Spirometry Flashcards
standard spirometry indices?
FEV1 (forced expiratory volume in 1 sec)
FVC (total volume of air which can be forcibly expelled in one breath)
FEV1/FVC (fraction of total air exhaled which can be exhaled in 1 sec)
additional indices?
VC (full relaxed breath volume, not done under force)
FEV6 (forced volume in 6 secs)
MEFR (mid-expiratory flow rate)
normal spirometry trace (volume/time)
sharp upward slope, then plateaus
volume at 1sec = FEV1
volume at 6secs = FVC
normal FEV1/FVC?
> 0.7 (70%)
remember to combine with history (eg you would expect a fit young person to be fair bit >0.7
3 obstructive diseases?
asthma
COPD
bronchiectasis
obstructive disease mainly affects inhalation or exhalation?
exhalation
obstructive spirometry trace?
shallower curve (not a sharp upward curve as cant expel lot of air quickly) some cases reach a normal FVC eventually, some dont
FEV1, FVC and FEV1/FVC in obstructive disease?
FEV1 = redcued FVC = can be normal or slightly reduced FEV1/FVC = reduced
how is COPD diagnosed in most cases?
clinical
symptoms and history
diagnostic test for COPD? (not usually needed)
post-bronchodilator FEV1/FVC
measure FEV1/FVC 15 mins after 400mcg salbutamol or equivalent
(has to be after bronchodilator to distinguish from asthma as asthma would basically resolve after bronchodilator)
examples of restrictive disease?
anything causing fibrosis (ILD, sarcoid, idiopathic pulmonary fibrosis etc)
obesity
neuromuscular problems
scoliosis
FEV1, FVC and FEV1/FVC in restrictive disease?
FEV1 = normal or mildly reduced FVC = <80% predicted FEV1/FVC = normal (both reduced same amount)
spirometry trace in restrictive disease?
same sharp upward curve but it stops short and plateaus at a lower volume
(so can expel at normal rate, just not as much overall)
what is a flow volume curve?
shows flow rate against volume rather than volume against time
exhalation on top and inhalation in bottom
shows peak flow
obstructive flow volume curve?
same sharp upstroke but stops short of normal peak flow rate
scooped out downstroke as airways start to close while exhaling (will close more quickly in more severe disease causing steeper drop off and bigger scoop out)
restrictive flow volume curve?
basically normal flow rate but doesnt last as long (less overall volume)
what is gas transfer?
measurement of ability of oxygen to be absorbed at alveolar level
gas transfer values?
DLCO (diffusion capacity of lung for carbon monoxide)
KCO = corrected DLCO for measured alveolar volume
how is DLCO measured?
breathe in a known amount of CO then check how much is breathed out, if a lot breathed back out then not good transfer
how is COPD mainly graded?
ABCD A = few symptoms or exacerbations B = more symptoms, few exacerbations C = few symptoms, more exacerbations D = more symptoms and exacerbations
