Lung Function Testing

Question 0

Describe the measurement of forced vital capacity (FVC) and forced expiratory volume in one second (FEV1)

Answer 0

FVC - maximum inspiration –> maximum expiration
FEV1 - forced expiratory volume in 1s
FEV1:FVC normally >70%

Question 1

Explain common tests of lung function including simple spirometry

Answer 1

Spirometry - take a deep breath in –> breathe out as fast and as far as possible in the spirometer until it feels as if lungs are completely empty
Spirometry produces a vitalograph trace (volume expired vs time)

Question 2

Explain obstructive and restrictive patterns of spirometry

Answer 2

Obstructive - narrowed airways, lungs fill but air comes out more slowly (FVC normal), FEV170%

Question 3

Explain expiratory and inspiratory flow volume loops and how they are affected by upper and lower respiratory airway obstruction

Answer 3

Flow volume curve (flow vs volume expired)
Peak expiratory flow rate (PEFR) used as an insensitive screening test
Full lungs (airways stretched) = maximal flow rate
As lungs compress (increased resistance) = flow rate falls
Scalloping pattern with asthma

Question 4

Describe in principle the measurement of residual volume and transfer factor

Answer 4

Residual volume:
Helium dilution test - measures functional residual capacity
Helium can’t transfer across alveolar membrane so contained in lungs
Residual volume = functional residual capacity - expiratory reserve volume
Transfer factor:
Measures diffusion conductance
Carbon monoxide has a high affinity for Hb –> CO from alveolar blood limited by diffusion capacity of lung

Question 5

Explain the nitrogen washout curve

Answer 5

Determines anatomical dead space
Patient takes maximum inspiration of 100% O2
O2 reaching alveoli mixes with N2, dead space = 100% O2
Patient exhales through one way value that measures N2