Ventilation/Perfusion relationship

Question 1

What is ventilation?

Answer 1

The provision of gas to an area

Question 2

What is perfusion?

Answer 2

The provision of blood to an area/ flow of blood to alveolar capillaries

Question 3

What is the ‘ideal’ ratio of ventilation and perfusion?

Answer 3

1:1 ratio

Question 4

What is the typical VQ ratio and why can we get away with it?

Answer 4

0.8:1 , but we can get away with it because we have functional reserves

Question 5

Is there more gas or blood at the base of the heart?

Answer 5

More gas, so Q is higher

Question 6

Is there more gas or blood at the apex of the heart?

Answer 6

More blood, so V is higher

Question 7

What can disruption of the V/Q ratio lead to?

Answer 7

clinical hypoxia

Question 8

What determines the partial pressure of oxygen?

Answer 8

the amount of oxygen entering the alveoli and the amount of oxygen being removed by capillary blood flow

Question 9

What determines the partial pressure of carbon dioxide?

Answer 9

The amount of co2 that diffuses into the alveoli from the capillary blood and the amount of carbon dioxide being removed from the alveoli through alveolar ventilation

Question 10

What is the effect of increasing/ decreasing ventilation on the partial pressure of oxygen?

Answer 10

As ventilation increases, more oxygen enters the alveolus therefore the ppO2 increases (and vice versa)

Question 11

What is the effect of increasing/decreasing perfusion on the ppO2?

Answer 11

As perfusion increases, more oxygen is removed from the blood, therefore the ppO2 decreases and vice versa

Question 12

What is the effect of increasing/ decreasing ventilation on PaCo2?

Answer 12

As ventilation increases, more Co2 is removed from the blood therefore ppCO2 decreases and vice versa

Question 13

What is the effect of increasing/decreasing perfusion on PaCo2?

Answer 13

Increasing perfusion brings more Co2 carrying blood back for elimination therefore the PaCo2 increases and vice vers a

Question 14

What is the consequence of the V/Q ratio increasing?

Answer 14

Overventilation or underperfusion

Question 15

What is underperfusion?

Answer 15

Ventilating dead space

Question 16

What is the consequence of V/Q decreasing?

Answer 16

Underventilation (shunting blood away) or over perfusion

Question 17

What is V(d) dead space ventilation?

Answer 17

The volume of blood that is ventilated but not exchanged with pulmonary capillary blood

Question 18

What occurs to the deoxygenated blood when VQ is too low?

Answer 18

deoxygenated blood flows to the left side of the heart and is then circulated meaning the patient will be hypoxemic,

Question 19

What is true shunting?

Answer 19

Blood enters left circulation without an increase in oxygen concentration as the blood has not had a chance to gas exchange with functional alveoli

Question 20

What is Hypoxic pulmonary vasoconstriction?

Answer 20

A physiological reflex when the pulmonary arteries constrict in the presence of hypoxia

Question 21

Why do pulmonary arteries constrict during hypoxia?

Answer 21

So they can direct blood to the parts of the lung with more oxygen

Question 22

Why do arteries in systemic circulation dilate during hypoxia?

Answer 22

So they can allow for increased blood flow

Question 23

What is the end aim for HPV (hypoxic pulmonary vasoconstriction?)

Answer 23

Normalise the VQ ratio by redistributing blood from poorly to well ventilated areas

Question 24

What causes the patient to be hypoxaemic?

Answer 24

Shunting, which occurs when the V/Q ratio is too low
deoxygenated blood is circulated around the body

Question 25

What occurs to the alveoli when there is no ventilation at all (also known as the true shunt)

Answer 25

alveolar collapse

Question 26

What are the two different types of shunting?

Answer 26

capillary and anatomic