Basic Lung Function Testing Flashcards
Why do we perform lung function tests?
1) Detect if lung disease is present
2) Quantify the severity of the lung disease
3) Assess the effectiveness of intervention eg. surgical, therapeutic, pharmacological
4) Pre-operative evaluation
5) Assess the extent of airways reversibility
6) Assess the extent of airway hyper sensitivity
When is Peak Expiratory Flow measured?
- PEF on it’s own is not generally a good diagnostic tool unless it is performed serially
- Serial PEFs are used in asthma to assess for diurnal variation
- Also used in occupational situations to check for any differences between PEF at work and at home
How would you measure serial PEFs for asthma?
- Asthma: Perform 4 readings per day for 2 weeks
- Occupational asthma: Perform 8 readings per day for 4 weeks.
- Diurnal variation can be calculated in a number of ways:
e. g. : Highest PEF-Lowest PEF / predicted PEF (%) - 15-20% on most days would be indicative of asthma.
- Generally performed pre bronchodilator for analysis.
What is spirometry?
An objective measurement of lung function.
Measures lung size (VC & FVC).
Measures airway calibre (FEV1).
Indicates airflow obstruction (FEV1/FVC).
Measures Flow (PEF)
Define Vital Capacity
Maximum volume blown out steadily, following a full inspiration.
Define Forced Vital Capacity
Maximum volume blown out as hard as possible, following a full inspiration
Define Forced Expiratory Volume in 1 second (FEV1)
Volume of air blown out in the first second of a forced blow out. Important to look at ratio of first second compared to rest.
Define Peak Expiratory Flow
Maximum flow rate achieved within first 100ms following a full inspiration.
What would you ask patient to avoid on the day of spirometry tests?
- Smoking 24hrs prior to testing
- No alcohol consumption within 2hrs
- Eating a substantial meal
- Wearing clothing that restricts full chest expansion
- Performing vigorous exercise within 30 mins
What is a restrictive disease?
Reduced volume in the lungs due to inability of lungs to expand.
1) Intrapulmonary diseases
- Pulmonary fibrosis
2) Extra-pulmonary conditions
- Obesity
- Rib cage deformity (scoliosis)
- Respiratory muscle weakness.
What is an obstructive disease?
Persistent slowing of airflow during breathing.
How would you know there is airway obstruction?
Low FEV1/FVC ratio
What are the parameters used to check for extra thoracic airway obstruction?
- Empey index (FEV1/PEF) >8.0
- MEF50/MIF50 >1.0
- VISUAL INSPECTION OF FVL
How does FEV1 change in restrictive or obstructive diseases?
Reduced in restrictive
Reduced in obstructive
How does FVC change in restrictive or obstructive diseases?
Reduced in restrictive
Can be reduced in severe obstruction
How does FEV1/FVC change in restrictive or obstructive diseases?
Normal in restrictive
Reduced in obstructive
How does VC change in restrictive or obstructive diseases?
Reduced in restrictive
Normal in obstruction unless very severe
How does PEF change in restrictive or obstructive diseases?
Normal to high in restrictive, but can be reduced.
Mostly reduced in obstruction
Give some examples of restrictive diseases
- Sarcoid
- Fibrosis
- Kyphosis
- Heart failure
- Tumour
- Obesity
Give some examples of obstructive diseases
- COPD
- Asthma
- Emphysema
- Bronchiectasis
- Cystic Fibrosis
- Tumour
What static lung volumes are measured?
Total lung capacity (TLC), Functional Residual Capacity (FRC) and Residual Volume (RV)
How would you measure the static lung volumes (TLC, FRC, RV)?
- Can be measured by using helium dilution, nitrogen washout or body plethysmpgraphy
- Provides the only way to see true restriction (by reduced TLC and FRC) due to intra pulmonary (fibrosis) or extra pulmonary conditions (obesity)
- Shows hyperinflation (increased FRC and TLC) and increased RV (gas trapping), due to loss of elasticity (emphysema)
- % RV to TLC in normal subjects should be <40%
Why perform gas transfer?
1) Gives information about how the alveoli gas exchange is working
2) We measure transfer coefficient (KCO) and derive TLCO (Transfer factor/diffusing capacity) from: KCO x VA
- VA=single breath measurement of TLC using helium
- KCO is measured using carbon monoxide
- Corrected values are corrected for haemoglobin – lower Hb levels=lower KCO
What is the equation to calculate TLCO?
TLCO = KCO x VA
What would you expect the pulmonary function test (PFT) to be in a healthy individual?
PFT = FEV1/FVC x 100
You would expect it to be around 80%
What would you expect the pulmonary function test (PFT) to be in an individual with an obstructive disease?
PFT = FEV1/FVC x 100
Their FEV1 would be decreased
So you would expect PFT to be <80%
What would you expect the pulmonary function test (PFT) to be in an individual with a restrictive disease?
PFT = FEV1/FVC x 100
Their FVC would be decreased
So you would expect PFT to be >80%
What is a typical tidal volume in a healthy individual?
500ml
What is the total lung capacity TLC in an average adult male?
6 litres
How does the flow-volume loop change in obstructive disease?
1) The whole loop shifts to the left because there is an increased FRC and TLC due to gas trapping
2) There is a characteristic ‘kink’ in the forced expiration due to the obstruction
How does the flow-volume loop change in restrictive disease?
The whole loop shifts to the right because there is a reduced TLC
