Pulmonary Function
Studies: Review
By Elizabeth Kelley Buzbee AAS, RRTNPS, RCP
Lone Star college Systems- Kingwood
• Identify the indications for PFT
answer
• according to the AARC CPG, PFT need to be done to:
[1]
diagnosis restrictive defects,
[2]
to differentiate between restrictive and
obstructive defects,
[3]
assess the patient’s response to interventions
[4]
pre-op assessment of patients at risk for
pulmonary limitations
[5]
evaluate pulmonary disability
[6]
Quantify air trapping; is it getting worse, better
• What are the hazards of PFT?
answer
• According to the AARC CPG, the relative
contraindications include
• [1]
untreated pneumothorax
• [2]
hemoptysis
• [3] unstable hemodynamics
• [4]
aneurysms.
– If persons have claustrophobia, upper body
paralysis or cast that makes the ‘body box’
impossible, this single test may be deferred.
• Identify this type of pulmonary function study
answer
• This is a flow volume loop used to find both
obstructive and restrictive defects.
• The shape of the curve can give the RCP
information about where an obstruction is
located: intra-thoracic large airway, large fixed
or small airways
•
• Read the FVC of the blue tracing and compare it to
the normal one
answer
• The FVC of the blue tracing on the flow
volume loop is 200 ml [the line starts at 100 so
we need to subtract that from the end point]
• The FVC of the normal flow volume loop is
600 ml.
• The percent of predicted is 200/600 or 33% of
predicted
• There is very severe derangement of the FVC
values
• Is the blue tracing consistent with a restrictive defect or an
obstructive defect?
answer
• The blue tracing is 33% of predicted which
demonstrates a very severe restrictive defect.
• Identify the peak inspiratory flow rate of the blue tracing
• Identify the peak expiratory flow rate of the blue tracing
answer
• the peak inspiratory flow rate of the blue
tracing is about 65 LPM
• The peak expiratory flow rate is also about 65
LPM
• Compare the blue tracing of the PIFR to the
normal one
• Compare the blue tracing of the PEFR to the
normal one
answer
• PIFR is about 80 LPM so 65/80 = 81%
predicted or normal
• PEFR is about 100 LPM so 65/100 is 65% of
predicted which is consistent with mild airway
obstruction
• Discuss the clinical significance of VT that is
50% of predicted.
answer
• A VT by itself is not too helpful; we could have
a restrictive defect or an obstructive one.
• The most use we get out of this value is during
weaning parameters.
• Discuss the clinical significance of a FEV1 that
is 45% of predicted
answer
• A FEV1 that is 45% of predicted implies that there
is a severe obstructive defect, but we need to see
the FVC also
• If both are down, we may have restrictive defect
• If FVC is ok, but there is a lower FEV1 then it is
clear we have obstruction
• Calculate the FEV1/FVC. A normal person should
be able to exhale 70% of his FVC in the first
second
•
• Discuss the clinical significance of a FEV1/FVC
that is higher than normal.
answer
• The person with a FEV1/ FVC that is high may
have a normal exhaled flow, but have a low
FVC due to a restrictive defect.
• Discuss the clinical significance of an elevated
FRC.
answer
• High FRC implies that there is air trapping
which is associated with obstructive defects
• Discuss the clinical significance of a TLC that is
135% of predicted
answer
• TLC that is elevated shows significant
hyperinflation if the FRC is also higher than
normal
• If a person’s RV is increased what problems
does this imply?
answer
• An elevated RV implies that there is airtrapping associated with obstructive defects
such as asthma, COPD or emphysema
• How do we ask a patient to perform the flow
volume loop?
answer
• We ask him to perform a FVC into the
computer which will display the graphics
• We ask him to inhale as deeply as possible
from the end expiratory of a normal breath
then exhale as completely and as quickly as
possible
• What is the function of the MVV?
answer
• The MVV is used to monitor the ability of a
patient to maintain rapid and deep breaths over a
period of time
• The person with significant obstruction cannot do
this because he will start to air trap
• The person with restrictive defect will have
problems getting a big enough VT with each
breath---the most important diagnostic benefit of
looking at the MVV is assessing the patient for his
ability to tolerate pulmonary rehabilitation
• How do we measure a value like the RV that
cannot leave the body?
answer
• To collect the value of the RC which is needed
to calculate the FRC, we need to measure this
volume indirectly by helium dilution studies or
by N2 washout [over several minutes]
• What is the function of the single breath N2
washout study
answer
• In the single-breath N2 washout study we are
looking at gas distribution which is directly
related to the level of airway obstruction
• What is the significance of having a higher
TGV by body box than TLC by helium dilution
answer
• If the body box results in a higher volume than
the helium dilution, it is because there are
airways that have not been exposed to the
other airway—they are completely obstructed
• What circumstances can result in decreased
diffusion of Carbon monoxide during diffusion
studies?
answer
• Any disorder that results in hypoxemia can
result in diffusion defect.
• If there are no s/s of restrictive or obstructive
defects on PFT, but there is diffusion, we
worry about disorders such as pulmonary
emboli.
Case study # 1
• Your patient is a 45 YO Asian male who
presents with episodes of SOB associated with
weather changes and increased activity.
• He is tested in the Pulmonary function lab:
• you see the following:
FVC - 63% predicted
Slow VC - 88% predicted
What does this imply?
answer
• If the slow VC is higher than the forced VC, we
may have an obstructive defect without a
restrictive componant
• He also has this:
– IC – 89% predicted
– FRC- 136% predicted
– PEFR – 65% predicted
– PIFR 91% predicted
answer
– IC – 89% predicted- this is WNL and shows that
there is no restrictive defect
– FRC- 136% predicted- this shows that there is no
restrictive defect. But that there is obstructive
defect associated with air trapping
– PEFR – 65% predicted- the peak flow is decreased
showing mild obstructive defect
– PIFR 91% predicted is WNL; there is no upper
airway obstruction
•
•
•
•
•
He has the following data:
FEV1 62% predicted
FEV1/FVC 67% predicted
FEV 25-75% 65% predicted
MVV – 54% of predicted
answer
• FEV1 62% predicted: implies that there is
moderate obstructive defect
• FEV1/FVC 67% predicted: supports this
obstructive defect
• FEV 25-75% 65% predicted- mild obstruction in
the smaller airway
• MVV – 54% of predicted: shows that this
patient would have poor exercise tolerance,
but could undergo pulmonary rehab
• What is your overall impression of this
patient?
answer
• This patient has several indices for mildmoderate obstructive defect with air trapping
• This patient has no evidence of restrictive
defect
Case study #2
• Your patient is a 58 YO LAF who presents with
the following s/s: She is in considerable
respiratory distress at rest with RR 25 BPM, HR
109 with sinus tachycardia. Systemic BP is
156/99. She is afebrile at this time, but has
recurrent pneumonias over the last few years.
On 12-lead EKG we see right axis deviation.
•
•
•
•
•
She has the following PFT:
FVC - 49% predicted
Slow VC - 49% predicted
IC – 50% predicted
FRC- 45% predicted
answer
• FVC - 49% predicted: implies there is might
be a severe restrictive or obstructive defect
• Slow VC - 49% predicted: supports a severe
restrictive defect
• IC – 50% predicted: implies moderate
restrictive defect
• FRC- 45% predicted: implies there is severe
restrictive defect
answer
• The patient has the following parameters on PFT:
• PEFR – 88% predicted before and after BD: no obstructive
defect
• PIFR 95% predicted no obstructive defect
• FEV1 120% predicted: WNL no obstructive defect
• FEV1/FVC 145% predicted: implies there is restrictive defect
• FEV 25-75% 98% predicted: no obstruction in the small airways
• MVV – unable to complete
• What is your overall impression of this
patient?
answer
• This patient has moderate-severe restrictive
defect with no obstruction