breathing mechanics II

Question 1

What are four ways in which lung function can be investigated?

Answer 1

1) LUNG VOLUMES: what total volume of air can an individual breathe in/out?
2) VENTILATION: what volume of fresh air reaches respiratory surfaces over a given time?
3) LUNG COMPLIANCE: how much force is required to overcome the recoil of the lungs?
4) AIR FLOW: at what rate can air be moved between the lungs and the atmosphere?

Question 2

Describe the pathway air needs to take in order to reach the alveoli

Answer 2

• Trachea
	• Primary bronchi 
	• Smaller bronchi 
	• Bronchioles 
Alveoli

Question 3

What 2 things does the rate of airflow depend on?

Answer 3

Pressure gradient

Level of airway resistance

Question 4

Describe Ohms law

Answer 4

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

* This means that a bigger change in pressure will result in more airflow 
* This means greater resistance will result in less airflow

Question 5

Hagen-Poiseuille equation

Answer 5

Resistance = 1/radius^4
R= 8ηl/πr^4
As an airways radius decreases, the resistance increases (and the airflow decreases) DRAMATICALLY

Question 6

What type of airflow increased airway resistance?

Answer 6

Turbulent airflow (producing a wheezing noise)

Question 7

Describe the structure of a healthy airway

Answer 7

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

Question 8

Describe the structure of an airway of someone with COPD

Answer 8

No radial traction = bronchioles collapse

Question 9

How do you calculate the % of total lung capacity an individual can exhale in the first second

Answer 9

100 x FEV1/FVC
FVC: forced vital capacity
FEV1: forced expiratory volume in 1 second

Question 10

Give an example of an obstructive airway and explain how it is different to a normal airway

Answer 10

FEV1/FVC < 70%
Example: asthma
Increased resistance in airway

Question 11

Give an example of a restrictive airway and explain how it is different to a normal airway

Answer 11

FVC < 80%
FEV1/FVC > 70%
Example: fibrosis
Less compliance in airway

Question 12

If a patients FEV1= 2.4L and FVC=4.3L then what sort of respiratory disease is indicated by the spirometry reading?
Answer this given that the normal readings should be:
FEV1: 3.9L
FVC: 4.7L

Answer 12

Asthma because FEV1/FVC < 70% (it is 55.8%)

Question 13

What is and how is the transpulmonary pressure calculated?

Answer 13

Alveolar pressure - intrapleural pressure
• Transpulmonary pressure is roughly equal to the level of force acting to expand the lung
Transpulmonary pressure reflects the difference between P(alveoli) and P(intrapleural pressure) and is equivalent to the level of force being exerted to change lung volume

Question 14

What is meant by lung compliance?

Answer 14

The relationship between transpulmonary pressure and the lung volume
Compliance = change in volume/ change in pressure

Question 15

What is lowered compliance caused by?

Answer 15

1. Scoliosis
   
   2. Muscular dystrophy
   3. Obesity
   4. NRDS
2. Fibrosis (scarring and deposition of collagen; lung is VERY stiff)

Question 16

What is higher compliance caused by?

Answer 16

COPD
Emphysema (elastin degradation; lung is equivalent to plastic bag = WEAK)

Question 17

Describe the graphical changes when lung compliance is affected by disease

Answer 17

Higher compliance:
Shifts normal curve up and left
Lower compliance:
Shifts normal curve down and right

Question 18

How does the alveoli resist inflation?

Answer 18

Alveoli are lined with fluid to enable gas exchange (allowing gas molecules to dissolve into water before diffusing)
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 19

What law can be used to describe the pressure generated by the surface tension within a bubble?

Answer 19

The collapsing forces generates pressure. The amount within a specific bubble is described by the law of Laplace
P= 2T/r
P: pressure
T: surface tension
R: radius
Therefore is T remains constant, then P = 1/r
Meaning the smaller the alveoli, the larger the pressure generated

Question 20

What would happen if 2 bubbles of different radius were connected to each other (eg-different size alveoli connected via airways)?

Answer 20

Pressure gradients would be created between different sized alveoli, resulting in smaller alveoli emptying into larger ones. This would make inflation of the lungs very difficult. The alveolar surface tension is reduced by the presence of pulmonary surfactant, secreted by type II pneumocytes.

Question 21

What is pulmonary surfactant secreted by and what is its function?

Answer 21

Pulmonary surfactant is secreted by type II pneumocytes.
Function: reduces alveolar surface tension
It acts by equalising the pressure and volume across varying alveoli
• As the alveoli expand, the concentration of surfactant molecules decreases, increasing the surface tension

Question 22

Pulmonary surfactant helps to prevent alveolar oedema, explain how

Answer 22

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. This is observed in patients with insufficient surfactant.

Question 23

What happens in patients with low pulmonary surfactant?

Answer 23

Decreases hydrostatic pressure in tissues surrounding capillary
Fluid pulled from capillary into alveolus
This produces a collapsing force produced by surface tension

Question 24

Describe how neonatal respiratory distress syndrome is caused and its outcomes

Answer 24

CAUSED BY INSUFFICIENT PRODUCTION OF PULMONARY SURFACTANT
• 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

Question 25

State 2 ways insufficient surfactant production can be treated

Answer 25

1. Maternal glucocorticoid supplementation

2. Artificial surfactant supplementation of infant

Question 26

State the possible outcomes of neonatal respiratory distress syndrome

Answer 26

1. Pulmonary vasoconstriction
   
   2. Endothelial damage
   3. Acidosis
2. Pulmonary and cerebral haemorrhage

Question 27

Describe how neonatal respiratory distress syndrome arises

Answer 27

1. Premature birth
   
   2. Maternal diabetes
2. Congenital developmental issues