Body
Plethysmography
By
Hossam El-Din Mohamed
lecturer of chest diseases
Ain Shams University
• The word plethysmograph is derived from the
Greek plethusmos (enlargement)
• the fundamental function of a whole-body
plethysmograph is the measurement of
intrathoracic gas volume (TGV) and volume
change.
• It is also used to measure airway resistance and
conductance.
• resistance of the respiratory system :
lung resistance= resistance of lung tissue +
airway resistance (Raw)
• total respiratory resistance(Rtotal)
R total=chest wall +lung tissue +R aw
and it is usually measured by IOS.
• R aw= flow resistance in the airway
between mouth and alveoli.
And it is usually measured using body
plethysmography.
• Method for measuring airway resistance:
1-esophageal balloon.
2-IOS.
3-Body plethysmography.
AIRWAY RESISTANCE
The relationship between pressure and
flow tells us about airway resistance.
Flow
Pressure
Low Resistance
High Resistance
Airways Resistance
Flow
Breathe IN
ΔPbox
Breathe Out
 Contraindication for use of body box:
1-Mental confusion, muscular
incoordination,body cast or any other
condition that prevent the patient from
entering the box.
2-Claustrophobia.
3-Presence of devices or other condition such
as continuous I.V infusion
Or any condition that interfere with pressure
changes (e.g chest tube, Trans tracheal O2
catheter, or rupture ear drum).
4-Coninous O2 therapy that can not be
removed.
N.B: The relationship between box pressure
and flow at mouth is the resistance.
Indication for R aw measurement:
1-Further evaluation of airflow limitation beyond
spirometry.
2-Determining the response to B.D.
3-Determination of bronchial hyperreactivity
the commonly used limit for bronchoprovocation is
a 15 or 20% decrease in FEV1 relative to control
baseline FEV1. The comparable limit for sRtot is
100%, for Rtot 50% increase and for sGtot 40%
decrease from baseline, respectively.
4-Diff. between types of obstructive lung disease
having similar spirometeric configuration.
5-Following the course of the disease and
response to treatment.
Principles of whole-body
Plethysmography:
• The fundamental principle of the variable-pressure plethysmograph
is that changes in alveolar pressure (PA) may be inferred from
changes in plethysmograph pressure.
• A shutter mechanism is positioned close to the mouth in the
plethysmograph. This shutter may be closed to provide transient
airway occlusion. Voluntary respiratory efforts are performed
against the closed shutter, during which the change in PA (ΔPA), is
estimated by recording the change in mouth pressure (ΔPm).
• Pm (PA) is plotted against simultaneous plethysmographic pressure
changes during respiratory efforts against a closed shutter to
measure absolute TGV.
• The same relationship between alveolar and plethysmographic
pressure measured during respiratory efforts against a closed
shutter is then extended to dynamic events during free breathing to
measure Raw, where airflow is related to PA.
• respiratory flow (ΔV') at the patient's mouth, sensed by a
pneumotachograph and the thoracic movements, resulting in volume
changes (ΔVbox) in the cabin, sensed by a box pressure transducer, are
recorded and displayed in form of a xy-plot on the application screen.
• In a constant volume whole-body plethysmograph, Specific airway
resistance (sRaw) is determined from the relationship between variations
in respiratory flow and volume shift in the box.
• During the measurement, the gas exchange between
inspiration of ambient air at ambient temperature and
pressure (ATP) and expiration of air at body temperature,
pressure and water vapor saturation (BTPS) has to be
considered.
• By means of an automatic, numerical compensation (ASC"automatic loop compensation") with intelligent software
algorithms, the compensation for body temperature,
barometric pressure at water vapor saturation (BTPS), gas
compression and decompression can be almost completely
achieved.
•
•
•
•
•
In the first part of the measurement, the determination of Specific airway
resistance, the
patient should sit upright.
He has to hold his head in neutral position or in slight extension, avoiding flexion
or rotation.
He is asked to breathe normally through the pneumotachograph.
Care has to be taken, that the lips are firmly closed around the mouthpiece and
the nose is clipped.
Test sequence : - Patient should breath spontaneously.
- Adaptation phase until patient breathes regularly.
- Define slight hyperventilation with a breathing frequency
of 20-25 / min only if specific resistance loops are normal.
- Set electronic loop compensation for body temperature and barometric pressure at
vapour saturation.
Quality control : - Wait for regular, repeatable and best closed loops.
- Store the last 5 loops by activating the shutter (determination of ITGV).
Determination of Intrathoracic gas
volume
• After successful determination of sRaw, the
corresponding Intrathoracic gas volume (ITGV) can
be measured.
• Initiated by a manual keystroke of the assistant, the
patient's following inspiration is automatically
interrupted by a shutter (at end of expiration and
beginning of inspiration respectively).
• The patient should try to continue normal breathing
against the shutter, without arising breathing
muscles activities.
Methodology of the volume
determination
• The volume measurement is based on the Boyle-Mariotte's law (1660,
1676)
P * V= const. which is applicable to closed systems.
• The shutter creates a closed lung chambers and prevents further
respiration of the patient.
• The pressure, generated by continuous breathing activities at the airway
opening in front of the shutter (ΔPv) is registered by a pressure transducer.
Simultaneously, the thoracic movements produce a volume shift (ΔVbox)
in the box.
• The report of these two signals in an xy-plot presents the requested ITGVloop.
• The Intrathoracic gas volume is determined, following the BoyleMariotte's law.
• R aw is most frequently measured while
the patient is enclosed in a whole body
plethysmography designed to measure
pressure changes and flow.
• There is an inverse relationship between
R aw and lung volume.
• During inspiration, lung volume increase
and R aw decrease due to ↑ -ve
intrapleural pressure.
During expiration, lung volume decrease and
R aw increase.
i.e. the diameter of airway change during
breath cycle lead to change in Raw and lung
volume.
– G aw ( airway conductance is the reciprocal
form (1/ Raw) of airway resistance.) and
there is linear relationship between G aw
and lung volume.
– As Raw and G aw measured by body box
lung volume adjusted measurement may
made.
The lung volume adjusted Raw and G aw
is called specific airway resistance and
conductance (sR aw& sG aw)= Raw X
lung volume or G aw / lung volume.
Parameter of airway resistance:
1-sReff ( specific effective airway
resistance). And it reflect larger; central
airways some what more prominently
than sR tot.
2- sRtot(specific total airway resistance).
and it reflect smaller; peripheral airways
3- The parameter of sR0.5 reflects the
behavior of larger , more proximal
airways with mush less sensitivity to
peripheral airways.
Definition of abnormal lung
function
• Threshold to abnormality for Rtot and Reff in
adults: 0.3 kPa/(L/s)
• Predicted values for Rtot and Reff in children:
normal if below 150% of predicted
• Standard for RV:
abnormal, if above 120-140 % of predicted
• Standard for TLC:
abnormal, if above 120-140 % of predicted
• Bronchial hyperresponsiveness
Povocation:
+PD/C 50 in Raw equivalent to -PD/C 20 in FEV1
+PD/C 100 in sRaw equivalent -PD/C 20 in FEV1
-PD/C 40 in sGaw equivalent -PD/C 20 in FEV1
Dilatation:
>25 % response to bronchodilator (children
aged 2-5) [1]
• Reversibility in relation to basic measurement
- no reversibility no changes at all
- partial reversible improvement, without
reaching normal range
- complete reversible improvement into the
normal range
K. G. Nielsen, H. Bisgaard, "Discriminative
Capacity of Bronchodilator Response
Measured with Three Different Lung
Function Techniques in Asthmatic and
Healthy Children Aged 2 to 5 Years", Am J
Respir Crit Care Med; Vol 164, pp 554-559,
2001
Types of plethysmograph
• The constant-volume or variable-pressure
plethysmograph is used to measure small volume
changes due to compression and decompression of gas
within the lungs.
• The constant-pressure or volume-displacement
plethysmograph is used to measure large changes in
lung volume associated with gas flow into and out of
the lungs such as the slow or forced vital capacity
(FVC).
• The pressure-corrected variable-volume
plethysmograph combines the advantages of both the
plethysmographs described above.
Schematic representation of specific resistance loops in a) a normal subject, b) a subject with
increased large airway resistance, c) a subject with chronic airflow obstruction d) and a
subject with upper airway obstruction. Mouth flow (V') is plotted on the vertical axis, with
inspiration positive and expiration negative
Lung volume
Lung volume tell us about:
1-disease severity.
2-recovery from exacerbation.
3-limited by hyperinflation.
Aim :
1- to measure TLC.
2- to measure RV.
3- to measure FRCpleth.=ITGV
The most significant volume for
evaluating the effect of pulmonary
disorder are VC,FRC, RV, TLC.
A useful tool in evaluating lung volume
studies is the RV/TLC %.
Normal value of RV/TLC % in normal
young adult 20 -35 %.
Increase value of RV/TLC % indicate air
trapping, hyperinflation of the lung is
demonstrated when in addition to the
increase RV/ TLC %. The TLC is
significantly greater than normal
Two general pattern of lung volume
changes can results from pulmonary
disorder. Restrictive pattern which
demonstrate reduction in all lung
volumes. And Obstructive pattern which
tend to demonstrate increase in only
some volume.
The exception to the general pattern of
increase lung volume for obstructive
disorder is that either no or even
decrease in VC.
VOLUME
Restrictive
Air
pattern
trapping
Hyperinflation
RV/TLC%
Normal
Increase
Increase
TLC
Decrease
Normal
Increase
RV
Decrease
Increase
Increase
FRC
Decrease
Increase
Increase
Decrease Decrease
Normal
VC
Two obstructive pattern are possible one
where there is increase RV results in
proportional reduction in VC where TLC
remain normal ( air trapping )
The 2nd , RV increase with little or no
changes in VC this cause an increase in
TLC in direct proportion with RV
(hyperinflation)
An abnormally increase in RV/TLC% will
demonstrated in both pattern
Severity of lung volume disorder
TLC ( N.80 -120 %of predicted)
Degree
Restrictive
Obstructive
Mild
70 -80 %
120 -130 %
Moderate
60 -70 %
130 -150 %
Severe
< 60 %
> 150 %
VC ( N. > 90% of predicted )
Degree
Restrictive
Obstructive
Mild
70 -90 %
70 -90 %
Moderate
50 -70 %
50 -70 %
Severe
< 50 %
< 50 %
FRC ( N. 65 -135 % of predicted)
Degree
Restrictive
Obstructive
Mild
55 -65 %
135 -150 %
Moderate
45 -55 %
150 -200 %
Severe
< 45 %
> 200 %
RV ( N. 65 – 135 % of predicted)
Degree
Restrictive
Obstructive
Mild
55 - 65 %
135 -150 %
Moderate
45 – 55 %
150 - 250 %
Severe
< 45 %
> 250 %
How to perform the test?
The body plethysmography program
allows an analysis of the complete
breathing mechanics. It principally
includes the measurement of the airway
resistance and intrathoracic gas volume.
In addition, all important parameters of
the slow spirometery (ERV,VC,……)and
the forced spirometery ( FEV1, FVC,
MEF50, PEF ….)
The program is called up from the main
group. Click the
“ Body plethysmography” icon.
Ask the patient to take a seat in the box (
but not to put the mouthpiece into his
mouth yet ).
Shut the box door. The intercom system
is automatically activated.
After approximately one minute for
temperature compensation ask the
patient to approach the mouthpiece and
close his nose with nasal clip.
The measurement is started
automatically.
A real- time display of the specific
resistance loops and the spirogram
appears in the window.
Once you are satisfied with the display of
the resistance curves, start the ITGV
measurement.
Click the “ ITGV “ icon.
At the beginning of the next breath the
shutter is closed.
Ask the patient to continue breathing
normally, i.e. without increasing effort
even after the shutter is closed ( he / she
should not suck ).
It is useful to perform several shutter
maneuver (> 2).
A Spirometery / Flow- volume
measurement should be performed
immediately after having opened the
shutter.
Finally, save the measurement and exit
the program with “F12”.
Interpretation Flow Chart
Interpretation Flow Chart - Paul L.
Enright MD
FEV1/FVC
Normal
Low
VC
VC
Lo
w
TLC
Normal
TLC
Normal or
high
Low
Restriction
Spirometry
Normal
DLCO
Normal
or high
Normal
Low
Normal
Low
PV
Disorder
Normal
or high
Obstruction
Chest wall or
Neuromuscular
Disorders
Obstructive &
Restrictive Defects
DLCO
DLCO
Normal
or high
Low
Low
ILD or
Pneumonitis
Normal
or high
Asthma or
Chronic
Bronchitis
Low
Emphysema
DLCO
Normal
or high
Chest wall,
Neuromuscular
Disorders,
Asthma, or
Chronic
Bronchitis
Low
ILD,
Pneumonitis,
or
Emphysema
Thank you