Prandtl–Meyer function: Difference between revisions

Revision as of 15:15, 20 April 2013

The partial pressure of oxygen (pO₂) in the pulmonary alveoli is required to calculate both the alveolar-arterial gradient of oxygen and the amount of right-to-left cardiac shunt, which are both clinically useful quantities. However it is not practical to take a sample of gas from the alveoli in order to directly measure the partial pressure of oxygen. The alveolar gas equation allows the calculation of the alveolar partial pressure of oxygen from data that is practically measurable. It was first characterized in 1946.^[1]

Assumptions

The equation relies on the following assumptions:

Inspired gas contains no carbon dioxide (CO₂) or water
Nitrogen (and any other gases except oxygen) in the inspired gas are in equilibrium with their dissolved states in the blood
Inspired and alveolar gases obey the ideal gas law
Carbon dioxide (CO₂) in the alveolar gas is in equilibrium with the arterial blood i.e. that the alveolar and arterial partial pressures are equal
The alveolar gas is saturated with water

Equation

$p_{A} O_{2} = F_{I} O_{2} (P_{A T M} - p H_{2} O) - \frac{p_{a} C O_{2} (1 - F_{I} O_{2} [1 - R Q])}{R Q}$

If F_IO₂ is small, or more specifically if
$F_{I} O_{2} [1 - R Q] ≪ 1$
then the equation can be simplified to:
$p_{A} O_{2} \approx F_{I} O_{2} (P_{A T M} - p H_{2} O) - \frac{p_{a} C O_{2}}{R Q}$ where:

Quantity	Description	Sample value
p_AO₂	The alveolar partial pressure of oxygen (pO₂)	107 mmHg (14.2 kPa)
F_IO₂	The fraction of inspired gas that is oxygen (expressed as a decimal).	0.21
P_ATM	The prevailing atmospheric pressure	760 mmHg (101 kPa)
pH₂O	The saturated vapour pressure of water at body temperature and the prevailing atmospheric pressure	47 mmHg (6.25 kPa)
p_aCO₂	The arterial partial pressure of carbon dioxide (pCO₂)	40 mmHg (4.79 kPa)
RQ (RER)	The respiratory quotient (Respiratory Exchange Ratio)	0.8

Sample Values given for air at sea level at 37°C.

References

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External links

Template:Respiratory physiology

Template:Med-diagnostic-stub

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The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang

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[1]

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+The [[partial pressure]] of oxygen (pO<sub>2</sub>) in the [[pulmonary alveoli]] is required to calculate both the [[alveolar-arterial gradient]] of oxygen and the amount of right-to-left [[cardiac shunt]], which are both clinically useful quantities. However it is not practical to take a sample of gas from the alveoli in order to directly measure the partial pressure of oxygen. The alveolar gas equation allows the calculation of the alveolar partial pressure of oxygen from data that is practically measurable. It was first characterized in 1946.<ref name="pmid16709734">{{cite journal |author=Curran-Everett D |title=A classic learning opportunity from Fenn, Rahn, and Otis (1946): the alveolar gas equation |journal=Adv Physiol Educ |volume=30 |issue=2 |pages=58–62 |date=June 2006 |pmid=16709734 |doi=10.1152/advan.00076.2005 |url=http://advan.physiology.org/cgi/content/full/30/2/58?ck=nck}}</ref>
+==Assumptions==
+The equation relies on the following assumptions:
+* Inspired gas contains no carbon dioxide (CO<sub>2</sub>) or water
+* Nitrogen (and any other gases except oxygen) in the inspired gas are in equilibrium with their dissolved states in the blood
+* Inspired and alveolar gases obey the [[ideal gas law]]
+* Carbon dioxide (CO<sub>2</sub>) in the alveolar gas is in equilibrium with the arterial blood i.e. that the alveolar and arterial partial pressures are equal
+* The alveolar gas is saturated with water
+==Equation==
+<math>p_AO_2=F_IO_2(P_{ATM}-pH_2O)-\frac{p_aCO_2(1-F_IO_2[1-RQ])}{RQ}</math>
+If F<sub>I</sub>O<sub>2</sub> is small, or more specifically if<br /><math>F_IO_2[1-RQ] \ll 1</math><br />then the equation can be simplified to:<br /><math>p_AO_2 \approx F_IO_2(P_{ATM}-pH_2O)-\frac{p_aCO_2}{RQ}</math>
+where:
+{| class="wikitable"
+! Quantity
+! Description
+! Sample value
+|-
+| p<sub>A</sub>O<sub>2</sub>
+| The alveolar partial pressure of oxygen (pO<sub>2</sub>)
+| 107 mmHg (14.2 kPa)
+|-
+| F<sub>I</sub>O<sub>2</sub>
+| The fraction of inspired gas that is oxygen (expressed as a decimal).
+| 0.21
+|-
+| P<sub>ATM</sub>
+| The prevailing atmospheric pressure
+| 760 mmHg (101 kPa)
+|-
+| pH<sub>2</sub>O
+| The saturated vapour pressure of water at body temperature and the prevailing atmospheric pressure
+| 47 mmHg (6.25 kPa)
+|-
+| p<sub>a</sub>CO<sub>2</sub>
+| The arterial partial pressure of carbon dioxide (pCO<sub>2</sub>)
+| 40 mmHg (4.79 kPa)
+|-
+| RQ (RER)
+| The [[respiratory quotient]] (Respiratory Exchange Ratio)
+| 0.8
+|}
+Sample Values given for air at sea level at 37°C.
+==See also==
+* [[Pulmonary gas pressures]]
+==References==
+{{reflist}}
+==External links==
+* [http://vam.anest.ufl.edu/simulations/alveolargasequation.php Free interactive model of the simplified and complete versions of the alveolar gas equation (AGE)]
+* [http://www.surgery.ucsf.edu/eastbaytrauma/Protocols/Formulas%20pages/formulasaalvgasequation.htm Formula at ucsf.edu]
+* [http://ceaccp.oxfordjournals.org/content/4/1/24.full Derivation and explanation from Continuing Care in Anaesthesia, Critical Care, and Pain]
+*[http://www.medfixation.com/alveolar-gas-equation-pao2/ Online Alveolar Gas Equation and iPhone application] by Medfixation.
+{{Respiratory physiology}}
+{{DEFAULTSORT:Alveolar Gas Equation}}
+[[Category:Respiratory physiology]]
+{{med-diagnostic-stub}}

Prandtl–Meyer function: Difference between revisions

Revision as of 15:15, 20 April 2013

Contents

Assumptions

Equation

See also

References

External links

Navigation menu

Prandtl–Meyer function: Difference between revisions

Revision as of 15:15, 20 April 2013

Assumptions

Equation

See also

References

External links

Navigation menu

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