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10 Cards in this Set

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  • Back
What (4) factors affect diffusion of a gas between the alveolus and the pulmonary capillary?
Area, Thickness, Pressure gradient, Diffusion coefficient

V(gas)=[A x D (P1 - P2)] / T
How is capillary reserve time affected by increased exercise?
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.
How is CO used to measure diffusion capacity [D(L)]?
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
How does the ventilation perfusion ratio (V/Q) determine PO2 & PCO2 of blood emerging from the alveolar/pulmonary capillary?
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
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
What are (2) basic causes of abnormal V/Q ratios?
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
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
How can the body maintain V/Q matching in a healthy lung?
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.
How would be calculate A-a gradient and what is a normal A-a gradient?
A-a gradient is the P(A)O2 - P(a)O2

Normal A-a gradient is 5-15 mm Hg
What is the significance of an elevated A-a gradient?
It could be due to a physiological or anatomical shunt where deoxygenated blood is entering the systemic arterial circulation