LFT Interpretation Flashcards
(17 cards)
What are predicted values based on?
Sex
Age
Height
Ethnicity
What is the normal SD range?
(Z score)
+/- 1.645
Why is Z score better than percent predicted
It compares directly to data to say if something is in normal range, whereas percent predicted may be wrong, for example in old people may over diagnose
Restrictive patterns
Intra pulmonary
And
Extra pulmonary
Intra : inside lung e.g fibrosis
Extra: outside lung e.g scoliosis which compresses the lung
What does a volume time graph plot
Volume y
Time x
Volume time graph for obstructive disease
FEV1 decreased
FVC normal
Slow start, which keeps rising due to gas trapping
Volume time graph for restrictive disease
FEV1 and FVC decreased
Graph is smaller than normal
Flow volume loop shape for obstructive pattern
Limited on expiration, so concave limb with normal insp
Flow volume loop shape for restrictive pattern
Squashed shape compared to normal due to decreased FEV1 and FVC
Besides disease what may affect the shape of a flow volume loop?
Poor technique
Interpretation of FEV1/FVC ratio
> 70% = normal or restrictive disease
Use ratio alongside flow volume loop for full diagnosis
Check Z score
Z scores for severity of obstructive disease
< -1.645 normal
< -2 mod
< - 2.5 mod-sev
< -3 sev
< -4 very sev
What is a significant change in reversibility test?
Z score change by 0.7
FEV1 increase > 8%
What do static lung volumes assess
Size of lungs at different states of inflation
Functionality of lung
Elasticity of lung
Can show gas trapping
What does TLCO represent in gas transfer
Gas transfer as a whole
What is KCO
Transfer coefficient
Rate of transfer of gas between alveoli and RBCs in capillaries
What is VA in gas transfer
Alveolar volume of ventilated areas
Shows distribution of gas in the lung
