Natalie - Pulmonary Exam Questions

Question 1

Explain intra pleural pressure

Answer 1

Pressure in the pleural cavity

Question 2

How does intra-pleural pressure affect ventilation
(4)

Answer 2

Lower than atmospheric pressure

Lower than alveolar pressure (at rest) so alveoli push outwards and lungs remain inflated

Balanced by recoil pressure of lungs -> lungs recoil on exhalation to balance PIP

Pleural fluid doesn’t expand so its pressure drops on inhalation (more negative)

Question 3

Explain intra-alveolar pressure
(3)

Answer 3

Pressure within the alveoli
themselves

Pressure is determined by:
- amount of air in the alveoli
- the volume of the alveoli themselves

Question 4

How does intra-alveolar pressure affect ventilation
(3)

Answer 4

This pressure is higher than intra-pleural pressure (lungs exert pressure outwards so they don’t collapse)

Pressure = -1 mmHg during inhalation

Pressure = +1 mmHg during exhalation

Question 5

What is a pneumothorax

Answer 5

The presence of air within the pleural space

Question 6

How does a pneumothorax affect ventilation

Answer 6

Intra-pleural pressure exceeds intra-alveolar pressure and the lung collapses

Question 7

Define compliance
(2)

Answer 7

A measure of the ease at which our lungs can stretch

The change in lung volume that results from a given change in transpulmonary pressure

Question 8

Describe compliance in the normal lung

Answer 8

Compliance is higher as we inhale -> lung is very compliant when we inhale -> stretches out

Question 9

Give the equation for lung compliance

Answer 9

Change in lung volume/change in transpulmonary pressure

Question 10

What is the normal value for lung compliance?

Answer 10

200mls/cmH2O

Question 11

What is compliance the inverse of?

Answer 11

Elastic recoil

Question 12

Why is large lung compliance a good thing?

Answer 12

Because a smaller change in transpulmonary pressure is needed to bring a given volume of air

Therefore less work or muscle contraction is required

Question 13

What can affect compliance?
(3)

Answer 13

The compliancy of the chest wall

Compliance of the thorax - changes in arthritis

Upper body obesity

Question 14

Why are the lungs normally compliant

Answer 14

Elastic natures of tissues (elastin and collagen)

Surfactant

Question 15

How does the normal healthy alveolus function

Answer 15

It resists stretching

It recoils back into shape after stretching

Question 16

What does emphysema do to the lung?
(Affect on compliance)
(5)

Answer 16

Lung is more compliant on inhalation because the spaces fill quickly

Air cannot get out

Loss of alveoli

Loss of some large airways

Small airways are narrowed and reduced in number

Question 17

There is a loss of alveoli in the lung in emphysema, what affects does this have
(3)

Answer 17

Alveoli near the terminal bronchioles -> airways become narrowed because alvoli around them collapse and cannot stay open (loss of radial traction)

Initially compliance increases but this leads to reduced compliance because air becomes trapped

Less diffusion occurs

Question 18

Why is the initial increase in compliance not beneficial for patients in emphysema

Answer 18

Not beneficial as it traps air in the lung and increases the residual volume

This leads to barrel chest syndrome

Question 19

Define airway resistance

Answer 19

Airway Resistance refers to the resistance of
the entire system of airways in the respiratory system

Question 20

How does lung disease affect resisistance

Answer 20

ho

Question 21

Why is Poseuille’s Law used?

Answer 21

The tubes (airways) in the lung are branching
(tortuous) so this Law is most appropriate to
determine resistance in these airways

Question 22

What is the equation for Poseuille’s Law

Answer 22

Resistance = 8 x n x L / pi x R4

n = viscosity
L = length
R = radius
pi = pi

Question 23

Define Poseuille’s Law

Answer 23

The resistance is directly proportional to the
viscosity of the fluid and the length of the tube and is inversely proportional to the fourth power of the radius of the tube

Question 24

Describe the relationship between Poseuille’s law and resistance

Answer 24

small changes in radius produce large changes in
resistance. E.g. if radius is cut in half, the resistance is multiplied by 16 because resistance is inversely
proportional to the radius to the fourth power

Question 25

Describe the resistance in a normal lung
(2)

Answer 25

resistance in the lung is
normally low, even though there are more smaller tubes than larger ones.

Resistance overall does not increase in
the lung because the resistance is evened out across the
smaller airways

Question 26

Why is low resistance in the lung good?

Answer 26

This low resistance
means that alveolar pressure need not differ much from
atmospheric pressure to achieve normal rates of airflow
under normal conditions

Question 27

What factors affect resistance in the lung?
(5)

Answer 27

Increased contractile activity of smooth muscle in the bronchioles. (Asthma and bronchitis)

Secretion of mucous into the airways. (Asthma and
bronchitis)

Airway collapse because of loss of alveoli. (Emphysema)

Forced expiration aggravates airway collapse.
(Coughing)

Intra-pleural pressure can be increased to greater
than airway pressure. (Pneumothorax

Question 28

What causes a pneumothorax?
(4)

Answer 28

Pneumothorax is the presence of air within the
pleural space

Due to disruption of parietal, visceral or mediastinal
pleura

May also occur from spontaneous rupture of
subpleural bleb - tall athletic young males.

A tension pneumothorax occurs when pleura form a
one-way flap valve