8. Interpretation of Lung Function Flashcards
List some lung function tests.
What patient features are values dependant on?
What does a spirometer measure? What are the most common measurements? What does this technique depend on?
Spirometry, PEF (peak expiratory flow), Lung volume, Gas exchange.
Age, height, sex, BMI, ethnic origin.
Amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Most common measurements: FEV1 (amt of air blown out in 1 sec), FVC (total amt of air blown out in 1 breath), FEV1/FVC. Highly dependent on pt cooperation and effort. More reproducable than PEF. Detects changes mostly in smaller airways.
How do spirometry results differ in obstructive and restrictive lung diseases? List some obstructive and restrictive lung diseases.
What is PEF (peak expiratory flow)?
Obstructive: (e.g. asthma, COPD, CF, endobronchial tumour, foreign body) FEV1 decreases so FEV1/FVC decreases (below 70%).
Restrictive: (e.g. PAINT - Pleural (e.g. PE, chronic empyema), Alveolar (oedema, haemorrhage), Intersitial (e.g. fibrosis), Neuromuscular (myasthenia gravis), Thoracic cage (obesity, kyphoscoliosis, ascites)) FEV1 and FVC both decrease so FEV1/FVC stays roughly the same or slight increase (70% or above).
Values < 0.70 are suggestive of airflow limitation with an obstructive pattern.
Max rate that a person can exhale during a short maximal expiratory effort after a full inspiration. Useful for detecting changes/trends in a pt’s asthma control. Significant testing variability. PEFR test commonly performed at home. Detects changes mostly in larger airways.
Label A-F.
What is A + D known as?
What is A + D + B known as?
A) Inspiratory reserve volume
B) Functional residual capacity
C) Vital capacity
D) Tidal volume
E) Expiratory reserve volume
F) Residual volume
IRV + TV = Inspiratory capacity
IRV + TV + FRC = total lung capacity (TLC)
“capacity” = 2 or more volumes
What lung capacities cannot be measured by simple spirometry and why?
How are these capacities measured?
How is gas transfer (O2 transfer) measured?
What is flow volume loop analysis?
RV (left in lungs after maximal expiration so cannot be measured by simple spirometry) and the capacities conntaining RV i.e. FRC and TLC.
To measure RV, use tracer gas (He) which mixes with the air in the lung but doesn’t diffuse out of lung. Volume then determined by amount that this tracer gas is diluted as it mixes with the air in the lungs.
Indirectly using CO.
REMEMBER SPIROMETRY, LUNG VOL and GAS TRANSFER = main 3!
Provides graphical analysis of inspiratory and expiratory flow. Can calculate values (pic) Amount of air can breathe out in 1sec. Gives additional info to spirometry.
What type of lung disease do A-C show? Give examples of diseases.
A) Obstruction - volume dependent e.g. asthma
B) Obstruction - pressure dependent e.g. severe emphysema
C) Obstruction - rigid obstruction e.g. tracheal stenosis (box shape)
What do A and B indicate on these flow volume loops?
A) Extrathoracic tracheal obstruction e.g. vocal chord dysfunction e.g. dysphonia. Inspiratory loop flatter
B) Intrathoracic large airway obstruction e.g. endobrochial tumour - flatter expiratory loop
What is the important rule to remember when looking at these results showing spirometry, lung volume and gas transfer?
Comment on this pt’s results and deduce their pathology.
Usual range = 80 - 120% predicted - normal (EXCEPT FEV1/FVC = 70%).
FEV1 and FVC low (18 and 69%). FEV1 is grossly reduced compared to FVC and ratio is 23 -> obstructive cause.
TLC = upper limit of normal, RV = 214% (too high!). So pt not exhaling all air -> trapping.
TLCO = too low, KCO = 62% so gas transfer reduced.
THUS: obstructed picture, air trapping and decreased gas transfer -> COPD emphysema.
NB: KCO = gas transfer for individual alveoli unit
Comment on this pt’s results and deduce their pathology.
FEV1/FVC high so restrictive.
TLC and RV low so smaller lung volume.
Gas transfer: TLCO low but KCO 98% so OK. (NB TLCO covers whole lung = 39% but each alveoli unit ok)
THUS: restricted picure, small lung volume, normal gas transter for each alveoli. Thus fewer alveolar units? Pt lost half a lung! Thus has TLC 50% of what it should be but functioning on 1 lung!
Comment on this pt’s results and deduce their pathology.
FEV1 ok, FVC normal, ratio 79 so could be normal?
TLC and RV normal.
TLCO and KCO normal.
THUS: normal lungs.
Comment on this pt’s results - what has happened?
Gave salbutamol - FEV1 increase = reversible airways disease. Reversibility testing.
What has happened here?
22% improvement with salbutamol. Initially pt’s FEV1 was a baseline normal but see further improvement with vasodilator. Thus can see asthma with normal lung function too!
Comment on this pt’s results and deduce the pathology.
Ratio normal but FEV1 and FVC low (48.6% and 43.3%) = restrictive.
Reduced small lung volume (52.1%).
Reduced gas transfer (58.9%).
THUS: sarcoidosis = lung fibrosis in both lungs.
