M103 T4 L1

Question 1

What are the three inspiratory muscles?

Answer 1

diaphragm
intercostals
accessory muscles

Question 2

Which inspiratory muscle is primarily responsible for inspiration? What proportion of volume change is it responsible for?

Answer 2

The diaphragm, 75%

Question 3

How far down does the diaphragm push during tidal breathing and during forced inspiration?

Answer 3

inspiration - 1cm

forced - 10cm

Question 4

What happens when the external intercostal muscles contract?

Answer 4

pulled upwards and forwards
(act like a bucket handle)
increases thoracic volume

Question 5

What is a clinical sign of respiratory distress?

Answer 5

The accessory muscles being involved in respiration

particularly the scalene and sternomastoid muscles

Question 6

Describe the process of inspiration

Answer 6

Contraction of inspiratory muscles
Intrathoracic volume increases
Decrease in intrapleural pressure
Lungs pulled into more expanded position
Pressure in the airways becomes negative
Air moves in down the concentration gradient
Pressures are now equal
Lungs recoil

Question 7

What is the standard intrapleural pressure?

Answer 7

-2.5 mmHg

Question 8

Describe the process by which transpulmonary pressure is generated

Answer 8

The chest wall exerts a distending pressure on the pleural space
This pressure is transmitted to the alveoli to increase its volume, lower its pressure and generate airflow backwards

Question 9

What is the relationship between transpleural and the elastic recoil pressure?

Answer 9

For any given value, the transpleural pressure is equal to and opposite to elastic recoil pressure of the lung

Question 10

What is the average lung capacity among healthy adults?

Answer 10

about 6 liters

Question 11

Describe compliance in the normal lung

Answer 11

compliance is just right
Good compliance for low work of inhalation
Good retention of elasticity of alveolar units
allows for effective exhalation

Question 12

Describe compliance in a lung suffering from interstitial fibrosis

Answer 12

compliance is decreased

alveolar walls are more stiff due to fibrosis

Question 13

Describe compliance in a lung suffering from emphysema

Answer 13

complience is increased due to loss of alveolar interdependence

Question 14

Why can surface tension lead to the collapse of alveolar?

Answer 14

due to the tendency of water molecules to form spheres due to surface tension pressures
surface tension can increase with emphysema and age

Question 15

How does DPPC work to reduce surface tension?

Answer 15

the hydrophobic and hydrophilic ends repel eachother and interfere with lipid molecule attraction resulting in lower surface tension

Question 16

What are the two main clinical syndromes of surfactant deficiency?

Answer 16

neonatal respiratory distress syndrome

Surfactant dysfunction

Question 17

Why is surfactant important?

Answer 17

Increases lung compliance
Promotes alveolar stability
Prevents alveolar collapse
tends to suck fluid from the capillaries into the alveoli

Question 18

What causes airway resistance?

Answer 18

Friction between the air and the mucosa

Question 19

What does normal lung compliance look like on a graph?

Answer 19

Hysteresis loop. Difference in compliance is due to the increased level of energy required for inspiration. More volume in deflation than inflation, as some of the pressure in inflation is being used to recruit and inflate the alveoli

Question 20

What are the two elastic components of the lung?

Answer 20

Elastin fibres in the alveolar walls, bronchioles and capillaries, and alveolar surface tension

Question 21

What is the functional residual capacity?

Answer 21

Balance point where lungs and chest are in equilibrium (after exhaling); lungs sit at this position naturally

Question 22

What do inspiration and expiration do to the intrapleural pressure?

Answer 22

Makes it more negative, and expiration makes it more positive so air is forced out of the lungs as chest wall and diaphragm relax

Question 23

How does pressure change during the quiet breathing cycle in inspiration?

Answer 23

1. Flow line before breathing = 0, increases inwards and RR slows and stops
2. to generate flow, create pressure gradient through a change in alveolar pressure; this drives flow and changes lung volume
3. reflects static compliance of lungs + generation of driving force of negative alveolar pressure

Question 24

How does pressure change during expiration in the quiet breathing cycle?

Answer 24

1. Flow increases, going outwards, rate slows + stops - back to zero
2. At end of breath, alveolar pressure back to 0. Changing pressure down drives flow out
3. Intrapleural pressure again reflects the compliance and pressure creating this alveolar pressure. Faster lung contraction creates an increase in alveolar pressure

Question 25

What is the Poiseuille equation and what does it represent?

Answer 25

Resistance is inversely proportional to 4th power of radius; flow is inversely proportional to the viscosity of a fluid. I.e more flow for less viscous liquid

Question 26

What are the factors in airway resistance?

Answer 26

Inflammation, mucus, bronchodilators, steroids, gas density

Question 27

What increases the likelihood of turbulent flow?

Answer 27

High velocity, large tube diameter

Question 28

Where does turbulent flow occur?

Answer 28

Trachea