Session 3

Question 1

What is Fick’s first law of diffusion?

Answer 1

Flux of molecules across a barrier is proportional to the product of the permeability of the molecules, transfer surface area for diffusion and concentration gradient.

Question 2

Is carbon dioxide more or less soluble than oxygen? What effect does this have?

Answer 2

More soluble, allows it to diffuse easily with a smaller gradient.

Question 3

How are the lungs adapted for diffusion?

Answer 3

Large SA; small diffusion barrier; lung distension makes the diffusion barrier smaller.

Question 4

How does inspired air differ from expired air?

Answer 4

Dry; lower oxygen content; higher carbon dioxide content; same nitrogen content; same overall pressure.

Question 5

How is carbon dioxide transported in the blood?

Answer 5

Most as bicarbonate ions in the plasma; some as carboxyhaemaglobin.

Question 6

What conditions can affect membrane thickness in the lungs?

Answer 6

Oedema of the interstitial space or alveoli; fibrotic disease.

Question 7

What conditions can affect lung surface area?

Answer 7

Removal of a lung; emphysema.

Question 8

What is seral dead space?

Answer 8

The volume of the conducting portions of the airways where no gas exchange occurs.

Question 9

What is distributive dead space?

Answer 9

Parts of the lungs which don’t support gas exchange: dead or damaged alveoli; alveoli with poor perfusion.

Question 10

What is physiological dead space?

Answer 10

Combination of seral and distributive dead space.

Question 11

What is alveolar ventilation rate?

Answer 11

Pulmonary ventilation rate - dead space volume x resp rate.

Question 12

What is the normal value for AVR?

Answer 12

5 litres per minute.

Question 13

What is normal ventilation-perfusion rate?

Answer 13

1.

Question 14

What is tidal volume?

Answer 14

Volume in and out with each breath.

Question 15

What is inspiratory reserve volume?

Answer 15

Additional volume that can be inspired above that at rest.

Question 16

What is expiratory reserve volume?

Answer 16

Additional volume that can be expired above that at rest.

Question 17

What is residual volume?

Answer 17

The volume remaining after maximal expiration.

Question 18

What is vital lung capacity?

Answer 18

The largest breath a person can take.

Question 19

What is inspiratory capacity?

Answer 19

The maximum volume inhaled from resting expiratory level.

Question 20

What is functional residual capacity?

Answer 20

The volume in the lungs at resting expiratory level.

Question 21

What is total lung capacity?

Answer 21

The volume in the lungs at the end of maximal inspiration.

Question 22

What factors can influence vital capacity?

Answer 22

Compliance of the lungs and force of insporatory muscles on inspiration; airway resistance on expiration.

Question 23

What does spirometers produce?

Answer 23

A volume/time graph for ventilation.

Question 24

What can be interpreted from single-breath spirometers?

Answer 24

FEV1.0, FVC.

Question 25

How is residual lung volume measured?

Answer 25

Helium dilution: set amount of helium is inhaled; helium dilutes gases in the lungs but isn’t metabolised; level of dilution allows amount of air already in the lungs to be calculated.

Question 26

How is serial dead space measured?

Answer 26

Nitrogen washout: patient breathes in pure oxygen; breathes out through a meter measuring nitrogen concentration; volume expired before nitrogen is found is the serial dead space volume.

Question 27

Describe what is seen in obstructive pattern respiratory problems.

Answer 27

Airways are narrowed so lungs are easy to fill but hard to empty: FEV1.0 is reduced but FVC is normal.

Question 28

If obstructive respiratory problems are relieved by bronchodilators, what does this suggest?

Answer 28

Asthma.

Question 29

Describe restrictive respiratory problems.

Answer 29

Lungs are difficult to fill: FVC is reduced and FEV1.0:FVC is raised.

Question 30

Why is peak flow useful?

Answer 30

Can be used to screen for airway narrowing.