Week 3 - Lung function tests

Question 1

Explain simple spirometry

Answer 1

• Pt takes larges forces inspiration and blows as hard as they can for as long as they can
• The results are plotted on a volume vs time on a vitalograph
• Measurements are compared to standards accounting for age, sex and height (normogram)
• Gives you many different readings such as TLC, FEV1/FVC etc

Question 2

What is the normal picture of a vitalograph? What does it show?

Answer 2

• Initial rapid rise with plateau
• Shows forced vital capacity and forced expiratory volume in 1 second
• FEV1:FVC = 70%

Question 3

What is FVC?

Answer 3

• Forced vital capacity

- Maximum volume which can be expired from full lungs

Question 4

What is FEV1?

Answer 4

-Forced expiratory volume in 1 second

Question 5

Describe an obstructive pattern on a vitalograph

Answer 5

-Same FVC but with decreased slope so FEV1:FVC

Question 6

Give 3 diseases which produce obstructive vitalographs

Answer 6

• COPD
• Asthma
• Emyphysema

Question 7

Describe a restrictive pattern on a vitalograph

Answer 7

-Decreased FVC with not effected FEV1 producing a normal or high ratio
(lungs cannot fill)

Question 8

Give 3 causes of restrictive lung diseases

Answer 8

• Fibrosis
• Interstitial lung disease
• Pneumothorax

Question 9

Define tidal volume

Answer 9

-Volume of air in and out with each breath (typically 0.5L)

Question 10

Define Inspiratory reserve volume

Answer 10

-Extra vol which can be breathed in over that at rest

Question 11

Define expiratory reserve volume

Answer 11

-Extra vol which can be breathed out over rest

Question 12

Define residual volume

Answer 12

-vol remaining in lungs after maximum expiration

Question 13

What is a capacity?

Answer 13

-two or more volumes added together

Question 14

define vital capacity

Answer 14

-max inspiration to max expiration (TV+IRV+ERV)

Question 15

Define inspiratory capacity

Answer 15

-maximum inspiration from resting expiration (TV+IRV)

Question 16

Define functional residual capacity

Answer 16

-vol air in lungs at resting expiratory level (ERV+RV)

Question 17

Define total lung capacity

Answer 17

-Vol of air after maximal inhalation (VC+RV)

Question 18

What factors influence vital capacity?

Answer 18

Inhalation factors
-Lung compliance 
-Force of inspiratory muscles
Exhalation factors
-airway resistance

Question 19

What is a disadvantage of single breath spirometry?

Answer 19

-technique greatly effects result ie very user dependant

Question 20

What are the advantages of lung-function tests?

Answer 20

• Non-invasive
• Cheap
• Technically simple
• Measures volume and flow

Question 21

If the obstructive pattern on a vitalograph is reversible what does it indicate?

Answer 21

-Asthma

Question 22

What is Peak expiratory flow rate?

Answer 22

-Simple cheap measurement screening for airway narrowing by measuring the peak flow rate when the lungs are full so there is minimal resistance

Question 23

What is a flow volume curve?

Answer 23

-A graph which plots volume vs flow using the measurements from a vitalograph

Question 24

Why when the lungs are full is flow the fastest?

Answer 24

-Airways stretched meaning minimal resistance with maximum recoil -> fastest flow

Question 25

What are the advantages of volume flow curves?

Answer 25

• Sensitive
• Can detect problems early in disease
• Can discriminate where in the tract the problem lies

Question 26

Describe and explain an obstructive pattern of disease on a volume flow curve

Answer 26

• Normal upwards slope with an indented downwards slope
• As exhalation occurs and the airways begin to narrow, the obstruction greatly increases resistance more than usual and the flow declines
• the narrower the airways to start the more rapidly it falls

Question 27

Describe a restrictive pattern of disease on a volume flow curve

Answer 27

-Narrowed flow volume curve as there is no problem with flow but an overall decrease in volume

Question 28

How do you measure residual volume? Describe this test

Answer 28

• Helium dilution
• helium is a non-toxic inert gas which cannot cross capillary membrane
• Pt. breaths in helium from container with known He conc until equilibrium is reached
• The new conc of He in the chamber is used to calculate FRC from which you can calcuate RV

Question 29

Describe Nitrogen washout

Answer 29

• Measures anatomical deadspace
• Patient takes max inspiration of 100% O2
• O2 reaching alveoli mixes with residual volume where as air in conducting portion will be 100% O2
• Pt exhales through one way valve and %N2 in inhaled air and volume of air calculated
• A graph of n2 vs exhaled vol is plotted
• initially n=0% but as alveolar air exhaled and mixes with deadspace air a plateau is reached after which only alveolar air exhaled
• Deadspace determines from graph where area A = Area B

Question 30

Describe a test used to measure diffusing capacity of the lung

Answer 30

• CO transfer factor
• Measures rate of transfer of CO from alveoli to blood in ml/min/kPa
• CO has increased affinity for Hb so only limiting factor is diffusion capcity
• Pt. takes rapid and full inspiratory vital capacity of air containing low CO conc.
• Breath held for 10 seconds
• Alveolar sample collected mid expiration (discard dead space)
• remaining conc of CO in sample measured