticed—a [[Freediving blackout#Shallow water blackout|shallow water blackout]]—as a result. If a person loses consciousness underwater, there is considerable danger that they will [[Drowning|drown]]. An alert diving partner or nearby lifeguard would be in the best position to rescue such a person. Static apnea blackout occurs at the surface when a motionless diver holds their breath long enough for the circulating oxygen in blood to fall below that required for the brain to maintain consciousness. It involves no pressure changes in the body and is usually performed to enhance breath-hold time. It should never be practiced alone, but under strict safety protocols with a safety guard or equipment beside the diver.

==Apneic oxygenation==
Because the exchange of gases between the blood and airspace of the lungs is independent of the movement of gas to and from the lungs, enough oxygen can be delivered to the circulation even if a person is apneic, and even if the [[thoracic diaphragm|diaphragm]] does not move. With the onset of apnea, low pressure develops in the airspace of the lungs because more oxygen is absorbed than CO<sub>2</sub> is released. With the airways closed or obstructed, this will lead to a gradual collapse of the lungs and suffocation. However, if the airways are open, any gas supplied to the upper airways will follow the pressure gradient and flow into the lungs to replace the oxygen consumed. If pure oxygen is supplied, this process will serve to replenish the oxygen stored in the lungs and resume sufficient ventilation. The uptake of oxygen into the blood will then remain at the usual level, and the normal functioning of the organs will not be affected. A consequence of this hyperoxygenation is the occurrence of "nitrogen washout", which can lead to [[atelectasis#Absorption (resorption) atelectasis|atelectasis]].<ref>{{cite web|title=preoygenation, reoxygenation and Delayed Sequence Intubation in the Emergency Department|website=medscape.com|url=http://www.medscape.com/viewarticle/745228_2|access-date=10 August 2015|archive-date=4 March 2016|archive-url=https://web.archive.org/web/20160304235821/http://www.medscape.com/viewarticle/745228_2|url-status=live}}</ref>

However, no CO<sub>2</sub> is removed during apnea. The [[partial pressure]] of CO<sub>2</sub> in the airspace of the lungs will quickly equilibrate with that of the blood. As the blood is loaded with CO<sub>2</sub> from the metabolism without a way to remove it, more and more CO<sub>2</sub> will accumulate and eventually displace oxygen and other gases from the airspace. CO<sub>2</sub> will also accumulate in the tissues of the body, resulting in [[respiratory acidosis]].

Under ideal conditions (i.e., if pure oxygen is breathed before onset of apnea to remove all [[nitrogen]] from the lungs, and pure supplemental oxygen is [[Insufflation (medicine)|insufflated]]), apneic oxygenation could theoretically be sufficient to provide enough oxygen for survival of more than one hour's duration in a healthy adult.{{Citation needed|date=August 2011}} However, accumulation of carbon dioxide (described above) would remain the limiting factor.

Apneic oxygenation is more than a physiologic curiosity. It can be employed to provide a sufficient amount of oxygen in [[thoracic surgery]] when apnea cannot be avoided, and during manipulations of the airways such as [[bronchoscopy]], [[intubation]], and surgery of the upper airways. However, because of the limitations described above, apneic oxygenation is inferior to extracorporal circulation using a [[heart-lung machine]] and is therefore used only in emergencies, short procedures, or where extracorporal circulation cannot be accessed. Use of [[PEEP valve]]s is also an accepted alternative (5&nbsp;cm H<sub>2</sub>O in average weight patients and 10&nbsp;cm H<sub>2</sub>O significantly improved lung and chest wall compliance in morbidly obese patients).<ref>{{cite book|title=Perioperative Medicine: Managing for Outcome|publisher=PerioperBy Mark F. Newman, Lee A. Fleisher, Mitchell P. Fink|pages=517}}</ref>

In 1959, Frumin described the use of apneic oxygenation during anesthesia and surgery. Of the eight test subjects in this landmark study, the highest recorded [[Arterial blood gas|PaCO<sub>2</sub>]] was 250 [[Torr|millimeters of mercury]], and the lowest arterial [[pH]] was 6.72 after 53 minutes of apnea.<ref>{{cite journal|first1=M.J. |last1=Frumin |first2=R.M. |last2=Epstein |first3=G. |last3=Cohen |title=Apneic oxygenation in man|journal=Anesthesiology| volume=20|issue=6| pages=789–798|date=November–December 1959|doi=10.1097/00000542-195911000-00007|pmid=13825447|s2cid=33528267 |doi-access=free}}</ref>

== Apnea scientific studies ==
Studies found spleen volume is slightly reduced during short breath-hold apnea in healthy adults.<ref name=":0">{{cite journal | last1= Inoue |first1=Y |last2=Nakajima |first2=A |last3=Mizukami |first3=S |last4=Hata |first4=H | year = 2013 | title = Effect of Breath Holding on Spleen Volume Measured by Magnetic Resonance Imaging | journal = PLOS ONE | volume = 8 | issue = 6| page = e68670 | doi = 10.1371/journal.pone.0068670 | pmid = 23840858 | pmc = 3694106 | bibcode = 2013PLoSO...868670I | doi-access = free }}</ref>

==Apnea test in determining brain death==
A recommended practice for the clinical diagnosis of [[brain death]] formulated by the [[American Academy of Neurology]] hinges on the conjunction of three diagnostic criteria: a [[coma]], absence of [[brainstem]] reflexes, and apnea (defined as the inability of the patient to [[breath]]e unaided: that is, with no [[life support]] systems like [[Ventilator|ventilators]]). The apnea test follows a delineated protocol.<ref>[[American Academy of Neurology]]. [http://www.aan.com/professionals/practice/pdfs/pdf_1995_thru_1998/1995.45.1012.pdf "Practice Parameters: Determining Brain Death in Adults"] {{webarchive|url=https://web.archive.org/web/20090206010138/http://aan.com/professionals/practice/pdfs/pdf_1995_thru_1998/1995.45.1012.pdf |date=6 February 2009 }}. Published 1994. Accessed 2008-01-06.</ref> Apnea testing is not suitable in patients who are hemodynamically unstable with increasing vasopressor needs, metabolic acidosis, or require high levels of ventilatory support. Apnea testing carries the risk of arrhythmias, worsening hemodynamic instability, or metabolic acidosis beyond the level of recovery and can potentially make the patient unsuitable for organ donation (see above). In this situation a confirmatory test is warranted as it is unsafe to perform the apnea test to the patient.<ref name=":0" />

==Etymology and pronunciation==
The word ''apnea'' (or ''apnoea'') uses [[classical compound|combining forms]] of ''[[wikt:a-#Prefix|a-]]'' + ''[[wikt:-pnea#Suffix|-pnea]]'', from {{langx|el|ἄπνοια}}, from ἀ-, [[privative]], πνέειν, to breathe. [[Shortness of breath#Collation of -pnea transcriptions|See pronunciation information at ''dyspnea''.]]

==See also==
{{Portal|Medicine}}
{{div col}}
*[[Apnea of prematurity]]
*[[Apnea–hypopnea index]]
*[[Expiratory apnea]]
*[[Freediving]]
*[[Freediving blackout]] 
*[[Hypopnea]]
*[[List of terms of lung size and activity]]
*[[Mechanical ventilation]]
*[[Respiratory arrest]]
*[[Shallow water blackout]]
*[[Sleep apnea]]
{{div col end}}

==References==
{{Reflist}}‌
==Sources==
*{{cite book |first=J. F. |last=Nunn |title=Applied Respiratory Physiology |publisher=Butterworth-Heinemann |isbn=0-7506-1336-X |edition=4th |year=1993 |url-access=registration |url=https://archive.org/details/nunnsappliedresp0004nunn }}

== External links ==

{{Wiktionary}}

*[https://web.archive.org/web/20130518160704/http://apneacalculator.com/ apneacalculator.com], information about Apnea and the apnea-calculator for clinical treatment of Obstructive Sleep Apnea
*[https://freedivers.co.uk/ Freediving Courses & Training in the UK], information about learning the sport of Freediving, the club is called Apneists UK
*[https://web.archive.org/web/20140913081135/http://divewise.org/education/freediver-blackout/ DiveWise.Org] Non-profit scientific and educational resource for apnea divers
*[https://web.archive.org/web/20120602232113/http://www.diversalertnetwork.org/research/workshops/ DAN Breath-Hold Workshop] Divers Alert Network 2006 Breath-Hold Diving Workshop PDF
{{Medical resources
|  ICD10      = 
|  ICD9       = {{ICD9|786.03}}
|  MeshID=D001049
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{{Respiratory system symptoms and signs}}
{{Authority control}}

[[Category:Breathing abnormalities]]
[[Category:Neonatology]]