Respiratory Physiology: Resistance to Breathing

Question 1

1. How many ml out of 500ml of tidal volume does not reach alveoli for gas exchange?

Answer 1

150ml

Question 2

2. What is physiological dead space

Answer 2

Perfused and non-ventilated
alveoli

Question 3

3. Give 2 sources of resistance to breathing and examples of them

Answer 3

A. Elastic forces and Surface Tension
Mechanical resistance

B. Airflow (Airway) resistance
airflow turbulence

Question 4

4. What type of process in expiration

Answer 4

passive process.

Question 5

what fibres are needed for expiration

Answer 5

elastic fibres

Question 6

5. What in lung parenchyma resists expansion

Answer 6

elastin

Question 7

6. What 2 types of collagen are in the lungs?

Answer 7

• Type 1
• Type 3

Question 8

7. What happens if you have emphysema?

Answer 8

• You lose the elastic fibres, so you lose elastic recoil and need to use accessory muscles to compensate.

Question 9

how is emphysema characterised and why?

Answer 9

so emphysema is characterised with shortness of breath and fatigue because energy is used breathing in AND out.

Question 10

What is surface tension?

Answer 10

Atoms on the surface of an air-water interface have no neighbouring atoms above them so show stronger attractive forces upon their neighbours on the surface, resulting in an inward directed force at the air-water interface.

Question 11

9. What happens if the force that resists expansion of alveoli is not impeded

Answer 11

alveoli collapse and fill with fluid as water is attracted into them.

Question 12

10. What is the medical term for lung collapse.

Answer 12

at atelectasis

Question 13

11. What is surfactant and what does it do?

Answer 13

• chemical compound emulsifier
• reduces surface tension

Question 14

12. What percentage of surfactant is lipid?

Answer 14

90%

Question 15

13. What percentage of surfactant is protein?

Answer 15

10%

Question 16

14. What is the chemical name for surfactant and what is the abbreviation for it?

Answer 16

Dipalmitoylphosphatidylcholine (DCCP)

Question 17

15. How does surfactant do what it does?

Answer 17

acts like a detergent and breaks the molecular bonds between air and liquid

Question 18

16. What secretes surfactant

Answer 18

pneumocyte type II aka Clara cells

Question 19

17. Give the weeks when surfactant is produced in gestation:

Answer 19

Start of production: Wk 20
Max Production: Wk 28-32
Mature levels: Wk 34-35

Question 20

18. what causes Neonatal Respiratory Distress Syndrome (NRDS)?

Answer 20

Caused by deficiency of surfactant

Question 21

19. What is the relationship between incidence and severity of NRDS and gestational age?

Answer 21

Incidence and severity is inversely proportional to gestational age

Question 22

20. What is the mortality rate in infants under 1kg with NRDS?

Answer 22

50% in infants

Question 23

21. When will increasing respiratory distress happen with an infant?

Answer 23

around 2nd to 7th day

Question 24

23. How do bronchioles control the airflow rate

Answer 24

abundant smooth muscle which allows the bronchiole to constrict or dilate which changes resistance

Question 25

24. What acts on receptors to change resistance and give an example of this

Answer 25

Nerves and hormones act on receptors to change this resistance. example: adrenaline - works on beta-2-adrenoreceptors to cause bronchodilation

Question 26

25. What is the major airflow resistance in the body?

Answer 26

Airway resistance is the major resistance

Question 27

26. What is the simple version of Poiseuille’s Law equation?

Answer 27

Flow (Q) = change in driving pressure (ΔP)/ resistance (R)

Question 28

27. What is the relationship between resistance and bronchiole radius?

Answer 28

Resistance is inversely related to Bronchiole radius 4

Question 29

28. What is the complex version of Poiseuille’s Law and define what each symbol means.

Answer 29

Q = ΔP (πr^4)/8nl π = pi P = pressure difference between the two ends r = radius of tube n = viscosity l = length

Question 30

29. What percentage of airway resistance is the medium sized bronchioles

Answer 30

80% of all airway resistance

Question 31

what does in series tubes (eg bronchi, bronchioles) mean for the resistances

Answer 31

it means you add the individual resistances

Question 32

what does in parallel bronchioles mean for resistances

Answer 32

it means you add the reciprocal of the resistances

Question 33

31. Give 3 reasons bronchioles constrict during asthma

Answer 33

- Parasympathetic nerves - cough reflex - Histamine

Question 34

32. give 1 reason as to why bronchioles dilate

Answer 34

Sympathetic nerves by stimulating b2-adrenoceptors

Question 35

what are 4 ways respiratory resistance is affected in everyday life

Answer 35

- Respiratory diseases - Postural muscle tone of the upper airways and the accessory muscles - Mucociliary clearance - Cough reflex etc