6.12 - Pulmonary Function Tests

Question 1

What are restrictive disorders?

Answer 1

• extra-airway diseases that restrict the ability for the lungs to fill
• ‘bear-hug disorders’
• tissue-based change that doesn’t allow itself to expand in thorax
• can be due to something outside the thorax e.g. obesity or inside e.g. pulmonary fibrosis

Question 2

What are obstructive disorders?

Answer 2

• airway diseases that are associated with obstructed airflow
• e.g. goblet cells secreting mucus with inflammation that has thickened the walls
• e.g. emphysemic breakdown of parenchyma (alveoli) connective tissue - ability for lung to recoil and resist stretch is lower due to loss of elastance and more compliance (more willing to distort under pressure) = larger total lung capacity and reduced vital capacity (due to amplified residual volume)
• e.g. asthma, COPD

Question 3

What are peak flow meters used for?

Answer 3

• measuring airway resistance by measuring peak expiratory flow rate
• cheap and accessible kit
• you blow into the tube as hard and fast as you can and it moves a thing up inside it
• then compare the reading on that to a chart for gender and height

Question 4

What is FVC?

Answer 4

• forced vital capacity - the maximum amount of air you can breathe out
• total lung capacity - reserve volume
• TV + ERV + IRV

Question 5

What is FEV1?

Answer 5

• forced expiratory volume - forced expiratory volume (how much air you breathe out) in the first second
• read off volume for 1s on volume-time curve

Question 6

What are the units for a volume-time curve?

Answer 6

• X-axis - time (seconds)
• Y-axis - volume (litres)

Question 7

What can you derive from a volume-time curve?

Answer 7

• FVC - maximum point - where the curve plateaus
• FEV1 - volume expired at 1s on X-axis
• peak expiratory flow rate - gradient of steepest part of the curve, multiplied by 60 to get it in L/min

Question 8

What is the protocol for making a volume-time curve?

Answer 8

1. patient wears noseclip
2. patient inhales steadily to total lung capacity
3. patient wraps lips around mouthpiece
4. patient exhales as hard and fast as possible
5. exhalation continues until reserve volume is reached
6. visually inspect performance and volume-time curve and repeat if necessary - look out for inconsistencies with clinical picture and interrupted flow data

Question 9

What does an obstructive line look like on a volume-time curve?

Answer 9

• more shallow due to more airway resistance so reduction in rate of air which can be moved
• reduced FVC due to increase in residual volume due to emphysema of tissues/muscles not strong enough to inflate lungs
• lower gradient, longer to plateau

Question 10

What does a restrictive line look like on a volume-time curve?

Answer 10

• FVC is lower than expected
• FEV1 pretty much expels all air - most air expelled in one second

Question 11

What are the FEV1/FVC ratios of normal, restrictive and obstructive curves?

Answer 11

• normal: 75-100% (84%)
• restrictive: 100% - normally 100%, a restrictive ratio does not always mean disease, since small sporty people with large airways and small lungs can empty lungs quickly
• obstructive: <75% (53%) - not necessarily disease

Question 12

What is the protocol for making a flow-volume loop?

Answer 12

1. patient wears noseclip
2. patient wraps lips around mouthpiece
3. patient completes at least one tidal breath (A&B)
4. patient inhales steadily to total lung capacity (C)
5. patient exhales as hard and fast as possible (D)
6. exhalation continues until residual volume is reached (E)
7. patient immediately inhales to total lung capacity (F)
8. visually inspect performance and volume-time curve and repeat if necessary - look out for inconsistencies with clinical picture and interrupted flow data

Question 13

What is the flow envelope?

Answer 13

• the red triangle expiration part of graph
• if your expiration is truly maximal effort, you can never get past the flow envelope i.e. it is the maximum flow rate change at any one point of you breathing out

Question 14

What is PEF from flow-volume loop?

Answer 14

Peak expiratory flow rate (x60 to get in L/min, giving an answer in the 100s) - highest y-axis point

Question 15

How do you calculate vital capacity from flow-volume loop?

Answer 15

highest point where curve crosses X-axis - origin

Question 16

How do you calculate IRV from flow-volume loop?

Answer 16

first point where curve crosses X-axis (after origin) - origin

Question 17

How do you calculate tidal volume from flow-volume loop?

Answer 17

second point where curve crosses X-axis - first point where curve crosses X-axis

Question 18

How do you calculate ERV from flow-volume loop?

Answer 18

highest point where curve crosses X-axis - second point where curve crosses X-axis

Question 19

What does a mild obstructive disease flow-volume loop look like?

Answer 19

• curve is narrower - reduced vital capacity
• coving - lower rate of expiration
• lower maximum flow rate
• indented exhalation curve

Question 20

What does a severe obstructive disease flow-volume loop look like?

Answer 20

• smaller loop size means worse disease
• reduced FVC
• reduced PEFR
• indented exhalation curve

Question 21

What does a restrictive disease flow-volume loop look like?

Answer 21

• normal gradient at the start and peak slightly lower as less stretch in system
• lower vital capacity (characteristic feature - narrower curve) since you cannot fill to max volume due to the ‘bear hug’ but the air we do have we can get rid of easily

Question 22

What does variable extrathoracic obstruction flow-volume loop look like?

Answer 22

• blunted inspiratory curve, otherwise normal
• this obstruction lets you breathe out like normal but restricts rate of breathing in - inspiratory flow limitation
• lower portion of curve is shorter

Question 23

What does variable intrathoracic obstruction flow-volume loop look like?

Answer 23

• blunted expiratory curve, otherwise normal
• this obstruction lets you move air into the lung easily but for expiration the blockage creates a flow limitation so rate of expiration blunted - expiratory flow limitation
• upper portion of curve is shorter

Question 24

What does a fixed airway obstruction flow-volume loop look like?

Answer 24

• if the blockage is not variable, we get blunting on both sides at a matched rate
• blunted inspiratory and expiratory curve, otherwise normal
• upper and lower portions shorter

Question 25

What factors affect healthy lung volumes?

Answer 25

• age
• sex
• height