Lung Function Tests Flashcards
Vital capacity
Volume that can be exhaled after maximum inspiration = good indicator of total lung volume (requires adequate compliance: good muscle force and low resistance)
Residual volume
Volume of air left in lungs after exhalation
Functional residual capacity
FRC = ERV + RV
Inspiratory capacity
IRV + TV
What’s the most reliable measure of airway diameter?
FEV1
Draw a time-volume curve for healthy and obstructed lungs
…
Why test lung function?
Provides aid to diagnosis
Can assess response to treatment
Useful in symptomatic patients and those at risk of pulmonary disease
In lab can assess specific changes in response
What do air flow rate and vital capacity measure?
Air flow rate - airway diameter
Vital capacity - total lung volume
Outline Expiratory Peak Flow testing/diaries
Easy and cheap - use a diary to record values and symptoms
Looks at maximal achievable flow of diameter of bronchial tree and muscle power (L/min)
Check pointer is 0, sit comfortably, hold flow meter horizontally, take a deep breath out, in then out again into the meter (as hard as you can using maximal force), check the reading on the pointer and set back to 0
Record 3 times and the highest value
On a peak flow chart, what % of variability is diagnostic of asthma?
> 20% when untreated
Readings will then gradually improve (flow rate increases) with inhaler use, but there will still be slight differences between AM and PM
Outline Spirometry
Measures FEV1 and FVC
Little risk, very effective but is expensive and requires trained technician and there’s criteria so results are universal (there are also normal values for different populations)
What’s restrictive spirometry?
FVC reduced due to restricted lung inflation (weak inspiratory muscles)
Reduction in vital capacity is best indicator of restrictive lung disease when combined with symptoms, as most common cause can just be failure to breathe out fully during test
Restrictive diseases: obesity, interstitial pulmonary fibrosis, muscle weakness
What will be reduced in obstructive airway disease and why? What other clinical sign might there be
FEV1 - increased resistance during expiration as airways are narrowed
But RV increases as there is more air trapped behind obstructed bronchi = barrel shaped chest
Heard as wheeze due to turbulent flow
How will FEV1 change in asthma with treatment?
Obstruction is reversible with a bronchodilator (salbutamol) so FEV1/FVC will recover
Name some obstructive airway diseases and again how they will be characteristic in spirometry
Asthma, COPD, Emphysema, Tracheal stenosis, airway tumours
Reduced FEV1 and larger RV
