Mechanics of Breathing II

Question 1

What allows the lungs to expand?

Answer 1

negative pressure

Question 2

What forces inter pulmonary pressure to be -ve?

Answer 2

Elastic recoil of lungs - collapse inwards
Elastic recoil of chest - expand outwards

Question 3

What happens when pleural membranes move apart?

Answer 3

Increase interpleural space volume -> reduces pressure

Question 4

What determines airflow?

Answer 4

Difference in pressure between alveoli and atmosphere

Question 5

What is transpulmonary pressure?

Answer 5

Pressure holding lung open -> determines lung volume
Ptp = Palv - Pip

Question 6

What does chest wall pressure oppose?

Answer 6

Outward elastic recoil of chest wall
Pcw = Pip - Patm

Question 7

What is the equation for airflow?

Answer 7

F = Palv-Patm/R

Question 8

What is Pip and Palv at end of expiration?

Answer 8

Pip = -4mmHg
Palv = 0

Question 9

What does pressure changes of Pip, Palv and Ptp show?

Answer 9

Different phases of the respiratory cycle

Question 10

When does air flow stop moving down its pressure gradient?

Answer 10

When intrapleural pressure = atmospheric pressure

Question 11

When does gas flow stop moving down its pressure gradient during expiration?

Answer 11

Until intrapulmonary pressure is 0

Question 12

Why is lung volume never zero?

Answer 12

Some air in lung without any expanding pressure

Question 13

Why is inspiratory volume less than expiratory in intrapleural pressure?

Answer 13

Elastic recoil on expiration always less than pressure require to inflate lungs

Question 14

What is lung compliance?

Answer 14

Magnitude of change in lung volume produced by a given change in intrapleural/transpulmonary pressure
C = ∆V/ ∆P

Question 15

What does the greater compliance mean?

Answer 15

Easier it is to expand the lungs at a given change in pressure

Question 16

What is normal compliance?

Answer 16

200mls.cmH2O^-1

Question 17

What is the consequence of higher expanding pressure?

Answer 17

Lungs are stiffer = less compliannt

Question 18

What is a restrictive disorder?

Answer 18

Pulmonary fibrosis

Question 19

What are 2 features of pulmonary fibrosis?

Answer 19

Deposition of fibrotic tissue
Hard to distend

Question 20

What is a disease associated with increased compliance?

Answer 20

Emphysema - alveoli air sacs are damaged

Question 21

What happens in emphysems?

Answer 21

Inner walls of air sacs weaken and rupture - creating larger air spaces

Question 22

What are 2 major determinants of compliance?

Answer 22

Stretchability of lung tissue
Surface tension

Question 23

What is surface tension?

Answer 23

Force acting on surface of a liquid in an air-water interface within alveoli

Question 24

What law describes surface tension?

Answer 24

Law of Larplace
P=2T/r
r - radius of alveoli

Question 25

What causes the collapsing pressure to increase according to Law of Larplace?

Answer 25

Surface tension increasing Radius of sphere decreases

Question 26

Do smaller or larger alveoli have a greater tendency to collapse (greater collapsing pressure)?

Answer 26

Smaller

Question 27

What is surfactant made up of?

Answer 27

Lipids and proteins

Question 28

What cell secretes surfactant?

Answer 28

Type II pneumocytes

Question 29

How does surfactant reduce surface tension?

Answer 29

Hydrophilic end inserts into water layer lining alveoli -> inhibit water molecules coming close together

Question 30

What stimulates surfactant secretion?

Answer 30

Taking a deep breath

Question 31

What are 3 advantages of surfactant?

Answer 31

Reduces surface tension Prevents alveolar collapse Increases stability

Question 32

What does loss of surfactant cause?

Answer 32

Low compliance - stiff lungs Alveoli filled with water Common with premature babies

Question 33

What happens when air is introduced into pleural space?

Answer 33

Raised pressure -> lung collapse -> chest wall springs out -> pneumothorax