Basic lung function tests Flashcards
Why are lung function tests useful?
Diagnosis, symptom analysis, treatment monitoring
Useful in both symptomatic patients and those at risk of pulmonary disease
What are the 3 commonly assessed functions of the respiratory system?
Diameter of airways (air flow rate)
Total lung volume (vital capacity)
Effectiveness of oxygen diffusion into blood
How can you measure the diameter of airways?
Peak flow and FEV1
How do you measure the total lung capacity?
FVC
How can you measure how well oxygen diffuses into the blood?
DLCO (Diffusion capacity for carbon monoxide)
- assesses permeability of respiratory system
What are the advantages of spirometry?
Readily available
No risk to patient (or clinician)
Instant results
Easily repeatable
What are the disadvantages of spirometry?
Expensive equipment
Requires patient compliance
Requires training
Give examples of obstructive lung diseases
COPD (emphysema, bronchitis)
Asthma
Cystic Fibrosis
Bronchiectasis
What is the difference between obstructive and restrictive lung disease?
Obstructive - patients tend to have difficulty emptying their lungs due to narrowing or airways or damage to lungs - leads to increased RV
Restrictive - patients tend to have difficulty filling their lungs - leads to reduced inspiratory capacity
Give examples of restrictive lung diseases
Pulmonary Fibrosis
Obesity
Scoliosis
How do spirometry results differ in obstructive and restrictive lung diseases?
FEV1:FVC <0.7 = obstructive
FEV1:FVC >0.7 (but with significantly reduced FVC) = restrictive
What are the contraindications of spirometry?
Haemoptysis Pneumothorax Unstable CV status Aneurysms Acute illness Recent thoracic, abdominal or ENT surgery Pain Pregnancy
What is the inspiratory reserve volume?
The maximum amount of additional air that can be drawn into the lungs by forced inspiration (after normal inspiration)
What is the tidal volume?
The amount of air breathed in and out during normal (quiet) respiration
What is the expiratory reserve volume?
The maximum amount of additional air that can be expired from the lungs by forced expiration (after normal expiration)
What is the residual volume?
The amount of air left in the lungs following normal tidal respiration
What is the functional residual capacity?
ERV + RV
Amount of air left in lungs following passive expiration
What is inspiratory capacity?
TV + IRV
The total amount of air that can be drawn into the lungs after normal expiration
What is vital capacity?
The maximum amount of air that can be expired from the lungs following deep inspiration (e.g. peak flow)
[Measured from maximum inspiration to maximum expiration]
Reduction in vital capacity indicates lung restriction
What is total lung capacity?
The total amount of air contained in the lungs following maximal forced inspiration
What differences on a peak flow chart is indicative of asthma?
> 20% variability between morning and evening
[Slight variability is normal]
What does spirometry measure?
Measurement of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC)
What causes a wheeze?
Turbulent flow on expiration due to airway narrowing
