Respiratory medicine post graduate

1. DR ANUSHA CM
BODY PLETHESMOGRAPHY

2. INTRODUCTION
 Body plethysmography is a well-established technique of
lung function determination
 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.

3.  Spirometry is considered the gold standard in lung
function.
 It can, however, not provide information on, e.g.,
lung residual volume (RV) and total lung capacity
(TLC),

4. WHAT WE CAN MEASURE

5. INDEX USEFULLNESS
Vital Capacity Useful marker for the effect of
disease and assessing outcomes
from exercise (6MWT)
Expiratory Reserve Volume Effects of obesity on lung volumes,
particularly where BMI > 35 kg.m-2
Inspiratory Capacity Marker of Bronchodilator response
where FEV1
shows no significant change –
effects of BD on hyperinflation

6. WHAT WE CANNOT MEASURE
Index Usefulness
Total Lung Capacity Marker of effects of obstructive
airways
disease and key index to confirm the
presence of a restrictive ventilatory
defect
Functional Residual Capacity Marker of hyperinflation and reflects
changes in PV relationships of chest
wall
and/or lungs.
FRC/TLC ratio reflects the degree of
hyperinflation
Residual Volume Marker of “gas trapping”.
Reflects the effects of obstructive or
restrictive disease on lung volumes.
RV/TLC ratio reflects poor gas mixing
and
hence gas trapping

7. WAYS TO MEASURE FRC
 Multi-breath He dilution measurement
 Nitrogen washout
 Body plethysmography- BEST METHOD

8. HISTORY
 1790 Menzies - Dissertation on
Respiration
 Plunged a man into water in a
hogshead up to his chin and measured
the rise and fall of the level in the
cylinder round the chin.
 With this method of body
plethysmography he determined the
tidal volume

9. MODERN DAY PLETHESMOGRAPHY
Dubois et al 1956
Forms the basis of constant-volume Plethysmography
in use today for lung volume and airway resistance
measurements

10. BODY PLETHESMOGRAPHY TODAY

11. TYPES OF BODY PLETHESMOGRAPH
1. PRESSURE PLETHESMOGRAPH- in which
pressure during breathing varies and volume
remains constant
2. VOLUME PLETHESMOGRAPH- in which volume
during breathing varies and pressure remains
constant
3. PRESSURE FLOW PLETHESMOGRAPH- couples
pressure plethesmograph fidelity of response to
high speed events with the volume
plethesmography ability to follow large changes in
volume

12. PRINCIIPLE OF BODY
PLETHESMOGRAPH
 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).

13.  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

14. Based on BOYLE LAW
 Boyle’s Law: for fixed mass of gas at constant
temperature: P1V1 = P2V2
 Brief occlusion at airway opening to seal a fixed
mass of gas in the lungs (V1) - i.e. the FRC to be
measured
 Pressure within lungs at end expiration (P1) ~
atmospheric pressure.
 P2 and V2 represent the pressure and volume in the
lungs after a respiratory effort against the occlusion.

15. Thus -
PV = (P + deltaP).(V - deltaV)
= V(P - deltaP) + (P - deltaP) deltaV
= PV - VdeltaP + (P - deltaP) deltaV
Re-arranging -
Delta PV = (P - deltaP) deltaV
VL = (P - deltaP)(deltaV/deltaP)
Delta P is such a small fraction of P
(barometric pressure)
that it can be omitted without loss of
accuracy
VL = P(delta V/deltaP)

16.  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.

17.  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( impulse oscillometry)
3.Body plethysmography

18. 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.Continous O2 therapy that can not be removed.

19. INDICATION OF RAW
1.Further evaluation of airflow limitation beyond
spirometry.
2.Determining the response to B.D.
3.Determination of bronchial hyperreactivity
4.Diff. between types of obstructive lung disease
having similar spirometeric configuration.
5.Following the course of the disease and response to
treatment.

22.  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.

23.  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).

25. SUMMARY OF THE PROCEDURE

26. DETERMINATION OF INTRATHORASIC 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.

27. METHODOLOGY OF 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.

28.  The report of these two signals in an xy-plot presents
the requested ITGV-loop.
 The Intrathoracic gas volume is determined,
following the Boyle-Mariotte's law.

29.  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.

30. 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.

31. SHIFT VOLUME
 This is the change in volume within the lungs in
relation to the change in box pressure used as a
surrogate marker of changes in volume.
 As the subjects breathes against the shutter, the
lung volume changes, so the box pressure changes.
 By calibrating the box pressure for volume change,
the actual change in volume – the shift volume can
be estimated
 The shift volume is useful in assessing the effects of
disease on resistance

32. 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

33. INTERPRETATION OF THE RESULTS
• In patients with obstructive diseases
– airway closure occurs at an abnormally high lung volume
Increased FRC (functional residual capacity)
Increased RV (residual volume)
• Patients with reduced lung compliance (e.g., diffuse
interstitial fibrosis)
– stiffness of the lungs + recoil of the lungs to a smaller
resting
volume
Decreased FRC
Decreased RV

34. CLINICAL APPLICATION AND
INTERPRETATION
INCREASED FRC
 Gas trapping due to intrathoracic airway obstruction
 Cystic lung disease
DECREASED FRC
 Abnormal alveolar development
 Reduced recoil of chest-wall
 Decreased lung compliance
 Atelectasis

35.  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

36.  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

37. VOLUME Air
trapping
Restrictive
pattern
Hyperinflation
RV/TLC% Increase Normal Increase
TLC Normal Decrease Increase
RV Increase Decrease Increase
FRC Increase Decrease Increase
VC Decrease Decrease Normal

38. OBSTRUCTIVE LUNG DISEASE