Spirometry/Lung function Flashcards
Draw a normal flow-volume loop and volume-time loop
What are LLN?
The Lower Limits of Normal (LLN) is the lower fifth percentile of the Gaussian bell curve: 95% of healthy people can blow better than the LLN value. (Note that this means there is still a 5% chance of false positives!)
LLN is calculated for every parameter and takes into account age, ethnicity, gender and height. If a spirometry value is lower than the LLN it is considered to be abnormal. This also applies to the FEV1/FVC ratio or Tiffeneau index: according to the new interpretation method a FEV1/FVC ratio of 71% can be too low for a young adult where a FEV1-ratio of 68% can be perfectly normal for an elderly person.
What is the z-score?
Another way of describing the LLN is the Z-score or Standard Score: a Z-score is the number of standard deviations a certain value is above the mean value of the data set (the Z-score will be negative if the value is lower than the mean). A spirometry value is considered too low if it is more than -1.64 standard deviations from the predicted value (which is the same as the lower 5 percentile).
The advantage of Z-score is that it permits comparison of values between different populations.
Draw obstructive flow-volume loop
Draw a restrictive flow-volume loop
Draw variable extra thoracic compression vs variable intrathoracic compression vs fixed
List causes of
a)variable extra-thoracic obstruction
b)variable intra-thoracic obstruction
c) fixed airway obstruction
a)laryngeal tumour, goitre, vocal cord paralysis
b)tumour intrathoracic part of trachea
c)tracheal stenosis by intubation or circular tracheal tumour
What are causes of low TLCO?
Reduced surface area:
Anaemia
Emphysema
Lung/lobe resection
Multiple emboli
Increased thickness of membrane:
ILD - IPF, aspestosis, HSP, drug induced fibrosis
Pulmonary hypertension
CCF
What are the causes of high KCO?
Asthma
Pulmonary hemorrhage
Pneumonectomy
Neuromuscular disease
Chest wall disease
Obesity
AVM
Causes of low TLCO but normal/high KCO
=Extrapulmonary restrictive defect
obesity
neuromuscular disease
skeletal deformity
post pneumonectomy
Pleural disease - thickening, effusion, tumour
