Measuring lung function Flashcards
How does a patient take a spirometry test?
- Can be done slowly or “forced”
- Most often done as forced expiration
FVC or “Tiffeneau” manoeuvre
- Take a deep breath in
- Don’t hold your breath
- Put your lips round the outside of the tube
and blow out as hard as you can
for as long as you can
How do you interpret spirometry results?
A patient’s PFT values (except the FEV1/FVC ratio) are compared to predicted values, which are derived from a healthy population of people of the same gender and of similar age and height
What does this spirometry graph show?
Age-related loss of lung elasticity -> decline in FVC and FEV1
What do spirometry results vary by?
Vary by gender, height, and age
What is classed as an abnormal spirometry result?
Abnormal result: any result < 80% of the predicted value
Or: any results < lower limit of normal
What does this show?
Normal spirometry result
What is the lower limit of normal?
The lower limit of normal (LLN) is taken to be equal to the 5th percentile of a healthy, non-smoking population
What FEVI/FVC ration shows obstruction?
FEV1/FVC ratio: should exhale > 70% of FVC in first second
If FEV1/FVC < 0.7, then obstruction is present
What does this spirometry show?
Obstruction
What does this spirometry show?
Severe obstruction
What type of graph is this?
Flow Volume loop
What does the lilac line show?
Early Airflow Obstruction
What does early airway obstruction look like on an expiratory flow-volume loop?
PEFR may be normal
Mid-Expiratory Flow Rate usually more affected
Lilac line
What does the orange line show?
What type of graph is this?
Severe Airflow Obstruction
Expiratory Flow-Volume Loop
What does the orange line show?
What type of graph is this?
Extra-Thoracic Obstruction (including tracheal stenosis, retrosternal goitre, etc)
Expiratory flow-volume loop
What do flow-volume loops indicate?
Flow volume loops can indicate where obstruction is located in the tracheobronchial tree
Complete the diagram on what the obstruction is in these flow-volume loops
What are the benefits of peak flow rate?
Easy to perform
Easy to maintain device
What are peak flow rates used for?
- Diagnosis – asthma, not COPD
- Monitoring day to day variation
- Picking up exacerbations
- Assessing response to treatment
The peak flow rate test is mandatory for which patients?
Asthma ptients on nebulised medicine
What does this graph show?
Peak expiratory flow
Morning dips shouldn’t be there - went with inhaled corticosteroids
consistent with diagnosis of asthma
What is the equation for flow?
Flow = (Pressure gradient) / (Raw)
Raw - airway resistance
What is the equation for airway resistance?
What could cause a decrease in the radius of an airway?
What is the consequence of this?
- Mucous or other obstruction
- Bronchoconstriction
- Compression (from a mass)
Increased resistance
How can lung volumes be measured?
Cannot be obtained from spirometry
Methods of measurement
- Helium dilution
- Plethysmography “Body Box”
What are the 4 volumes that can be measured?
TV – tidal volume
IRV – inspiratory reserve volume
ERV – expiratory reserve volume
RV – residual volume
What are the 4 capacities that can be measured?
TLC – total lung capacity
VC – vital capacity, slow (SVC) or forced (FVC)
FRC – functional residual capacity
IC - inspiratory capacity
Complete the diagram on lung volumes and capacities
What graph is this?
Relaxation pressure volume curve
Complete the diagram of the Relaxation pressure volume curve?
What are the features of restrictive lung disease?
- Reduced TLC, FRC, and RV
- Preserved tidal volume
- Reduced IRV / inspiratory capacity
Reduced vital capacity (FVC and SVC)
What does each colour represent?
What combination of colours is -
Inspiratory capacity
Functional residual capacity
Vital capacity
Total lung capacity
What condition does this indicate?
Fibrotic lung disease
What are the causes of restriction and deceased lung volumes?
- Alveolar filling process (e.g. pneumonia)
- Lung tissue disease: Fibrotic lung disease
- Pleural disease: pneumothorax, large pleural effusion, fibrosis of pleural tissue (“trapped lung”)
- Chest wall disease (e.g. kyphoscoliosis)
- Weakness (due to nerve and/or muscle disease)
What does the second x-ray show?
Hyperinflation
What causes hyperinflation in COPD?
In emphysema: loss of elastic recoil -> Cl curve plateau occurs at a larger volume -> increased TLC
What condition does this show?
COPD
Where does gas exchange occur?
Takes place at alveoli
What factors influence gas exchange?
- Depends on adequate ventilation of alveoli
- Influenced by alveolar surface area and thickness of alveolar membrane
What is the purpose of gas exchange?
- Delivers oxygen to blood where it combines with Hb
- Gets rid of CO2 into exhaled air
What are the causes of abnormal gas exchange?
- Airway disorders (asthma & COPD)
- Alveolar destruction (emphysema)
- Fibrotic lung disease (idiopathic lung fibrosis, asbestosis etc)
- Abnormal ventilatory control
- Abnormal environment (altitude)
How is gas transfer (diffusing capacity) measured?
- CO diffuses like Oxygen
- CO binds to Hb and is carried away
- Inhale known volume of gas with low concentrations of CO and Helium
- Hold breath for known time
- Measure CO and He in expired air
Helium dilution gives alveolar volume
What is the effect of pulmonary diseases on total lung capacity (TLCO)?
Note: conditions of reduced surface area (first 3 listed) and increased thickness (scarring/inflammation)
What is the effect of cardiovascular /haematological disease on total lung capacity (TLCO)?
Name 4 other lung function tests used in clinical practice
- Assessment of airway ‘reversibility’
- Assessment of ventilation
- Fitness to fly
- Respiratory muscle assessment
