Term
| What does VdotO2 or VdotCO2 stand for? and what are the units? |
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Definition
total volume of gas entering the lungs per unit time
ml/min |
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Term
| What two factors of diffusibility determine Vdot? |
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Definition
1. pressure gradient across the alveolocapillary membrane
2. membrane conductance |
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Term
| What does DLO2 or DLCO2 mean? |
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Definition
| They are diffusion capacity terms that describe conductance of the membrane |
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Term
| What is the equation for conductance of the alveolocapillary membrane? |
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Definition
DLO2 = (DO2*A)/T
diffusing capacity = gas diffusion constant time area for gas exchange divided by thickness of the membrane |
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Term
| How is the diffusion constant calculated? |
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Definition
| Diffusion constant = solubility/√(molecular weight) |
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Term
| Is the flux of CO across the alveolocapillary membrane diffusion or perfusion limited? |
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Definition
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Term
| Is the flux of N2O across the alveolocapillary membrane diffusion or perfusion limited? |
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Definition
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Term
| Is O2 in the blood normally perfusion or diffusion limited? |
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Definition
| perfusion limited, but can become diffusion limited in disease |
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Term
| How much more affinity does CO have for RBCs than O2? |
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Definition
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Term
| How quickly does normal O2 saturate as it goes through the capillary exchange zone? |
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Definition
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Term
| What factors could make O2 become closer to diffusion limited than perfusion limited? |
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Definition
| a decrease in membrane conductance due to decreased area or increased membrane thickness |
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Term
| How does exercise affect O2 diffusion across capillary membrane? |
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Definition
| Moderate exercise does not affect O2 diffusion, but severe exercise decreases O2 diffusion time across the capillary membrane because of the major increase in cardiac output |
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Term
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Definition
(VdotO2) = (DLO2) x (PAO2 – PcapO2)
volume flow of oxygen across membrane = conductance times the partial pressure |
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Term
| How can the diffusing capacity of the lung for oxygen be solved using CO? |
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Definition
DLO2 = DLCO x (DO2 / DCO)
the conductance of O2 is equal to the conductance of CO times the ratio of gas diffusion constants |
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Term
| Why can the conductance of CO be determined experimentally when the conductance of O2 cannot? |
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Definition
the partial pressure of CO in the capillaries is zero because it is all taken up by hemoglobin
3.Conductance for O2: DLO2 = VdotO2 / (PAO2 – PcapO2), but only VdotO2 and PAO2 can be measured.
4.
4.However, if the gas carbon monoxide is used, the PcapCO falls out as zero, giving: DLCO = VdotCO/ PACO.
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Term
| in the fluid phase, how much faster is CO2 diffusion than O2 diffusion? |
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Definition
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Term
| in air phase, how fast does CO2 diffuse compared to O2? |
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Definition
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