Ventilation and perfusion Matching

Question 1

What is ventilation?

Answer 1

The change in volume through the respiratory cycle

Question 2

How is gas distributed in the lung and why?

Answer 2

• More gas goes to the base of the lung than the apex.
• Lower ribs are more curved and mobile than upper, the action of the diaphragm expands the lower lobes more than the upper, partly because upper lobes are attached to main bronchi and upper airways, so less easily stretched than tissue of lower lobes, and compliance alters across lung

Question 3

What lobes have greater compliance?

Answer 3

The lower lobes

Question 4

What vein does the conducting portion of the bronchial arteries join?

Answer 4

The pulmonary vein (diluting it and making it slightly deoxygenated)

Question 5

What do the bronchial arteries supply specifically?

Answer 5

• Lung parenchyma
• Airway smooth muscle
• Pulmonary arteries and veins
• Pleura

Question 6

What is the volume of blood in the pulmoanry network at rest?

Answer 6

100 ml

Question 7

What is the stroke volume of the heart?

Answer 7

70 ml

Question 8

What is the mean pressure within the pulmonary circulation?

Answer 8

15 mmHg - only needs to be sufficient enough to lift blood to apex

Question 9

What is the transmural pressure? @@@@@@@

Answer 9

The balance between alveolar pressure and blood pressure (blood flow in lungs is dependant on @@@@ @@@@ @@@@ @@@@ @@@ @@

Question 10

When will blood flow in the lungs?

Answer 10

Only if blood pressure is greater than alveolar pressure

Question 11

What is the differnce in hydrostatic pressure between the base and apex of te lung?

Answer 11

23 mmHg

Question 12

What is zone 1?

Answer 12

Apex of lungs if capillaries are closed then they are ventilated but not perfused and are therefore considered alveolar dead space.
Healthy individuals no zone 1

Question 13

What is zone 2

Answer 13

Alveolar pressure is lower than systolic arterial pressure but may be higher than diastolic arterial presure and venous pressure. Flow is determined by arterial-alveolar pressure difference

Question 14

What is zone 3

Answer 14

Alveolar pressure is lower than both arterial pressure and venous pressure - the capillaries are distended as a consequence of the transmural pressure and there is continous flow

Question 15

What is the V/Q ratio for the overall lun?

Answer 15

0.85 (perfect match would be 1)

Question 16

What is the V/Q at the base?

Answer 16

0.6 there is good perfusion and ventilation

Question 17

Where is the V/Q 1?

Answer 17

About 2/3 up the lung (rib 3)

Question 18

What is the V/Q at the apex?

Answer 18

3

Question 19

What improves more rapidly as you move down the lung blood flow or ventilation?

Answer 19

Blood flow

Question 20

What is the O2 content like at well ventilated areas of the lung

Answer 20

Normal

- Poorly ventilated areas have low O2 content

Question 21

Where in the lung is CO2 accumulated more?

Answer 21

Base of the lung because ventilation is low (V/Q low), CO2 not taken away as rapidly and a higher steady state of cO2 occurs

Question 22

Where is the lowest steady state PO2 ?

Answer 22

At the base of the lung as low V/Q therefore O2 taken up by blood is not fully replenished by new air

Question 23

How is blood diverted away from poorly ventilated areas?

Answer 23

Hypoxic vasoconstriction intrinsic effect (active control of blood flow)

Question 24

When is the hypoxic effect important?

Answer 24

At birth,

- When born, before 1st breath, lungs vasoconstricted and resistance is high