Respiratory: Lung function tests Flashcards Preview

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Flashcards in Respiratory: Lung function tests Deck (16)
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1
Q

Define Tidal volume

A

Tidal volume is the volume in and out with each breath

Can be measured with spirometry

2
Q

Define Inspiratory reserve volume

A

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

3
Q

Define Expiratory reserve volume

A

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

4
Q

Define Residual volume

A

The volume remaining after maximal expiration

Cannot be measured with spirometry

5
Q

Define vital capacity and give a value

A

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

6
Q

Define inspiratory capacity and give a value

A

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

7
Q

Define functional residual capacity and give a value

A

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

8
Q

Define total lung capacity and give a value

A

The volume of air in the lungs after maximal expiration

Typically 5.8L

9
Q

What factors can affect vital capacity?

A

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

10
Q

What is FEV1.0?

A

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

11
Q
What will happen to.....
FVC
FEV1.0
The ratio
....in an obstructive pattern?
A

FVC - normal
FEV 1.0 - reduced
The ratio will decrease

12
Q
What will happen to.....
FVC
FEV1.0
The ratio
....in a restrictive pattern?
A

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

13
Q

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

A

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

14
Q

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

A

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

15
Q

What method can we use to measure residual volume?

A

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.

16
Q

What method can we use to measure serial dead space?

A

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.

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