Pulmonary function testing Flashcards
spirometry. what is measured. how is it performed.
evaluates air flow.
6 s exhalation with a smooth curve and 3 reproducible inhale/exhale loops.
FVC. Definition and normal values
forced vital capacity
volume of air expaled during full forced exhalation after full inhalation (inspiratory reserve vol. + tidal vol + expiratory reserve vol)
Normal: >70%
FEV1. Definition and normal values
vol of air exhaled during FVC in the first second.
FEV1/FVC ratio should be >70%
MMEFR
mid maximum expiratory flow rate. rate btw 25% and 75% of maximum exhalation during FVC
PEF
peak expiratory flow. max flow on forceful expiration.
2 big types of airway obstruction
intrathoracic (COPD, emphysema, asthma, tumor) or extrathoracic (laryngeal tumor, tracheal stenosis).
Airway obstruction results
FEV1/FVC < 70% and characteristic flow volume loop. MMEFR often reduced. Air trapping also possible: loss of plateu on the time vs. vol plot. (this loss of plateua represents slow release of trapped air).
Intrathoracic obstruction spirometry results
FEV1/FVC <70%
decreased peak expiratory flow
concavity on expiration
tube goes in on expiration and out on inspiration.
Extrathoracic obstruction spirometry results
tube in on inspiration, out on expiration.
blunt inspiratory and expiratory curve if a fixed obstruction is present.
blunt on just one half of the loop for variable extrathoracic obstruction.
When should I work up for restrictive issues?
if FEV1/FVC is normal and loop is normal but both seem small
Lung volume measurements and normal values
2 ways: He test and body plethysmography. He test basically involves inhaling known conc. and vol. of He and then measuring new conc. of He to calculate new vol.
Normal is >80% predicted
Diffusion testing. Normal results
this involves breathing in CO, which can only leave lungs via diffusion and has a very high affninity for Hb. Normal is less than 70%; usually more likely to desaturate below 50%.
Causes of decreased diffusion (DLCO)
interstitial lung disease:
Low DLCO + restriction –> parenchymal
Normal DLCO + restriction -> extra-pulmonary
emphysema
decreased intrathoracic/pulmonary blood volume (pulmonary vascular disease)
low Hb or abnormal Hb
Restriction results for lung volume testing
<80%. may be pulmonary (fibrosis, edema) or extrapulmonary (obesity, pleural effusion)
Causes of increased DLCO
recruitment of pulmonary capillaries, as in exercise or supine position
alveolar hemorrhage
polycythemia (too many RBCs)
air trapping without parenchymal abnormalities (asthma)
