Lung Function Tests Flashcards
What are some of the types of pulmonary function tests?
- Spirometry and flow volume loops
- SpO2
- End tidal CO2
- Maximum inspiratory/expiratory pressures
- Sleep studies
Why is spirometry performed?
Because impaired ventilatory function is one of the most common physiological abnormalities affecting the lung
What are some of the indications for spirometry?
- Respiratory disease
- Differentiating respiratory from cardiac disease
- Differentiating obstructive from restrictive disease
- Assessing response to treatment
- Preoperative risk stratification
What is vital capacity?
The useable portion of a person’s lung volume (i.e. excludes residual volume)
What does spirometry require?
Maximal effort inspiration/expiration and patient cooperation
What is forced vital capacity (FVC)?
Maximum inspiration, then exhaling as fast/hard as possible - total amount of air exhaled (mLs or Ls)
What is FEV1?
The forced amount of air exhaled after 1 second when measuring FVC
What does spirometry quantify?
Volume expelled from the lung per unit of time
Why is the volume of gas recorded by a spirometer less than that displaced by the lungs?
- Because the spirometer is cold compared to the lungs (20 degrees vs. 37 degrees)
- Gas shrinkage at lower temps
- Condensation of water vapour
What are the major factors that affect spirometry?
- Age: increases with age until 20 (f) or 25 (m), then decreases
- Gender: males > females
- Height
- Ethnic origin: caucasian > african > chinese > polynesian
What is the normal % of predicted value for FEV1 & FVC?
80-120% of predicted value, abnormal = < 80%
What are the normal ranges for FEV1 & FVC?
FEV1: 3.64-5.46
FVC: 4.49-6.73
What FEV1/FVC ratio indicates significant airway obstruction?
< 70%
How is flow measured?
Volume/time, i.e. litres/second at BTPS
What does quiet breathing look like on an expiratory flow volume curve?
A circle
When does peak expiratory flow rate (PEFR) occur?
Early in forced expiration
Why is peak expiratory flow limited in accuracy?
Because there is insufficient data for initial assessment
Peak expiratory flow is used in monitoring of asthmatics to identify -?
- Trends in lung function
- Effects of treatment
- Trigger factors
What do maximal expiratory manoeuvres generate?
Large positive intra-pleural pressure
What is the equal pressure point?
The point at which pressure inside the airway equals the intrapleural pressure
Why is flow from the lungs limited at lower lung volumes?
At higher volumes, there’s more traction on the airways, while at lower volumes the airways aren’t held open as well
What is FEF 25-75%?
Average forced expiratory flow rate over the middle 50% of expiration (L/min)
What is the difference between an obstructive disorder and a restrictive disorder?
Obstructive: Something is trapping air in the lungs, patient takes a long time to blow all their air out
Restrictive: Something is stopping air getting into the lungs, but they can blow out easily
What causes an obstructive disorder?
- Bronchitis: Partial occlusion of the airway lumen
- Asthma, bronchitis: The wall of airway, i.e.e bronchial smooth muscle contraction, inflammation
- Emphysema: Destruction of the lung parenchyma
What causes a restrictive disorder?
- Lung parenchyma, e.g. interstitial fibrosis
- Disease of the pleura, e.g. pleural effusion, pneumothorax
- Chest wall disorder
- Neuromuscular disorder
What is considered to be a significant improvement of FEV1 in adults (i.e. reversibility of obstruction)?
> 12% or > 0.2L
How is the degree of obstruction quantified?
- FEV1/FVC < 75% = mild
- FEV1/FVC < 60% = moderate
- FEV1/FVC < 40% = severe
What values indicate the presence of a restrictive disorder?
- FEV1/FVC > 70% (indicates normal or supra-normal)
- Plus FVC < 80%
- FEV1 may be normal or < 80% if more severe restriction
What values indicate the presence of an obstructive disorder?
- FEV1/FVC < 70%
- Plus FEV1 < 80%
- FVC may be normal or < 80% if severe obstruction
What does the volume time curve look like for a patient with an obstructive disorder?
Long & flat (patient takes a long time to get the air out of their lungs)
What does the volume time curve look like for a patient with a restrictive disorder?
Very short (i.e. all air is out of the lungs in a very short amount of time due to patient not being able to achieve a high VC - cannot inspire maximum volumes)
What is the flow volume loop look like for a patient with an obstructive disorder?
- Concavity in expiration
- Due to small airways collapsing (not enough traction around the airways)
What is the flow volume loop look like for a patient with a restrictive disorder?
- More short & round
- Due to patient not being able to get enough air into their lungs initially
What do increased FRC and increased RV represent?
- FRC: Hyperinflation (loss of elastic recoil)
- RV: Air trapping (airway closure)
