Pulmonary Function Testing Flashcards
Types of pulmonary function tests?
Effort dependent tests - involve breathing out maximally, with effort
Effort independent tests - breathing out with no effort
Gas diffusion tests - information obtained about gaseous diffusion across alveolar bed
Examples of effort dependent tests?
Measuring Forced Expiratory Volumes (FEV) - spirometry
Measuring flow rates - volume exhaled in given time (purest measure of airflow obstruction)
Limitation of effort dependent tests?
Not a physiological maneuvre; essentially involves forced expiratory volume (FEV) - an artificial maneuvre
Examples of effort independent tests?
Relaxed vital capacity (VC) - spirometry
Helium/N2 washout - for STATIC LUNG VOLUMES, with N2 being used more than helium
Whole body plethysmography - for static lung volume
Impulse oscillometry
Exhaled breath nitric oxide
Examples of gas diffusion tests?
CO transfer factor
Arterial blood gases (resting)
SaO2 during exercise
Dynamic lung volumes?
Forced expiratory volume in 1 second (FEV) - proportion of FVC expired in 1st second
Forced vital capacity - FVC
Forced expiratory ratio (FER) - FEV1 / FVC
Relaxed vital capacity - RVC
Difference between normal and asthmatic airways?
During FEV, no small airway closure normally so FEV1/FVC > 75%
During FEV in asthmatic patient, small airways start closing so it takes longer to reach FVC in asthma that normal
Difference between FVC of asthma and COPD
ASTHMA - normally, FVC is PRESERVED (takes longer to reach); exception is when airway remodelling has occured
COPD - lots of small airway closure and scarring, so FVC is NEVER REACHED
FEV1/FVC ratio in obstructive lung diseases?
FEV1 is DISPROPORTIONATELY decreased, compared to FVC
FEV1/FVC ratio in restrictive lung disease?
FEV1 has PROPORTIONATELY decreased, compared to FVC, so ratio will be >75%
Essentially, reduced lung volume but there is no issue with exhalation
FUNDAMENTAL difference between obstructive and restrictive lung disease
What does a peak flow meter measure?
Peak expiratory flow rate - maximum speed that can be attained during expiration
Peak expiratory flow rate in asthma?
Peak flow rate becomes blunted/concave as there is dynamic small airway closure
When does volume dependent expiratory airway closure occur?
Asthma
Chronic bronchitis
Peak expiratory flow rate decreases and curve becomes concave
When does pressure dependent expiratory airway closure occur?
Emphysema
Peak expiratory flow rate is even lower than in asthma & chronic bronchitis
Briefly explain what the forced expiratory flow rate is?
FEFR at a % of FVC - Forced expiratory flow 50%, FEF25-75% Flow (or speed) of air coming out of the lung during the middle portion of a forced expiration
Describe bronchial challenge testing?
Used to assess bronchospasm/twitchiness Induced in different ways:
Exercise
Metacholine/histamine/mannitol (MARKER OF AIRWAY HYPER-RESPONSIVENESS ) - conc. chosen to produce a 20% decrease in FEV1
Allergens/chemicals are used to check if there is an early/late response and can be used to diagnose occupational asthma
How does bronchial challenge testing using metacholine work?
Using metacholine, post-ganglionic M3 receptors are stimulated with muscarinic agonists, so bronchoconstriction occurs
Bronchial challenge testing using metacholine/histamine/mannitol in normal vs asthma?
FEV1 decrease to 80% of full value (20% decrease)
Even if not asthmatic, FEV1 would still fall but, with ASTHMA, a LOWER DOSE of inducer is required
How does FEV1 vary in exercise?
Increases during exercise but, after exercise has stopped, FEV1 decreases in asthma due to rebound worsening
Describe exercise testing and where it can be used
FEV1 or peak expiratory flow (PEF)
DECREASES in ASTHMA
Decreased SaO2, during exercise, in insterstitial lung disease (used to monitor treatment response)
CPET (full cardiopulmonary exercise test) - differentiates between cardiac and respiratory dyspnoea (breathlessness), by comparing heart rate, oxygen uptake and ventilatory rate
Static lung volume tests?
Via effort INDEPENDENT tests
Can be measured using helium dilution/N2 washout to find functional residual capacity
Changes in static lung volumes and when they occur?
Total lung capacity increased in hyper-inflation (emphysema) - elasticity decreases
Total lung capacity decreases in restrictive lung disease
In COPD, GAS TRAPPING occurs (due to small airway closure) and hyper-inflation of static lung volume occurs
Abbreviation of transfer factor?
AKA TLCO or DLCO (Transfer factor of Lung for Carbon Monoxide or Diffusing capacity of Lung for Carbon Monoxide)
What does transfer factor measure?
CO diffusion across alveolar-capillary barrier (extent to which oxygen passes from the air sacs of the lungs into the blood)
KCO is corrected for alveolar volume
When does TLCO decrease?
Anaemia
Emphysema
Interstitial lung disease
Pulmonary oedema
Pulmonary embolus
Bronchiectesis
Example of what is TLCO used for?
To monitor treatment response in interstitial lung disease
How is airway resistance measured?
Whole body plethysmography
More common/easier is IMPULSE OSCILLOMETRY (IOS)
How does impulse oscillometry work?
Measures airway resistance during quiet tidal breathing (at different resonant frequencies to give total resistance (@5Hz) and central resistance (20Hz) - peripheral airway resistance by subtraction of R5 - R20
So, smaller frequency reflects distal airways and higher frequencies reflect promximal airways
When is impulse oscillometry useful?
Useful in patients, like kids, where it is easier to breathe at tidal volume than doing a forced expiratory maneuvre
Describe exhaled breath condensate measurement and when it is used
Exhaled breath nitric oxide is measured at flow of 50 ml/s (FeNO)
Non-invasive marker of EOSINOPHILIC AIRWAY INFLAMMATION in ASTHMA - high level of exhaled NO reflect uncontrolled asthmatic inflammation
Not useful in COPD (NO suppressed by smoking)
Used as an adjunct to bronchial challenge to assess asthmatic inflammation (esp. when spirometry is normal)
Compare obstructive and restrictive lung disease?
PEFR:
Obstructive - decreases
Restrictive - normal
FEV1:
Obstructive - decreases
Restrictive - decreases
FVC:
Obstructive - normal in asthma and reduced in COPD
FEV1/FVC:
Obstructive 75%
Gas transfer (TLCO):
Obstructive - decreased in emphysema and normal in asthma
Restrictive - decreased
FEV1 response to β2-agonist:
Obstructive - >15% in asthma and
