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| {{Blood gas, acid-base, & gas exchange terms}}
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| In [[physiology]], '''dead space''' is the volume of air which is inhaled that does not take part in the gas exchange, either because it (1) remains in the conducting airways, or (2) reaches alveoli that are [[Ventilation/perfusion ratio|not perfused or poorly perfused]]. In other words, not all the air in each breath is available for the exchange of [[oxygen]] and [[carbon dioxide]]. Mammals [[breath]]e in and out of their lungs, wasting that part of the inspiration which remains in the conducting airways where no gas exchange can occur.<ref name = wasted>{{cite web|url=http://www.ccmtutorials.com/rs/mv/strategy/page16.htm |title=Wasted Ventilation |publisher=Ccmtutorials.com |date= |accessdate=2013-11-27}}</ref>
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| Benefits do accrue to a seemingly wasteful design for ventilation that includes dead space.<ref name=WestPhysiology>{{cite book|last=West|first=John B.|title=Respiratory physiology : the essentials|year=2011|publisher=Wolters Kluwer Health/Lippincott Williams & Wilkins|location=Philadelphia|isbn=978-1-60913-640-6|edition=9th ed.}}</ref>
| | Eczema, also called dermatitis, may be one of the hardest skin conditions to experience. It's itching, flaking, blistering, redness, oozing and even bleeding might day to day activities uncomfortable carry out. It can affect anything you do and perhaps even can be a factor in what kind of clothing you wear. Various other words, eczema can cause certain restrictions in an every day atmosphere.<br><br>"Everyone's Irish on Saint. Patrick's Day!" And who wouldn't want to be, when everywhere you turn, floats, parades and people in green show proof of fun and happiness. But this can be a time of expression why blend i'm able to crowd preference can show your unique awesomeness!<br><br><br><br>These small projects consist of insulation of pipes, fixation of leaks and replacement of the valves. There are certain tools which are must haves in the comprehensive resource which are wrenches, tapes, caulks, bolts and nuts etc. You will recognize that also come handy a few have additional problem to fix up.<br><br>Jewellery - Just like clothing, even jewellery can be quite a chore in the neck (pun intended) throughout a summer wedding ring. Wear something will not cause rashes if you start sweating end result of the atmosphere.<br><br>I just had suer who just finally started telling herself the truth about why she wasn't in a relationship. She was in denial for so time intensive. And before she came to realize that, what sort of men think she was attracting? LIARS!<br><br>A national day off is in order and leads that Street. Patrick's Day couldn't come any extra quickly. Annually anticipated, March 17 is marked in every calendar as a day loosen up and remember.<br><br>Online clothes shopping is one of the easiest approaches to shop, will not need waste power walking, it will save you fuel, and suddenly your stress level stays highly affordable. When you find your favorite apparel site, do not forget to mark it on pc so can easily go back later. Receiving your item in the mail can be exciting, it's almost like opening a great gift.<br><br>If you beloved this article and also you would like to obtain more info with regards to [http://usmerch.co.uk/ gas monkey garage] generously visit our own web page. |
| #Carbon dioxide is retained, making a [[Acid–base homeostasis|bicarbonate-buffered]] blood and interstitium possible.
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| #Inspired air is brought to body temperature, increasing the affinity of [[hemoglobin]] for [[oxygen]], improving O<sub>2</sub> uptake.<ref name=Williams1996>
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| {{cite journal|last=Williams|first=R|coauthors=Rankin, N; Smith, T; Galler, D; Seakins, P|title=Relationship between the humidity and temperature of inspired gas and the function of the airway mucosa.|journal=Critical Care Medicine|date=November 1996|volume=24|issue=11|pages=1920–9|pmid=8917046}}</ref>
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| #Particulate matter is trapped on the mucus that lines the conducting airways, allowing its removal by [[Mucociliary clearance|mucociliary transport]].
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| #Inspired air is humidified, improving the quality of airway mucus.<ref name=Williams1996 />
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| In humans, about a third of every resting breath has no change in O<sub>2</sub> and CO<sub>2</sub> levels. In adults, it is usually in the range of 150 mL.<ref name = wasted />
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| Dead space can be increased (and better envisioned) by breathing through a long tube, such as a [[Snorkel (swimming)|snorkel]]. Even though one end of the snorkel is open to the air, when the wearer breathes in, they inhale a significant quantity of air that remained in the snorkel from the previous exhalation. Thus, a snorkel increases the person's dead space by adding even more "airway" that doesn't participate in gas exchange.
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| ==Components==
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| The ''total'' dead space (also known as '''physiological dead space''') is the sum of the anatomical dead space plus the alveolar dead space.
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| ===Anatomic dead space===
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| Anatomical dead space is that portion of the airways (such as the [[mouth]] and [[Vertebrate trachea|trachea]] to the bronchioles) which conducts gas to the [[alveoli]]. No gas exchange is possible in these spaces. In healthy lungs where the alveolar dead space is small, [[Fowler's method]] accurately measures the anatomic dead space by a [[nitrogen]] washout technique.
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| <ref name=fowler1948>{{cite journal | author = Fowler W.S. | year = 1948 | title = Lung Function studies. II. The respiratory dead space | url = | journal = Am. J. Physiol | volume = 154 | issue = | pages = 405–416 }}</ref><ref>{{cite journal | author = Heller H, Könen-Bergmann M, Schuster K | title = An algebraic solution to dead space determination according to Fowler's graphical method | journal = Comput Biomed Res | volume = 32 | issue = 2 | pages = 161–7 | year = 1999 | pmid = 10337497 | doi = 10.1006/cbmr.1998.1504}}</ref> | |
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| The normal value for dead space volume (in ml) is approximately the lean mass of the body (in pounds), and averages about a third of the resting [[tidal volume]] (450-500 mL). In Fowler's original study, the anatomic dead space was 156 ± 28 ml (n=45 males) or 26% of their tidal volume.<ref name=fowler1948 /> Despite the flexibility of the trachea and smaller conducting airways, their overall volume (i.e. the anatomic dead space) changes little with bronchoconstriction or when breathing hard during exercise.<ref name=fowler1948 /><ref>{{cite journal|last=Burke|first=TV|coauthors=Küng, M; Burki, NK|title=Pulmonary gas exchange during histamine-induced bronchoconstriction in asthmatic subjects.|journal=Chest|year=1989|volume=96|issue=4|pages=752–6|pmid=2791669|url=http://chestjournal.chestpubs.org/content/96/4/752.long}}</ref>
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| Birds have a disproportionately large anatomic dead space (they have a longer and wider trachea than mammals the same size), reducing the airway resistance. This adaptation does not impact gas exchange because birds flow air through their lungs - they do not breathe in and out like mammals.<ref>{{cite journal|last=West|first=JB|title=Comparative physiology of the pulmonary blood-gas barrier: the unique avian solution.|journal=American journal of physiology. Regulatory, integrative and comparative physiology|year=2009|volume=297|issue=6|pages=R1625-34|pmid=19793953|pmc=2803621|doi=10.1152/ajpregu.00459.2009}}</ref>
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| ===Alveolar dead space===
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| Alveolar dead space is sum of the volumes of those alveoli which have little or no blood flowing through their adjacent pulmonary [[capillaries]], i.e., alveoli that are ventilated but not perfused, and where, as a result, no gas exchange can occur.<ref name=WestPhysiology /> Alveolar dead space is negligible in healthy individuals, but can increase dramatically in some [[lung disease]]s due to [[ventilation-perfusion mismatch]].
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| ==Calculating the dead space==
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| Just as dead space ''wastes'' a fraction of the inhaled breath, dead space ''dilutes'' alveolar air during exhalation. By quantifying this dilution it is possible to measure anatomical and alveolar dead space, employing the concept of '''[[mass balance]]''', as expressed by [[Bohr equation]].<ref name=Bohr>
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| Bohr, C. (1891). Über die Lungenathmung. Skand. Arch. Physiol. 2: 236-268.
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| </ref><ref>{{cite journal | author = Klocke R | title = Dead space: simplicity to complexity | journal = J Appl Physiol | volume = 100 | issue = 1 | pages = 1–2 | year = 2006 | pmid = 16357075 | doi = 10.1152/classicessays.00037.2005}} [http://jap.physiology.org/cgi/content/full/100/1/1#R2 article]</ref> | |
| ::<math>\frac{V_{\,d}}{V_{\,t}} = \frac {P_{\,a\,CO_2} - P_{\,e\,CO_2}} {P_{\,a\,CO_2}}</math>
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| :where <math>V_{\,d}</math> is the dead space volume and <math>V_{\,t}</math> is the tidal volume;
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| ::<math>P_{\,a\,CO_2}</math> is the partial pressure of carbon dioxide in the arterial blood, and
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| ::<math>P_{\,e\,CO_2}</math> is the partial pressure of carbon dioxide in the expired (exhaled) air.
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| ===Physiologic dead space===
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| The concentration of carbon dioxide (CO<sub>2</sub>) in healthy alveoli is known - it is equal to its concentration in blood since CO<sub>2</sub> rapidly equilibrates across the alveolar-capillary membrane. The quantity of CO<sub>2</sub> exhaled from the healthy alveoli will be diluted by the air in the conducting airways, and by air from alveoli that are poorly perfused. This dilution factor can be calculated once the CO<sub>2</sub> in the exhaled breath is determined (either by electronically monitoring the exhaled breath or by collecting the exhaled breath in a gas impermeant bag - a Douglas bag - and then measuring the mixed gas in the collection bag). Algebraically, this dilution factor will give us the '''physiologic dead space''' as calculated by the Bohr equation:
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| :<math>\frac{V_{\,physiologic\,dead\,space}}{V_t} = \frac {P_{\,a\,CO_2} - P_{\,mixed\,expired\,CO_2}} {P_{\,a\,CO_2}}</math>
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| ===Alveolar dead space===
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| When the poorly perfused alveoli empty at the same rate as the normal alveoli, it is possible to measure the '''alveolar dead space'''. In this case, the end-tidal sample of gas (measured by [[capnography]]) contains CO<sub>2</sub> at a concentration that is less than that found in the normal alveoli (i.e. in the blood):<ref>{{cite journal|last=Severinghaus|first=JW|coauthors=Stupfel, MA; Bradley, AF|title=Alveolar dead space and arterial to end-tidal carbon dioxide differences during hypothermia in dog and man.|journal=J Appl Physiol|date=May 1957|volume=10|issue=3|pages=349–55|pmid=13438782|url=http://jap.physiology.org/content/10/3/349.long}}</ref>
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| :<math>\frac{V_{\,alveolar\,dead\,space}}{V_t} = \frac {P_{\,a\,CO_2} - P_{\,end\ tidal\,CO_2}} {P_{\,a\,CO_2}}</math>
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| ::'''Caution:''' The end tidal CO2 concentration may not be a well defined number.
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| ::#Poorly ventilated alveoli do not generally empty at the same rate as healthy alveoli. Particularly in emphysematous lungs, diseased alveoli empty slowly, and so the CO<sub>2</sub> concentration of the exhaled air increases progressively throughout the expiration.<ref name=WestPhysiology />
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| ::#Monitoring alveolar dead space during a surgical operation ''is'' a sensitive and important tool in monitoring airway function.<ref>{{cite book|last=Gravenstein|first=J.S. (ed.), Jaffe, M.B. (ed.), Gravenstein, N. (ed.), Paulus, D.A. (ed) |title=Capnography.|year=2010|publisher=Cambridge University Press|location=Cambridge|isbn=978-0521514781|edition=2nd}}</ref>
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| ::#During strenuous exercise, CO<sub>2</sub> will rise throughout the exhalation and may not be easily matched to a blood gas determination, which led to serious errors of interpretation early in the history of dead space determinations.<ref name=Bohr />
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| ::'''Example''': For a tidal volume of 500 mL, an arterial carbon dioxide of 42 mmHg, and an end-expired carbon dioxide of 40 mmHg:
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| :::<math>\frac{V_{\,alveolar\,dead\,space}}{500\ ml} = \frac {42\ mmHg - 40\ mmHg} {42\ mmHg}</math>
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| :::and so <math> V_{\,alveolar\,dead\,space}= 24\ ml.</math>
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| ===Anatomic dead space===
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| A different maneuver is employed in measuring anatomic dead space: the test subject breathes all the way out, inhales deeply from a 0% nitrogen gas mixture (usually 100% oxygen) and then breathes out into equipment that measures nitrogen and gas volume. This final exhalation occurs in three phases. The first phase has no nitrogen, and is the air that entered the lung only as far as the conducting airways. The nitrogen concentration then rapidly increases during the brief second phase and finally reaches a plateau, the third phase. The '''anatomic dead space''' is equal to the volume exhaled during the first phase plus half that exhaled during the second phase. (The Bohr equation is used to justify the inclusion of half the second phase in this calculation.)<ref name=fowler1948 /> | |
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| ==Dead space and the ventilated patient==
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| The depth and frequency of our breathing is determined by chemoreceptors and the brainstem, as modified by a number of subjective sensations. When ventilated, the patient breathes at a rate and tidal volume that is dictated by the machine.
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| Because of dead space, taking deep breaths more slowly (e.g. ten 500 ml breaths per minute) is more effective than taking shallow breaths quickly (e.g. twenty 250 ml breaths per minute). Although the amount of gas per minute is the same (5 L/min), a large proportion of the shallow breaths is dead space, and does not allow oxygen to get into the blood.
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| ==In breathing apparatus==
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| '''Dead space''' in a [[breathing apparatus]] is space in the apparatus in which the [[breathing gas]] must flow in both directions as the user breathes in and out, increasing the necessary respiratory effort to get the same amount of usable air or breathing gas, and risking accumulation of [[carbon dioxide]] from shallow breaths. It is in effect an external extension of the physiological dead space.
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| It can be reduced by:
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| * Using separate intake and exhaust passages with one-way valves placed in the mouthpiece. This limits the dead space to between the non return valves and the user's nmouth and/or nose. The additional dead space can be minimized by keeping the volume of this external dead space as small as possible, but this should not unduly increase work of breathing.
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| * With a [[full face mask]] or [[Diving helmet#Lightweight demand helmets|demand diving helmet]]:
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| ** Keeping the inside volume small, or
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| ** Having a small internal [[orinasal mask]] inside the main mask, which separates the external respiratory passage from the rest of the mask interior.
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| **In a few models of full face mask a mouthpiece like those used on diving regulators is fitted, which has the same function as an orinasal mask, but can further reduce the volume of the external dead space, at the cost of forcing mouth-breathing.
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| ** In medicine this{{clarify|date=September 2013}}<!-- what is "this"--> is corrected by a ventilator set-up check that determines the dead space volume in the ventilator circuit.
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| A smaller volume around the mouth increases distortion of speech. This can make communication more difficult.
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| Free-flow diving helmets avoid the dead space problem by supplying far more air than the diver can use, this makes the whole interior of the helmet effectively fresh air.
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| ==See also==
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| * [[Bohr equation]]
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| * [[Christian Bohr]]
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| * [[Respiratory physiology]]
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| * [[Ventilation (physiology)]]
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| ==References==
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| <references/> | |
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| ==Further reading==
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| Arend Bouhuys. 1964. "Respiratory dead space." in ''Handbook of Physiology. Section 3: Respiration.'' Vol 1. Wallace O. Fenn and Hermann Rahn (eds). Washington: American Physiological Society.
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| John B. West. 2011. ''Respiratory Physiology: The Essentials.'' Lippincott Williams & Wilkins; Ninth edition. ISBN 978-1609136406.
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| ==External links==
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| * [http://oac.med.jhmi.edu/res_phys/Encyclopedia/DeadSpace/DeadSpace.HTML the ''Dead space'' page on Johns Hopkins School of Medicine '''Interactive Respiratory Physiology''' website.]
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| * [http://www.ccmtutorials.com/rs/mv/strategy/page16.htm The ''Mechanical ventilation tutorial'' in Patric Neligan's '''Critical care medicine tutorials''' website]
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| {{Respiratory physiology}}
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| {{Diving medicine, physiology and physics}}
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| [[Category:Respiratory physiology]]
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| [[Category:Respiratory therapy]]
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| [[Category:Pulmonary function testing]]
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| [[Category:Medical terminology]]
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| [[Category:Underwater diving]]
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