{{short description|Flow of the respiratory current into an organism}} {{More citations needed|date=March 2020}} {{redirect|Inhale|the 2013 Marsheaux album|Inhale (album)}} thumb|Diagram showing inhalation '''Inhalation''' (or '''inspiration''') happens when air or other gases enter the lungs.
== Inhalation of air == Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions in some disease states) and does not need conscious control or effort. However, breathing can be consciously controlled or interrupted (within limits).
Breathing allows oxygen (which humans and a lot of other species need for survival) to enter the lungs, from where it can be absorbed into the bloodstream.
== Other substances – accidental == Examples of accidental inhalation includes inhalation of water (e.g. in drowning), smoke, food, vomitus and less common foreign substances<ref>{{Cite journal|last2=Lauriello|first2=M|last3=Bellussi|first3=L|last4=Passali|first4=GC|last5=Passali|first5=FM|last6=Gregori|first6=D|date=2010|title=Foreign body inhalation in children: an update|pmc=2881610|journal=Acta Otorhinolaryngol Ital|pmid=20559470|last1=Passàli|first1=D|volume=30|issue=1|pages=27–32}}</ref> (e.g. tooth fragments, coins, batteries, small toy parts, needles).
== Other substances – deliberate ==
=== Recreational use === Nitrous oxide ("laughing gas") has been used recreationally since 1899 for its ability to induce euphoria, hallucinogenic states and relaxation, and is legal in some countries.
Helium can be inhaled to give the voice a reedy, duck-like quality, but this can be dangerous as the gas is an asphyxiant and displaces the oxygen needed for normal respiration.<ref name="Grass">{{Cite journal| title = Suicidal asphyxiation with helium: Report of three cases Suizid mit Helium Gas: Bericht über drei Fälle| journal = Wiener Klinische Wochenschrift| volume = 119|issue =9–10|date = 2007|doi = 10.1007/s00508-007-0785-4|author = Grassberger, Martin|author2 = Krauskopf, Astrid |pages = 323–325 |language=de, en| pmid = 17571238|s2cid = 22894287}}</ref>
Various illegal gaseous, vapourised or aerosolized recreational drugs exist, and are classed as inhalants.
=== Medical use ===
==== Diagnostic ====
Various specialized investigations use the inhalation of known substances for diagnostic purposes. Examples include pulmonary function testing (e.g. nitrogen washout test, diffusion capacity testing (carbon monoxide, helium, methane)) and diagnostic radiology (e.g. radioactive xenon isotopes).
==== Therapeutic ====
Gases and other drugs used in anaesthesia include oxygen, nitrous oxide, helium, xenon, volatile anaesthetic agents. Medication for asthma, croup, cystic fibrosis and some other conditions.
== Mechanism == Inhalation begins with the contraction of the muscles attached to the rib cage; this causes an expansion in the chest cavity. Then takes place the onset of contraction of the thoracic diaphragm, which results in expansion of the intrapleural space and an increase in negative pressure according to Boyle's law. This negative pressure generates airflow because of the pressure difference between the atmosphere and alveolus.
The inflow of air into the lungs occurs via the respiratory airways. In health, these airways begin with the nose.<ref name=cc>{{cite web |url=https://health.clevelandclinic.org/breathe-mouth-nose/ |title=Should You Breathe Through Your Mouth or Your Nose? |access-date=2020-06-28 |last=Turowski |first=Jason |date=2016-04-29 |publisher=Cleveland Clinic }}</ref><ref name="guardian">{{cite web|title=Your Nose, the Guardian of Your Lungs|url=https://www.bmc.org/otolaryngology-head-neck-surgery/resources/your-nose-guardian-your-lungs|access-date=2020-06-29|publisher=Boston Medical Center}}</ref> It is possible to begin with the mouth, which is the backup breathing system. However, chronic mouth breathing leads to, or is a sign of, illness, and there is no mucus in the mouth to trap unwanted substances unlike the nostrils.<ref name=harmful>{{cite web |url=https://www.nbcnews.com/healthmain/mouth-breathing-gross-harmful-your-health-1C6437430 |title='Mouth-breathing' gross, harmful to your health |access-date=2020-06-28 |last=Dahl |first=Melissa |date=2011-01-11 |publisher=NBC News }}</ref><ref name="role">{{cite web |url=https://www.journal-imab-bg.org/issues-2018/issue1/JofIMAB-2018-24-1p1878-1882.pdf |title=THE ROLE OF MOUTH BREATHING ON DENTITION DEVELOPMENT AND FORMATION |access-date=2020-05-31 |last=Valcheva |first=Zornitsa |date=January 2018 |publisher=Journal of IMAB }}</ref><ref name="nesnpr">{{cite web |url=https://www.npr.org/transcripts/862963172 |title=How The 'Lost Art' Of Breathing Can Impact Sleep And Resilience |access-date=2020-06-23 |last=Gross |first=Terry |date=2020-05-27 |publisher=National Public Radio (NPR)/Fresh Air }}</ref> They end in the microscopic dead-end sacs (alveoli) always opened, though the diameters of the various sections can be changed by the sympathetic and parasympathetic nervous systems. The alveolar air pressure is therefore always close to atmospheric air pressure (about 100 kPa at sea level) at rest, with the pressure gradients that cause air to move in and out of the lungs during breathing rarely exceeding 2–3 kPa.<ref name="Chrisvan L 1995">{{cite journal |last1=Koen |first1=Chrisvan L. |last2=Koeslag |first2=Johan H. | title=On the stability of subatmospheric intrapleural and intracranial pressures |journal= News in Physiological Sciences | date=1995 |volume=10 |issue=4 |pages=176–178 |doi=10.1152/physiologyonline.1995.10.4.176}}</ref><ref name="Williams & Wilkins">{{cite book |last1=West |first1=J.B. |title=Respiratory physiology: the essentials. |location=Baltimore |publisher=Williams & Wilkins |date=1985| pages= 21–30, 84–84, 98–101 }}</ref>
Other muscles that can be involved in inhalation include:<ref>{{cite book| title= Essentials of Human Physiology| first= Thomas M. |last= Nosek| chapter=Section 4/4ch2/s4ch2_10 |chapter-url=http://humanphysiology.tuars.com/program/section4/4ch2/s4ch2_10.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section4/4ch2/s4ch2_10.htm|archive-date=2016-03-24}}</ref> * External intercostal muscles * Scalene muscles * Sternocleidomastoid muscle * Trapezius muscle
==Hyperinflation== {{For-multi|another similar term|Dynamic hyperinflation|the Economics term|Hyperinflation}}
''Hyperinflation'' or ''hyperaeration'' is where the lung volume is abnormally increased, with increased filling of the alveoli. This results in an increased radiolucency on X-ray, a reduction in lung markings and depression of the diaphragm. It may occur in partial obstruction of a large airway, as in e.g. congenital lobar emphysema, bronchial atresia and mucus plugs in asthma.<ref>{{cite web|url=http://www.medcyclopaedia.com/library/topics/volume_vii/h/hyperinflation.aspx|archive-url=https://archive.today/20111208222639/http://www.medcyclopaedia.com/library/topics/volume_vii/h/hyperinflation.aspx|url-status=dead|archive-date=2011-12-08|title=Hyperinflation|publisher=GE|work=Medcyclopaedia}}</ref>
==Yoga== Yogis such as B. K. S. Iyengar advocate both inhaling and exhaling through the nose in the practice of yoga, rather than inhaling through the nose and exhaling through the mouth.<ref name=yj>{{cite web |url=https://www.yogajournal.com/practice/take-a-breath |title=Q&A: Is Mouth Breathing OK in Yoga? |access-date=2020-06-26 |date=2017-04-12 |publisher=Yoga Journal }}</ref><ref name=dummies>{{cite web |url=https://www.dummies.com/health/exercise/yoga/yogic-breathing-tips-for-breathing-through-your-nose-most-of-the-time/ |title=Yogic Breathing: Tips for Breathing through Your Nose (Most of the Time) |access-date=2020-06-26 |last=Payne |first=Larry |publisher=Yoga For Dummies, 3rd Edition }}</ref><ref name=guide>{{cite web |url=https://www.himalayaninstitute.org/wisdom-library/yogic-breathing-study-guide/ |title=Yogic Breathing: A Study Guide |access-date=2020-06-26 |last=Himalayan Institute Core Faculty |first=Himalayan Institute Core Faculty |date=2017-07-13 |publisher=Himalayan Institute of Yoga Science and Philosophy }}</ref> They tell their students that the "nose is for breathing, the mouth is for eating."<ref name=dummies/><ref name=sparks>{{cite book |url=https://books.google.com/books?id=QPk_nshsngoC&q=%22the+nose+is+for+breathing%2C+the+mouth+is+for+eating%22+yoga&pg=RA1-PA11 |title=Yoga Sparks |access-date=2020-05-31 |last=Krucoff |first=Carol |date=2013 |publisher=New Harbinger Publications |isbn=9781608827022 }}</ref><ref name=run>{{cite book |url=https://books.google.com/books?id=fEm6XnTajm0C&q=%22the+nose+is+for+breathing%2C+the+mouth+is+for+eating%22+yoga&pg=PA108 |title=Eat and Run |access-date=2020-05-31 |last=Jurek |first=Scott |date=2012 |publisher=Houghton Mifflin |isbn=978-0547569659 }}</ref><ref name=yj/>
==See also== {{Wiktionary|inhalation|sniffing}} * Exhalation * Inhalant – psychoactive drugs consumed through inhalation * List of terms of lung size and activity * Mouth breathing * Obligate nasal breathing * Respiratory system * Smoking - a specific inhalation route * Breathing * Work of breathing
==Further reading== * {{Cite book|title=Breath: The New Science of a Lost Art |last=Nestor|first=James|publisher=Riverhead Books |year=2020|isbn= 978-0735213616 }}
==References== {{reflist}}
{{Dosage forms}} {{Respiratory physiology}}
Category:Respiration Category:Respiratory physiology