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10 Cards in this Set
- Front
- Back
What (4) factors affect diffusion of a gas between the alveolus and the pulmonary capillary?
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Area, Thickness, Pressure gradient, Diffusion coefficient
V(gas)=[A x D (P1 - P2)] / T |
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How is capillary reserve time affected by increased exercise?
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Blood enters the pulmonary capillary bed, spending 0.75 sec. in contact w/ the alveolus.
Of this, 0.25 sec. is needed for blood to go from PO2 of 40 mmHg to alveolar levels of 100 mmHg. This leaves 0.5 sec. as a 'capillary reserve time', the extra time blood is in contact w/ the alveolus. Increased CO, such as exercise, causes blood to move faster thus decreasing the capillary reserve time however still sufficient at oxygenating the blood. |
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How is CO used to measure diffusion capacity [D(L)]?
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D(L) = V(CO) / P(A)CO
Procedure: 1) Breath out to RV and then max inspiration w/ 0.3% CO 2) Hold breath for 10 sec 3) Measure diff. between inspired [CO] and expired [CO], which gives CO taken up by lung in 10 sec. Normal is 25 ml CO / mm Hg of CO |
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How does the ventilation perfusion ratio (V/Q) determine PO2 & PCO2 of blood emerging from the alveolar/pulmonary capillary?
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The ventilation perfusion ratio is ventilation / perfusion. (V/Q)
A high V/Q equates to normal PO2 & ↓PCO2 A low V/Q equates to ↓PO2 & ↑PCO2 |
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What is a normal V/Q?
Where is V/Q the highest, apex or base of lungs? Where is V/Q the lowest, apex or base of lungs? |
Normal V/Q ~0.8-1
V/Q is highest at the apex where PO2 is normal yet PCO2 is lower V/Q is lowest at the base where PO2 is lower and PCO2 is higher |
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What are (2) basic causes of abnormal V/Q ratios?
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Non-uniform V:
ie. Obstruction in conducting zone of one of the lungs causing a decrease in ventilation of that lung Non-uniform Q: ie. Decreased perfusion of one lung causes increased perfusion of the other even though ventilation is normal...could be blockage of vessel |
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What is a right-to-left shunt?
What is physiological dead space? What is the overall effects of right-to-left shunts and physiological dead space on O2 content of arterial blood? |
The bronchial circulation supplies the conducting airways w/ blood and then directly draining into the pulmonary vein. Thus 2-5% of the CO is shunted, which lowers arterial O2 content. This is called an "anatomical right-to-left shunt".
Physiological dead space is the total dead space or anatomical + alveolar dead spaces. Both shunts and dead space will decrease the overall O2 content of arterial blood. *A V/Q mismatch will always lower the O2 content of venous admixture & increase the A-a gradient |
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How can the body maintain V/Q matching in a healthy lung?
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Physiological shunts where areas w/ low perfusion, the blood flow to these areas is decreased through vasoconstriction. Thus blood is redirected toward areas of higher perfusion and maintaining a normal V/Q ratio.
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How would be calculate A-a gradient and what is a normal A-a gradient?
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A-a gradient is the P(A)O2 - P(a)O2
Normal A-a gradient is 5-15 mm Hg |
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What is the significance of an elevated A-a gradient?
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It could be due to a physiological or anatomical shunt where deoxygenated blood is entering the systemic arterial circulation
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