Ventilation

Question 1

What are the two components of the chest-wall?

Answer 1

Independent Lung

Independent rib cage and muscles

Question 2

What is Functional Residual Capacity?

Answer 2

FRC = ERV + RV
It is the volume of air remaining in the lungs at the end of a tidal breath. At FRC, the recoil inwards of the lungs and the recoil outwards of the chest wall are in equilibrium.

Question 3

Describe how the pleural cavity allows the chest wall and the lungs to move in unison.

Answer 3

The pleural cavity has a fixed volume and is at negative pressure. This means that when the chest wall expands, the lung gets pulled with it.

Question 4

How may the fixed volume of the pleural cavity be compromised?

Answer 4

The pleural lining could get punctured in the case of a haemothorax or pneumothorax.

Question 5

Which volumes make up each of the following capacities:
Total Lung Capacity
Vital Capacity
Functional Residual Capacity
Inspiratory Capacity

Answer 5

Total Lung Capacity - all the volumes together
Vital Capacity - expiratory reserve volume, inspiratory reserve volume + tidal volume
Functional Residual Capacity - ERV + RV
Inspiratory Capacity - TV + IRV

Question 6

Define Tidal Volume.

Answer 6

The amount of inspiration and expiration that meets metabolic demands.

Question 7

Why can’t we totally expel all air from our lungs?

Answer 7

The surfactant in the alveoli prevent the alveoli from collapsing and so you can’t expel all the air from the lungs.

Question 8

What unit is commonly used when describing lung pressures?

Answer 8

Unit: cm H2O

Question 9

What are the three main lung pressures involved in respiratory mechanics? Define them.

Answer 9

Transthoracic = pressure difference between pleural cavity and the atmosphere
Transpulmonary Pressure = difference between alveolar and intrapleural pressure
Transrespiratory Pressure = tells us the direction of airflow in the airways

These are collectively known transmural pressures

Question 10

Give two examples of positive pressure breathing.

Answer 10

CPR and Ventilators

Question 11

What is the difference in alveolar pressure between the end of a tidal expiration and the end of tidal inspiration? Explain your answer.

Answer 11

NO DIFFERENCE - during inspiration, the thoracic cavity expands and so the alveoli expand and the pressure decreases. Air is drawn in to the alveoli and the pressure becomes the same as it was at the end of expiration.

Question 12

Define Dead Space.

Answer 12

Parts of the airways and lungs that do not participate in gas exchange.

Question 13

What are the two different types of dead space?

Answer 13

Anatomical Dead Space and Alveolar Dead Space

Question 14

What is the normal physiological dead space of a healthy individual?

Answer 14

150 mL - physiological dead space is usually equivalent to anatomical dead space because normal healthy people don’t have alveolar dead space

Question 15

State two reversible procedures that can change dead space.

Answer 15

Tracheostomy and ventilators

Question 16

Explain the chest wall relationship diagram (volume against pressure).

Answer 16

Expanding the chest wall to 6 L takes relatively little pressure because its natural tendency is to expand. Expanding the lungs to 6 L takes a lot more effort and pressure because its natural tendency is to recoil inwards.

Question 17

Define FVC, FEV1 and FET.

Answer 17

Forced Vital Capacity - volume of air that can be expelled from the lungs after a full inspiration
Forced Expiratory Volume 1 - maximum volume of air that can be expired within 1 second
Forced Expiratory Time - time taken to fully empty the lungs (except residual volume)

Question 18

How would these values change for a) someone with obstructive lung disease, b) someone with restrictive lung disease?

Answer 18

Obstructive lung disease: FVC = decrease, FEV1 = decrease, FET = higher

Restrictive lung disease: FVC = decrease, FEV1 = high

Question 19

State normal FEV1/FVC values for a normal person, someone with obstructive lung disease and someone with restrictive lung disease.

Answer 19

Normal = 73, 
Obstructive = 53, 
Restrictive = 87

Question 20

Describe the general arrangement of a flow-volume loop.

Answer 20

Flow rate against volume - distance from the x axis indicates flow rate. Positive y direction indicates that the air is moving out (expiration) and a negative y direction suggests that the air is moving in (inspiration).

Question 21

Describe how the flow-volume loop changes for a) mild obstructive disease, b) severe obstructive disease and c) restrictive disease.

Answer 21

Mild Obstructive - the loop would move to the left because there is an increase in residual volume. The top right line will be indented.

Severe Obstructive - same as mild obstructive but the top right line will be even more indented.

Restrictive - the loop will be narrower and it may move to the right.

Question 22

Describe how the flow-volume loop will change for a) variable extrathoracic obstruction, b) variable intrathoracic obstruction and c) fixed airway obstruction.

Answer 22

Variable Extrathoracic - inspiratory curve will be flattened

Variable Intrathoracic - expiratory curve will be flattened

Fixed Airway Obstruction - both the inspiratory and expiratory curves will be flattened