11 V/Q

Question 1

At rest, what is V/Q?

Answer 1

0.8

Question 2

What happens to the P(O2) A-a difference with age?

Answer 2

it increases

Question 3

What are right-left shunts?

Answer 3

blood that has somehow by-passed oxygenation

Question 4

What is water perfusion?

Answer 4

V/Q mismatch

adding venous blood that hasn’t been oxygenation to arterial oxygenated blood

Question 5

Name two examples of natural R-L shunts

Answer 5

thesbian veins

bronchial circulation

Question 6

What 2 things might cause pathological shunts?

Answer 6

Pulmonary disease

Cardiovascular anatomical abnormalities

Question 7

What kind of shunt is produced by atrial / ventricular septal defects?

Answer 7

Left-Right

Question 8

What2 things dictate the distribution of pleural pressure through the lung?

Answer 8

compliance and gravity

Question 9

Which parts of the lung will have the less and most negative pleural pressure, why?

Answer 9

the apex has a greater retraction and has a more negative pleural pressure, the base has less retraction, there is more weight on top of the base of the lung

Question 10

What does the difference in pleural pressures around the lung mean in terms of ventilation?

Answer 10

There is more ventilation around the base of the lung, because the pleural pressure of the lung is on a very steep part of the compliance curve with a less negative pleural pressure, therefore for any given decrease in pleural pressure there will be a greater increase in volume

Question 11

How much more air does the base receive than the apex?

Answer 11

2.5x

Question 12

Where is the lung is there more perfusion, and by how much?

Why?

Answer 12

the base of the lung, by 6x more than the apex

gravity

Question 13

Across the lung (from left to right), what happens to blood flow pressure?

Answer 13

It decreases

Question 14

What is zone 2?

Answer 14

the area above the tricuspid valve where arterial pressure falls, alveolar pressure remains the same, and venous pressure falls (as a consequence of the arterial pressure falling)

Question 15

What is the driving force in zone2?

Answer 15

alveolar arterial difference, rather than the arterial-venous difference

Question 16

At which point will there be no blood flow?

Answer 16

when the alveolar-arterial difference is zero

Question 17

What is the rise in blood flow in zones 2 and 3 down to?

Answer 17

2 - recruitment

3 - distension

Question 18

What is the V/Q at different point in the lung?

Answer 18

> 1 at the apex

<1 at the base, because the base receives 6x more Q and 2.5 more V than the apex

Question 19

What does a V/Q of 0 mean?

Answer 19

no ventilation, but still perfusion

Question 20

Where would there be an infinite V/Q?

Answer 20

alveolar dead space

Question 21

Relatively how much O2 and CO2 will there be in the blood in a V/Q above 0.8?

Answer 21

higher in O2 and lower in CO2 than normal

Question 22

What are the 2 mechanisms for controlling V/Q?

Answer 22

alter bronchial tone to alter V

Alter arterial tone to alter Q

Question 23

In high V/Q, what will the regional P(A) effect be, and what will be the reflex response?

Answer 23

Hyeropxia, hypocapnia

vasodilation, bronchoconstriction

Question 24

In low V/Q, what will the regional P(A) effect be, and what will be the reflex response?

Answer 24

hypoxia, hypercapnia

vasoconstriction, bronchodilation

Question 25

How does hypoxia stimulate vasoconstriction?

Answer 25

hypoxia inhibits K+ efflux, depolarising the membrane, stimulating Ca2+ VGC’s

Question 26

What 3 things will increase the O2 A-a difference?

Answer 26

excessive V/Q inequality
increased a-v shunting
impaired diffusion

Question 27

How would you calculate a normal A-a diffreence?

Answer 27

age x 0.03 + 0.3