Week 3 - Lung Function Tests

Question 1

What do lung function tests give an assessment of?

Answer 1

Mechanical conditions of the lungs, resistance of airways, alveolar membrane

Question 2

What is spirometry?

Answer 2

Breath from a closed chamber over water and the volume changes with ventillation

Question 3

What is tidal volume?

Answer 3

Volume in and out with each breath

Question 4

What is inspiratory reserve volume?

Answer 4

Extra volume that can be breathed in past the usual tidal volume

Question 5

What is expiratory reserve volume?

Answer 5

Extra volume that can be breathed out past the usual tidal volume

Question 6

What is residual volume?

Answer 6

Volume remaining in lungs after maximal expiration

Question 7

Can residual volume be measure by spirometry?

Answer 7

No

Question 8

Why is it important to calculate residual volume?

Answer 8

Because it contributes to total lung capacity

Question 9

What is the difference between capacity and volume?

Answer 9

Capacity is 2 or more volumes added together, volumes can change depending on breathing pattern, capacities are fixed

Question 10

What is vital capacity?

Answer 10

Measured from maximum inspiration to maximum expiration, often changes with disease, usually about 5l in an adult

Question 11

How is vital capacity calculated?

Answer 11

Inspiratory reserve volume + tidal volume + expiratory reserve volume

Question 12

What is inspiratory capacity?

Answer 12

Biggest breath that can be taken from resting expiratory level which is lung volume at end of quiet expiration

Question 13

What is the typical value for inspiratory capacity?

Answer 13

3l

Question 14

What is functional residual capacity?

Answer 14

Volume of air in lungs at resting expiratory level

Question 15

How do you calculate functional residual capacity?

Answer 15

Expiratory reserve volume + residual volume

Question 16

What is the typical value for functional residual volume?

Answer 16

2l

Question 17

What is total lung capacity?

Answer 17

Volume of gas in lungs at end of maximal inspiration

Question 18

What is the typical value for total lung capacity?

Answer 18

5.8l

Question 19

What factors influence vital capacity?

Answer 19

Inspiration - compliance of lungs, force of inspiratory muscles
Expiration - airway resistance, increases as expiration proceeds

Question 20

What factors do you have to take into account when assesing capacity?

Answer 20

Height, sex, age

Question 21

What is single breath spirometry?

Answer 21

Fill lungs, breathe out as far and fully as possible, volume is measured over time, measuring how much and how fast the air is breathed out

Question 22

What is a vitalograph?

Answer 22

Plot of volume expired vs time

Question 23

What is FEV1.0?

Answer 23

Volume expired in first second

Question 24

What si the usual difference between FEV1.0 and forced vital capacity?

Answer 24

Normally >70%

Question 25

How will FEV1.0 and forced vital capacity be affected by affected by narrowed airway?

Answer 25

Will still fill easily by resistance increases on inspiration so air will come out more slowly This means FEV1.0 will be reduced but FEC will be relatively normal

Question 26

How is spirometry used to measure reversibility?

Answer 26

Performed before and after treatment with bronchodilator drugs and if its reversible suggests asthma

Question 27

If lungs are difficult to fill what does this suggest?

Answer 27

Stiff, weak muscles, problem with chest wall

Question 28

How would lungs that are difficult to fill affect FVC and FEV1.0?

Answer 28

They will start less full so FVC will be reduced but the air will come out normally so FEV1.0 will still be >70% of FVC

Question 29

What are flow volume curves?

Answer 29

Plots volume against flow

Question 30

What is peak expiratory flow rate used for?

Answer 30

Measures with a simple cheap device so often used as a screening test for airway narrowing but it is very insensitive

Question 31

Are flow volume curves good for interpreting disease?

Answer 31

Yes, can detect problems earlier in the course of disease than simple spirometry, can discriminate where in the tract the problem lies

Question 32

How would obstruction be shown on a flow volume curve?

Answer 32

Lungs are compressed, more air expired, airways begin to narrow, resistance increases and flow rate falls, the narrower the airways to start with the more rapidly it falls, curve will have normal peak but decreases faster

Question 33

How would a restrictive pattern show on a flow volume curve?

Answer 33

Curve narrowed, shape generally the same as normal but flow is always less at comparable volumes

Question 34

How is residual volume measured?

Answer 34

Helium is not metabolised by the body, patient breathes in a know volume of gas containing a known concentration of helium starting at functional residual capacity, as patient breathes the helium concentration changes as it gets diluted because its in a larger volume - adding air already in the lungs

Question 35

How is serial dead space measured?

Answer 35

The last gas in the airways is always the first gas out, take one normal breath of pure oxygen, breath out via a meter measuring % nitrogen, initially only oxygen expired and then a mixture of oxygen and air (inc nitrogen) from alveoli, volume that has been expired at this transition is the serial dead space

Question 36

What is fowlers method for calculating serial dead space?

Answer 36

Plot the nitrogen washout results on a graph, draw a line through the curve so the 2 areas are equal and the volume up until this line is the dead space

Question 37

How is diffusion conductance measured (ease at which gas can cross the membrane)?

Answer 37

Inhale gas mixture containing CO to total lung capacity, hold breath for 10 seconds, rate of CO diffusion is estimated, gives measure of conductance of CO from alveolar gas to Hb in pulmonary capillary blood cells