3. Ventilation : Perfusion Relationship

Question 1

What is ventilation linked with ?

Answer 1

Perfusion (local blood flow L/min)

Question 2

What is distribution of blood flow in the lung influenced by ?

Answer 2

Hydrostatic pressure and alveolar pressure

Question 3

What decreases with height across the lung ?

Answer 3

Both blood flow and ventilation

Question 4

Why is blood flow at the base of the lungs higher than ventilation ?

Answer 4

Arterial pressure exceeds alveolar pressure and vascular resistance, this compresses alveoli

Question 5

Why is blood flow at the apex of the lungs low ?

Answer 5

Arterial pressure is less than alveolar pressure, this compresses the arterioles and vascular resistance is increased

Question 6

Both ventilation and perfusion are greater where ?

Answer 6

At the base of the lung than the apex, but blood flow exceeds ventilation at base and ventilation exceeds ventilation at apex

Question 7

Where is there a ventilation-perfusion mismatch ?

Answer 7

At the base of the lung and the apex of the lung

Question 8

Where are ventilation and perfusion precisely matched ?

Answer 8

At rib 3

Question 9

Where is the biggest V/Q mismatch ?

Answer 9

ApexOver 75% of the height the healthy lung performs quite well in matching blood and air

Question 10

What is the optimal condition for ventilation ?

Answer 10

Ventilation = perfusionRatio = 1

Question 11

What is mismatch 1 (base) ?

Answer 11

Where ventilation < perfusionratio < 1 (Under oxygenated blood

Question 12

What is mismatch 2 (apex) ?

Answer 12

Ventilation > perfusionratio >1( can happen with too much breathing taking place compared to the rate of blood flow)

Question 13

What happens if ventilation decreases in a group of alveoli ?

Answer 13

PCO2 increases and PO2 decreases. Blood flowing past those alveoli does not get oxygenated

Question 14

How does blood get oxygenated when ventilation is decreased ?

Answer 14

Oxygenated blood is ‘shunted’ from better ventilated areas to dilute blood

Question 15

What does shunt mean ?

Answer 15

Passage of blood through areas of the lung that are poorly ventilated (Ventilation

Question 16

What happens when perfusion > ventilation ?

Answer 16

alveolar PO2 falls—> pulmonary vasoconstriction Alveolar PCO2 rises—> bronchial dilation

Question 17

What does decreased PO2 around under ventilated alveoli cause?

Answer 17

Constricts their arterioles, diverting their blood to better ventilated alveoliConstriction in response to hypoxia is is particular to pulmonary vessels (systemic vessels dilate)

Question 18

What does increased PCO2 cause?

Answer 18

Mild bronchodilation

Question 19

What is alveolar dead space ?

Answer 19

Alveoli that are ventilated but not perfused More air in alveoli than blood flow, so there is air not participating in gas exchange

Question 20

What happens when ventilation > perfusion ?

Answer 20

Alveolar PO2 rises—> pulmonary vasodilationAlveolar PCO2 falls—> bronchial constriction

Question 21

What is the opposite of shunt ?

Answer 21

Alveolar dead space

Question 22

What is physiological dead space ?

Answer 22

Alveolar DS + anatomical DS

Question 23

What is Respiratory sinus arrhythmia ?

Answer 23

Normal change in heart rate during the breathing cycle