Lung function testing Flashcards
Why do we measure lung function?
- Evaluation of breathlessness
- Screening for COPD or occupational lung disease
- Pre op assessment
- Lung cancer - fitness for treatment
- Disease progression and treatment response
- Monitoring of drug treatment toxic to the lungs
- Pulmonary complications of systemic disease
How would you explain how to do spirometry for a patient?
- Take a big breath in as far as you can and blow out as hard as you can for as long as possible then take a big breath all the way in
- Best of 3
What are the pitfalls of spirometry?
- Requires an appropriately trained technician
- Effort and technique dependent
- Patient frailty
- Pain, patient too unwell
What is tidal volume?
Volume of air breathed in and out in a single breath
What is inspiratory reserve volume?
volume breathed in by max inspiration at end
of normal inspiration
What is expiratory reserve volume?
volume of air expelled by max effort at the end
of normal expiration
What is residual volume?
Volume of air in the lungs at the end of maximum expiration
What is inspiratory capacity?
maximum volume of air inspired after a normal expiration
What is vital capacity?
The volume of air that can be breathed in after a maximum expiration
What is the normal FEV1/FVC ratio?
> 70%
What spirometry results suggest an obstructive lung disease?
- FEV1/FVC ratio <70%
* Reduced FEV1
What is the severity of COPD stratified by in terms of spirometry results?
Stratified by % predicted FEV1 •Mild >80% •Moderate 50-80% •Severe 30-50% •Very severe <30%
What is reversibility testing?
- Nebulised or inhaled salbutamol is given
- Spirometry performed before and 15 minutes after salbutamol
- 15% and 400ml reversibility in FEV1 is suggestive of asthma
Aside from spirometry, what tests can be done to investigate asthma?
•PEFR testing
- look for diurnal variation and variation over time
- Response to inhaled corticosteroid
- Occupational asthma
•Bronchial provocation
•Spirometry before and after trial of inhaled/oral corticosteroid
What are the spirometry results suggestive of a restrictive lung disease?
- It will have the same curve but will just be smaller as a regular spirometry result
- FEV1 and FVC reduced
- FEV1/FVC ratio >70%
What are the causes of restrictive spirometry results?
- Interstitial lung disease
- kyphoscoliosis/ chest wall abnormality
- Previous pneumonectomy
- Neuromuscular disease
- Obesity
- Poor effort/technique
Describe the test for measuring transfer factor
- Single breath of a very small concentration of carbon monoxide
- CO has a high affinity to Hb
- Measure concentration in expired gas to derive uptake in the lungs
What is transfer factor affected by?
- Alveolar surface area
- Pulmonary capillary blood volume
- Haemoglobin concentration
- Ventilation perfusion mismatch
What is transfer factor reduced in?
- Emphysema
- Interstitial lung disease
- Pulmonary vascular disease
- Anaemia (increased in polycythaemia)
What are the methods of measuring lung volumes?
- helium dilution (inspire a known quantity of an inert gas)
- Body plethysmography
What are the effects of restrictive and obstructive lung diseases on lung volumes?
- Lung volumes reduced in restrictive lung disease
* Increased reserve volume and total lung capacity in obstructive lung disease
What does a reliable oximetry result depend on?
Adequate perfusion
What are the main causes of hyperaemia?
- Hypoventilation (e.g. drugs, neuromuscular disease)
- Ventilation/perfusion mismatch (e.g. COPD, pneumonia)
- Shunt (e.g. congenital heart disease)
- Low inspired oxygen (altitude, flight)
What is ventilation perfusion mismatch?
- Happens to a degree in normal lungs (bottom better perfused, top better ventilation)
- Areas of the lung that are well perfused and not well ventilated
- Mixing of blood from poorly ventilated and well ventilated parts of the lung causes hypoxaemia
