pulmonary circulation

Question 1

What are the blood supplies to the lungs?

2

Answer 1

1. Bronchial
2. Pulmonary

Question 2

What is bronchial circulation?

Answer 2

• from thoracic aorta; systemic circulation
• supplies oxygenated blood to smooth muscle in lungs
• drains into pulmonary vein and enters LEFT ATRIUM

two consequences:
- pulmonary venous return > CO
- gas exhange never perfect

Question 3

What is pulmonary circulation?

Answer 3

• low pressure system
• low resistance
• same CO as systemic
• RV output is 4-6 l/min at rest and 25 l/min in exercise

Question 4

What are the pressure values in pulmonary circulation

Answer 4

• Right ventricular pressure: 25/0 mmHg
• Pulmonary artery pressure: 25/10* mmHg (about 1/5 systemic circulation)
• Pulmonary Pulse pressure: 15 mmHg (systolic - diastolic)
• Mean Pulmonary pressure: 15 mmHg (diastolic + 1/3 pulse pressure)
• Pulmonary capillary pressure: ~6 mmHg (range 6-10 mmHg)
• Left atrial pressure (LAP): ~2 mmHg (range 2-6 mmHg)

PA pressure falls more slowly than RV pressure after systole

Question 5

What are the pressure differences between pulmonary and systemic circulation?

Answer 5

Pulmonary
- 25/8mmHg
- mean: 15
- RV: 25/0
- RA:2

Systemic:
- 120/80mmHg
- mean: 100
- LV: 120/0
- LA: 5

Question 6

How is pulmonary pressure measured?

Answer 6

• Capillary wedge pressure
• catheter insterted into peripheral vein to right side of heart
• wedges at pulmonary capillaries
• used to estimate LA pressure
• usually 5mmHg, 2-3mmHg greater than LA pressure

Question 7

How does resistance change at different places of the lungs?

Answer 7

When lung volume increases:
- extra-alveolar vessels have low resistance
- alveolar capillaries have high resistance

Question 8

What is the effect of gravity on flow?

Answer 8

• zone 1 (apex): no blood flow if alveolar pressure > arterial pressure > venous pressure
• zone 2: intermittent blood flow if arterial pressure > alveolar pressure > venous pressure
• zone 3 (base): continuous blood flow if Pa > Pv > PA

hydrostatic pressure increases with gravity, but PA decreases, 1-2-3

Question 9

What is the flow equation?

Answer 9

• Q = P/R
• Flow = change in Pressure/Resistance

systemic: Pa - Pv, pulmonary zone 2: Pa - PA, Q is also CO

Question 10

Why can blood volume increase without pressure change?

Answer 10

• capillary recruitment
• distension

Question 11

How is pulmonary resistance controlled?

Answer 11

• recruitment + distension
• low neural/hormonal influence
• Oxygen is main factor

Question 12

What is Hypoxic Pulmonary Constriction?

Answer 12

• pulmonary arteries constrict to hypoxia
• controls capillary perfusion, shunting blood away from poorly ventilated areas

Question 13

What causes HPC?

Answer 13

• COPD
• high altitude

can lead to pulmonary hypertension, oedema and sometimes even right HF

Question 14

What is pulmonary oedema?

Answer 14

• filling of pulmonary interstitium and alveoli with fluid

Question 15

What causes pulmonary oedema?

Answer 15

• An imbalance of the Starling forces
• high hydrostatic pressure in capillary (left HF, high altitude)
• low colloid osmotic pressure in capillary (leaky capillaries in pneumonia)

low oncotic pressure means less fluid is held in capillary