10 - Spirometry

Question 1

What is the normal ventilation perfusion ratio?

Answer 1

1 = Optimal

• Ventilation rate: 4.9L/min
• Perfusion rate: 4.9L/min

Question 2

What is the commonest cause of hypoxaemia?

Answer 2

Ventilation Perfusion mismatch

Question 3

What happens when pulmonary artery capillaries pO₂ and pCO₂ fall?

Answer 3

O₂: Hypoxic vasoconstriction to divery blood to better ventilated alveoli

CO₂: bronchoconstriction to divert air to better perfused lung

Question 4

What are some causes of inadequate ventilation and therefore a ventilation perfusion mismatch?

Answer 4

• Pneumonia
• Ashtma (early stages)
• COPD
• RDS in newborns
• Pulmonary oedema

V/Q <1 so hypoxia

Question 5

What happens when V/Q falls below 1 to compensate?

Answer 5

Hyperventilation - increases CO₂ removal but not O₂ as oxygen is fully saturated at 13.3kPa and CO₂ does not need a mismatch

• Low pO₂ and normal to low pCO₂

Question 6

What does shunting in the blood mean?

Answer 6

Still perfusion but no ventilation

Question 7

What are some causes of inadequate perfusion and therefore a ventilation perfusion mismatch?

Answer 7

- Pulmonary embolism

• Hyperventilation has to occur as there is blood redirected to other areas of the pulmonary circulation so to match increased perfusion need to raise ventilation

Question 8

If there is a PE in the left upper lobar artery, what causes hypoxia in the circulation?

Answer 8

V/Q mismatch in right lung and left lower lobe

Question 9

Why might you do lung function tests?

Answer 9

Question 10

What equipment do we use for spirometry?

Answer 10

Vitalograph (electronic)

Question 11

Should a patient be seated or standing when measuring their FVC?

Answer 11

Seated as although higher in standing the high intrathoracic pressure can reduce cardiac output and cerebral blood flow so might faint

Question 12

How does a non-electronic bell jar spirometer work?

Answer 12

Question 13

Label the following parameters on a spirogram:

• Tidal volume
• IRV
• ERV
• RV
• VC
• Total lung capacity
• Functional reserve volume

Answer 13

Question 14

How do you work out the following:

• Inspirational capacity
• Functional residual capacity

Answer 14

IC: (Tidal volume + IRV) or (TLC - FRV)

FRC: ERV + RV

Question 15

Define the following terms:

• FVC
• FEV1
• PEF

Answer 15

Question 16

What can forced flow-volume measurements tell us?

Answer 16

• Restrictive or obstructive disorder
• Pattern can indicate site of obstruction
• Response to treatment
• Change with age and growth
• Progression of disease

Question 17

How can we predict FVC in a patient?

Answer 17

• Normogram using weight, height, gender

Question 18

How does a time-volume graph differ from a spirogram?

Answer 18

• Spirogram is one on left
• Time volume graph just looks at FVC not tidal volume before and after

Question 19

What does a volume-time graph look like in an obstuctive respiratory disease, give some examples of these and what are the parameters for FEV1 and FVC?

Answer 19

• Airway narrowed or blocked, e.g asthma, COPD
• FVC nearly normal
• FEV1 markedly reduced
• FEV1/FVC ration <70%
• PEF will be lowered

Question 20

What does a volume-time graph look like in a restrictive respiratory disease, give some examples of these and what are the parameters for FEV1 and FVC?

Answer 20

• Lungs stiff so cannot expand adequately OR inspiratory effort compromised e.g lung fibrosis or muscle weakness from injury or deformity
• Low FVC and FEV1
• FEV1/FVC ration > or equal to 70%

Question 21

What does a flow volume loop look like?

Answer 21

• Time like clock around the outside
• Expiration steep at first as air expired from largest airway first

Question 22

What does a flow volume loop look like in obstructive and restrictive respiratory disease?

Answer 22

- Obstructive: scalloping concave shape as small airways narrower. Give bronchodilator and will go normal

- Restrictive: tall and narrow as vital capacity lower but PEF fine as large airways not impacted

Question 23

What is the difference between the two obstructive diseases of asthma and COPD on a flow-volume loop?

Answer 23

More scalloping on COPD and now improvement after bronchodilator administration

Question 24

What will a laryngeal polyp or tracheal stenosis do to a flow volume loop?

Answer 24

Question 25

What does vocal cord dynsfunction look like on a flow volume loop?

Answer 25

Question 26

What would a flow volume lop look like with a mixture of obstructive and restrictive lung disease?

Answer 26

Question 27

How would you measure the PEFR in an OSCE?

Answer 27

Question 28

How can we measure the following as they cannot be measured in spirometry? - Residual volume - Dead space - Diffusion capacity

Answer 28

**- RV:** helium dilution **- DS:** nitrogen washout - **DC:** CO transfer factor as measured by resistance to diffusion across alveolar membrane

Question 29

What are some cases where spirometry should not be carried out?

Answer 29