Pulmonary function testing (PFT) evaluates the respiratory system through tests, patient history, and exams. PFT identifies the severity of lung impairment and helps clinicians understand lung disease. Tests measure lung volume, air flow, and gas exchange. Abnormal results can indicate conditions like asthma or COPD. PFT is used for diagnosis, monitoring disease progression, and pre-operative evaluation.

1. Pulmonary function testing
Pulmonary Function Testing (PFT) is a complete eval-
uation of the respiratory system including patient history,
physical examinations, chest x-ray examinations, arterial
blood gas analysis, and tests of pulmonary function. The
primary purpose of pulmonary function testing is to iden-
tify the severity of pulmonary impairment.[1]
Pulmonary
function testing has diagnostic and therapeutic roles and
helps clinicians answer some general questions about pa-
tients with lung disease. PFTs are normally performed by
a respiratory therapist.
1 Indications
Pulmonary function testing is a diagnostic and manage-
ment tool used for a variety of reasons, such as:
• Chronic shortness of breath
• Asthma
• Chronic obstructive pulmonary disease
• Restrictive lung disease
• Preoperative testing
• Impairment or disability
1.1 Pediatric neuromuscular disorders
Neuromuscular disorders such as Duchenne muscular
dystrophy are associated with gradual loss of muscle
function over time. Involvement of respiratory muscles
results in poor ability to cough and decreased ability to
breathe well and leads to collapse of part or all of the lung
leading to impaired gas exchange and an overall insuffi-
ciency in lung strength.[2]
Pulmonary function testing in
patients with neuromuscular disorders helps to evaluate
the respiratory status of patients at the time of diagnosis,
monitor their progress and course, evaluate them for pos-
sible surgery, and gives an overall idea of the prognosis.[3]
2 Measurements
2.1 Spirometry
Main article: Spirometry
Spirometry includes tests of pulmonary mechanics – mea-
surements of FVC, FEV1, FEF values, forced inspiratory
flow rates (FIFs), and MVV. Measuring pulmonary me-
chanics assesses the ability of the lungs to move large vol-
umes of air quickly through the airways to identify airway
obstruction.
The measurements taken by the spirometry device are
used to generate a pneumotachograph that can help to
assess lung conditions such as: asthma, pulmonary fi-
brosis, cystic fibrosis, and chronic obstructive pulmonary
disease. Physicians may also use the test results to diag-
nose bronchial hyperresponsiveness to exercise, cold air,
or pharmaceutical agents.[4]
2.1.1 Complications of spirometry
Spirometry is a safe procedure; however, there is cause
for concern regarding untoward reactions. The value of
the test data should be weighed against potential haz-
ards. Some complications have been reported, including
pneumothorax, increased intracranial pressure, fainting,
chest pain, paroxysmal coughing, nosocomial infections,
oxygen desaturation, and bronchospasm.
2.2 Lung volumes
Main article: Lung volumes
There are four lung volumes and four lung capacities. A
lung capacity consists of two or more lung volumes. The
lung volumes are tidal volume (VT), inspiratory reserve
volume (IRV), expiratory reserve volume (ERV), and
residual volume (RV). The four lung capacities are total
lung capacity (TLC), inspiratory capacity (IC), functional
residual capacity (FRC) and vital capacity (VC).
2.3 Maximal respiratory pressures
Measurement of maximal inspiratory and expiratory
pressures is indicated whenever there is an unexplained
decrease in vital capacity or respiratory muscle weak-
ness is suspected clinically. Maximal inspiratory pres-
sure (MIP) is the maximal pressure that can be produced
by the patient trying to inhale through a blocked mouth-
piece. Maximal expiratory pressure (MEP) is the max-
imal pressure measured during forced expiration (with
cheeks bulging) through a blocked mouthpiece after a
1

2. 2 6 REFERENCES
full inhalation. Repeated measurements of MIP and
MEP are useful in following the course of patients with
neuromuscular disorders.
2.4 Diffusing capacity
Main article: Diffusing capacity
Measurement of the single-breath diffusing capacity for
carbon monoxide (DLCO) is a fast and safe tool in the
evaluation of both restrictive and obstructive lung disease.
2.5 Oxygen desaturation during exercise
The six-minute walk test is a good index of physical
function and therapeutic response in patients with chronic
lung disease, such as COPD or idiopathic pulmonary fi-
brosis.[5][6][7]
2.6 Arterial blood gases
Arterial blood gases (ABGs) are a helpful measurement
in pulmonary function testing in selected patients. The
primary role of measuring ABGs in individuals that are
healthy and stable is to confirm hypoventilation when it is
suspected on the basis of medical history, such as respi-
ratory muscle weakness or advanced COPD.
ABGs also provide a more detailed assessment of the
severity of hypoxemia in patients who have low normal
oxyhemoglobin saturation.
3 Techniques
3.1 Helium Dilution
Main article: Helium dilution technique
The helium dilution technique for measuring lung vol-
umes uses a closed, rebreathing circuit.[8]
This technique
is based on the assumptions that a known volume and con-
centration of helium in air begin in the closed spirometer,
that the patient has no helium in their lungs, and that an
equilibration of helium can occur between the spirometer
and the lungs.
3.2 Nitrogen Washout
Main article: Nitrogen washout
The nitrogen washout technique uses a non-rebreathing
open circuit. The technique is based on the assumptions
that the nitrogen concentration in the lungs is 78% and
in equilibrium with the atmosphere, that the patient in-
hales 100% oxygen and that the oxygen replaces all of
the nitrogen in the lungs.[9]
3.3 Plethysmography
Main article: Plethysmograph
The plethysmography technique applies Boyle’s law and
uses measurements of volume and pressure changes
to determine lung volume, assuming temperature is
constant.[10]
4 Interpretation of tests
Professional societies such as the American Thoracic
Society/ European Respiratory Society have published
guidelines regarding conduct and interpretation of pul-
monary function testing to ensure standardization and
uniformity in performance of tests. The interpretation of
tests depends on comparing the patients values to pub-
lished normals from previous studies. Deviation from
guidelines can result in false-positive or false negative test
results. Mohanka MR et al. recently demonstrated that
only a small minority of pulmonary function laboratories
followed published guidelines for spirometry, lung vol-
umes and diffusing capacity in 2012. Ref. A survey of
practices of pulmonary function interpretation in labo-
ratories in Northeast Ohio Mohanka MR, et al. Chest.
2012;141(4):1040-1046
5 Significance
Changes in lung volumes and capacities are generally
consistent with the pattern of impairment. TLC, FRC,
and RV increase with obstructive lung diseases and de-
crease with restrictive impairment.
6 References
[1] Pulmonary terms and symbols: a report of the ACCP-
ATS Joint Committee on Pulmonary Nomenclature,
Chest 67:583, 1975
[2] Finder JD, Birnkrant D, Carl J, et al. Respiratory
care of the patients with Duchenne muscular dystro-
phy: ATS consensus statement. Am J Respir Crit Care
Med.2004;170 (4):456– 465
[3] Sharma GD (2009). “Pulmonary function testing in neu-
romuscular disorders.”. Pediatrics. 123 Suppl 4: S219–
21. doi:10.1542/peds.2008-2952D. PMID 19420147.
[4] Pulmonary Function Test in New York, Article. June
2010. Dr. Marina Gafanovich, MD - 1550 York Ave,

3. 3
New York NY 10028 - (212) 249-6218. NYC Pulmonary
Function Test.
[5] Enright PL (2003). “The six-minute walk test.”. Respir
Care 48 (8): 783–5. PMID 12890299.
[6] Swigris JJ, Wamboldt FS, Behr J, du Bois RM, King TE,
Raghu G, et al. (2010). “The 6 minute walk in idio-
pathic pulmonary fibrosis: longitudinal changes and min-
imum important difference.”. Thorax 65 (2): 173–7.
doi:10.1136/thx.2009.113498. PMC 3144486. PMID
19996335.
[7] ATS Committee on Proficiency Standards for Clin-
ical Pulmonary Function Laboratories (2002).
“ATS statement: guidelines for the six-minute walk
test.”. Am J Respir Crit Care Med 166 (1): 111–7.
doi:10.1164/ajrccm.166.1.at1102. PMID 12091180.
[8] Hathirat S, Renzetti AD, Mitchell M: Measurement of the
total lung capacity by helium dilution in a constant volume
system, Am Rev Respir Dis 102:760, 1970.
[9] Boren HG, Kory RC, Snyder JC: The veterans
Administration-Army cooperative study of pulmonary
function, II: the lung volume and its subdivisions in
normal men, Am J Med 41:96, 1966.
[10] Dubois AB, et al: A rapid plethysmographic method for
measuring thoracic gas volume: a comparison with a ni-
trogen washout method for measure FRC in normal pa-
tients, J Clin Invest 35:322, 1956.

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