Respiratory: Lung function tests

Question 1

Define Tidal volume

Answer 1

Tidal volume is the volume in and out with each breath

Can be measured with spirometry

Question 2

Define Inspiratory reserve volume

Answer 2

Inspiratory reserve volume is the extra volume that can be breathed in at rest
Can be measured with spirometry

Question 3

Define Expiratory reserve volume

Answer 3

Expiratory reseve volume is the extra volume that can breathed out at rest
Can be measured with spirometry

Question 4

Define Residual volume

Answer 4

The volume remaining after maximal expiration

Cannot be measured with spirometry

Question 5

Define vital capacity and give a value

Answer 5

Measure of the biggest breath that can be taken - from max inspiration to max expiration
Typically ~5L but often changes in disease

Question 6

Define inspiratory capacity and give a value

Answer 6

The biggest breath in from resting expiratory level (lung volume at end of quiet expiration)
Typically ~3L

Question 7

Define functional residual capacity and give a value

Answer 7

The volume of air in the lungs at resting expiratory level
(vital capacity minus inspiratory capacity)
Typically ~2L

Question 8

Define total lung capacity and give a value

Answer 8

The volume of air in the lungs after maximal expiration

Typically 5.8L

Question 9

What factors can affect vital capacity?

Answer 9

Inspiration - compliance of lungs or force of inspiratory muscles
Expiration - airway resistance

Question 10

What is FEV1.0?

Answer 10

The volume expired in the first second - decreases if airways are narrowed
FEV1.0 should normally be more than 70% of FVC

Question 11

What will happen to.....
FVC
FEV1.0
The ratio
....in an obstructive pattern?

Answer 11

FVC - normal
FEV 1.0 - reduced
The ratio will decrease

Question 12

What will happen to.....
FVC
FEV1.0
The ratio
....in a restrictive pattern?

Answer 12

FVC - reduced
FVC 1.0 - normal
The ratio will be normal

Question 13

What will a flow volume curve look like in an obstructive pattern?

Answer 13

PEFR will be normal and volume expired will be normal but the curve will be lower on the descent (look at an image) because there is increased resistance so flow rate will fall

Question 14

What will a flow volume curve look like in a restrictive pattern?

Answer 14

The shape will be the same as normal but narrowed. The volume expired will be less
(look at an image)

Question 15

What method can we use to measure residual volume?

Answer 15

Helium dilution: helium is not metabolised so pt breathes known volume of gas with known conc of helium.
As pt breathes the helium conc will reduce because it gets diluted in the larger volume eg the air already in the lungs is added.

Question 16

What method can we use to measure serial dead space?

Answer 16

Nitrogen washout: last gas in is the first gas out. Therefore pt takes 1 breath of pure O2 then breathes out via a meter measuring %nitrogen. Initially only O2 expired but then there is a mixture of oxygen and air - the volume expired at transition is serial dead space.