Lecture 7 - Matching lung ventilation and tissue perfusion

Question 1

What is ventilation

Answer 1

movement of gases in and out of the lungs. occurs through the airways

Question 2

What is Perfusion?

Answer 2

blood flow through any organ

eg. lungs perfusion occurs through blood vessels

Question 3

What are the regional differences in lung ventilation in different parts of the lung?

Answer 3

Apical alveoli - 4 x larger than basal alveoli when upright
due to effect of gravity
basal regions have lot better ventilation than apical regions
basal alveoli - expand more than apical alveoli

Question 4

How is pulmonary circulation brought about?

Answer 4

oxygenation of the venous blood
deox blood from right ventricles pumped into the pulmonary arteries to the lungs - then through the pulmonary veins to the left atrium to the left ventricle to the aorta and to the body.

Question 5

What are the structures that supply the lung tissue

Answer 5

Arteries - bronchial artery from thoracic aorta
bronchial vein - to SVC
2% of cardiac output

Question 6

How does the pulmonary circulation compare to the systemic?

Answer 6

lung receives full cardiac output (3-5 L/min)
but at a lower pressure to systemic circulation
aorta - 100 pulmonary artery - 15-30

Question 7

How does the pulmonary artery re-oxygenate the blood in the lungs?

Answer 7

PA carries deoxygenated blood from right ventricle and splits into right and left branches to supply the respective side lung .
then these split further following the airway divisions.

Question 8

What are the successive branches of the PA called while running through the lung parenchyma

Answer 8

they are called extra -alveolar vessels while running through the lung parenchyma

Question 9

Describe branching after terminal bronchioles

Answer 9

blood vessels form capillary beds (starting with smaller arterioles) where gas exchange starts
each alveoli - approx 1000 capillaries
280 billion capillaries
forms rich network of capillaries - large surface area
very efficient exchange system

Question 10

describe venous return from lungs to left atrium

Answer 10

ox blood flows into the pulmonary venules which unite to form large 4 veins emptying into the left atrium

Question 11

What happens in emphysema

Answer 11

Widespread destruction of vascular beds
regional destruction of vascular beds
poor gas exchange and hypoxia
overdilation of alveoli - become damaged

Question 12

Describe the regional differences in lung perfusion

Answer 12

Extra alveolar vessels:
- running through lung parenchyma
- diameter is affected by the lung volume  (via pull of the lung parenchyma)
Alveolar vessels 
- diameter dependent on many factors

Question 13

What is hydrostatic pressure

Answer 13

force exerted by weight of a fluid (blood/water) due to gravity

Question 14

how is lung perfusion at the top of the lung?

Answer 14

At the top: blood vessels collapse, halting flow

pressure at top is close to atmospheric pressure

Question 15

lung perfusion in the middle of the lung.

Answer 15

In the middle: blood flow increases, capillary and arterial pressure exceeds alveolar pressure.
venule pressure lower than alveolar pressure.

Question 16

Lung perfusion in the lower part of the lung

Answer 16

Alveolar pressure is lower than in capillaries veins and arteries.
Hence there is more perfusion.
circulation is dependent on arterial -venous pressure difference

Question 17

P arterial

Answer 17

hydrostatic/blood pressure at the arterial end of the capillary

Question 18

P venous

Answer 18

hydrostatic/blood pressure at the venous end of the capillary

Question 19

Zone 1: at the top of the lung

Answer 19

Alveolar dead space
good ventilation but no perfusion
Poor blood flow - lung apex above right ventricle
Apices of the lungs - very small area
alveolar pressure > P arterial > P venous
blood flow determined by difference in P alveolar and P arterial

Question 20

Zone 2: Recruitment zone

middle of lung

Answer 20

Lower down the lung
higher arterial pressure as more blood and higher hydrostatic pressure
recruitment of more alveolar unit especially in systole
P arterial > P alveolar > P venous
Blood flow determined by difference in P arterial and P alveolar

Question 21

During haemorrhage what happens to lung perfusion?

Answer 21

pathological expansion of zone 1 : bleeding. there is a drop in P arterial and there is a rise in alveolar pressure . positive pressure ventilation

Question 22

Zone 3: distention zone

Answer 22

lung bases
hydrostatic forces raise p arterial and p venous above p alveolar
p arterial> p venous > p alveolar
continuous blood flow
blood flow determined by difference p arterial and p venous

Question 23

ventilation - perfusion (V/Q) ratio

Answer 23

When ventilation and perfusion is equal the ratio is 1
Apex = 3.3 as there is good ventilation but no perfusion
base = 0.6 ( both ventilation and perfusion is high so there is less than a ratio)

Question 24

Anatomical dead space

Answer 24

conducting airways, no gas exchange

approx 2ml/kg or 150 ml in 70 kg man

Question 25

Alveolar dead space

Answer 25

unperfused or poorly perfused alveoli

Question 26

Physiological dead space

Answer 26

part of each breath that does not take part in gas exchange

Anatomical + Alveolar dead space

Question 27

What is a pulmonary embolism

Answer 27

blood clot from leg vein travels to the heart and is lodged inside a blood vessel in the lungs, blocking blood supply
fatal emergency
Blood clot inside a lung blood vessel blocking the blood supply.
blocks large or intermediate pulmonary arteries
severe hypoxia

Question 28

What does a pulmonary embolism do the alveolar dead space

Answer 28

enlarges alveolar dead space

Question 29

What happens when there is a shunt in blood

Answer 29

deoxygenated blood reaching left side of the heart bypassing the lungs or failing to get oxygenated in the lungs

eg. bronchial veins, pneumothorax, age related changes: low V/q ratio
- there is a minimal effect of oxygen supplementation on a large shunt

Question 30

What happens in pneumothorax

Answer 30

abnormal collection of air or gas in the pleural space.
treated by immediate needle decompression
chest drain connected to an underwater sealed system

Question 31

What happens to V/Q ratio during shunting

Answer 31

no ventilation
good perfusion - as there is a presence of blood flow
it is 0 or very low

Question 32

Which abnormality of oxygenation are you most likely to see in pneumonia?

Answer 32

nothing