Pulmonary Vascular Physiology

Question 1

There are 2 types of circulation

Answer 1

Pulmonary circulation and Bronchial circulation

Question 2

Pulmonary circulation

Answer 2

From Right Ventricle

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

Red cell transit time ≈5 seconds.

280 billion capillaries & 300 million alveoli.

Surface area for gas exchange 50 – 100 m2

Question 3

Bronchial circulation

Answer 3

2% of Left Ventricular Output

Question 4

Vessel wall of pulmonary arteries is thin

Answer 4

Vessel wall of systemic arteries is thick

Question 5

Muscularization of pulmonary arteries is minor

Answer 5

Muscularization of systemic arteries is major

Question 6

There is no Need for redistribution in pulmonary artery in normal state

Answer 6

There is Need for redistribution in systemic arteries

Question 7

What is the pressure in the RA? (MmHg)

Answer 7

5

Question 8

What is the pressure in the RV? (MmHg)

Answer 8

25/0

Question 9

What is the pressure in the PA? (MmHg)

Answer 9

25/8

Question 10

What is the pressure in the LA? (MmHg)

Answer 10

5

Question 11

What is the pressure in the LV? (MmHg)

Answer 11

120/0

Question 12

What is the pressure in the aorta? (MmHg)

Answer 12

120/80

Question 13

Left ventricle is larger than hothead right ventricle as

Answer 13

The left ventricle sees higher pressure than the right ventricle

Question 14

Pouiseuille’s Law

Answer 14

Resistance= (8 x L x viscosity) / (pi x r^4)

Question 15

Effect of Transmural Pressure on Pulmonary Vessels During Inspiration

Question 16

Ohms law

Answer 16

V= IR

Question 17

Pressure across circuit =

Answer 17

Cardiac output x Resistance

Question 18

Pressure across pulmonary circulation=

Answer 18

mPAP – Left Atrial Pressure x Pulmonary Vascular Resistance

Question 19

Pressure across pulmonary circulation

Answer 19

mPAP – PAWP = CO x PVR

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

Question 20

What happens to mPAP on exercise?

Answer 20

On exercise mPAP remains stable in normal subjects but CO increases significantly

Question 21

How is this possible?

Answer 21

Recruitment and Distention in Response to Increased Pulmonary Artery Pressure

Question 22

Two types of respiratory failure

Answer 22

Type I
Type II

Question 23

Type 1 Respiratory Failure

Answer 23

pO2 < 8 kPA
pCO2 <6 kPA

Question 24

Type II respiratory failure

Answer 24

pO2 < 8 kPA
pCO2 >6 kPA

Question 25

Causes of Hypoxaemia

Answer 25

Hypoventilation Diffusion Impairment Shunting V/Q mismatch

Question 26

Hypoventilation causes type II Respiratory failure as

Answer 26

Slide 33

Question 27

Diffusion Impairment

Answer 27

Gaseous diffusion impairment due to pulmonary oedema Blood diffusion impairment due to anaemia due to less haemoglobin being present for O2 to then diffuse into Membrane diffusion due to interstitial fibrosis- membrane can thicken

Question 28

Physiologic V/Q mismatch

Answer 28

V= ventilation (air going into the alveoli) Q= Perfusion (amount of blood flow to the alveoli) The lung is divided into 3 zones- the Ventilation: Perfusion ratio is higher at the apex of the lung. Towards the base of the lung the ventilation perfusion ratio is decreased Average Ventilation: Perfusion ratio is 0.8. This means there is more perfusion to the lungs and alveoli than there is ventilation. This differs through different parts of the lung and with diseases of the lung. In zone 1- apex of lung- the blood travelling to here will be decreased because of gravity- decreased perfusion at apex So In zone 3- increased perfusion Therefore, at the apex of the lung we have wasted ventilation as all the gas that goes to the alveoli is not exchanged efficiently because theres less perfusion At the base of the lung there is wasted perfusion as there is too much perfusion relative to ventilation Ventilation and perfusion is overall higher at the base of the lungs than the apex of the lungs The part of the lung Above the heart has larger alveoli. There’s reduced pulmonary intravascular pressure because of less blood flow to this area and so less perfusion. Because of the larger alveoli there’s also lower rates of ventilation. Despite the reduced ventilation the perfusion is much more lower so there’s wasted ventilation As you go to the the base of the lungs the alveoli becomes smaller because of the difference in intrapleural plush pressure More perfusion and more ventilation as the smaller alveoli are able to expand more. But ventilation increase isn’t as much as the increase in perfusion so the V:Q is lower here In zone 1: alveolar pressure is highest Pulmonary artery pressure is next highest Pulmonary vein pressure is lowest In zone 2: Pulmonary artery pressure exceeds alveolar pressure which then exceeds pulmonary ventilation In zone 3: alveolar pressure exceeds pulmonary ventricular pressure which exceeds pulmonary artery pressure In summary- The ventilation increases from the apex of the lung to the base of the lung But perfusion to the lungs and alveoli increases a lot more from the apex of the lung to the base of the lung

Question 29

Shunt v V/Q mismatch

Answer 29

V/Q=0 This is termed absolute pulmonary shunt No oxygen is coming into the alveoli, so overall low oxygen levels leaving the system but there is still a large build up of CO2 as it cannot be breathed out

Question 30

What is a shunt?

Answer 30

Blood going through the lung but not taking part in gas transfers Perfusion without ventilation Slide 43

Question 31

Causes of shunt- blood going through lung/part of lung but not taking part in any gas transfer

Answer 31

Physiological Bronchial arteries Thesebian veins Intracardiac Eg VSD - R-L Shunt (Eisenmenger’s Syndrome) Pulmonary ArterioVenous Malformation (AVM) Complete Lobar Collapse

Question 32

Eisenmenger’s Syndrome

Answer 32

Ventricular Septum defect (VSV)- Hole in septum When baby is born, blood will be higher in the left ventricle. So if this VSV is not closed then the net direction of flow will be left to right so there will be more blood than normal going through the arteries under higher pressure The pulmonary arteries, especially small pulmonary arteries, are not designed to cope with this, resulting in damage to them. The pulmonary arteries respond by narrowing down, increasing pressure and increasing resistance Once the resistance and pressure gets above a certain limit, then the pressure in the right ventricle is similar and sometimes higher than the left ventricle so there is now right to left movement. So there begins to be deoxygenated blood coming from the SBC into the right atrium and right ventricle and then it starts going from right to left So the deoxygenated blood is going straight into systemic circulation and is no longer taking part in just transfer Patients with this syndrome have low oxygen levels

Question 33

V/Q Mismatch

Answer 33

Physiological Pulmonary Embolism: a clot occludes the pulmonary capillary pr artery causing reduced perfusion which will subsequently increase the perfusion rate causing a mismatch Asthma Pneumonia Pulmonary Oedema

Question 34

Hypoxia Pulmonary Vasocontstriction

Answer 34

At high altitude all the vessels narrow down so one of the ventricles has a high pressure

Question 35

Hypoxic Pulmonary Vasoconstriction

Answer 35

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 36

Diseases of the Pulmonary Circulation

Answer 36

Pulmonary Embolism caused by VQ mismatch Pulmonary Hypertension caused by increased PVR Pulmonary AVMs caused by shunt