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PULMONARY FUNCTION
TESTING
LECTURE 1
Equipment

Introduction
 The most important function of the lungs is
gas exchange
› Dependent on:
 The diaphragm and thoracic muscles must be
capable of expanding the thorax and lungs to
produce a sub-atmospheric pressure
 The airway must be unobstructed to allow gas to
flow into the lungs and reach the alveoli
 The cardiovascular system must circulate blood
through the lungs and ventilated alveoli
 O2 and CO2 must be able to diffuse through the
AC membrane

Introduction
 Pulmonary Function Test (PFT) can
provide valuable information about the
important individual processes that
support gas exchange
 Various measurements are available to
aid in the diagnosis and assessment of
pulmonary disease, to determine the
need for therapy, and to evaluate the
effectiveness of respiratory care

Introduction
 Knowledge of these test and the ability
to interpret the measurements are
essential for assessing patients
objectively, and for planning and for
implementing effective patient care.

Evaluation of respiratory
system includes:
› Patient history
› Physical examination
› Chest x-ray
› Arterial blood gas
› PFT

Pulmonary Function Test (PFT)
 Three categories
› Dynamic flow rates of gases through the airways
› Lung volumes and capacities
› Ability of the lungs to diffuse gases
 A combination of these measurements
provide a qualitative picture of the lung
function
 PFT does not diagnose specific pulmonary
disease, the test identify the presence and
type of pulmonary impairment and the
degree of pulmonary disease present

Purposes
 Primary :
› To identify pulmonary impairment
› To quantify the severity of pulmonary
impairment if present

SPECIFIC PURPOSES OF PF
ASSESSMENT
1. Identification and quantification of
changes in pulmonary function.
▪ The most common purpose of pulmonary
function testing is to detect pulmonary
disease, and over time pulmonary function
tests help quantify the progress or the
reversibility of the disease.

ASSESSMENT
2. Epidemiological surveillance for
pulmonary disease.
› Screening programs may detect pulmonary
abnormalities caused by disease or
environmental factors in general
populations, occupational settings, smokers,
or other high-risk groups. In addition,
researchers have determined what normal
pulmonary function is by measuring the
pulmonary function of the average
population

ASSESSMENT
3. Assessment of postoperative pulmonary
risk.
➢ Preoperative testing can identify those
patients who may have an increased risk of
pulmonary complications after surgery.
Sometimes the risk for complications can be
reduced by preoperative respiratory care

ASSESSMENT
4. Aid in the determination of pulmonary
disability.
› Pulmonary function tests also can determine
the degree of disability caused by lung
diseases, including occupational diseases
such as pneumoconiosis of coal workers.
Some federal entitlement programs and
insurance policies rely on pulmonary
function Tests to confirm claims for financial
compensation.

ASSESSMENT
5. Evaluation and quantification of
therapeutic effectiveness.
› Pulmonary function tests may aid clinicians in
selecting or modifying a specific therapeutic
regimen or technique (e.g., bronchodilator
medication, rehabilitation exercise protocol).
Clinicians and researchers use pulmonary
function tests to objectively measure
changes in lung function before and after
treatment.

THREE COMPONENTS TO
PULMONARY FUNCTION TESTING:
(1) measuring lung volumes and
capacities,
(2) measuring airway mechanics, and
(3) measuring the diffusing capacity of
the lung (DL)
 For each component, there are a variety
of techniques and different types of
equipment that make the
measurements.

EQUIPMENT
 The types of instruments used for pulmonary
function testing are outlined as follows:
I. Devices that measure gas volume
A. Water sealed spirometers
B. Dry rolling seal spirometers
C. Bellows spirometer
II. Devices that measure gas flow
A. Pneumotachometers
B. Thermistors
C. Turbinometers
D. Sonic devices
E. Peak flow meters

SPIROMETERS
 Spirometer is a device for measuring
volume and/or flow changes at the
airway opening

VOLUME COLLECTING
SPIROMETERS
 Measure lung volume changes by
collecting exhaled gas into an
expandable container and noting the
amount of displacement that occurs
A. Water-sealed spirometers
B. Bellow spirometers
C. Dry rolling seal spirometers

WATER SEALED SPIROMETER –
Collin’s water sealed spirometer
 Consist of a large bell that is sealed from
the atmosphere by water
 The patient is connected to the bell in
rebreathing fashion by a breathing
circuit (tubing with one-way valves and
CO2 absorber)
 The bell is suspended by a chain and
pulley mechanism with a weight that
counterbalance the weight of the bell
 A pen attached to the chain and pulley
mechanism records bell movement on a
separate motor –driven rotating drum
called KYMOGRAPH

Water Sealed Spirometer –
Collin’s water sealed spirometer
 As patient exhales into the system, the bell moves upward and the
attached pen moves proportionately downward on graph paper,
creating a SPIROGRAM
 Inhalation causes the bell to move downward and the pen to move
upward
 Rotating drum can move at a constant speed which allows operator to
measure volume changes relative to time
› 32 mm/min
› 160 mm/min
› 1920 mm/min
 Slower speeds (32 and 160) measure
› Tidal volume
› Minute ventilation
› MVV
› Specialized measurement (DLCO)
 Fastest speed
› Recording volume changes during FVC maneuvers

Water Sealed Spirometer
 Collin’s water sealed
spirometer

Water sealed spirometer –
Stead Well’s spirometer
 Operates on principles similar to Collin’s
spirometer
 It has a lightweight bell that is not
counterweighted or supported by pulleys
 The plastic bell “floats” in the water well,
rising and falling with breathing excursion
 Recording pen attached directly to the bell
 Shows excellent frequency response
characteristics , especially when recording
rapid breathing maneuver (FVC, FEV timed
and MVV)
 Available in 7 , 10 and 14 L bell sizes

Water sealed spirometer –
Stead Well’s spirometer

Spirometers
 ATPS to BTPS
Coversion
› Actual values must be
corrected to body
temperature pressure
saturated (BTPS)

Water-Seal Spirometers
› Problems
 Cracks → Leaks
 Positioning
 Too high
 Too low
› Infection Control
 Hoses
 Mouth Pieces
 Filters

Water Sealed Spirometers
 Advantages:
› Simplicity
› Accuracy
› Direct mechanical
tracings can be
obtained
› Tracings can be
used for
comparison with
results derived
from computer or
analog recordings
 Disadvantages
› Manual calculations
of flow and volumes
› Leaks
› Improper positioning
of the spirometer
can cause
inaccurate
measurements
› Maintenance
includes draining of
water well and
checking for cracks
or leaks in the bell.

Dry-Rolling Seal Spirometers
 Canister containing a piston that is sealed to it
with a rolling diaphragm-like seal
 Gas entering the cylinder displaces the piston
 The piston is supported by a rod that rests on a
frictionless bearing
 The seal rolls on itself and rather than sliding as
the piston moves
 A pen recorder or potentiometer attached to
the cylinder shaft detects the piston movement
and register the signal on an output display

BELLOW SPIROMETERS
 Exhaled gases are collected into an
expandable bellows
 Air entering the bellows causes the free wall
of the bellows to move outward, and its
displacement is directly related to the
volume of air exhaled
 Volume changes can be recorded by
attaching a pen recorder or a
potentiometer to the free wall of the bellows

Flow Sensing Spirometers
 Pneumotachometer is the term used to
describe a device that measures flow
 Uses various principles to produce a signal
proportional to gas flow
 The signal is integrated to allow measurement
of volumes in addition to flow
 Integration is a process of in which flow is
divided into a large number of small intervals.
Integration can be performed by an electronic
circuit

Turbine Flow meters
 Uses a rotating vane or turbine to measure gas
flow
 As gas flows through the device, the vane turns
at a rate dependent on the flow rate of the gas
 The flow rate can be measured by counting the
number of times the vane turns, which can be
done mechanically ( linking the vane to a
needle attached to a calibrated display) or
electronically (by using a light beam that in
interrupted each time the vane turns)

Turbine Flow meters
 Are usually accurate for flows between 3 and
300 L/min
 Are portable and easy to use
 Slow to respond to flow changes due to
inertia
 Are good for measuring unidirectional flow

Pneumotachographs
 Fleisch type
 Screen
 Ultrasonic
 Peak Flow meter
➢ Fleisch and screen
operate on the
principle that gas flow
through them in
proportion to the
pressure drop that
occurs as the gas flows
across a known
resistance
➢ Ultrasonic rely on the
Doppler effect to
quantify the airflow
velocity

Pressure-Drop
Pneumotachographs
 The most common type of flow-sensing
device consist of a tube containing a
resistive element
 Resistive elements allows gas to pass
through it, but causes a pressure drop.
 The pressure difference across the
resistive element is measured by means
of a sensitive pressure transducer, with
pressure taps on either side of the
element
 The pressure difference across the
resistive element is proportional to the
flow of gas as long as the gas flow is
laminar
 Flow signal from the
pneumotachometer is electronically
intergarated to derive volume
measurement

Pressure- drop
pneumotachographs
 Fleisch – Type
 Screen type

Variable orifice
pneumotachographs
 Are disposable,
bidirectional, flow
measuring devices
that use a variable
area, flexible
obstruction for
measuring flow as a
function of the
pressure differential
generated by the
obstruction

Vortex ultrasonic
pneumotachographs
 Use struts to create a partial obstruction to gas flow
 As gases flow past these struts, whirlpool or vortices are
produced
 The frequency at which these whirlpools are produced
is related to gas flow through the struts
 An ultrasonic transmitter perpendicular to the flow
produces sound waves that are modulated by the
frequency of the vortices
 Each vortex passing through the ultrasonic beam
produces a pulse. Each pulse is proportional to a
specific volume
 Pulses are summed electronically, providing a
measurement of volume

Vortex ultrasonic
pneumotachographs

Thermal Flowmeters
Temperature drop pneumotachometer /thermal anemometer
 Based on the cooling
effect of gas flow
 The heated element,
usually a platinum wire or
small bead o a metal
called thermistor is situated
in a laminar flow tube
 Gas flow past the ement
causes a temperature
drop, so more current must
be supplied to maintain the
preset temperature of the
element.
 The amount of current
needed to maintain the
temperature is proportional
to the magnitude of the
gas flow

Peak Flowmeter
 Constructed of
plastic and operate
with a piston and
spring mechanism
 Exhaled air pushes
against the piston,
causing the needle
valve to move on a
calibrated scale

ATS standard for spirometry
 Standardization of the instruments and
techniques used during spirometry testing
 Goal was to improve performance
characteristics of spirometers and decrease
variablity of laboratory testing
 Most spirometer manufacturers has complied
with the standards suggested by the ATS

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Equipment
 Every measuring instrument has
CAPACITY, ACCURACY, ERROR,
RESOLUTION, PRECISION, LINEARITY AND
OUTPUT.
 The ideal instrument would have
unlimited capacity to measure every
pulmonary parameter, and it would
have perfect accuracy and precision
over its entire measurement range; there
are no ideal instrument

CAPACITY
 Range or limit of how much it can measure.
Most instruments have the capacity to
measure volumes and flow rates of all adults

ACCURACY
 How well it measures a known reference
value
› A standard reference value is provided by a 3
liters calibration syringe
3 – Liter Syringe
Used for volume calibration of
volume-based and flow-based
spirometers
ATS Standards
+/- 3%
Or +/- 0.05 L
Whichever is greater

ERROR
 difference between the reference value
and measured value
› The greater the accuracy, the lesser the error
 %accuracy = mean measured value/ref. value
x 100
 % error = mean measured value-ref. value/ ref.
value x100

RESOLUTION
 Smallest detectable measurement
› Instrument with the highest resolution can
measure the smallest volume, flow and time

PRECISION
 Synonymous with reliability of instrument
and opposite variability
› Decreased variability = increased precision

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