Mechanics of breathing

Question 1

What does the rate of airflow into the lungs depend on?

Answer 1

The rate of airflow depends on the pressure
gradient & level of airway resistance

Question 2

What is ohm’s law(airflow)?

Answer 2

Airflow(V)= change in pressure(P)/Resistance(R)

Question 3

What is the hagen poiseuille equation?

Answer 3

Resistance(R) is proportional to 1/radius^4

Question 4

What happens as airways radius decreases?

Answer 4

As an airway’s radius decreases, the resistance
increases (and the airflow decreases) dramatically

Question 5

What can airway resistance be further increased by?

Answer 5

Airway resistance is further increased
by turbulent airflow

Question 6

What does elastin in healthy alveoli provide and why is that?

Answer 6

Elastin in surrounding
alveoli provides radial
traction to splint
bronchioles against
positive Palv

Question 7

What does a lack of or no elastin due to COPD result in alveoli?

Answer 7

Without radial traction,
bronchioles collapse

Question 8

What does lung compliance quantify?

Answer 8

Lung compliance quantifies the relationship between the level of expansive force applied to the lung and the resulting change in lung volume

Question 9

What is the equation fro transpulmonary pressure?

Answer 9

Transpulmonary pres. (Ptp) = Alveolar pres. (Palv) – Intrapleural pres. (Pip)

Question 10

What is transpulmonary pressure?

Answer 10

the level of force acting to expand the lung

Question 11

What is lung compliance calculated by?

Answer 11

Lung compliance is calculated by dividing a change in lung
volume by the associated change in transpulmonary pressure
-Compliance(CL)=change in volume/change in pressure

Question 12

What does the gradient of the transpulmonary pressure against lung volume graph represent?

Answer 12

Compliance is expressed as the gradient of the curve.

Question 13

What does a steeper curve in a transpulmonary pressure against lung volume graph represent?

Answer 13

Steeper curve = Greater level of lung compliance

Question 14

What does it mean by a greater lung compliance?

Answer 14

‘Looser’/easier to inflate lung = greater lung
compliance

Question 15

What does it mean by a lower lung compliance?

Answer 15

Stiffer/harder to inflate lung = lower lung compliance

Question 16

What factors and diseases affect lung compliance by impacting chest wall mechanics?

Answer 16

1. Scoliosis
2. Muscular dystrophy
3. Obesity
   -These decrease CL

Question 17

What factors and diseases affect lung compliance by impacting alveolar surface tension?

Answer 17

NRDS
-Neonatal respiratory distress syndrome
-Increased alveolar surface tension
-This decreases CL

Question 18

What factors and diseases affect lung compliance by impacting elastin fibres?

Answer 18

-Fibrosis(decreases CL)
-COPD(Increases CL)

Question 19

What do air liquid interfaces generate and what do they resist?

Answer 19

Air-liquid interfaces (e.g. alveoli) generate
surface tension, which resists inflation

Question 20

What are alveoli lined with?

Answer 20

Alveoli are lined with fluid to enable gas exchange (the gas molecules
dissolve into water before diffusing.

Question 21

What arises and is exerted by the bubble formed by the water-air interface?

Answer 21

Within the bubble formed by the water-air interface, surface tension
arises due to H-bonds between the water molecules, exerting a
collapsing force toward the centre of the bubble.

Question 22

What does laplace’s law describe in relation to pressure?

Answer 22

The Law of Laplace describes the pressure
generated by the surface tension within a bubble

Question 23

What is the equation that describes the amount of pressure within a specific bubble?

Answer 23

P=2T/r

P is the pressure
T is surface tension
r is radius of bubble

Question 24

If T is constant, what does that mean for the P=2T/r equation?

Answer 24

If T remains constant, then P is proportional to 1/r
-The smaller the alveoli, the larger the pressure generated

Question 25

What is alveolar surface tension reduced by?

Answer 25

Alveolar surface tension is reduced by the presence of
pulmonary surfactant,

Question 26

What is pulmonary surfactant secreted by?

Answer 26

Secreted by type 2 pneumocytes

Question 27

How does pulmonary surfactant work?

Answer 27

Attractive forces at surface disrupted, reducing surface tension

Question 28

What are the 2 type of cells that the surface of alveoli primarily consist of?

Answer 28

-Type 1 is responsible for gas exchange
-Type 2 secretes pulmonary surfactant

Question 29

What does pulmonary surfactant act to equalise across varying alveoli?

Answer 29

Pulmonary surfactant acts to equalise
pressure & volume across varying alveoli

Question 30

What happens as to surface tension as alveoli expand and due to what?

Answer 30

As alveoli expand, the concentration of
surfactant molecules decreases, increasing
surface tension.

Question 31

What helps with consistent inflation of the lungs?

Answer 31

Now, larger alveoli tend to collapse into
smaller ones, helping consistent inflation of
the lungs.

Question 32

What does pulmonary surfactant help to prevent?

Answer 32

Pulmonary surfactant helps to prevent
alveolar oedema

Question 33

How is alveolar oedema prevented by pulmonary surfactant?

Answer 33

-Pulmonary surfactant helps to prevent
alveolar oedema
Surface tension produced at the air-liquid interface also reduces
hydrostatic pressure. Fluid is then pulled out of surrounding
capillaries and into the alveoli.
-By reducing surface tension, pulmonary surfactant helps to prevent
alveolar oedema, as observed in patients with insufficient surfactant.

Question 34

What is neonatal respiratory distress syndrome(NRDS) caused by?

Answer 34

Neonatal respiratory distress syndrome is caused
by insufficient production of pulmonary surfactant

Question 35

What are the steps involved in neonatal respiratory distress?

Answer 35

Premature birth, maternal diabetes, congenital
developmental issues
↓
Insufficient surfactant production
↓
Stiff (low compliance) lungs, alveolar collapse, oedema
↓
Respiratory failure
↓
Hypoxia
↓
Pulmonary vasoconstriction, endothelial damage,
acidosis, pulmonary + cerebral haemorrhage.