Mechanics of Ventilation and the Effect of IPPV on the Lungs

Question 1

In relation to the pressure-volume properties of the lung:

The elastic recoil of the lung is greater than that of the chest wall at end expiration

Answer 1

False. At end expiration the force generated by the elastic recoil of the lung is exactly balanced by that of the chest wall.

Question 2

In relation to the pressure-volume properties of the lung:

The work of breathing can be calculated from a pressure-volume loop

Answer 2

True. The area inside the pressure-volume loop is correlated to the work of breathing.

Question 3

In relation to the pressure-volume properties of the lung:

Hysteresis refers to the stiffness of the lungs

Answer 3

False. Hysteresis refers to the different curves generated on a pressure-volume curve during inspiration and expiration. This is due to the elastic properties.

Question 4

In relation to the pressure-volume properties of the lung:

The gradient of the pressure-volume curve is known as the compliance

Answer 4

True. A pressure-volume curve is also known as a compliance curve. A steep part of the curve equates to a greater compliance.

Question 5

In relation to the pressure-volume properties of the lung:

Compliance is higher at low lung volumes

Answer 5

False. The pressure-volume curve is flatter at the beginning, i.e. with low lung volume, and at the end, i.e. with high lung volume, so compliance is lower.

Question 6

Surface tension in the lung:

Helps to keep alveoli open

Answer 6

False. Surface tension tends to cause alveoli to collapse in order to occupy the smallest surface area.

Question 7

Surface tension in the lung:

Is governed by Laplace’s law

Answer 7

False. Surfactant negates Laplace’s law within the alveoli.

Question 8

Surface tension in the lung:

Is reduced by surfactant

Answer 8

True. Surfactant opposes the normal attractant forces between molecules within alveoli.

Question 9

Surface tension in the lung:

Results in a lower pressure in a small alveolus than in a large alveolus

Answer 9

False. Using Laplace’s law the smaller the radius the higher the pressure generated within the alveolus, if there is no surfactant.

Question 10

Surface tension in the lung:

Is the force acting between molecules of gas and molecules of liquid

Answer 10

False. Surface tension is the force acting between molecules of liquid on the inner surface of the alveolus.

Question 11

Regarding respiratory function tests:

FEV1.0 is the time taken to forcibly expire 1 litre of air after maximal inspiration

Answer 11

Incorrect. FEV1.0 is the volume of air expired in the first second of a forced vital capacity.

Question 12

Regarding respiratory function tests:

The FEV1.0 is reduced in obstructive disease

Answer 12

Correct. This is due to increased airway resistance.

Question 13

Regarding respiratory function tests:

A raised FEV1.0 /FVC is indicative of restrictive disease

Answer 13

Correct. In restrictive disease such as pulmonary fibrosis both the FEV1.0 and FVC are reduced therefore the ratio can be normal or greater than predicted.

Question 14

Regarding respiratory function tests:

Respiratory function is dependent on weight

Answer 14

Incorrect. It is related to gender, age, height and ethnic origin.

Question 15

Regarding respiratory function tests:

An observed FEV1.0 more than 50% of predicted indicates normal lung function

Answer 15

Incorrect. A value more than 80% of the predicted value represents normal lung function. 50% to 80% is mild disease, 30% to 50% is moderate disease and less than 30% is severe disease.

Question 16

Regarding the work of breathing:

It is greater in expiration than inspiration

Answer 16

False. Expiration is a passive process during normal respiration at rest due to elastic recoil of the lungs.

Question 17

Regarding the work of breathing:

It can be calculated from a pressure-volume loop

Answer 17

True. The curve is plotted and the area within the curve measured.

Question 18

Regarding the work of breathing:

It overcomes resistive forces in the airway

Answer 18

True. Work of breathing overcomes elastic forces of the lung and chest wall and resistive forces of the airway.

Question 19

Regarding the work of breathing:

It increases if the elasticity of the chest wall falls

Answer 19

True. As elasticity falls the lungs become relatively stiff and require greater effort to expand them.

Question 20

Regarding the work of breathing:

It decreases as lung compliance falls

Answer 20

False. Compliance is a measure of how easy it is to inflate the lungs. Therefore as compliance falls the lungs are harder to inflate and hence the work of breathing increases to overcome this.

Question 21

Lung compliance:

Possible answers:
A. Is greater during expiration than during inspiration
B. Decreases with age
C. Is not dependent on the size of the lung
D. In normal lung is 20 ml/cmH2O
E. Is none of the above

Answer 21

A

B. Incorrect. Lung compliance increases with age.

C. Incorrect. It is dependent on lung size but this can be accounted for by using specific compliance and therefore allowing comparisons.

D. Incorrect. It is normally 200 ml/cmH2O

Question 22

Regarding a normal alveolus:

The surface tension is directly proportional to the radius

Answer 22

False. Surfactant negates Laplace’s law.

Question 23

Regarding a normal alveolus:

Surfactant is present on the external surface

Answer 23

False. It is on the internal surface.

Question 24

Regarding a normal alveolus:

Attractive forces between surfactant molecules stabilize alveoli at low volumes

Answer 24

False. It is the repellent forces that prevent alveoli collapsing at low lung volumes.

Question 25

Regarding a normal alveolus:

Gas from a small alveolus moves down a pressure gradient into a large alveolus

Answer 25

False. Surfactant stabilizes alveoli by reducing surface tension. This means that alveoli with different radii have similar internal pressures therefore there is little movement of gas between alveoli.

Question 26

Regarding a normal alveolus:

Surfactant keeps the lungs dry

Answer 26

True

Question 27

Regarding gas flow through the airways:

The gas flow pattern is laminar

Answer 27

False. The pattern of flow is dependent on a number of variables and therefore flow is different in different parts of the airway.

Question 28

Regarding gas flow through the airways:

Flow is more likely to be turbulent if Reynolds number is greater than 2000

Answer 28

True. The velocity of flow and the diameter of the airway can be used to predict the likelihood of turbulent flow.

Question 29

Regarding gas flow through the airways:

Gas flow is transitional at bifurcations

Answer 29

True. This is due to a reduction in the diameter of the airway at this point.

Question 30

Regarding gas flow through the airways:

It can be affected by the length of the airway

Answer 30

True. Poiseuille’s law states that the resistance to flow is increased if the length of the tube increases. An increase in resistance reduces airflow.

Question 31

Regarding gas flow through the airways:

Flow is directly proportional to the density of the gas when it is laminar

Answer 31

False. When flow is laminar the resistance to flow is governed by Poiseuille’s law. It is the viscosity of the gas that is relevant.

Question 32

Regarding respiratory function tests:

A spirometer can be used to assess lung function

Answer 32

True

Question 33

Regarding respiratory function tests:

A normal FEV1.0/FVC ratio is 60%

Answer 33

False. A normal ratio is between 75% and 80%.

Question 34

Regarding respiratory function tests:

An FEV1.0/FVC ratio of 40% indicates restrictive disease

Answer 34

False. A low ratio is indicative of obstructive disease. The FEV1.0 is reduced due to increased airway resistance but the FVC may be normal or, if there is airway trapping, high.

Question 35

Regarding respiratory function tests:

An FEV1.0/FVC ratio of 95% represents excellent lung function

Answer 35

False. An increased ratio implies that both the FEV1.0 and the FVC are reduced indicating restrictive disease.

Question 36

Regarding respiratory function tests:

Predicted/normal values are dependent on ethnic origin

Answer 36

True. Predicted values are dependent on age, gender, height and ethnic origin.