Pulmonary Function Tests Flashcards
What are the two main types of respiratory disorders?
Obstructive and Restrictive
What are restrictive disorders?
Extra-airway disorders which restrict the ability of the lungs to entirely fill with oxygen
What are obstructive disorders?
Airways diseases which are associated with obstructed airflow
What is FVC?
Forced vital capacity – the maximum amount of air which you can forcibly exhale from your lungs after fully inhaling
On a flow volume loop, which direction is exhalation and which direction is inhalation?
Expiration = going up Inspiration = going down
How do you calculate the vital capacity from a flow volume loop?
The difference between the two x-intercepts
What is the tidal volume?
The amount of air inhaled and exhaled per breath
What is PEF?
- Peak expiratory flow – the maximum flow rate
- Taken by the peak of the flow loop
What are four reasons which spirometric pulmonary function tests might be undertaken?
- Evaluate symptoms eg breathlessness
- Monitor the progression of a lung disease over time
- Monitor the efficacy of the treatment
- Use it as a screening tool in the absence of sympoms
Describe how a flow volume loop would look for a patient with mild obstructive disease?
- Reduced FVC
- Indented exhalation curve (coving)
- Maximum flow rate decreases
What are the major disadvantages of the spirometric pulmonary function tests?
Heavy reliance on technique and can be rather uncomfortable for patients which reduces their motivation to apply maximum effort
What does a flow volume loop look like for a patient with severe obstructive disease?
- Reduced FVC
- Significantly indented exhalation curve (coving)
- Reduced peak expiratory flow
What is a flow volume loop like for patients with a restrictive disease?
- Reduced FVC
- Narrow curve
- Normal gradient at start with slightly lower peak due to reduced stretch
What is the flow volume loop like for someone with a variable extrathoracic obstruction?
Blunted inspiratory curve
Normal expiratory curve
What is the flow volume loop like for someone with a variable intrathoracic obstruction?
Blunted expiratory curve
Normal inspiratory curve
What is the flow volume loop like for someone with a fixed airway obstruction?
Blunted inspiratory cure
Blunted expiratory curve
Both at a matched rate
How do work out the PEF from a flow volume loop?
Highest observed y value
How to calculate the FEV1 from a spirometer pulmonary test?
Read the Y value from X=1 second
How to calculate the Peak Expiratory Flow Rate on spirometer graph?
Read up from x = 0.2 seconds
Multiply by 300 for L/minute
What does a spirometer curve look like in a obstructive disease?
Low peak expiratory flow
Reduced FEV1
Reduced FEV1/FVC ratio
Why does an obstructive condition result in a shallow spirometery curve?
- Severe airflow limitation caused by narrowing of the medium and small airways
- Respiratory muscle weakness and increased lung compliance means inability to generate the pressure to clear lungs quickly, hence increasing residual volume
Why might there be wavy airflow pattern after a certain period of time despite having normal airflow?
- Patients may be unable to hold the expiration further
- This is a manifestation of the Hering-Breuer reflex where afferent signals from the airways lead to simulation of inspiration and cessation of expiratory muscle force
What are some causes of extra-pulmonary restrictive diseases?
Obesity, Pneumoconiosis, Pulmonary fibrosis and severe burns
What does a spirometer curve look like in a restrictive disease?
FVC decreased
FEV1 nearly expels all air
What are the spirometry results for restrictive disease?
FVC lower (lung capacity restricted)
FEV1 normal unless airways affected
Thus FEV1/FVC normal or slightly higher than 0.7
What are the spirometry results for obstructive disease?
FEV1 < 80% of predicted value (can’t expel air quickly)
FVC is normal
FEV1/FVC < 0.7
Why is the following spirometry trace unrealistic?
- Rate of inspiration and expiration shouldn’t be the same
- Should be a plateau towards end of inspiration/expiration, as more effort is required to breathe in/out the last 10-20% of air
What does our body have to prevent airways collapsing?
Cartilaginous support in large extrapulmonary airways
What word describes a positive transmural pressure?
Patent
What word describes a negative transmural pressure?
Collapse
During inspiration why does the alveolar pressure decrease?
The diaphgram contracts, thoracic cavity increases in volume and intra-alveolar pressure decreases
During inspiration why does the pleural pressure decrease?
The adhesive force of the pleural fluid causes the lungs to expand along with the thoracic cavity, and the increase in volume of the pleural cavity decreases pleural pressure
How does the transmural pressure change during inspiration?
It increases due to alveolar and pleural pressure decreasing
Why does transmural pressure continue increasing towards end-inspiration?
During mid-inspiration, pleural pressure stays the same but alveolar pressure decreases due to gas exchange, so the difference between them increases
During hard-expiration, why is there the chance that the airways collapse?
- Hard expiration causes both pleural and airway pressures to increase
- If pleural exceeds airway pressure at any point, air flow can be cut off, thus causing collapse
