Pulmonary Vascular Physiology

Question 1

What are the two types of circulation?

Answer 1

Pulmonary Circulation
From Right Ventricle
100% of blood flow

Bronchial Circulation
2% of Left Ventricular Output

Question 2

What percentage of cardiac output does the pulmonary circulation receive?

Answer 2

Receives 100% of cardiac output (4.5-8L/min.)

Question 3

What is the red cell transit time in pulmonary circulation?

Answer 3

Red cell transit time ≈ 5 seconds.

Question 4

What is the surface area for gas exchange in pulmonary circulation?

Answer 4

50 – 100 m2

Question 5

What is Pouiseuille’s Law?

Answer 5

Resistance = (8 x L x viscosity)
(π r4)

Question 6

What is Ohm’s Law?

Answer 6

Voltage across circuit = Current x Resistance
V = IR

Question 7

What is the equation for pressure across circuit?

Answer 7

V = I R
Pressure across circuit = Cardiac Output x Resistance

Pressure across pulmonary circulation =
mPAP – Left Atrial Pressure x Pulmonary Vascular Resistance

mPAP (mean pulmonary arterial pressure),
PAWP (pulmonary arterial wedge pressure left atrial pressure),
CO (cardiac output), PVR (pulmonary vascular resistance)

Question 8

What is Type 1 respiratory failure?

Answer 8

pO2 < 8 kPA
pCO2 <6 kPA

Question 9

What is Type 2 respiratory failure?

Answer 9

pO2 < 8 kPA
pCO2 >6 kPA

Question 10

What are causes of Hypoxaemia?

Answer 10

Hypoventilation
Diffusion Impairment
Shunting
V/Q mismatch

Question 11

What is Hypoventilation?

Answer 11

Type II Respiratory Failure
pO2 < 8 kPA
pCO2 >6 kPA

Failure to ventilate the alveoli
- Muscular weakness
- Obesity
- Loss of respiratory drive

Question 12

What can cause Shunting?

Answer 12

Physiological
- Bronchial Arteries
- Thesebian veins

Intracardiac
- Eg VSD - R-L Shunt (Eisenmenger’s Syndrome)

Pulmonary
- ArterioVenous Malformation (AVM)
- Complete Lobar Collapse

Question 13

What is Eisenmengers syndrome?

Answer 13

Irregular blood flow in the heart and lungs.
This causes the blood vessels in the lungs to become stiff and narrow.

Question 14

What are symptoms of Eisemenger’s syndrome?

Answer 14

Cyanosis - not enough oxygen in blood
Clubbing - changes in the areas under and around the toenails and fingernails that occur with some disorders
Polycythaemia - too many red blood cells

Question 15

What is hypoxic pulmonary vasoconstriction?

Answer 15

• Poorly understood
• Local action of hypoxia on pulmonary artery wall
• Weak response as little muscle
• Aims to improve V/Q matching
  Local hypoxia (eg peanut)
  Generalised hypoxia (eg altitude)

Question 16

How does pulmonary embolism affect V/Q ratio?

Answer 16

• ## Clot occludes the pulmonary capillary or artery

Question 16

How does pulmonary embolism affect V/Q ratio?

Answer 16

• Clot occludes the pulmonary capillary or artery
• Reduced perfusion
• V/Q ratio is increased

Question 17

What is absolute physiological shunt?

Answer 17

Perfusion but no ventilation
V/Q ratio is 0

Question 18

What is absolute physiological deadspace?

Answer 18

• When perfusion to an area of the lungs is 0
• Gas enters alveoli but does not take part in gas exchange
• Trachea is dead space as air flow through but trachea doesn’t participate in gas exchange

Question 19

How does pulmonary oedema affect V/Q ratio?

Answer 19

• Fluid overload in lungs
• Reduced Ventilation
• V/Q ratio is decreased

Question 20

What is Pulmonary AVMs?

Answer 20

Structurally abnormal vascular communications that provide a continuous right-to-left shunt between pulmonary arteries and veins

Question 21

How does pneumonia affect V/Q ratio?

Answer 21

• Have consolidation
• Decrease in ventilation
• V/Q ratio is low

Question 22

Is Pulmonary circulation a high or low pressure system?

Answer 22

Low

Question 23

Is Systemic circulation a high or low pressure system?

Answer 23

High

Question 24

What 3 factors can lead to Thrombosis?

Answer 24

Circulatory Stasis
Endothelial Injury
Hypercoagulable State