Lecture 12: Perfusion of the lung

Question 1

Where is perfusion greatest in the lung?

Answer 1

Perfusion is greatest at the base of the lung

Question 2

What is the average pulmonary pressure?

Answer 2

14mmHg

• Pressure drops across the pulm. art to an arou nd 5mmHg in pulm. cap

Question 3

What are some notes about lung circulation?

Answer 3

2 systems

• High pressure bronchial -> drains into left heart (never 100% oxygenated when ejected then)
• Pulmonary circuit

Question 4

Describe capillaries of pulmonary circuit?

Answer 4

Not in tubes, they are wall structures giving a sheet like structure for cap. exchange.

Pillars support these walls.

Keeps walls thin and maximises exchange

Question 5

How is pulmonary circulation controlled?

Answer 5

1) Physical factors affecting blood flow
2) Chemical control of pulmonary blood vessels
3) Autonomic control of pulmonary arterioles

Question 6

What are the physical factors affecting blood flow?

Answer 6

Lungs can hold a lot of blood because of distension and recruitment of additional pulm. vessels (prevents oedema)

BUT

Conversely resistance decreases as pressure increases

Question 7

Why is alveolar blood flow resistance U-shaped?

Answer 7

Total pulmonary vascular resistance is u shaped. It is produced by the total of alveolar and extra-alveolar resistance.

Low inflated lungs have high extra alveolar resistance provided by vessel resistance and alveolar contribution is low.

As lung volume increases, alveolar resistance increases but extra-alveolar resistance decreases (the inflated alveoli must crush vessels and drive vasodilation?).

U-Shaped because of this (total resistance)

Question 8

Describe the chemical control of pulmonary blood vessels:

Answer 8

• Broncho agitation
  = Decreased PO2 = Hypoxia

This results in a regional vasoconstriction to redirect blood to better oxygenated alveoli.

i.e If alveoli cant oxygenate blood then redirect blood flow.

(Opposite to systemic where hypoxia dilates)

Question 9

What drives pulmonary vasoconstriction:

Answer 9

Vasoconstriction

1) Hypercapnia
2) Decreased pH
3) ANG 2
4) Adenosine

Question 10

What drives pulmonary vasodilation

Answer 10

1) Bradykinin
2) Histamine
3) Vasopressin

All endothelium dependent and mediated by NO

Question 11

What drives pulmonary hypertension?

Answer 11

Endothelial dysfunction and lack of NO

Question 12

Describe the autonomic control of pulmonary arterioles;

Answer 12

1) Symp innervation
- Vasocon
- Reduce pulm. blood flow by 30%

2) Muscarinic
- Vasodilation
- M3 receptor, depend on endothelium

Question 13

Wheres the highest blood flow in the lung?

Answer 13

At the base

Question 14

What drives the un-even blood flow?

Answer 14

Alveoli at the top of the lung are large and have less capillary density

Alveoli are smaller at the base and have a higher cap. density therefore higher blood flow

THIS IS THANKS TO GRAVITY (also pressure gradient)

Question 15

What is good about the un-even blood flow?

Answer 15

Built in capacity so that the apex of the lung can increase perfusion during exercise.

Question 16

Describe the perfusion ventilation mis-match;

Answer 16

Blood flow and ventilation decrease through the lung. But the proportion they decrease are different (blood flow slope is greater) and they cross around 0.8 in health lungs

AS these factors change in disease or physiologically then the ventilation perfusion ratio changes…

ADD graph

Question 17

How is ventilation perfusion ratio calculated???

Answer 17

Minute ventilation = V(t) x Hz

Alveolar ventilation = (Tidal vol - dead space) x Hz

CO = HR x SV

Ventilation / perfusion ratio = Alveolar ventilation / CO

Question 18

Whats the clinical importance of Va:Q ratio?

Answer 18

Blocked airway: Drops to near 0
Blocked vessels: Rises to 3+

Can use to determine disease

Question 19

What are disease states of the pulmonary circuit?

Answer 19

Pulmonary hypertension

• Right side HF
• Hypoxia = vasocon

Pulmonary oedema

• left HF
• Systemic hypoxia
• Breathlessness - dyspnoea