8. Pulmonary circulation and V/Q

Question 1

Passive effect of lung volume on arteries and arterioles

Answer 1

1) Increased lung volume
2) Reduces resistance
3) Interdependence

Question 2

Passive effect of lung volume on capillaries

Answer 2

1) Increased lung volume
2) Increases resistance of capillaries
3) Reduced radius

Question 3

Where is blood flow lowest in the lungs?

Answer 3

Apical capillaries

Question 4

Where is blood flow greatest in the lungs?

Answer 4

at bottom of lung

Question 5

Where is pulmonary arterial blood pressure lowest?

Answer 5

at the top of the lung

Question 6

Where is pulmonary arterial blood pressure highest?

Answer 6

at the bottom of the lung

Question 7

Is Alveolar pressure the same throughout the full height of the lung?

Answer 7

YES

Question 8

Flow zone 1

Answer 8

Top of lung; arterial pressure (Pa) is below alveolar pressure

Pv (pulmonary venous pressure) is below arterial

Intra-alveolar (intrapulmonary) pressure zero

pressure is higher in the alveoli than in the capillaries

this will collapse the capillaries; no flow will occur

ventilated but not perfused

Question 9

Flow zone 2

Answer 9

Middle of the lung; arterial pressure (Pa) is getting higher due the hydrostatic effect of the height of the lung

Pv is still below alveolar pressure

Intra-alveolar (intrapulmonary) pressure still zero

flow will occur in the first half of the capillary

arterial pressure is higher than alveolar pressure

As Pa falls, pressure will eventually fall lower than alveolar pressure

capillary will collapse nearer the venous end

some blood flow will occur but will cease at the venous end

Question 10

Flow zone 3

Answer 10

Bottom of the lung: arterial pressure (Pa) is highest due to the effect of gravity increasing hydrostatic pressure below the heart

Venous pressure Pv is also higher than alveolar pressure

thus flow will occur over the full length of the capillary

Question 11

Zone 1 conditions only seen in

Answer 11

1) Disease
2) Haemorrhage
3) Positive pressure ventilation

Question 12

What condition does most of the lung work under?

Answer 12

Zone 3

Question 13

Active control of pulmonary vascular resistance:

Hypoxic pulmonary vasoconstriction

Answer 13

Low PO2 of ALVEOLAR gas
Constriction of pulmonary arterioles
Possible local release of vasoconstrictor agents (Thromboxane A2?)
Diverts blood to better ventilated areas