10 - Spirometry Flashcards

1
Q

What is the normal ventilation perfusion ratio?

A

1 = Optimal

  • Ventilation rate: 4.9L/min
  • Perfusion rate: 4.9L/min
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2
Q

What is the commonest cause of hypoxaemia?

A

Ventilation Perfusion mismatch

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3
Q

What happens when pulmonary artery capillaries pO2 and pCO2 fall?

A

O2: Hypoxic vasoconstriction to divert blood to better ventilated alveoli

CO2: bronchoconstriction to divert air to better perfused lung

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4
Q

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

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

V/Q <1 so hypoxia

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5
Q

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

A

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
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6
Q

What does shunting in the blood mean?

A

Still perfusion but no ventilation

Shunt happens when venous and arterial blood mix and completely bypass the lungs (extrapulmonary shunt) or bypass the lungs without proper oxygenation (intrapulmonary shunt).

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7
Q

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

A

- 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
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8
Q

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

A

V/Q mismatch in right lung and left lower lobe

Pulmonary embolization causes hypoxemia by redistributing regional blood flow without changing ventilation
Leading to hypoxemia due to lack of perfusion, hypoxia

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9
Q

Why might you do lung function tests?

A
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10
Q

What equipment do we use for spirometry?

A

Vitalograph (electronic)

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11
Q

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

A

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

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12
Q

How does a non-electronic bell jar spirometer work?

A
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13
Q

Label the following parameters on a spirogram:

  • Tidal volume
  • IRV
  • ERV
  • RV
  • VC
  • Total lung capacity
  • Functional reserve volume
A
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14
Q

How do you work out the following:

  • Inspirational capacity
  • Functional residual capacity
A

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

FRC: ERV + RV

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15
Q

Define the following terms:

  • FVC
  • FEV1
  • PEF
A
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16
Q

What can forced flow-volume measurements tell us?

A

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

17
Q

How can we predict FVC in a patient?

A
  • Normogram using weight, height, gender
18
Q

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

A
  • Spirogram is one on left
  • Time volume graph just looks at FVC not tidal volume before and after
19
Q

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?

A
  • Airway narrowed or blocked, e.g asthma, COPD
  • FVC nearly normal
  • FEV1 markedly reduced
  • FEV1/FVC ration <70%
  • PEF will be lowered
20
Q

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?

A
  • 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%
21
Q

What does a flow volume loop look like?

A
  • Time like clock around the outside
  • Expiration steep at first as air expired from largest airway first
22
Q

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

A

- 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

23
Q

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

A

More scalloping on COPD and now improvement after bronchodilator administration

24
Q

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

A
25
Q

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

A
26
Q

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

A
27
Q

How would you measure the PEFR in an OSCE?

A
28
Q

How can we measure the following as they cannot be measured in spirometry?

  • Residual volume
  • Dead space
  • Diffusion capacity
A

- RV: helium dilution

- DS: nitrogen washout

  • DC: CO transfer factor as measured by resistance to diffusion across alveolar membrane
29
Q

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

A