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26 Cards in this Set
- Front
- Back
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What does ficks law concern? what is the equation?
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this is related to the rate of diffusion of gases
Rate of gas diffusion= (diffusion coefficient * surface area* pressure gradient)/ membrane thickness |
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What is the Rate of gas diffusion across a membrane inversely related to?
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the thickness of the membrane
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what is the driving force for the diffusion of a gas?
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the partial pressure difference
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What has a a higher diffusion coefficent, CO2 or O2? (aka which diffuses faster?
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CO2, due to its 20x higher diffusion rate
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How does the diffusing capacity of the lung change in emphysema? why?
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this will decrease the diffusion capacity, destroying alveoli, decreases the surface area for gas exhange
(V= (area* diff coeff* pressure difference)/ thickness |
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How does the diffusing capacity of the lung change in fibrosis or pulmonary edema?
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this decreases diffsuion capacity by increases in the thickness of alveolar wall
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How does the diffusing capacity of the lung change in anemia?
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this will decrease, as there is less Hb available to take up O2, allowing the partial pressures to equalize, thus eliminating the gradient/flow
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How does the diffusing capacity of the lung change in exercise?
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this will increase
due to increase perfusion of additional capillaries. this increases area of gas exchange |
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What is the equation for diffusing capacity of CO? what does it represent?
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this is DLco= Rate of CO (Vco)/ (PAco)
so the dffusion of Co= rate of CO volume change. (so note the amount of CO taken up per MIN, the test runs for 10 seconds, so multiply by 6). you then divide by the partial pressure of CO in the alveolus |
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Whats the normal range for DLco?
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20-30ml/min/mmhg
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What kinds of things decrease the diffusing capacity for CO? (the DLco test)
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anything that increases membrane thickness, decrease blood gas surface area, loss of lung tissue, increased age
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what kinds of things increase the diffusing capacity for CO? (the DLco test)
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this is increased by increases in body size, being male, or exercise
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What gas in the blood is never bound or modified?
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nitrogen
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what does henrys law state? when is it used? how does it relate to O2?
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this states the concentration of a gas in the blood= the pressure X its solubility. the solubility of O2 is .003
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What does daltons law deal with? what are the two equations for it?
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daltons law involves partial pressures
Partial pressure of gas= barometric pressure of gas X the fractional concentration of gas. WHEN humidified! Px= (Pb - Ph2o) X F |
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what is the water vapor pressure? when is it used? in what equation?
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47mmHg. This is used in daltons law of partial pressure, to compensate inspired air's humidification.
Px= (Pb-47mmHg) X fraction of total air (for O2 is .21) |
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what is the fractional concentration of O2 in inspired air?
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.21
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What are the PAo2 and PAco2 of fully saturated alveolar air?
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PAo2= 100mmHg
PAco2=40mmHg |
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What limits gas exchange of a diffusion limited gas? examples?
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this is limited by the rate of diffusion across the alveolar wall. CO is an example
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What limits a perfusion limited gas? examples?
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these are limited by the rate of blood flow to the lungs. N2O is an example of this
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What are the properties of a perfusion limited gas?
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these are gasses that do not bind to proteins in the blood, so they create a partial pressure in the blood. eventually equilibrating and stopping gas exchange (Vx= diffusion coeffic X area X pressure differential/ membrane thickness)
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What kind of limitation affects O2 transport across the lungs?
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this is perfusion limited!
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when can O2 transport across the lungs become diffusion limited?
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in fibrosis
due to low arteriol Po2 insufficient time for EQ to occur between blood and alveolar gas if Dl is very low |
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What is the pressure of oxygen at the beginning of the capillary?
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40 mmHg, essentially similar to the mixed venous blood O2 levels.
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how far along the capillary does O2 equilibration occur?
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about 1/3rd the way dowm, this makes this perfusion limited gas transfer
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In fibrosis, how does O2 gas transport change?
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this becomes diffusion limited, as it cannot equilibrate across the membrane
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