10 - Spirometry Flashcards
What is the normal ventilation perfusion ratio?
1 = Optimal
- Ventilation rate: 4.9L/min
- Perfusion rate: 4.9L/min
What is the commonest cause of hypoxaemia?
Ventilation Perfusion mismatch
What happens when pulmonary artery capillaries pO2 and pCO2 fall?
O2: Hypoxic vasoconstriction to divert blood to better ventilated alveoli
CO2: bronchoconstriction to divert air to better perfused lung
What are some causes of inadequate ventilation and therefore a ventilation perfusion mismatch?
- Pneumonia
- RDS in newborns
- Ashtma (early stages)
- COPD
- Pulmonary oedema
V/Q <1 so hypoxia
What happens when V/Q falls below 1 to compensate?
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
What does shunting in the blood mean?
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).
What are some causes of inadequate perfusion and therefore a ventilation perfusion mismatch?
- 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
If there is a PE in the left upper lobar artery, what causes hypoxia in the circulation?
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
Why might you do lung function tests?
What equipment do we use for spirometry?
Vitalograph (electronic)
Should a patient be seated or standing when measuring their FVC?
Seated as although higher in standing the high intrathoracic pressure can reduce cardiac output and cerebral blood flow so might faint
How does a non-electronic bell jar spirometer work?
Label the following parameters on a spirogram:
- Tidal volume
- IRV
- ERV
- RV
- VC
- Total lung capacity
- Functional reserve volume
How do you work out the following:
- Inspirational capacity
- Functional residual capacity
IC: (Tidal volume + IRV) or (TLC - FRV)
FRC: ERV + RV
Define the following terms:
- FVC
- FEV1
- PEF
How can we predict FVC in a patient?
- Normogram using weight, height, gender
How does a time-volume graph differ from a spirogram?
- Spirogram is one on left
- Time volume graph just looks at FVC not tidal volume before and after
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?
- Airway narrowed or blocked, e.g asthma, COPD
- FVC nearly normal
- FEV1 markedly reduced
- FEV1/FVC ration <70%
- PEF will be lowered
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?
- 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%
What does a flow volume loop look like?
- Time like clock around the outside
- Expiration steep at first as air expired from largest airway first
What does a flow volume loop look like in obstructive and restrictive respiratory disease?
- 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
What is the difference between the two obstructive diseases of asthma and COPD on a flow-volume loop?
More scalloping on COPD and now improvement after bronchodilator administration
What will a laryngeal polyp or tracheal stenosis do to a flow volume loop?
What does vocal cord dynsfunction look like on a flow volume loop?
What would a flow volume lop look like with a mixture of obstructive and restrictive lung disease?
How would you measure the PEFR in an OSCE?
What are some cases where spirometry should not be carried out?
