Lecture 2: PFTs Flashcards
How do you do a spirometry test for FVC?
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
What is FEV1?
Forced expiratory volume at 1 second
What is the lower limit of normal (LLN) taken to be?
Equal to the 5th percentile of a healthy, non-smoking population
What is an abnormal result in spirometry?
Any result < 80% of the predicted value
Or: any results < lower limit of normal
How do you know if an obstruction is present using spirometry?
If the FEV1/FVC < 0.7
How do you distinguish between mild obstruction and severe obstruction in spirometry?
In mild the FVC should be maintained
What are the benefits of peak flow rate?
Easy to perform
Easy to maintain device
Useful for:
- Diagnosis – asthma, not COPD
- Monitoring day to day variation
- Picking up exacerbations
- Assessing response to treatment
Mandatory for patients on nebulised treatment
What % of diurnal variation is concerning in asthma?
Greater than 20%
How can you measure lung volume?
Helium dilution
Plethysmography “Body Box”
What is a plethysmography “Body Box”?
Put people in fixed box with known volume and get them to do multiple manoeuvres – measure pressure changes – measure whats going on near the mouth and what is in the box – can make calculations about the other necessary measures
What is transpulmonary pressure?
The difference between the alveolar pressure and the intrapleural pressure in the pleural cavity
What determines FRC?
Volume at which:
1. Inward recoil pressure of lungs matched by equal and opposite outward spring of chest wall.
- The compliance of the lung and the chest wall are highest (steep slopes)
Comfortable resting place and easiest (lowest work) volume at which to start a breath
What is residual volume?
Smallest volume reached:
- Low chest wall compliance (reaches 0) limits further reduction in chest wall volume
Benefit of RV:
- Avoid work of overcoming surface tension of a collapsed alveolus: easier work of breathing if alveoli are partially inflated at the start of inhalation.
Continuous gas exchange
What lung volumes are affected by fibrotic lung disease?
Decreased inspiratory capacity
Decreased vital capacity
Decreased functional residual capacity
Decreased reserve volume
Decreased total lung capacity
What are some causes of restriction and decreased lung volumes?
Lung tissue disease: Fibrotic lung disease
Alveolar filling process (e.g. pneumonia)
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)
