V/q Ratio

Front 1

What is the V/Q ratio?

Back 1

It is the ratio between the amount of air getting to the alveoli.
(the alveolar ventilation, V, in ml/min and the amount of blood being sent to the lungs(the cardiac outputor O- also in ml/min.

Front 2

How do you calculate the V/Q ratio?

Back 2

V/Q= alveolar ventilation/cardiac output
V/Q =(4l/min)/(5l/min)
V/Q= 0.8

Front 3

The V/Q ratio is the balance between the ventilation(bringing O2 into/removing CO2 from the alveoli) and the perfusion(removing O2 from the alveoli and adding CO2). True/False

Back 3

True. The V/Q ratio is important because the ratio between the ventilation and perfusion is a major factor affecting the alveolar(and arterial) levels of O2 and CO2.

Front 4

What exactly does the 0.8 calculated ratio represent?

Back 4

4 liters of ventilation each minute enter the respiratory tract while 5 liters of blood go through the pulmonary capillaries.

Variable Normal Value
PAO2 100mm/Hg
PACO2 40mm/Hg

Front 5

What are the 2 ways that one can change the V/Q ratio?

Back 5

One can change the ventilation and/or the perfusion.

Front 6

A decrease in the V/Q ratio is produced how?

Back 6

This is done by either decreasing ventilation or increasing blood flow(other variable is not altered).
These will have the same effect; the alveolar(and arterial) levels of O2 will diminish and the CO2 will increase.

Front 7

A decrease in ventilation, without a change in perfusion, means what?

Back 7

This means that we are not bringing in enough O2 to meet our metabolic need for O2(O2 consumption) as well as not blowing enough CO2 to get rid of the CO2 we produced.

Front 8

Regarding decreasing V/Q ratio; is it true that an increase in perfusion will have the same effect on the blood gases?

Back 8

Yes. This is because an increase in perfusion(without a change in ventilation), means more RBCs are coming to remove O2 from the alveolus as they deliver more CO2 than will be exhaled.

Front 9

What are the three most important concepts to remember regarding a decrease in the V/Q ratio?

Back 9

1. Ventilation is not keeping pace with perfusion.
2.The alveolar O2 levels will decrease, which will lead to a decrease in arterial O2 levels(PAO2)
3. The alveolar CO2 levels will increase(not getting rid of it as fast), also resulting in an increase in arterial CO2.

Front 10

What are the two things one can do to produce an increase in the V/Q ratio?

Back 10

1. Increase ventilation(bring in more O2 to the alveoli, blow off more CO2 from the lungs)
2. Diminish the perfusion(so the blood takes away less O2, delivers less CO2).

Front 11

Everytime one stands up, the blood flow to the different parts of the lung(apex vs base) changes due to gravity. True/False

Back 11

True. This creates a V/Q mismatch and changes the blood gas values of the arterialized blood leaving each region of the lungs.

Front 12

In standing up, where does most of the blood go to?

Back 12

More blood goes to the base of the lung, while less air gets there. We see a low V/Q ratio and low PAO2. Blood leaving the base of the lungs is estimated to have a PAO2 of 89mm/Hg and a PACO2 of 42mm/Hg.

Front 13

At the apex of the lung, we get relatively less blood. True/false

Back 13

True. Gravity pulls it down, and relatively high ventilation, so we have a high V/Q ratio. This leads to an increase in alveolar and arterial O2 levels while decreasing the CO2. The blood leaving the apex of each lung in a standing person is estimated to have a PAO2 of 130mm/Hg and a PACO2 of 28mm/Hg.

Front 14

What can be said regarding the middle regions of the lungs?

Back 14

This region has a good match of blood to ventilation. The arterial blood leaving this area of the lungs is generally believed to have our standard blood gas values: PAO2=100mm/Hg, and PACO2= 40mm/Hg.

Front 15

In a patient, regions of zero blood flow will result from a pulmonary embolism that obstructs blood flow. True/false

Back 15

True. Assuming little blood can get through, this blood will be very well oxygenated(lots of ventilation, and little perfusion and have a very low CO2.

Front 16

In the above example, what will be the arterial blood gas levels?

Back 16

They will approach(but not become atmospheric)(PAO2=140mm?hg, PACO2=0mm/Hg.
Not much blood gets through to these alveoli, so the volume of blood in this condition is very low.
% liters of blood is still coming to the lungs every minute , the blood that can't get to the area of lung affected by the embolism gets shunted to other parts of the lung(leading to a low V/Q ratio in those parts of the lung.

Front 17

Regarding the decreasing of the V/Q ratio, what is the easiest way to produce a V/Q ratio of zero?

Back 17

One would need to stop ventilation to a part of the lung(inhaling an object). This will produce a V/Qatio of zero and lead to blood being sent to alveoli that don't have fresh air coming to them.

Front 18

Regarding the above answer, is it correct to say that the arterial blood will leave the alveolus looking exactly like it did when it was at the venous end.

Back 18

Yes. Our arterial blood gases will be the same as our venous blood(PAO2= 40mm/Hg, PACO2= 45mm/Hg).

Front 19

What is a physiological shunt?

Back 19

In the above example, we wasted cardiac effort to send the blood to the lungs even though nothing happened to it as far as O2 and CO2 go. This is a physiological shunt, although the blood traveled to the lungs, it did not get any O2.

Front 20

What is an anatomical shunt?

Back 20

This is when the blood physically doesn't enter the lungs(right to left shunt)- the blood jumps straight from the right ventricle to the left ventricle bypassing the lungs. The end result is the same, some of the arterial blood has very low O2 and high CO2.

Front 21

Many lung diseases produce changes in the V/Q ratio that aare not consistent throughout the lung. True/false

Back 21

True. COPD and Emphysema are 2 examples.

Front 22

Describe COPD/Emphysema V/Q ratio changes.

Back 22

This disease causes the destruction of the alveoli, leading to the creation of large air spaces and loss of capillaries in the lungs.
The large air spaces means that some of the inhaled air gets no where close to a blood cell, while the loss of capillaries means that some areas of the lung are not getting much blood, while others are getting too much.

Front 23

Regarding the above example, what effect does this have on the V/Q ratio?

Back 23

Some areas of the lung have a high V/Q ratio(good arterial blood gases, but,too little blood going there to make a real difference), and others have a low V/Q ratio(lots of blood going there, but the arterial blood has low O2 and high CO2.

Front 24

What is hypoxic vasoconstriction?

Back 24

In cases where the V/Q ratio is low(lots of blood or too little ventilation). This can occur and cause the blood coming into the area to be directed to other parts of the lung.

Front 25

Decreasing the perfusion of the hypoxic region, will do what?

Back 25

This will raise the V/Q ratio and bring the arterial blood gases closer to what we expect.

Front 26

Describe bronchoconstriction and V/Q ratio.

Back 26

In cases of high V/Q ratio, the bronchi will constrict slightly to increase the resistance and decrease the amount of ventilation coming into an area that is not well perfused.
This limits the amount of alveolar dead space that occurs and minimizes the wasted work that occurs with alveolar dead space.