Mechanisms of Breathing

Question 1

What do changes in lung volume induce?

Answer 1

→ Changes in alveolar pressure which generate pressure gradients between alveoli & atmosphere, causing air to flow.

Question 2

why any differences in pressure between the alveoli and atmosphere not instantly negated by the movement of air?

Answer 2

There is a delay due to the time taken for air to move.

Question 3

What does rate of airflow depend on?

Answer 3

pressure gradient & level of airway resistance

Question 4

Ohm’s law…

Answer 4

𝐴𝑖𝑟𝑓𝑙𝑜𝑤 (𝑉) =(Δ𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 (𝑃))/(𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑅)

Question 5

Hagen-Poiseuille equation…

Answer 5

𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑅) ∝ 1/𝑟𝑎𝑑𝑖𝑢𝑠^4

Question 6

What happens to resistance as airway radius increase?

Answer 6

→the resistance increases (and the airflow decreases) dramatically

Question 7

What are some causes of reduced airway lumen?

Answer 7

→Contraction of airway smooth muscle, →excessive mucus secretion, →oedema/swelling of the airway tissue, →damage to the integrity of the airways structure (i.e. loss of patency

Question 8

When does turbulent airflow occur?

Answer 8

→where high velocities of airflow are achieved (e.g. during forced breathing manoeuvres)
→if there is a sudden decrease in luminal area such as in obstructed airways.

Question 9

What produces the wheezing sound?

Answer 9

The vibration generated by the turbulent airflow

Question 10

What is patency?

Answer 10

the state of being open or unobstructed; a ‘loss of patency’ = closing/obstruction

Question 11

How are open structures maintained?

Answer 11

by elastic fibres within the wall of the airway and radial traction.
→the airways are pulled open by their connections to the surrounding tissue

Question 12

How can intrapleural space reduce airway patency?

Answer 12

When intrapleural pressure becomes positive (as can occur during forced expiration), collapsing force will be exerted onto the airways
→In healthy individuals, the structural integrity of the airways is sufficient to prevent collapse

Question 13

Why is decreased structural integrity of the airways problematic in COPD?

Answer 13

the simultaneous loss of elastic recoil within the lung tissue means that both radial traction of the airways and lung recoil and reduced.
→greater force is required to compress the lungs during expiration,
→however the more force that is exerted to maintain ventilation and airflow, the more obstructed the patient’s airways will become

Question 14

How is transpulmonary pressure calculated?

Answer 14

(Ptp = Palv – Pip)

Question 15

What is lung compliance?

Answer 15

→relationship between the change in lung volume produced by a particular changed in transpulmonary pressure
→describes how easily the lungs can be distended

Question 16

What does high and low compliance mean for elastic recoil and force required to inflate, and volume change?

Answer 16

Higher lung compliance = less elastic recoil = less force required to inflate = ↑ volume change per pressure change (↑gradient on volume-pressure curve)

Lower compliance = more elastic recoil = more force required to inflate = ↓volume change per pressure change (↓ gradient on volume-pressure curve)

Question 17

Equation for compliance

Answer 17

volume/pressure

Question 18

How do you calculate lung compliance from a graph?

Answer 18

by a graph of lung volume vs. transpulmonary pressure,

→as lung compliance = the gradient of the curve

Question 19

What is the difference between static and dynamic compliance?

Answer 19

static= measurements taken whilst airflow =0, the steepest part of the curve is used

dynamic=measurements taken in the presence of airflow, the gradient between the end tidal inspiratory and end tidal expiratory points is used

Question 20

How does scoliosis affect compliance?

Answer 20

reduction

→ through chest wall mechanics

Question 21

How does neonatal respiratory distress syndrome affect compliance?

Answer 21

reduction

→ through alveolar surface tension

Question 22

How does fibrosis and COPD affect compliance?

Answer 22

reduction
→ through collagen deposition

COPD:
increases compliance

Question 23

What is emphysema?

Answer 23

involves degradation of elastin fibres making the lung less stiff and more complaint but reducing recoil

Question 24

What is pulmonary fibrosis?

Answer 24

scarring and deposition of structural fibres such as collagen making the lung stiff and less compliant.

Question 25

How is a bubble created?

Answer 25

The water-air interface formed between the lining fluid and pseudo-spherical alveolar airspace

Question 26

How does surface tension arise within a bubble?

Answer 26

due to the relative strength of hydrogen bonds between water molecules combining to exert an overall collapsing force toward the centre of the bubble.

Question 27

What is Laplace's law and how is it associated with pressure?

Answer 27

The amount within a specific bubble is described by the Law of Laplace ``` →𝑃 =2𝑇/𝑟 Pressure →Surface tension (e.g. water = 0.075N/m) Radius of bubble (i.e. alveoli) →(The smaller the alveoli, the larger the pressure generated) ```

Question 28

Q: What would happen if 2 bubbles of different radius were connected to each other (e.g. different size alveoli connected via airways)?

Answer 28

Pressure gradients would be created between different sized alveoli, resulting in smaller alveoli emptying into larger ones →This would thus make inflation of the lung very difficult

Question 29

How is the potential problem of smaller bubbles lowering into larger ones resolved?

Answer 29

→by the presence of pulmonary surfactant →acts to disrupt the attractive forces between water molecules, reducing surfacing tension and the collapsing pressure generated

Question 30

What are surfactants?

Answer 30

→phospholipoprotein secreted by type II pneumocytes (alveolar cells →amphipathic, will naturally position themselves at the air-liquid interface.

Question 31

How do surfactants equalise pressure between varying alveoli sizes?

Answer 31

→As alveolar size increases during inflation, the concentration of surfactant molecules at the interface decrease →surface tension (and thus pressure generated) increases with increasing alveolar surface area. →air will naturally flow from larger (more inflated) alveoli to smaller ones, helping to distribute air across the lung during inspiration

Question 32

How does surfactants tension reduce alveolar oedema?

Answer 32

→reduces hydrostatics pressure in the alveolar tissue. →acts to pull fluid out of the surrounding pulmonary capillaries and into the alveoli and interstitial tissue. →By reducing surface tension, pulmonary surfactant helps to prevent alveolar oedema due to excessive fluid being pulled from capillaries

Question 33

What is the neonatal respiratory distress syndrome?

Answer 33

→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. →innervating capillaries

Question 34

How is NRDS treated?

Answer 34

→supplementation of affected infants with artificial surfactant → maternal administering glucocorticoids (which increase surfactant production via maturation of type 2 pneumocytes) t

Question 35

What happens with saline filled lungs ex vivo?

Answer 35

lungs required less pressure to inflate (↑ compliance)

Question 36

What happens with washed lungs then inflation?

Answer 36

produced lungs that required more pressure to inflate (↓ compliance).