Pulmonary Function Testing Flashcards
What are 3 types of pulmonary function test?
- Effort dependent tests
- Effort independent tests
- Gas diffusion tests
What are examples of effort dependent tests?
- Forced expiratory volumes/flow rates
How are forced expiratory volumes measured?
Spirometry
What are examples of effort independent tests?
- Relaxed vital capacity
- Helium/N2 without static lung volumes
- Whole body plethysmography
- Impulse oscillometry
- Exhaled breath nitric oxide
What are examples of gas diffusion tests?
- CO transfer factor
- Arterial blood gases (resting)
- SaO2 during exercise
How is relaxed vital capacity measured?
Spirometry
What is a forced expiratory manoeuvre?
From TLC to RV
What is the forced expiratory volume in 1 second?
FEV1 (litres)
What is the forced expiratory ratio?
FER = FEV1/FVC
What is relaxed vital capacity?
Patient breathes out in their own time
What is the normal value of FER?
> 75%
In asthma, how does FEV1, FVC and FER compare with a normal individual?
- FEV1 is reduced
- FVC is the same (just takes longer)
- FEV1/FVC is reduced
In COPD, how does FEV1, FVC and FER compare with a normal individual?
- FEV1 is reduced
- FVC is reduced
- FEV1/FVC is the same
Why is FEV1/FVC ratio preserved in COPD?
FEV1 is reduced in proportion to FVC
What is a volume-time curve?
Plots volume in litres (FVC and FEV1) against time (s)
What is a flow-volume curve?
Flow rate (l/s) plotted against forced expiratory volume (l)
What affects the shape of the expiratory flow-volume curve?
- Volume dependent expiratory airway closure - asthma, chronic bronchitis
- Pressure dependent expiratory airway closure - emphysema
What causes volume dependent expiratory airway closure in asthma?
Small airways close off earlier in expiration (wheeze)
What causes pressure dependent expiratory airway closure in COPD?
Small airways close off extremely early in expiration
How is peak expiratory flow rate (PEF) measured?
Peak flow meter
What are the units of peak expiratory flow rate?
l/min
How does obstructive airway disease affect peak expiratory flow rate?
Peak expiratory flow rate is reduced in obstructive disease
What is the FEV1/FVC ratio of someone with asthma?
<75%
What is the FEV1 response to B2-agonist in asthma?
Increases by approx 15%
How does restrictive airway disease affect peak expiratory flow rate?
Peak expiratory flow rate is normal in restrictive airway disease
Why is peak expiratory flow rate not affected in restive airway disease?
In restrictive disease, no problem with conducting airways so flow rate is normal
Why is there no FEV1 response to B2 agonist (e.g. salbutamol) in restrictive airway disease?
Conducting airways are normal
What are methods of bronchial challenge testing?
- Exercise (will produce bronchoconstriction - cold air)
- Metacholine/histamine/mannitol (markers of airway hyper-responsiveness)
- Allergens/chemicals (early and late responses)
How is metacholine/histamine/mannitol used in bronchial challenge testing?
Provocative dose to produce 20% fall in FEV1
How is exercise testing used to diagnose respiratory disease?
- Fall in FEV1 or peak expiratory flow rate = asthma
- Decrease in SaO2 during exercise in interstitial lung disease - to monitor treatment response
- Full cardiopulmonary exercise test (CPET) - differentiate cardiac vs respiratory dyspnoea (HR vs oxygen uptake vs ventilatory rate)
What type of test is the measurement of static lung volumes?
Effort independent test
What information can helium dilution/N2 washout provide?
Functional residual capacity
What is the equation for residual volume?
RV = FRC - ERV
What is the equation for total lung capacity?
TLC = VC + RV
When does TLC increase beyond normal values?
In hyperinflation - emphysema
When does TLC decrease below normal values?
In restrictive lung disease - ILD
What is the equation for gas trapping in COPD?
RV/TLC x 100
What is CO transfer factor?
Co diffusion across alveolar-capillary barrier
What is TLCO?
Total lung transfer for CO (diffusing capacity)
What conditions can cause TLCO to decrease?
- Anaemia
- Emphysema
- Interstitial lung disease
- Pulmonary oedema
- Pulmonary embolus
- Bronchiectesis
What can TLCO be used for?
To monitor treatment response in lung disease
How is airway resistance measured?
- Whole body plethysmography
* Impulse oscillometry (more common)
What is impulse oscillometry?
Measures airway resistance during quiet tidal breathing at different resonant frequencies to give:
- total resistance (5Hz)
- central resistance (20Hz)
- and hence peripheral airway resistance by subtraction
What is a non-invasive marker of eosinophilic airway inflammation in asthma?
Exhaled breath nitric oxide measured at flow of 50ml/s (FeNO)
Why is exhaled breath nitric oxide measurement not useful in COPD?
Nitric oxide suppressed by smoking
What do high levels of NO (>35ppb) measured in exhaled breath indicate?
Uncontrolled asthmatic inflammation
When is exhaled breath nitric oxide measured?
In adjunct to bronchial challenge to assess asthmatic inflammation - especially when spirometry is normal
