Pulmonary Function Testing
INTRODUCTION
• http://www.youtube.com/watch?v=WyhOJR8
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• http://www.youtube.com/watch?v=ZIgQGAWJ
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Introduction
• Pulmonary function testing has come into widespread
use since the 1970s.
• This has been facilitated by several developments.
Because of miniaturization and advances in computer
technology, microprocessor devices have become
portable and automated with fewer moving parts.
Testing equipment, patient maneuvers, and testing
techniques have become widely standardized
throughout the world through the efforts of
professional societies.
• Widely accepted normative parameters have been
established.
Introduction
• Pulmonary function testing is a valuable tool for evaluating the
respiratory system, representing an important adjunct to the
patient history, various lung imaging studies, and invasive testing
such as bronchoscopy and open-lung biopsy.
• Insight into underlying pathophysiology can often be gained by
comparing the measured values for pulmonary function tests
obtained on a patient at any particular point with normative values
derived from population studies.
• The percentage of predicted normal is used to grade the severity of
the abnormality.
• Practicing clinicians must become familiar with pulmonary function
testing because it is often used in clinical medicine for evaluating
respiratory symptoms such as dyspnea and cough, for stratifying
preoperative risk, and for diagnosing common diseases such as
asthma and chronic obstructive pulmonary disease.
Introduction
• Pulmonary function tests (PFTs) is a generic
term used to indicate a battery of studies or
maneuvers that may be performed using
standardized equipment to measure lung
function. PFTs can include simple screening
spirometry, formal lung volume measurement,
diffusing capacity for carbon monoxide, and
arterial blood gases. These studies may
collectively be referred to as a complete
pulmonary function survey.
Introduction
• Before a spirogram can be meaningfully interpreted, one needs to inspect
the graphic data (the volume-time curve and the flow-volume loop) to
ascertain whether the study meets certain well-defined acceptability and
reproducibility standards.
• Tests that fail to meet these standards can provide useful information
about minimum levels of lung function, but, in general, they should be
interpreted cautiously. The interpretive strategy usually involves
establishing a pattern of abnormality (obstructive, restrictive, or mixed),
grading the severity of the abnormality, and assessing trends over time.
• Various algorithms are available. Automated spirometry systems usually
have built-in software that can generate a preliminary interpretation,
especially for spirometry; however, algorithms for other pulmonary
function studies are not as well established and necessitate appropriate
clinical correlation and physician oversight.
Flow Volume Loops
Categories of Pulmonary Function
Tests
• Pulmonary function studies use a variety of
maneuvers to measure and record the properties of
four lung components. These include the airways
(large and small), lung parenchyma (alveoli,
interstitium), pulmonary vasculature, and the
bellows-pump mechanism. Various diseases can
affect each of these components.
Categories of Pulmonary Function
Tests
• Measurement of dynamic flow rates of gases
through the airways
• Measurement of lung volumes and capacities
• Measurement of the lung’s ability to diffuse gases
Indications for Pulmonary
Function Testing
• Evaluation of the cause of pulmonary symptoms
such as dyspnea, coughing, wheezing, and exercise
intolerance
• Evaluation of abnormalities noted on chest X-ray
• Determination of the course of a disease and the
response to treatment of the disease
Indications for Pulmonary
Function Testing
• Evaluation of risk for perioperative pulmonary
complications
• Performance of epidemiological surveillance for
pulmonary disease
Indications for Pulmonary
Function Testing
• Rule out significant pulmonary pathology in people
with high risk for pulmonary dysfunction, such as
smokers, firefighters, and those exposed to asbestos
• Evaluation of degree of disability
Monitoring
•To assess therapeutic interventions Bronchodilator therapy
•Steroid treatment for asthma, interstitial lung disease, etc.
•Management of congestive heart failure
•Other (antibiotics in cystic fibrosis, etc.)
•To describe the course of diseases affecting lung function
Pulmonary diseases
•Obstructive small airway diseases
•Interstitial lung diseases
•Cardiac diseases
•Congestive heart failure
•Neuromuscular diseases
•Guillain-Barré syndrome
Evaluation of Disability or Impairment
To assess patients as part of a rehabilitation
program Medical
•Industrial
•Vocational
To assess risks as part of an insurance evaluation
•To assess persons for legal reasons Social
Security or other government compensation
programs
•Personal injury lawsuits
•Other
Contraindications for Pulmonary
Function Testing
• Performing lung function tests can be physically demanding
for a minority of patients. It is recommended that patients
should not be tested within 1 month of a myocardial
infarction.
• Chest or abdominal pain of any cause
• Oral or facial pain exacerbated by a mouthpiece
• Stress incontinence
• Dementia or confusional state
• Patients with any of the conditions are unlikely to achieve
optimal or repeatable results
• Age of patient, ages of 8 and less render less accurate results
Patient Position for Pulmonary
Function Testing
• Testing may be performed either in the sitting or
standing position, and the position should be
recorded on the report
• Sitting is preferable for safety reasons in order to
avoid falling due to syncope. The chair should have
arms and be without wheels. If a wheelchair is used,
the wheels should be
• locked. If the standing position is used, a chair can be
placed behind the patient/subject, so that they can
be quickly and easily moved into a sitting position if
they become lightheaded during the maneuver.
Patient Position for Pulmonary
Function Testing
• Obese subjects, or those with excessive weight at the
mid-section, will frequently obtain a deeper
inspiration when tested in the standing position.
Consequently, forced expiratory volumes and flows
may improve with the standing position in these
individuals.
• Normal-weight subjects typically have equivalent
values when tested sitting or standing, but, for
longitudinal studies, the same test position should be
used each time.
PATIENT DETAILS for Pulmonary
Function Testing
• Age, height and weight
• The patient’s age, height and weight (wearing indoor clothes
without shoes) are recorded for use in the calculation of
reference values. The age should be expressed in years.
Height and weight should be expressed with the units in use
in the country, corresponding to the ones of the selected
reference equation.
• Body mass index should be calculated as kg. The height
should be measured without shoes, with the feet together,
standing as tall as possible with the eyes level and looking
straight ahead, and using an accurate measuring device.
PATIENT DETAILS for Pulmonary
Function Testing
• Age, height and weight
• For patients with a deformity of the thoracic cage,
such as kyphoscoliosis, the arm span from fingertip
to fingertip can be used as an estimate of height.
Arm span should be measured with the subject
standing against a wall with the arms stretched to
attain the maximal distance between the tips of the
middle fingers. A regression equation using arm
span, race, sex and age has been found to account
for 87% of the variance in standing height with the
standard error of the estimate for height ranging
from 3.0 to 3.7 cm.
PATIENT DETAILS for Pulmonary
Function Testing
• Therapy
• The operator should record the type and dosage of
any (inhaled or oral) medication that may alter lung
function and when the drugs were last administered.
• Typically SVN therapy is withheld to render a more
reflective exam.
PATIENT DETAILS for Pulmonary
Function Testing
• Subject preparation
• Subjects should avoid the activities listed below and
these requirements should be given to the patient at
the time of making the appointment. On arrival, all
of these points should be checked, and any
deviations from them recorded
•
•
•
•
Smoking within at least 1 h of testing
Consuming alcohol within 4 h of testing
Performing vigorous exercise within 30 min of testing
Wearing clothing that substantially restricts full chest and
abdominal expansion
• Eating a large meal within 2 h of testing
PATIENT DETAILS for Pulmonary
Function Testing
• Subject preparation
• Subjects should be as relaxed as possible before and
during the tests. The decision to avoid long- and
short-acting bronchodilators is a clinical one,
dependent on the question being asked. If the study
is performed to diagnose an underlying lung
condition, then avoiding bronchodilators is useful. If
the study is carried out to determine a response to
an existing therapeutic regimen, then one may
choose not to withhold bronchodilator medications.
PATIENT DETAILS for Pulmonary
Function Testing
• Subject preparation
• Patients should be asked to loosen tight-fitting
clothing.
• Dentures should normally be left in place; if they are
loose, they may interfere with performance and are,
therefore, best removed.
PATIENT DETAILS for Pulmonary
Function Testing
• LABORATORY DETAILS
• Ambient temperature, barometric pressure and time of day
must be recorded. Temperature is an important variable in
most pulmonary function tests and is often measured directly
by the instrument.
• The way in which it is measured and used may vary from
instrument to instrument. For example, it may be measured
with a simple thermometer or an internal thermistor.
• Ideally, when patients return for repeat testing (e.g. at a
clinic), the equipment and the operator should be the same,
and the time of day should be within 2 h of previous test
times
PATIENT DETAILS for Pulmonary
Function Testing
• LABORATORY DETAILS
• The order for performing lung function tests should take into
account the optimum work flow in the laboratory, potential
influences of one test on another and the ability of the
subject to undertake the test.
• Possible order for undertaking lung function tests in a
laboratory
• Dynamic studies: spirometry, flow–volume loops, PEF
• Static lung volumes
• Inhalation of bronchodilator agent (if used)
• Diffusing capacity
• Repeat dynamic studies (if a bronchodilator was given)
PATIENT DETAILS for Pulmonary
Function Testing
• LABORATORY DETAILS
• The choice of order of testing should consider the potential
effect of one test on the subsequent test. For example, the
measurement of carbon monoxide diffusing capacity of the
lung (DL,CO) immediately after a nitrogen washout
measurement of the total lung capacity (TLC) will be affected
by the increased oxygen content in the lungs, unless enough
time has passed to allow the oxygen concentration to return
to normal.
PATIENT DETAILS for Pulmonary
Function Testing
• LABORATORY DETAILS
• Also, tidal breathing maneuvers may be disturbed by a
recently performed maximal forced expiratory maneuver.
• Bronchodilator administration may affect static lung volumes,
reducing hyperinflation by up to 0.5 L .
• While bronchodilators do not seem to affect diffusing capacity
when measured, they may allow 10% of patients to obtain a
measurement of diffusing capacity that was not possible prebronchodilator
PATIENT DETAILS for Pulmonary
Function Testing
• Quality Control
• Quality control is important to ensure that the laboratory is
consistently meeting appropriate standards. In any quality
control program, an important element is a manual of
procedures that contains the following: calibration
procedures, test-performance procedures, calculations,
criteria, reference values source, and action to be taken when
‘‘panic’’ values are observed.
• Calibration of the equipment should always be done prior to
any pulmonary function test
• http://www.youtube.com/watch?v=uqGXNLq
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American Thoracic Society
Standards
• Developed in conjunction with the European
Respiratory Society and published in 2005
• http://thoracic.org/career-development/residents/ats-readinglist/pulmonary-function-testing.php
American Thoracic Society
Standards
• Sets standards for equipment used in testing
– Able to measure volumes between 0.5 and 8 L
– Able to measure flow from 0 to 14 L/sec
– Capable of accumulating volume for 15 seconds
American Thoracic Society
Standards
• Sets standards for equipment used in testing
– Maximum allowable error of ± 3% or ± 0.05 L, whichever
is greater
– Resistance and back pressure < 1.5 cm H2O/L/sec
American Thoracic Society
Standards
• Details considerations of patients being tested
– Lists determination of patient height and weight
– Suggests patient activities that should be avoided and
interval between activity and test
American Thoracic Society
Standards
• Sets standards for infection control of pulmonary
function equipment
• Lists qualifications for personnel administering
pulmonary function testing
List of abbreviations and meanings
• ATPD Ambient temperature,
ambient pressure, and dry
• ATPS Ambient temperature
and pressure saturated with
water vapor
• BTPS Body temperature (i.e.
37°C), ambient pressure,
saturated with water vapor
• COHb Carboxyhemoglobin
• DLCO Diffusing capacity for
the lungs measured using
carbon monoxide, also
known as transfer factor
• DLCO/VA Diffusing capacity
for carbon monoxide per
unit of alveolar volume, also
known as KCO
• DM Membrane-diffusing
capacity
• DT Dwell time of flow .90%
of PEF
• EFL Expiratory flow
limitation
• ERV Expiratory reserve
volume
• EV Back extrapolated
volume
List of abbreviations and meanings
• EVC Expiratory vital capacity
• FEF25-75% Mean forced
expiratory flow between
25% and 75% of FVC
• FEV1 Forced expiratory
volume in one second
• FEVt Forced expiratory
volume in t seconds
• FRC Functional residual
capacity
• FVC Forced vital capacity
• IC Inspiratory capacity
• MVV Maximum voluntary
ventilation
• PEF Peak expiratory flow
• RV Residual volume
• STPD Standard temperature TGV
(or VTG) Thoracic gas volume
• TLC Total lung capacity
• Tr Tracer gas
• VA Alveolar volume
• VC Vital capacity
• VD Dead space volume
• VI Inspired volume
• VS Volume of the expired sample
gas
Differentiation of Obstructive and
Restrictive Disease
Characteristic
Obstructive Disease
Restrictive Disease
Anatomy affected
Airways
Lung parenchyma,
thoracic pump
Breathing phase
difficulty
Expiration
Inspiration
Pathophysiology
Increased airway
resistance
Decreased lung and/or
thoracic compliance
Useful measurements
Flow rates
Volumes and/or
capacities
Lung Volumes
• Residual volume (RV)
– Volume of gas remaining in the lung after a maximal
exhalation
– Normal value – 1.2 L, approximately 20 % of total lung
capacity
Lung Volumes
• Expiratory reserve volume (ERV)
– Volume of gas that can be exhaled after a normal
exhalation
– Normal value – 1.2 L, approximately 20% of total lung
capacity
Lung Volumes
• Tidal volume (VT)
– Volume of gas inspired during a normal inhalation
– Normal value – 0.5 L, approximately 10% of total lung
capacity
Lung Volumes
• Inspiratory reserve volume (IRV)
– Volume of gas that can be inspired after a normal
inspiration
– Normal value – 3.1 L, approximately 50% to 55% of total
lung capacity
Lung Capacities
• Total lung capacity (TLC)
– Volume of gas contained in the lung at maximum
inspiration
– TLC = RV + ERV + VT + IRV
– Normal – 6.0 L
Lung Capacities
• Inspiratory capacity (IC)
– Maximum volume of gas that can be inhaled after a
normal exhalation
– IC = VT + IRV
– Normal – 3.6 L, approximately 60% of TLC
Lung Capacities
• Vital capacity (VC)
– Maximum volume of gas that can be exhaled following
a maximal inhalation
– VC = IRV + VT + ERV
– Normal – 4.80 L, approximately 80% of TLC
Lung Capacities
• Functional residual capacity (FRC)
– Volume of gas that remains in the lung following a
normal exhalation
– FRC = RV + ERV
– Normal – 2.4 L, approximately 40% of TLC
Spirogram
Lung Volumes & Capacities
Lung Volumes & Capacities
Physiology
• Ventilation is the process of generating the forces
necessary to move the appropriate volumes of air from the
atmosphere to the alveoli to meet the metabolic needs of
the body under a variety of conditions.
• Simply, the contraction of the diaphragm and other
inspiratory muscles expands the thorax, generating
negative pressure in the pleural space.
• One component of pleural pressure, known as
transpulmonary pressure, causes a flow of air into the
airways and lungs (inspiration). When the transpulmonary
and alveolar pressures equilibrate, airflow stops, the
inspiratory muscles relax, and the lungs and chest wall
elastic recoil raise pleural pressure, forcing air out of the
lungs (expiration)
Physiology
• With a forced exhalation, the early portion of the
spirometry maneuver is characterized by high flows, mostly
from large airways, and the latter portion is characterized
by low flows with a larger contribution from the smaller
airways.
• Forced inspiration is generally not flow limited and is a
function of overall muscular effort. In contrast, a variety of
factors affect expiratory flow, including the overall driving
pressure, airway diameter, overall distensibility of the lungs
and chest wall, dynamic airway collapse (from a flowlimiting segment), and muscular effort. The overall driving
pressure is the pressure head at the alveolus, or PALV, which
is the difference between pleural pressure (PPL) and
negative transpulmonary pressure (PTP).
Physiology
• PALV = PPL + PTP
• The mechanism for the maximal expiratory
airflow limitation seen in normal airways results
from the gradual drop in pressure inside the
conducting airways from the alveoli to the
mouth, creating a transmural pressure gradient
with the pleural pressure. This can cause dynamic
airway compression and narrowing or closure of
airways that have lost elastic recoil support from
the lung parenchyma.
Spirometry
• Tests basic pulmonary mechanics
• Measures forced vital capacity (FVC), forced expiratory
volumes (FEV), forced expiratory flows (FEF), forced
inspiratory flows (FIF), and maximum voluntary ventilation
(MVV)
• Can be done at bedside or in a lab via handheld spirometer
Spirometry
• Vital capacity
– Technique – subject breaths normally for several
breaths, followed by a maximal inspiration and a
maximal exhalation
– Resting expiratory level must be stable to obtain valid
results
Spirometry
• Forced vital capacity (FVC)
– Technique – subject breaths normally for several
breaths, then inspires maximally and exhales as
forcefully and fully as possible
– Should be within 200 mL of VC
Spirometry
• Forced expiratory volume (most commonly FEV1)
– Volume which can be exhaled in one second using
maximum patient effort
– Determined from the FVC
– Decrease in value indicates obstructive changes in small
airways
Spirometry
• Forced Expiratory Volume (Most Commonly FEV1)
– FEV1% - Percentage of FVC That can be Expired in one
Second (can Measure any Time Interval by Changing
Subscript)
– FEV1% =
𝐹𝐸𝑉1
𝐹𝑉𝐶
x 100
Spirometry
• Forced expiratory volume (most commonly FEV1)
– Normal values
• FEV0.5% − 50% to 60% of FVC
• FEV1% − 75% to 85% of FVC
• FEV3% − 95% to 100% of FVC
Spirometry – FEV
Spirometry
• Forced expiratory volume (most commonly FEV1)
– FEV1% tends to decrease with age as lung elasticity
decreases
– Decrease in value is the most important indicator of
obstructive lung disease
– May be increased or normal in restrictive lung disease
Spirometry
• FEF25%-75%
– Average expiratory flow rate of the middle 50% of the
FVC
– Measured in liters per second
– Indicates flow from medium and small airways
– Changes from smoking occur in medium airways prior to
changes in small airways
Spirometry – FEF25%-75%
Spirometry
• FEF200-1200
– Average expiratory flow rate between the first 200 mL
and 1200mL of exhaled volume of the FVC
– Measured in large airways
– Reflects flow from large airways
Spirometry – FEF200-1200
Spirometry
• Maximum voluntary ventilation (MVV)
– Calculates the maximum volume of gas that a patient can
ventilate in one minute
– Technique – subject is directed to breathe rapidly and
deeply for 12 to 15 seconds; the total volume inspired or
expired is measured; the volume is extrapolated to one
minute
Spirometry
• Maximum voluntary ventilation (MVV)
– Normal value – 150 to 200 L/min
– Decrease indicates increase in airway resistance or
obstruction, decrease in lung or thoracic compliance, or
ventilatory muscle weakness
Spirometry – MVV
Spirometry
• Peak expiratory flow (PEF)
– Highest expiratory flow rate
– Generally occurs during early part of exhalation
– Normal value – males: 400 to 600 L/min; females: 300
to 500 L/min
Flow Volume Loop
Graphic depiction of flow rate plotted against volume change
during an FVC maneuver
Flow-Volume Loop
• Technique – subject maximally inspires, followed
by a single forced exhaled vital capacity (FEVC)
and forced inspired vital capacity (FIVC)
Examples of Flow-Volume Loops in
Disease States
Examples of Flow-Volume Loops in
Disease States
Review
• http://www.youtube.com/watch?v=70KO9gs6
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• http://www.youtube.com/watch?v=9sUk8981
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• http://www.youtube.com/watch?v=gBIG_wcA
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Measurement of Total Lung Capacity
Helium Dilution
• Helium is a metabolically inert gas; based on
assumption that, with a known concentration of
helium in the air of a closed system and no helium
in the patient’s lungs, equilibration will occur
between the spirometer and the lungs
Measurement of Total Lung Capacity
Helium Dilution
• Spirometer is filled with a known volume of air
and helium is added until approximately a 10%
concentration is achieved
• The concentration and volume are then measured
precisely
Measurement of Total Lung Capacity
Helium Dilution
• The patient breathes through a valve-mouthpiece
connected to a rebreathing system with a carbon
dioxide absorber
• Oxygen is added at the rate of the patient’s
oxygen consumption in order to maintain a
concentration of approximately 21%
Measurement of Total Lung Capacity
Helium Dilution
• The valve is opened at the end of expiration and
the patient breathes on the closed circuit until the
concentration of helium stabilizes; for healthy
patients, this is usually from 2 to 5 minutes; for
patients with obstructive disease, equilibration
may take as long as 20 minutes
Measurement of Total Lung Capacity
Helium Dilution
• At stabilization, the concentration of helium in the
system is measured
• A correction factor of 30 mL of helium is
subtracted from the volume for each minute of
helium breathing, up to a total of 200 mLs
Measurement of Total Lung Capacity
Helium Dilution
• Functional Residual Capacity is Calculated
– FRC =[
𝑣𝑜𝑙𝐻𝑒
𝐹𝑖𝐻𝑒
]x [
(𝐹𝑖𝐻𝑒−𝐹𝑓𝐻𝑒)
]
𝐹𝑓𝐻𝑒
Measurement of Total Lung Capacity
Nitrogen Washout
• Nitrogen composes approximately 80% of the air
in the lung, including 80% of the FRC; therefore
the volume of nitrogen in the total exhaled gas
will equal approximately 80% of the FRC
Measurement of Total Lung Capacity
Nitrogen Washout
• Patient breathes 100% oxygen through a valvemouthpiece system for seven minutes or until the
alveolar concentration of nitrogen decreases to
approximately 1%
• A valve is opened at the end of a normal exhalation,
allowing the patient to breathe into the closed circuit
Measurement of Total Lung Capacity
Nitrogen Washout
• A rapid response nitrogen analyzer and a spirometer
measure breath-by-breath nitrogen concentration
and exhaled volume
• Values are summed to provide the total volume of
nitrogen washed out
Measurement of Total Lung Capacity
Nitrogen Washout
• Functional residual capacity is calculated
– FRC = (VE x FEN2) / (0.78 – FAN2)
where VE is the total volume of gas exhaled during the
test, FEN2 is the fractional concentration of exhaled
nitrogen in the total gas volume, and FAN2 is the
fractional concentration of nitrogen in the alveoli at
the end of the test
Measurement of Total Lung Capacity
Nitrogen Washout
Measurement of Total Lung Capacity
Nitrogen Washout
• Also used to determine closing volume (CV) and
closing capacity (CC)
– Closing volume - volume of gas remaining in the
patient’s vital capacity when the small airways
start to close
Measurement of Total Lung Capacity
Nitrogen Washout
• Also used to determine closing volume (CV) and
closing capacity (CC)
– Closing capacity – volume of gas remaining in the
patient’s lungs when the small airways start to
close (CV + RV)
– Used to determine small airway disease
Measurement of Total Lung Capacity
Plethysmography
• Test calculates the total thoracic gas volume,
including gas trapped distal to completely
obstructed airways or located in the abdomen or
intestines
• The patient is placed in the plethysmography or
body box and breathes through a mouthpiece
Measurement of Total Lung Capacity
Plethysmography
• The mouthpiece contains a shutter valve that,
when closed, obstructs the airway
• Airway pressure at the mouth is measured using a
pressure transducer attached to the mouthpiece
Measurement of Total Lung Capacity
Plethysmography
• During testing, patient breathes gas while within
the box
• Patient pants at 1 to 2 breaths per second while
pressures within the box and at the mouth are
measured simultaneously
Measurement of Total Lung Capacity
Plethysmography
• At FRC, the shutter valve is closed briefly to
obstruct the airway and pressures are again
measured
• Changes in lung volume are reflected by changes
in box pressure
Measurement of Total Lung Capacity
Plethysmography
• Mouth pressure theoretically equals alveolar
pressure when the shutter valve occludes the
airway as flow drops to zero
• The total volume of the plethysmograph is known
and the volume displaced by the patient is
calculated
Measurement of Total Lung Capacity
Plethysmography
• The volume of the thoracic gas is calculated using
Boyle’s law
– VTG1 x Palv1 = VTG2 x Palv2
where VTG is the thoracic gas volume before and after
occlusion and Palv is the alveolar pressure before and after
occlusion
Measurement of Total Lung Capacity
Plethysmography
Measurement of Total Lung Capacity
Plethysmography
Diffusion Capacity (DL) – Purpose
• Assess ability of the lungs to exchange gas
across the alveolar-capillary membrane
Diffusion Capacity (DL)
• Also known as the transfer factor
• Expressed as mL/min/mm Hg
Diffusion Capacity (DL) – Rationale
• By measuring the difference between an inhaled
volume of carbon monoxide (single breath) and
the exhaled volume, the amount of carbon
monoxide that diffused across the alveolarcapillary membrane can be calculated
Diffusion Capacity (DL) – Rationale
– Carbon monoxide (CO) used because of its strong
affinity for hemoglobin
– Only limiting factor is the surface area of the
alveoli
– Normally, the partial pressure of CO in the
alveolus is 0 mmHg
Factors Affecting Diffusion
• Diffusion coefficient of the gas
• Surface area of the membrane
• Thickness of the membrane
Factors Affecting Diffusion
• Hemoglobin and blood flow in the pulmonary
capillaries
• Distribution of the inspired gas
(ventilation/perfusion ratio)
Diffusion Capacity (DL)
• The patient maximally inhales from a mixture of
gases containing 0.3% CO with 10% He and the
balance room air
• Patient holds breath for 10 seconds
Diffusion Capacity (DL)
• Patient exhales; following exhalation of a volume
approximating the anatomic dead space, the
remaining gas is collected
• Sample is analyzed to determine concentrations of
CO and He in the exhaled alveolar gas
Diffusion Capacity (DL)
• The change in He concentration reflects
dilution and is used to calculate the initial
mean capillary partial pressure of CO prior to
diffusion
Diffusion Capacity (DL)
• DLCO is Calculated Using the Following Equation:
– DLCO =
𝑉𝐶𝑂
𝑃𝐴𝐶𝑂−𝑃𝐶𝐶𝑂
Where 𝑉CO is the Pulmonary Capillary Uptake of CO in
mL/min, PACO is the Mean Alveolar Partial Pressure of CO,
and PCCO is the Mean Capillary Partial Pressure of CO,
Usually Zero
Diffusion Capacity (DL) – Normal
Values
• Males – 25 mL/min/mm Hg CO
• Females – slightly lower due to smaller lung
volumes
• May increase 2 to 3 times during exercise
Bronchial Provocation Tests – Purpose
• Assess patients with normal PFT results and
symptoms of bronchospasm
• Quantify severity of asthma and assess changes in
airway reactivity
• Screen those at risk from or to document the effects
of environmental or occupational exposure to toxins
Bronchial Provocation Tests
• Before the test
– Patients must be asymptomatic
– Bronchodilators and antihistamines must be withheld prior
to the test (duration of time determined by the individual
bronchodilator)
– No smoking or caffeine on the day of the test
– No exercise prior to the test
Bronchial Provocation Tests –
Procedure
• Obtain baseline spirometry
• Administer SVN treatment with normal saline
– Perform spirometry
– If FEV1 decreases by less than 20%, proceed with protocol
Bronchial Provocation Tests –
Procedure
• Administer 3 mL of 0.031 mg/mL Methacholine
– Use noseclip to ensure mouth breathing
– Administer treatment over 2 minutes
Bronchial Provocation Tests –
Procedure
• Perform spirometry
– If FEV1 has decreased < 20%, administer next larger
dose
– If FEV1 has decreased ≥ 20%, test is concluded
Bronchial Provocation Tests –
Procedure
• Repeat sequence of administering methacholine
and performing spirometry, doubling dose of
methacholine each administration until either
the FEV1 has decreased ≥ 20% or the dosage of
methacholine is 16 mg/mL, whichever occurs first
Interpreting the DLCO
113
Interpreting the PFT Report
• The FEV1/FVC ratio is a good place to start; reduced
(<70%) with obstructive lung disease
• If TLC less than 80% of predicted normal and
FEV1/FVC is normal, restrictive disease is present.
• If DLCO is <80% of normal, a diffusion defect is
present.
– Reduced surface area = emphysema
– Thickened AC membrane = pulmonary fibrosis
114
Interpretation
115