Mechanics Of Breathing And Gas Exchange

Question 1

What is the term for the stretchiness of the lungs?

Answer 1

Compliance

Question 2

Give some features of lung fibrosis

Answer 2

Low compliance, stiff lungs
Exposed to asbestos/coal dust 
Collagen laid down 
Stops elastin moving 
Lungs cannot fill very much

Question 3

Give some features of emphysema

Answer 3

Loss of elasticity, high compliance
More air into lungs
No elastic recoil as elastin has been destroyed by elastases
Expiration is difficult

Question 4

Give some factors that decrease lung compliance

Answer 4

Laying supine/prone
Laparoscopic surgical interventions (increased abdo pressure)
Severe restrictive pathologies
Hydrothorax (pleural effusion)
Pneumothorax
High standing of diaphragm (obesity, pregnancy)

Question 5

What is surface tension?

Answer 5

The water molecules of the lining fluid of the lungs attract each other (H bonds)
The interface of air and fluid makes the surface resistant to stretching
(Why we need surfactant)

Question 6

Why do we need lining fluid in the lungs?

Answer 6

To be able to move gases

Question 7

Why do we have surfactant in the lungs?

Answer 7

To reduce the surface tension
Is a detergent that interrupts the H bonds
Makes the alveoli easier to inflate

Question 8

What are the constituents of surfactant?

Answer 8

90% phospholipids
Phosphatidylglycerol
Protein

Question 9

Where is lung surfactant produced?

Answer 9

Type 2 pneumocytes

Simple cuboidal epithelial cells

Question 10

Surfactant works better for: bigger or smaller breaths?

Answer 10

Smaller

Quiet breathing uses less energy

Question 11

What is Laplace’s law for working out the pressure inside a bubble?

Answer 11

Pressure = (2 x surface tension) / radius

Question 12

Define the law of bubbles

Answer 12

If a big bubble is connected to a small bubble, air will flow from the higher pressure (small bubble) into the lower pressure (big bubble). Therefore the small bubble will collapse into the big bubble.

Question 13

How does surfactant help to keep alveoli open?

Answer 13

Equalises the pressure between different sized alveoli so that they do not collapse into each other

Question 14

Define atelectasis

Answer 14

Parts of the lung collapsing

Question 15

Describe infant respiratory distress syndrome

Answer 15

Babies born prematurely (<36 weeks) have too little surfactant
Lungs are very stiff
Few, very large alveoli
Surfactant is dripped into the lungs and the baby is put on a low pressure ventilator

Question 16

Why don’t you put the infants with RDS on a high pressure ventilator?

Answer 16

Would cause the lungs to rupture or pneumothorax

Question 17

Describe adult RDS

Answer 17

Not due to a lack of surfactant
Usually trauma
More difficult to treat because of the widespread inflammation in the lungs

Question 18

What different factors are taken into account in Fick’s first law of diffusion?

Answer 18

Pressure difference
Solubility of gas in solution
Cross sectional area of fluid 
Distance molecules most travel 
Molecular weight of the gas
Temperature of the fluid

Question 19

How much more soluble in CO2 than O2?

Answer 19

20x more soluble

Question 20

The diffusion coefficient is proportional to:

Answer 20

Solubility / square root of molecular weight

Question 21

What is the equation for permeability?

Answer 21

(Diffusion coefficient x solubility) / thickness of the membrane

Question 22

At 37’C what is the partial pressure of H2O in inspired air?

Answer 22

6.26 kPa

Question 23

What happens to carbon dioxide when it enters the RBCs?

Answer 23

Reacts with water to form carbonic acid
Dissociates to form bicarbonate ions and H+ ions
Bicarbonate moves into plasma
H+ buffered by Hb

Question 24

How is carbon dioxide carried in the blood?

Answer 24

90% carried as bicarbonate ions in the plasma
5% carried as dissolved CO2 in plasma
5% carried as carboxyhaemoglobin on proteins

Question 25

What is the partial pressure of oxygen in alveolar air?

Answer 25

13.3 kPa

Question 26

What is the partial pressure of carbon dioxide in the alveoli?

Answer 26

5.3 kPa

Question 27

What are the approximate partial pressures of oxygen and carbon dioxide in normal air?

Answer 27

Oxygen = 20.8 kPa

Carbon dioxide = 0.04 kPa

Question 28

What fraction of the time that the blood is in the pulmonary capillaries is required for gas exchange?

Answer 28

1/3

Question 29

What is the approximate surface area of the lungs?

Answer 29

100 m^2

Question 30

How thick is the blood-gas barrier?

Answer 30

0.6 micro meters

Question 31

What is dead space in the lungs?

Answer 31

Areas that do not operate gas exchange but are filled with air

Question 32

Physiological dead space is the sum of:

Answer 32

Anatomical (serial) dead space + distributive (alveolar) dead space

Question 33

What is anatomical dead space?

Answer 33

Volume of gas within the conducting zone

Question 34

What is the alveolar dead space?

Answer 34

Volume of gas within unperfused alveoli

Usually negligible in the health, awake patient

Question 35

What is the ratio of physiological dead space to tidal volume?

Answer 35

1 to 3

Question 36

What is the equation for working out AVR?

Answer 36

(Tidal volume - dead space volume) x resp rate

Question 37

What is the rate of AVR approximately?

Answer 37

5 L/min