110714 spirometry Flashcards
transpulmonary pressure equals
Palv-Ppl
what determines airflow, particularly during expiration?
flow = (Palv-Patm)/airway resistance
where is resistance largest along the respiratory tract?
medium sized bronchi
conductance and resistance relationship
inverse
the only lung pressure we can measure i
pleural pressure
how can we calculate lung compliance?
volume/pressure change for transpulmonary pressure
use points of zero alveolar pressure to find transpulmonary pressure
in emphysema, compliance is
increased relative to normal subject
in expiration, there are two phases called?
effort dependent
effort independent flow rate phase
indications for PFTs
diagnostic (symptoms, signs, abnormal labs)
assess effects of diseases and therapies
screening (smokers, occupational exposures, preoperative risk, disability, prognosis)
spirometry will never tell you the disease-true or false?
true
what kind of graphs are there in spirometry?
volume time curve
flow volume loop
what portion of flow volume loop is effort independent
btwn FEF25 and FEF75
inspiratory flow rate on flow volume loop measures what?
how well upper airway is doing
upper airway=what’s outside of the chest wall
expiratory flow rate on flow volume loops measures what?
what’s happening in the intrathoracic airways (anything affecting resp sys inside chest wall; not just lungs and airway)
with asthma, what would you observe in the mid lung volume range and where on the flow volume loop?
in the expiratory flow rates, you would see decrease in expiratory flow rate in mid lung volume range
FEF50 and FIF50 relationship in normal pts
normally equal
hallmark of obstructive disease on flow volume loop
decreased flow rates
small airway–scalloping effect
restrictive disease
you never get a lung capacity that goes out to normal because there’s scarring and not not expanding normally
total lung capacity is going to be too low
flow volume loop:
shape of curve is similar to normal curve
FVC is expired in how many seconds normally
6
keys to spirometry interpretation
FEV1/FVC ratio (must be close to 100% of predicted to be normal)
FEV1
FVC
how do you interpret a NOT low ratio of FEV1/FVC?
normal ventilatory fxn and restrictive processes
how do you interpret a LOW ratio of FEV1/FVC?
obstructive process
what is normal FEV1/FVC ratio?
0.70-0.87, depending on demographics of pt
what is considered normal spirometry result?
FEV1/FVC ratio is normal
AND
VC (FVC) is normal
what is considered a normal FVC
greater than or equal to 80% of predicted (within the 95% confidence level)
if FEV1/FVC ratio is low, how do you determine the degree of obstruction?
look at percent of predicted FEV1
see slide 20 for values
when should you assess bronchodilator responsivity?
for all pts with spirometry showing low FEV1/FVC ratio
for all pts suspected of asthma or chronic obstructive lung dis
bronchodilator respponsivity
significant response to a bronchodilator is shown when the FVC or FEV1 increases at least 12% AND 200mL
shows reversible obstruction–asthma
ex of restrictive ventilatory defects
interstitial lung disease: sarcoidosis, collagen vascular dis, pulmonary fibrosis
penumonectomy
pleural disease: pleural effusion
chest wall dis: kyphosis, neuromuscular disorders
extrathoracic conditions: obesity
true hallmark of restrictive ventilatory defect
reduced TLC
how to determine if supports restrictive ventilatory defect?
normal FEV1/FVC ratio
reduced TLC–see slide 24 for values for degree of restrictive disease
if cannot obtain lung volumes, then grade FVC via the obstructive FEV1 criteria–see slide 25
looking at shapes of flow volume loops-what to look for
beware of flattened inspiratory curve
check FEF50/FIF50 ratio
FEF50/FIF50 of 1 or less is normal
FEF50/FIF50 greater than 1 is variable extrathoracic airway obstruction
FEF50/FIF50 a little over 1 is fixed extrathoracic airway obsrtuction
FEF50
forced expiratory flow of 50%–look at y axis and halve it to determine
