Session 3 - part II

Question 1

What is non invasive lung testing?

Answer 1

Lung function is inferred by measuring volumes, pressures, flows, composition (at mouth)

Question 2

What limits vital capacity?

Answer 2

Maximum inspiration (effected by compliance of the lungs, force of muscles)
Maximum expiration (effected by airway resistance)

Question 3

Why might vital capacity be lower than expected?

Answer 3

The patient may not be able to breathe out or in maximally.

Question 4

How can you investigate the reason for vital capacity being lower than expected?

Answer 4

Single breath spirometry (The patient fills their lungs with atmospheric air and breathes out as far and fast as possible)

Question 5

What is a Vitalograph trace?

Answer 5

A plot of volume expired Vs time. Would be an initial rapid rise followed by a plateau

Question 6

What is FEV1?

Answer 6

Volume expired in the first second

Question 7

Define Forced vital capacity

Answer 7

Maximum volume that can be expired from full lungs which is usually 5L

Question 8

What effects FEV1?

Answer 8

How quickly air slows down. So it is lower if the airways are narrowed. It is usually >70% FVC

Question 9

What is FVC?

Answer 9

The percentage of the total volume that leaves in the first second

Question 10

What can effect FVC?

Answer 10

Restrictive defects. The lungs are harder to fill due to them being stiff, muscle weakness or problems with the chest wall. This causes the lungs to begin being less full so FVC will be reduced. Air will still leave normally so FEV1 will still be >70% of FVC

Question 11

What causes FEV1 to be reduced?

Answer 11

An obstructive defect. The airways are narrowed, but still easy to fill the lungs. However, resistance will increase in expiration so air will come out more slowly therefore FEV1 will be longer. FVC will be relatively normal

Question 12

What are flow volume curves?

Answer 12

A plot of volume expired Vs flow rate. Derived from Vitalograph trace

Question 13

When is flow rate maximal?

Answer 13

When the lungs are full as little air is expired. The airways are stretched so resistance is minimum

Question 14

What is PEFR?

Answer 14

Peak Expiratory Flow Rate (Effected in asthma. Limited by larger airways)

Question 15

When does flow rate fall?

Answer 15

As the lungs are compressed, more air is expired. The airways begin to narrow and resistance increases. The narrower the airways are to begin with, the more rapidly it falls

Question 16

What is a good indicator of airway narrowing?

Answer 16

Flow volume curves

They can also show whether the narrowing airways is a large or small airway

Question 17

How can you measure Residual volume?

Answer 17

With a helium dilution (Helium as it is not naturally occurring in the air and it is insoluble in blood)

Question 18

How does a Helium dilution test work?

Answer 18

A known concentration of Helium is breathed in

Starting at the FRC and see how much the concentration is reduced by mixing with the residual air already in the lungs.

Question 19

What is a nitrogen wash out used for?

Answer 19

Serial dead space and indirectly can measure ventilation perfusion matching

Question 20

How is a nitrogen wash out performed?

Answer 20

The patient takes a breath of pure O2 (Mixes with the air already in the lungs)
Patient then breathes out via a meter measuring % nitrogen
O2 leaves, then O2 and air (including N2 from alveoli)
The volume expired at the transition is the serial dead space

Question 21

Define conductance

Answer 21

How easily a gas passes across a barrier

Question 22

How do you measure the conductance of O2?

Answer 22

Has a similar conductance to CO and it is not usually in the blood so use CO in the test,
Patient breathes in a known volume of CO, then can measure CO in blood so can infer how much has crossed the alveolar barrier