Respiratory: Lung function tests Flashcards Preview

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

Define Tidal volume

Tidal volume is the volume in and out with each breath
Can be measured with spirometry

2

Define Inspiratory reserve volume

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

3

Define Expiratory reserve volume

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

4

Define Residual volume

The volume remaining after maximal expiration
Cannot be measured with spirometry

5

Define vital capacity and give a value

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

6

Define inspiratory capacity and give a value

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

7

Define functional residual capacity and give a value

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

8

Define total lung capacity and give a value

The volume of air in the lungs after maximal expiration
Typically 5.8L

9

What factors can affect vital capacity?

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

10

What is FEV1.0?

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

11

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

FVC - normal
FEV 1.0 - reduced
The ratio will decrease

12

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

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

13

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

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

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

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

15

What method can we use to measure residual volume?

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

What method can we use to measure serial dead space?

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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