Pulmonary function tests provide objective assessments of respiratory symptoms and can help diagnose respiratory diseases. Spirometry is the most widely used test and measures volumes like FVC and FEV1. Restrictive diseases reduce total lung capacity while obstructive diseases cause decreased FEV1/FVC ratio. Other tests include lung volume measurements using plethysmography or gas dilution, diffusing capacity to assess gas exchange, and methacholine challenge for asthma diagnosis. Bedside tests can also help evaluate respiratory function.

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PULMONARY FUNCTION
TESTS
Speaker : Maj SR Jaiswal
DNB Resident Medicine

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Indications
• Differential diagnosis of dyspnea
• Provides objective assessment of symptoms
versus severity
• Determine fitness for surgery
• To guide therapy
• To follow the course of a disease

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Physiologic classification of
disease
• Obstructive Impairment- Airway limitation due
to the resistive properties of the respiratory
system
• Restrictive Impairment- Loss of volume
capacity of the lung due to loss of air space
units or inability to expand the respiratory
system

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Obstructive Processes
• L ocal obstruction
• A sthma
• C hronic bronchitis (COPD)
• E mphysema

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Restrictive Processes
• P leural disease
• A lveolar filling processes
• I nterstial lung disease
• N euromuscular diseases
• T horacic cage abnormailites

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Spirometry
• Most widely performed study and is important
in initial screening of patients
• Easily and quickly performed in many settings

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Prior to testing

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Performing the maneuver
• It is a forced expiratory maneuver and the
patient must be sitting upright in a chair with lips
around a mouthpiece
• After a maximal inspiration, a forced and rapid
expiration is made
• Quality of the maneuver needs to be assessed
noting that the patient started at zero, had a
maximal initial efffort and lasted 6 seconds.

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Normal spirometry
• FVC - The maximum volume of air that is forcefully
exhaled after a maximum inspiration
• FVC >80% of predicted (normal)
• FEV1 - The volume of air exhaled during the first
second of the FVC maneuver
• FEV1 >80% of predicted (normal)
• Lung volume = 80 - 120% of predicted (normal)

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Normal Flow - Volume curve
PEF - peak expiratory flow;
RV - residual volume;
TLC - total lung capacity

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Measurements
• FVC
• FEV1
• FEV1/FVC

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FVC Measurement

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FEV1 Measurement

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Effort

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Poor effort

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Acceptability
• Test acceptability is best determined by
studying the flow-volume loops
• Criteria
– Freedom from artifacts
– Good starts
– Satisfactory expiratory time

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Reproducibility of data
• Criteria
– The two largest forced vital capacity (FVC) –
0.2 L or 5% of each other
– The two largest FEV1 –
0.2 L or 5% of each other
Up to eight efforts may be performed

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Obstructive Ventilatory Defects
FEV1: FVC <70% (OVD)
• Once the diagnosis of an OVD has been made
the defect needs to be fully characterized by
– Quantifying the severity of the OVD
– Assessing the reversibility of the obstruction
– Determining whether there is hyperinflation
– Determining whether there is air trapping

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Quantifying the
severity of the OVD
• Normal: FEV1 >80% of predicted
• Mild: FEV1 = 65 - 80% of predicted
• Moderate: FEV1 = 50 - 64% of predicted
• Severe: FEV1 <50% of predicted

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Assessing the reversibility
• Postbronchodilator FEV1 improves by both
12% and 200 mL,
OR
• Postbronchodilator FVC improves by both
12% and 200 mL

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Hyperinflation
• TLC >120% of predicted,
OR
• RV >120% of predicted

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Air trapping
• SVC > FVC by both 12% and 200 mL

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The methacholine challenge test
• Asthma - reversible obstructive airway disease
• Multiple pfts may only demonstrate normal spirometry
• Bronchial provocation testing

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• The administration of a sterile saline aerosol
• FEV1 after 3 - 5 mins
• Increasing concentrations of methacholine
at 5-min intervals
(0.003 mg/mL to 16 mg/mL)
• FEV1 is measured 3 - 5 mins
• Decrease in FEV1 >20% is a positive response

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Upper Airway Obstruction
Variable extrathoracic
obstruction
Variable intrathoracic
obstruction
Fixed upper airway
obstruction

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Restrictive Ventilatory Defects
• TLC <80% of predicted (RVD)
• Normal or increased FEV1: FVC ratio
• The defect needs to be quantified
– Normal: TLC >80% of predicted
– Mild: TLC = 65 - 80% of predicted
– Moderate: TLC = 50 - 64% of predicted
– Severe: TLC <50% of predicted

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Bronchodilator Response

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Bronchodilator testing
• No short acting agents for 4 hrs
• No long acting beta agonists for 12 hrs
• No theo for 12 hrs
• No smoking for 1 hr
• Beta agonist given recommended 4 puffs and
wait 10-15 minutes later

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Lung Volumes
• May be measured by multiple methods
• Is important to understand what volumes the
lung is composed of
• The total volume of the lung is TLC
• The subdivisions include ERV, IRV, TV,and RV
• Capacities are composed of 2 or more volumes.

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Volumes : (1) tidal volume (VT), (2) inspiratory reserve volume (IRV),
(3) expiratory reserve volume (ERV), (4) residual volume (RV)
Capacities: (1) total lung capacity (TLC), (2) vital capacity (VC),
(3) inspiratory capacity (IC), (4) functional residual capacity (FRC)

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Methods
• Body Plethysmography
– Pressure (Closed-Type) Plethysmograph
– Volume (Open-Type) Plethysmograph
– Pressure-Volume Plethysmograph
• Gas Dilution Methods
– The opencircuit nitrogen (N2) method
– The closed-circuit helium (He) method

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The Opencircuit Nitrogen (N2)
method
Involves having nitrogen in
patients lung being washed out
by inhaling 100% O2 for several
minutes.
Widely used, easy to perform
but may underestimate bullous
lung disease
Performed by having the patient
breath comfortably for several
minutes and then turn in to
100% O2 at FRC.
Monitor N2 concentrations and
test ends when falls below 1%
Easy to see leaks

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Nitrogen Washout
• Concept is C1V1= C2V2
– C1 = Nitrogen concentration at the start of the
test
– V1 = FRC volume
– C2 =N2 concentration in exhaled volume
– V2 = Total exhaled volume during O2 breathing
period
– Nitrogen is measured by photoelectric principle

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The closed-circuit helium (He)
method
• Uses an inert gas, helium and by a closed
circuit technique, allow it to come to
equilibrium and FRC is measured
• May underestimate lung volumes in bullous
lung disease

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• Measure functional residual
capacity (FRC).
• 10% He

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Body Plethsymography
• Is a sealed box with a fixed volume
• Uses Boyle’s Law that changes in pressure are
brought about by changes in volume and
pressure for the person seated in the box
• P1V1= P2V2

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Pressure (Closed-Type) Plethysmograph
The subject breathes through a
shutter / pneumotachygraph
When the shutter is closed, mouth
pressure is measured by a pressure
transducer (1).
The pneumotachygraph measures
airflow with another transducer (2).
Plethysmograph pressure is
measured by a third transducer (3).
The signals from the three
transducers are processed by a
computer.

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Volume (Open-Type) Plethysmograph
This constant-pressure, variable-volume type
of Plethysmograph
The subject breathes through a shutter /
pneumotachygraph.
In the closed-shutter mode mouth pressure is
measured by a transducer (1)
The pneumotachygraph measures flow via
another transducer (2)
Flow is integrated electronically to obtain
volume, Changes in volume of the
plethysmograph, reflecting movement of the
chest wall, are measured with a spirometer
and a linear volumedisplacement
transducer (LVDT)

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Pressure-Volume Plethysmograph
This type of plethysmograph
combines features of the closed and
open types

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Lung volume measurements
• FRC is directly measured as well as SVC
• Other volumes and capacities can be calculated
• Lung volume measurements are important to
confirm RLD
• TLC and RV the usual volumes assessed

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Interpretation
• RLD
– TLC is reduced in all
– Predicted values and
interpret same as FVC
and FEV1
• OLD
– TLC can be increased
and is then called
hyperinflation (120%)
– RV can be increased in
asthma and COPD
indicating air trapping

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Lung Elastic Recoil
• Lung elastic recoil pressure, or transpulmonary pressure (PL)
• PL = Palv – PPl
– Palv - the alveolar pressure,
– Ppl - the pleural pressure
• The muscles of inspiration must maintain a pleural pressure of
about 12 cm H2O below atmospheric pressure (pPl = -12 cm
H2O).
• Under conditions of no flow, pressure at the mouth, alveoli,
and atmosphere are equal: pL = 0 - (-12 cm h2o)
• PPl rises from -12 to 0 cm H2O and palv from 0 to +12 cm H2O
at the instant before flow begins

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All that is needed to measure lung
elastic recoil pressure and lung
compliance is a measurement of PPl in
relation to lung volume.
Because the esophagus passes through
the pleural space
Pressure within the esophagus
approximates pPl

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Diffusing Capacity
• Provides information about the transfer of gas
between the alveoli and the pulmonary capillary bed
• It is the only noninvasive test of gas exchange
• Performed by a single breath technique and uses CO
as the inert gas

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Diffusing Capacity
• Diffusion of a gas is dependent of the area, the
concentrations, the thickness of the membrane and
the diffusing properties of the gas
• Diffusion is the rate at which a gas is transferred
across the alveolar capillary membrane, the plasma,
the RBC and ultimately combined with Hgb

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Diffusing Capacity
• CO is typically used because it is freely diffusable
• It usually is not present in significant amounts in the
blood except in some heavy smokers
• Helium or methane is also used to measure volume
• A single maximal inspiration is taken and held for 10
sec

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Diffusing Capacity
• Normal result is >80%
• Can be reduced in interstitial diseases such as sarcoid
or asbestosis
• Can be reduced also in emphysema or pulmonary
vascular diseases
• False low measurements in anemia or lung resection
and elevated in alveolar hemm

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Bedside evaluation of
Pulmonary Function
• Snider’s match blowing test
• Modified Snider’s test
• Seberese’s single breath count
• Seberese’s breath holding test
• Cough test
• De Bono’s Whistle test
• Wright’s peak flow meter test
• Bed side pulse oximetry
• Blow against the hand

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Snider’s match blowing test
• Mouth wide open
• Match held at 15 cm distance
• Chin is supported
• No head tilting
• Match stick and mouth at the
same level
• Cannot blow out a match
– MBC < 60 L / min
– FEV1 < 1.6 L
• Able to blow out a match
– MBC > 60 L / min
– FEV1 > 1.6 L
Modified Snider’s test
• When the Match is placed
at a distance of
– 3 inches – MBC > 40 L / min
– 6 inches – MBC > 60 L / min
– 9 inches – MBC > 150 L min

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Seberese’s single breath count
• Deep breath followed by
cunting 1,2,3,…….. Till the
time the subject cannot hold
the breath
• Shows treands of
deterioration / improving
pulmonary function in pre
and post op patients
Seberese’s breath holding test
• Subject is asked to take a
normal tidal inspiration and
hold the breath
– Normal ->= 40 sec
– < 15 sec is a C/I for elective
surgery

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Cough Test
• Observe for ability to
cough,strength and
effectiveness
• Wet productive cough
candidate for pulmonary
complications
• Inadequate cough
FVC < 20 ml / kg
De Bono’s whistle test
• Ability to blow into the
whistle is tested

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Wright’s peak flow meter
• Volume < 200 L / min in surgical
candidate suggest impaired
cough efficiency
• Normal males 450 – 700 L / min
• Normal females 300 –500 L/min
Blow against the closed hand
• Check I : E ratio

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Summary
• Spirometry- Most commonly performed and useful
screening test.
• Lung volumes- Can be measured several different
ways. Are used to evaluate for restrictive disease and
will also show air trapping
• Diffusing Capacity - Transfer of gas across the
alveolar membrane

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References
• Murray & Nadel's Textbook of Respiratory
Medicine, 4th ed
• Washington Manual(R) Pulmonary Medicine
Subspecialty Consult
• Oxford Handbook of Respiratory Medicine
• Current recommendation is NHANES III