Pulmonary Function Tests Flashcards
What are the pulmonary function tests?
Effort dependent tests - FEV1/FVC - spirometry
Effort independent tests - relaxed vital capacity spirometry, helium/N2 washout, exhaled breath nitric oxide
Gas diffusion tests - CO transfer factor, arterial blood gases, SaO2 during exercise
What are the dynamic lung volumes that can be measured in spirometry?
Forced expiatory manouvre: from TLC to RV Forced expiatory volume in 1s: FEV1 Forced vital capacity Forced expiatory ratio Relaxed vital capacity
How does the spirometry curve change in COPD and asthma?
Asthma will reach the same FVC as normal people but it will happen slower
COPD will never reach the same FVC as normal people
What are the expiratory flow rates based on?
The volume is dependent on expiraotry airway closure - asthma, chronic bronchitis
The pressure is dependent on expiratory
What is the peak expiratory flow rate measured in?
Expressed in L/min (L/s x 60)
Measurable with a simple linear peak flow meter
FEFR is a % of FVC and is usually between 25-75%
What are the differences in lung volumes in obstructive airway disease?
PEFR is decreased
FEV1 is decreased
FVC is normal in asthma but decreased in COPD
FEV1/FVC ratio is more than 75%
FEV1 response to beta agonist is more than 15%
What are the differences in lung volumes in restrictive lung disease?
PEFR is normal FEV1 is decreased FVC is decreased FEV1/FVC ratio is less than 75% FEV1 to beta agonist has no response
How do you test bronchial challenge test?
Exercise
Methacholine/histamine/mannitol airway hyper-responsiveness. Need a concentration to produce a 20% reduction in FEV1
Allergens/chemicals - early and late responses, diagnosis of occupational asthma
What will exercise testing show?
A decreased FEV1 or PEF post exercise - asthma
A decreased SaO2 during exercise in interstitial lung disease
Full cardiopulmonary exercise test to differentiate between cardiac and respiratory dyspnoea (shortness of breath)
What are static lung volumes and how are they tested?
Effort independent test Helium dilution/ N2 washout: functional residual capacity Increase in hyperinflation (emphysema) Decreased in restrictive lung disease Gas trapping in COPD
How is airway resistance measured?
Measured be either the whole body plethysmography or with an impulse oscillometry
Impulse oscillometry measures airways resistance during quiet tidal breathing at different resonant frequencies to give total resistance
Useful in patients where easier to breathe at tidal volumes than doing forced expiratory manoeuvre
How is exhaled breath condenste measured?
Measured at flow of 50ml/s (FeNO) - a non invasive marker of eosinophilic airway inflammation in asthma
Why is measuring exhaled breath nitric oxide not useful in COPD?
The nitric oxide is supressed by smoking
What do high levels of exxhaled NO reflect?
OVer 35 ppb reflects uncontrolled asthmatic inflammation
