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Old 06-28-2011
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Lungs Alveoli diagram; Respiratory Physiology Question

The diagram below shows two lung units (S & T) with their blood supplies. Lung unit S has an ideal relationship between blood flow and ventilation. Lung unit T has a compromised blood flow. What is the relationship between alveolar dead space (AlveolarD), physiologic dead space (PhyD) and anatomic dead space (AnatD) for these lung units?

Alveoli diagram; Respiratory Physiology Question-screen-shot-2011-06-28-7.25.13-pm.png
click image to enlarge

-----Lung Unit S -------------- Lung Unit T
A) PhyD < AnatD ---------- PhyD = AnatD
B) PhyD = AlveolarD ----- PhyD > AlveolarD
C) PhyD = AnatD ----------- PhyD < AnatD
D) PhyD = AnatD ----------- PhyD > AnatD
E) PhyD > AnatD ----------- PhyD < AnatD
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Old 06-28-2011
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the ans is D)
we know that physiologic dead space =anatomic dead space +alveolar dead space....
due to decreased blood fow alveoli T has alveolar dead space more.
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Old 06-28-2011
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Originally Posted by bebix View Post
The diagram below shows two lung units (S & T) with their blood supplies. Lung unit S has an ideal relationship between blood flow and ventilation. Lung unit T has a compromised blood flow. What is the relationship between alveolar dead space (AlveolarD), physiologic dead space (PhyD) and anatomic dead space (AnatD) for these lung units?

Attachment 1629
click image to enlarge

-----Lung Unit S -------------- Lung Unit T
A) PhyD < AnatD ---------- PhyD = AnatD
B) PhyD = AlveolarD ----- PhyD > AlveolarD
C) PhyD = AnatD ----------- PhyD < AnatD
D) PhyD = AnatD ----------- PhyD > AnatD
E) PhyD > AnatD ----------- PhyD < AnatD
Not sure b/w C and D.
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Star I guess

D) PhyD = AnatD ----------- PhyD > AnatD
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Old 06-28-2011
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Default D.

in optimal conditions (no V/Q mismatch) anatomic dead space = phys dead space and thats as high as it can get so its IMPOSSIBLE for anaDS to become more than physDS
so answer is D
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Old 06-29-2011
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Default D

the ans is D
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Correct Answer correct answer

correct answer is D) PhyD = AnatD ----------- PhyD > AnatD

The anatomic dead space (AnatD) is the air that a person breathes in that fills the respiratory passage-ways but never reaches the alveoli. Alveolar dead space (AlveolarD) is the air in the alveoli that are ventilated but not perfused. Physiologic dead space (PhyD) is the sum of AnatD + AlveolarD. AlveolarD is zero in lung unit S (the ideal lung unit), so AnatD and PhyD are equal. In the lung unit T (poor blood supply) the AlveolarD is substantial. Thus, PhyD is greater then either AnatD or AlveolarD.
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bebix, can u tell me y in lung s the alveolar dead space is 0? i dun get that.
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Originally Posted by star123 View Post
bebix, can u tell me y in lung s the alveolar dead space is 0? i dun get that.

Alveolar dead space is caused by air contacting alveoli without bloodflow in their adjacent pulmonary capillaries, i.e. ventilation without perfusion. As a result, no gas exchange can occur.

In this case, lung unit S is just an "ideal lung unit"....then, alveolar dead space = 0...

Just remember, alveolar dead space is negligible in healthy individuals, but can increase dramatically in some lung diseases.
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Originally Posted by bebix View Post
Alveolar dead space is caused by air contacting alveoli without bloodflow in their adjacent pulmonary capillaries, i.e. ventilation without perfusion. As a result, no gas exchange can occur.

In this case, lung unit S is just an "ideal lung unit"....then, alveolar dead space = 0...

Just remember, alveolar dead space is negligible in healthy individuals, but can increase dramatically in some lung diseases.
thank u so much! i get it now
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Quote:
Originally Posted by bebix View Post
The diagram below shows two lung units (S & T) with their blood supplies. Lung unit S has an ideal relationship between blood flow and ventilation. Lung unit T has a compromised blood flow. What is the relationship between alveolar dead space (AlveolarD), physiologic dead space (PhyD) and anatomic dead space (AnatD) for these lung units?

Attachment 1629
click image to enlarge

-----Lung Unit S -------------- Lung Unit T
A) PhyD < AnatD ---------- PhyD = AnatD
B) PhyD = AlveolarD ----- PhyD > AlveolarD
C) PhyD = AnatD ----------- PhyD < AnatD
D) PhyD = AnatD ----------- PhyD > AnatD
E) PhyD > AnatD ----------- PhyD < AnatD

Answer is D.. because normally Both physiologic and anatomic Dead space are equal..
in case of decreased perfusion..it will lead to increased physiologic dead space (which the sum of alveolar and anatomic dead space)..
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