التهوية - التروية Ventilation-Perfusion

Which would make your V/Q ratio closet to 1 ?
1- sleep
2- meditation
3- snoring
4- pulmonary emboli
5- slow walking

I'm sorry...
just forget that question!!

When the ventilation/perfusion ratio of a lung unit increases:

a) the alveolar PO2 rises
b) the alveolar CO2 rises
c) end capillary PO2 increases
d) arterial PO2 increases
e) hypoxic pulmonary vasoconstriction will compensate for any change in gas exchange

Question-1 (plz overlook it!)

Question-2 (just above this one)

Questions-3 & 4:

3- A 55-year-old man has a pulmonary embolism (PE) that partially blocks the blood flow to his to his right lung.
Which point on the ventilation-perfusion line of the O₂-CO₂ diagram above corresponds to the alveolar gas in his right lung?

A
B
C
D
E

- - - - - - - - -

4- A 67-year-old man has a solid tumor that pushes against an airway, partially obstructing airflow to the distal alveoli.
Which point on the ventilation-perfusion line of the O₂-CO₂ diagram above corresponds to the alveolar gas in these distal alveoli?

A
B
C
D
E

3 Qs waitin' for asnwers

I'm sorry, ur answer for Q-2 is incorrect..
Your answers for Qs 3 & 4 are, however, close.. but not quite the correct answers..

try again..

Alright...
Thank you freezoom for your answers.. n' since there's nobody else answerin', I'll just post the answers n' explanations:

Q-3: Answer: D
Explanation:
A pulmonary embolism decreases blood flow to the affected lung, causing ventilation to exceed blood flow. An increase in V/Q caused by the partially obstructed blood flow in this problem causes the alveolar PO₂ and PCO₂ to approach the values achieved when V/Q = ∞. When an embolism completely blocks all blood flow to an area of the lung, the gas composition of the inspired air entering the alveoli equilibrates with the blood trapped in the alveolar capillaries, so that within a short time, the gas composition of the alveolar air is identical to that of inspired air. This situation, in which V/Q is equal to infinity, corresponds to point E on the diagram (inspired gas).

Q-4: Answer: B
Explanation:
A reduction in V/Q (caused by the partially obstructed airway in this problem) causes the alveolar PO₂ and PCO₂ to approach the values achieved when V/Q=0. When the ventilation is reduced to zero (V/Q=0), alveolar air equilibrates with the mixed venous blood entering the lung, which causes the gas composition of the alveolar air to become identical to that of that of the blood. This occurs at point A on the diagram, where the alveolar PO₂ is 40 mmHg and the alveolar PCO₂ is 45 mmHg.

Q-2: Answer: D
But I'm sorry, I got this Q from a different source than the other two.. n' they're not offerin' any explanations!

thanks knighty0
??????????but did u understand Ans for the 2nd Q

Good question!
I'll just talk about what I think of this question:
When the ventilation-perfusion increases, that suggests that the ventilation is greater than the perfusion (and possibly increasingly greater). Keep in mind that the normal V/Q ratio is 0.8, so ideally that ventilation has to be slightly less than the perfusion..

When we have ventilation of a part of the lung that's receiving less blood, it seem that additional oxygen-carrying air is reaching the alveoli, but that oxygen is not ripped off that air sufficiently because there's no enough blood to carry it.. so "logically" we'd have a decreased partial pressure of oxygen in the arterial blood.. (therefore, decreased end capillary PO2, so choice c is not likely to be the correct answer) because the alviolar capillary blood is not oxygenated enough as it would be when the V/Q ratio is 0.8.. so I still don't understand why the answer is d !

On the other hand, and since not much blood is reaching the alveoli (compared to amount of alviolar ventilation) then there would be less carbon dioxide "throwing" out of the venous blood, so we're not getting rid of enough carbon dioxide from the venous blood, so it won't be increased in the alviolar air, so choice b is not likely to be the correct answer..

However, and as we mentioned, we have increased alviolar oxygen-carrying air & decreased alviolar blood flow so the partial pressure of oxygen in the alviolar air (choice a) would not decrease (as it would normally) due to not much gas exchange taking place, so the alviolar PO2 would increase compared to normal states, if that's what they meant by "alviolar PO2 rises". However, if they meant that the alviolar PO2 rises (meaning it gains more oxygen when it gets to the alvioli) the that's of course incorrect..

And as for the last choice, e, I'm not totally sure, but I think that pulmonary vasoconstriction only occurs in the case of hypoxia (decreased partial pressure of oxygen in the arterial blood). Hypocapnia, however, which is the decreased arterial carbon dioxide (usually occurs in the case of hyperventilation) inhibits this vasoconstriction, since it's vitally important to have a good blood flow to well-ventilated alvioli to get rid of the carbon dioxide present in the arterial blood, so I don't think that e is the answer either..

Tricky question, I know!.
If I had faced this question in an exam, my answer would be a, although not totally sure about it.