Body Plethysmography - · PDF fileBODY PLETHYSMOGRAPHY Adrian H Kendrick BA, PhD, PgD, RPGST...
Transcript of Body Plethysmography - · PDF fileBODY PLETHYSMOGRAPHY Adrian H Kendrick BA, PhD, PgD, RPGST...
BODY PLETHYSMOGRAPHY
Adrian H Kendrick BA, PhD, PgD, RPGST
Consultant Clinical Scientist
Department of Respiratory Medicine
University Hospitals, Bristol, England
DECLARATIONS
The presenter has no conflicts of interest
Where drug names are used, these relate to those
used in peer-reviewed publications quoted within
this presentation
Pictures of equipment within this presentation are
used to illustrate aspects of the presentation and
should not be represented as an endorsement by
the presenter of the equipment shown
2
OUTLINE OF TODAY
What do we need to measure?
History of Body Plethysmography
Underlying Principles
Constant Volume - Lung Volumes/Airways Resistance
Variable Volume - outline
Technical Issues
Applications
Routine Applications
Beyond Routine
Summary and Conclusions
3
WHAT DO WE NEED TO MEASURE?
4
LUNG VOLUMES
5
WHAT WE CAN MEASURE EASILY
6
Sim
ple
Sp
iro
metr
y
WHAT WE CAN MEASURE
7
Index Usefulness
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 BD response where FEV1
shows no significant change –
effects of BD on hyperinflation
WHAT WE CANNOT MEASURE SO EASILY
8
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 9
HOW TO MEASURE TLC AND RV?
Use FRC to obtain measurements -
Multi-breath He dilution measurement
Nitrogen washout
Body plethysmography
Use TLC only
Single-breath He/CH4 measurement (TLco) - VA
Radiographic – CXR and/or CT
10
AIRWAYS RESISTANCE
Provides useful information on airway functions
Can be applied to various techniques –
Bronchodilator response
Bronchial Provocation Testing – Histamine, Manitol etc
Pre & Post surgery for upper airway disorders
Various Techniques –
Impulse Oscillometry
Body Plethysmography
11
BRIEF HISTORY OF BODY
PLETHYSMOGRAPHY
12
HISTORY - 1
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
13
HISTORY - 2
1868 - Bert P: Total Body Plethysmography.
Experiments with animals in a closed total body
plethysmographic system.
Presented his studies to the ‘Société de Biologie’ under
the title ‘Changement de pression de l’air dans un poumon
pendent les deux temps de l’acte respiratoire’ ['Alterations
of the pulmonary air pressure during the two periods of
respiration']
He did not do spirometric measurements together with the
plethysmography, nor did he do plethysmographic
measurements on humans. 14
MODERN BODY PLETHYSMOGRAPH - 1
Dubois et al 1956
Most quoted couplet of papers in JCI ever!
Forms the basis of constant-volume plethysmography
in use today for lung volume and airway resistance
measurements
15
MODERN BODY PLETHYSMOGRAPH - 2
Diagram of the apparatus for measuring lung volume.
B, body plethysmograph; S, shutter which occludes airway; L, lung; C, capacitance
manometer to record pressure changes in the plethysmograph (which are proportional to
the change in body volume); P, capacitance manometer to record pressure changes in
the mouth (which are equal to alveolar pressure when there is no airflow); O, cathode ray
oscillograph with x and y axes.
DuBois, AB, Botelho, SY, Bedell, GN, Marshall, R, Comroe (Jr), JH. A rapid plethysmographic
method for measuring thoracic gas volume: a comparison with a nitrogen washout method for
measuring functional residual capacity in normal subjects. J. Clin. Invest. 1956. 35:322-326.
16
MODERN BODY PLETHYSMOGRAPH - 3
Diagram of the apparatus for measuring airways resistance.
DuBois, AB, Botelho, SY, Comroe (Jr), JH. A new method for measuring airway resistance in man
using a body plethysmograph; values in normal subjects and in patients with respiratory disease. J.
Clin. Invest. 1956. 35:327-335.
17
DuBois, AB. Airway resistance. Am. J. Resp. Crit. Care Med. 2000. 162:345-346.
18
MEAD BODY PLETHYSMOGRAPH
Mead J. Volume displacement body plethysmograph for respiratory measurements in human subjects
J Appl Physiol 1960; 15: 736 - 740
19
BODY PLETHYSMOGRAPHS TODAY
20
ADULTS
21
CHILDREN
22
CHILDREN
23
ANIMALS
24
TYPES OF BODY PLETHYSMOGRAPH
25
CONSTANT VOLUME & VARIABLE VOLUME
Dubois Mead Original Mead Modern
26
CONSTANT VOLUME
Dubois Type
Subject sealed inside the box
Box volume 700 litres
Subject breathes from within the box
Pneumotachograph (pn) records flow
Shutter (S) occludes airway/breathing
Changes in mouth pressure recorded directly
Changes in box volume recorded as changes in box
pressure 27
VARIABLE VOLUME - 1
Mead Type Box
Patient breaths from outside the box
Volume changes recorded with a
water-filled (Krogh-type) spirometer
Mouth pressure recorded directly
Flow at mouth recorded outside the
box using pneumotachograph (pn)
Shutter (S) occludes airflow
28
VARIABLE VOLUME - 1
Mead Type Box – modern update
Patient breaths from outside the box
Volume changes recorded with a
wall mounted pneumotachograph
Mouth pressure recorded directly
Flow at mouth recorded outside the
box using pneumotachograph (pn)
Shutter (S) occludes airflow
29
WHICH BOX – FOR WHAT?
Static Lung Volumes
Dynamic Lung Volumes
Airways Resistance
Static Lung Volumes
Dynamic Lung Volumes
Airways Resistance
Compliance measures
Gas compression studies
Constant Volume Variable Volume
30
WHICH IS EASIER TO USE?
Easy to calibrate
Simpler measures can
be made using
computerized systems
Fun to calibrate!
More difficult to make
measurements –
limited software, better
measurements made
by hand
Constant Volume Variable Volume
31
PRINCIPLES OF LUNG VOLUME
MEASUREMENTS USING A BODY
PLETHYSMOGRAPH
32
PRINCIPLES
Based on Boyle’s law -
PV = k
Assumes temperature remains constant
When subject breathes in and out against a
shutter, changes in pressure and volume occur
33
BOYLES LAW
34
LUNG VOLUMES
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.
35
LUNG VOLUMES
Thus -
PV = (P + P).(V - V)
= V(P - P) + (P - P) V
= PV - VP + (P - P) V
Re-arranging -
PV = (P - P) V
VL = (P - P)(V/P)
P is such a small fraction of P (barometric pressure) that it can be omitted without loss of accuracy
VL = P(V/P)
36
CONSTANT VOLUME BODY - BOX
37
THE CONSTANT VOLUME BOX
Specifications and Calibration 38
KEY FACTORS
In tidal breathing, the chamber pressure changes
are small, only a few hPa (or cmH2O).
Disturbances may be caused by
Patient-related temperature increase within the chamber
(body heat),
Breathing-related air temperature and humidity changes
Pressure changes related to external pressure variations
To attain adequate pressure equilibration between
mouth and alveolar space, panting during the
shutter manoeuvre should be avoided
39
CONSTRUCTION
The characteristics of the body plethysmograph
chamber are key to ensure good measuring quality.
Some of the features are:
Rigidity of the enclosure
Heat transfer characteristics of the chamber walls
Built-in equilibration vessel
BTPS compensation
Calibration unit
Adjustment of a defined leak
Type and speed of the shutter assembly
40
PATIENT SYSTEM
Bacterial Filter
Pneumotachograph
Shutter
Mechanism
41
CONSTANT VOLUME BODY - BOX
Characteristics of the constant volume body
box need to be accounted for
Volume changes are recorded in terms of
pressure changes. This needs to be calibrated
Pump air into the box - 50ml sinusoidal pump
with box sealed and record deflection
VL = PB(V/P). Cbox = VTGV
where PB is the barometric pressure and Cbox
is the box calibration factor
42
CONSTANT VOLUME BODY - BOX
TGV is thoracic gas volume. This is the total
volume of compressible gas in the thorax, and
will include any compressible gas in the
stomach and abdomen
TGV will be higher than FRC in normal
subjects due to this difference and the fact
that the shutter may not close at exactly FRC
43
BODY BOX SPECIFICATIONS
Box must be airtight
All pressure transducers should be calibratable
with a known pressure
Volume calibration with a 3 or 7 litre calibration
syringe
Time constant for leaks tested daily
44
INTERNATIONAL GUIDELINES
45
BODY BOX SPECIFICATIONS
Item Specification
Mouth Pressure range
Accuracy
-2 to +2 kPa
± 0.01 kPa
Plethysmograph
Pressure range
Accuracy
At least ± 0.02 kPa
± 5 x 10-5 kPa
Volume deflection
Accuracy
-200 to +200 ml
± 0.5 ml
P and V In phase up to 10 Hz
46
CALIBRATION
47
Mouth pressure is verified with a
mercury or water barometer
Flows are verified with a rotometer
(flow-metering device) or a 3-liter
syringe
Box pressure is calibrated by using
a sine-wave rotary pump that
simulates changes in the
inspiratory and expiratory volumes
BODY BOX - CALCULATIONS
Information required -
Barometric pressure - PB
Volume of box - Vbox
Subjects mass (kg) - W
Angle of deflection -
Box pressure calibration - Boxcal
Mouth pressure calibration - Pcal
48
EFFECTS OF BODY WEIGHT
When a patient sits inside the box, their body mass
displaces air from within the box
The density of human flesh etc is 1.07 that of air
Therefore need to adjust the volume of the air
within the box for the mass of the human
Wcorr = (Vbox - W/1.07)/Vbox
Alternatively – calibrate the box with the patient
inside it.
49
BODY BOX - CALCULATIONS
VL = PB(V/P). Cbox = TGV
TGV = (Boxcal/Pcal) x (PB-47) x Wcorr x 1.33 x Tan -1
RV = TGV - ERV
TLC = RV + IVC
or
TLC = TGV + IC
RV = TLC - EVC
50
CALCULATION OF TANGENT
51
52
ACCURACY OF MEASUREMENTS
Duplicate measurements of TGV should be within
5% for a skilled operator and good coaching of the
patient
Different operators, assessing the same patient
should get similar accuracy, but slight variations in
techniques and encouragement may reduce the
accuracy
Computer software generated line plots MUST
always be verified by the operator and adjusted if
required.
53
CONSTANT VOLUME BOX
Procedure 54
CONTRAINDICATIONS FOR BOX TESTING
Preventing Patient entering the box Mental confusion
Poor muscular co-ordination
Body cast
Wheelchair
Claustrophobia
Extreme Obesity
Presence of devices - continuous I.V. infusion
Conditions that interfere with pressure changes
Chest tube
Trans-tracheal O2 catheter
Ruptured ear drum.
Continuous O2 therapy that cannot be removed
55
56
http://www.artp.org.uk/en/patient/lung-function-tests/lung-volumes.cfm
PROCEDURE
Seat subject upright in box, seal door and
allow subject to temperature equilibrate within
the box (½ - 2 mins)
Vent the box to release any pressure build up
due to thermal changes
When equilibrium occurs, Boyle’s law applies
Attach subject to mouthpiece, apply noseclip
and place flats of hands on sides of face and
under chin
57
PROCEDURE – BEFORE SHUTTER CLOSES
Situation at end expiration, prior to any
respiratory efforts against an occlusion valve
58
PROCEDURE
During tidal breathing, close shutter at FRC
and ask subject to breath in and out gently
against the shutter an open glottis at a rate of
0.5 - 1 Hz (30 – 60 breaths/min)
After 1 to 2 breaths against the shutter, open
shutter and ask subject to breathe fully out
(ERV) and then fully in (IVC) and then breathe
normally
Release vent, seal box and repeat, obtaining
3 technically acceptable traces are obtained 59
PROCEDURE – SHUTTER OCCLUSION
During inspiratory efforts against the occlusion
As lung volume increases,
box volume decreases and
box pressure increases
P1 -ΔP
Changes in box pressure
calibrated in terms of volume
using a calibrated syringe
As lung volume
increases, alveolar
pressure decreases
and hence pressure
at mouth decreases
60
SUMMARY OF PROCEDURE
61
VISUAL DISPLAY
62
Body Plethysmography
Advantages • Rapid method of multiple
estimations of VTGV
• Good repeatability
• Raw and SGaw obtainable
• Measures all gas within
thorax
Disadvantages • Expensive equipment
• Few reference values
• Claustrophobia
• Inaccurate in severe airflow
obstruction
63
CRITERIA OF ACCEPTABILITY
Manoeuvre shows a closed loop without drift
Tracing does not go off the screen
Breathing is at 0.5 – 1 Hz
Tangents should be within 10%
At least 3 TGV values should agree within 5% and the
mean value reported
64
PRINCIPLES OF AIRWAYS
RESISTANCE MEASUREMENTS
65
AIRWAY RESISTANCE - PHYSIOLOGY
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.010
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Airway Generation
Re
sis
tan
ce
(S
IUn
its
)
66
AIRWAY RESISTANCE - PHYSIOLOGY
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Airway Generation
Cu
mu
lati
ve
Re
sis
tan
ce
(%
of
tota
l)
67
AIRWAY RESISTANCE - PHYSIOLOGY
R1 R2 R3
SERIES
RTOT = 0.01 + 0.02 + 0.03 = 0.06 units
PARALLEL
R1
R2
= 0.01
= 0.01
1/RTOT = 1/ 0.01 + 1/0.01 = 200
RTOT = 0.005 units 68
RESISTANCE
Ohm’s Law
V
P
I
VR
Electrical Lungs
69
AIRWAYS RESISTANCE
Resistance to airflow in the upper airways and the
tracheobronchial tree
Changes in airways resistance may be useful in
assessing response to interventions
Newer techniques may be able to assess both the
upper airways and changes in the peripheral
airways during tidal breathing
70
RESISTANCE & MEASUREMENT
Rth
Rti
Raw (small)
Mouth
Larynx
2-3mm Airway
Alveoli
Pleural Space
Chest Surface
Sum
Raw (large)
Glottis
Rtotal
0.05
0.05
0.02
0.02
0.12
0.26
R(SI)
Ple
thysm
ogra
ph
y
Inte
rupte
r
Oe
sophageal ballo
on
Fo
rced O
scill
ation
71
AIRWAY RESISTANCE - BOX
Record airflow against
box pressure with shutter
open
Record mouth pressure
against box pressure
with shutter closed
72
AIRWAY RESISTANCE - BOX
Box Pressure
Mo
uth
Pre
ss
ure
Box Pressure
Air
flo
w
Shutter Open; Box sealed
Recording of Airflow from
pneumotachograph versus
Box Pressure.
Shutter Closed; Box sealed
Recording of Mouth pressure versus
Box Pressure as subject breathes
against the shutter
73
AIRWAY RESISTANCE - BOX
AwAlv
Box
AlvBox RV
P
P
Px
V
P
AwRRcTan
Tank
74
AIRWAY RESISTANCE - BOX
GAW = 1/RAW
SGAW= GAW/TGV
75
AIRWAY RESISTANCE & LUNG VOLUME
0.0
0.1
0.2
0.3
0 1 2 3 4 5 6 7
Lung Volume (litres)
Air
way R
esis
tan
ce (
SI
Un
its)
TLC
RV
FRC
0
5
10
15
20
25
0 1 2 3 4 5 6 7
Lung Volume (litres)
Air
way C
on
du
cta
nce (
SI
Un
its)
TLC
FRC
RV
76
PHYSIOLOGICAL MATHS!
77
76
PHYSIOLOGICAL MATHS!
V
r = 0.75 P = 2.5
r4 = 0.3164 R1 = 3.16
R1 = 3.16 = 0.79
r = 0.375 P = 2.5
r4 = 0.0198 R2 = 50.57
R2 = 50.57 = 0.049
R2 ÷ R1 = 16 Flow by 94%
78
77
DETERMINANT OF RESISTANCE
Laminar and Turbulent Flow
Airway diameter/x-sectional area (A)
Gas Density () and Viscosity ()
Reynolds Number
79
FLOW IN TUBES
80
DETERMINANT OF RESISTANCE
Rn < 100 – laminar flow
Rn > 10,000 – turbulent flow
Rn ~ 1500 – trachea
He/O2 vs N2/O2 vs SF6/O2
81
AIRWAY RESISTANCE MEASUREMENTS
Assessing -
Reversibility of inhaled drugs
Effect of bronchoconstrictor agents
Large and small airway function
Monitoring changes in disease
82
EFFECTS OF DISEASE
0
0.1
0.2
0.3
0.4
0.5
0.6
Normal Mild Airflow
Obstruction
Emphysema Asthma Pre -
BD
Asthma Post
- BD
Air
way
Res
ista
nce
(kP
a.l-1
.s)
83
TECHNICAL ISSUES FOR BODY
PLETHYSMOGRAPHIC
MEASUREMENTS
84
TECHNICAL ISSUES
Shift Volume
Inaccuracy of Measurements in AWO
Linked and Unlinked spirometry
Panting frequency
Abdominal Gas Volume
85
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 86
SHIFT VOLUME
87
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.
INACCURACY IN AWO
A number of papers have demonstrated that body
plethysmography can over-estimate TGV and hence
TLC in patients with asthma and severe AWO.
The major assumption in the technique is that Pmouth is
the same as PAlv and this is effectively true in normal
subjects and in patients with mild airflow obstruction.
In moderate to severe airflow obstruction, there is a time
lag between Pmouth and PAlv due to the characteristics of
the airways resulting in an underestimation of PAlv and an
overestimation of TGV
To overcome these issues, slow panting/breathing
against the shutter is advised 88
PANTING FREQUENCY
In AWO, there is a delay between alveolar pressure
and mouth pressure – out of phase with each other
This results in an overestimation of TGV and hence
TLC
This artefact is exacerbated when –
Airways are very narrow (Raw)
Very compliant airways
High panting frequency
Panting/breathing at < 1Hz allows more time for
mouth and alveolar pressures to equalize, thereby
reducing the phase differences 89
DIFFERENCES IN TLC IN CHRONIC AWO
90 S G a w c m H 2 O
-1s e c
-1
Dif
fere
nc
e (
TL
Cm
- T
LC
es)
0 .0 2 0 .0 4 0 .0 6 0 .0 8 0 .1 0-0 .2
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0
1 .2
1 .4
1 .6
Rodenstein & Stanescu Am Rev Respir Dis 1982; 126: 1040 - 1044
LINKED AND UNLINKED SPIROMETRY
TLC and RV are calculated as –
TLC = RV + VC = FRC + IC
RV = FRC – ERV = TLC – VC
Does it matter if the VC manoeuvre is done immediately
after the shutter opens or using a different device?
Purist approach – linked as FRC may change between
manoeuvres
Acceptable alternative - unlinked
91
UNLINKED AND UNLINKED SPIROMETRY
92 Williams & Bencowitz. Differences in plethysmographic lung volumes. Chest 1989; 95: 117 - 123
Mean ± SEM
ABDOMINAL GAS VOLUME (AGV)
AGV accounts for about 115 ml1
The effects of AGV may be dependent on level of panting. FRC appears to be the best level to pant at2
TGV may be lower by 900 ml if the subject pants using diaphragm and abdominal muscles rather than intercostal and accessory muscles3
AGV equates to about 360 ml3
1. Bedell et al 1956
2. Brown et al, 1978
3. Habib & Engel, 1978
93
BODY PLETHYSMOGRAPHY
VERSUS OTHER TECHNIQUES
94
AGREEMENTS OF METHODS
In Normal subjects -
VA and TLCHe agree ~ 300 - 400 ml
VA and TLCBox agree ~ 400 - 500 ml
TLCBox and TLCHe agree ~ 300 – 400 ml
Similar results observed in patients with mild airflow
obstruction and in restrictive ventilatory defects
95
AGREEMENTS OF METHODS
Moderate to severe airflow obstruction
TLCBox > TLCHe > VA
Note: -
if TLCBox > VA by 3+ litres
then emphysematous bulla may be present
96
WHY DIFFERENCES IN TLC MEASURES
97
DIFFERENCES IN TLC & VA
0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 00
1
2
3
4
5
6T L C H e - V A
T L C p le th - V A
F E V 1 % p re d ic te d
TL
Cx
x -
VA
(lit
re
s)
Data from T Goddard, ERS 2011 with permission
98
GAS DILUTION – NORMAL/RESTRICTIVE
1min 2min 5 min
In 1 minutes, 75% of the lung volume will be measured In 5 minutes, 100% of the lung volume will be measured
75% 20% 5%
Model 1
99
GAS DILUTION – SEVERE AWO
5min 20min 30min
In 5 minutes, 65% of the lung volume will be estimated In 10 minutes, 80% of the lung volume will be measured
65% 25% 10%
Model 2
100
BODY BOX – ANY PATIENT!
5min 20min 30min
In 15 seconds all the lung volume will be estimated
65% 25% 10%
1min 2min 5 min
75% 20% 5%
+ Xml + Xml Model 3
101
INTERPRETATION OF RESULTS
102
ATS/ERS INTERPRETATION STRATEGY
103
ATS/ERS INTERPRETATION STRATEGY
Uses Standardized Residuals for each index to
assess the Lower Limit of Normal (LLN)
Based on physiologically and statistically sound
approach to interpretation of lung function
ATS/ERS guidelines do not state which test of lung
volumes – Body plethysmography, Helium Dilution
or Nitrogen washout should be used within the
interpretation strategy.
104
Interpretation of Results
• In patients with obstructive diseases
– airway closure occurs at an abnormally high lung volume
FRC (functional residual capacity)
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
FRC
RV 105
CLINICAL APPLICATIONS &INTERPRETATION
106
FRC
Gas trapping due to intrathoracic airway obstruction
Cystic lung disease
FRC
Abnormal alveolar development
Reduced recoil of chest-wall
Decreased lung compliance
Atelectasis
OBSTRUCTIVE LUNG DISEASE
107
EMPHYSEMA: PRESSURE-VOLUME CURVES
108
LUNG VOLUME REDUCTION SURGERY
109
LUNG VOLUME REDUCTION SURGERY
Current guidelines recommend the use of Body
Plethysmography for the measurement of lung volumes
Measures all lung volume within the chest, not just that
which is accessible through gas dilution techniques
110
RESULTS OF LVRS
111
Gerald M. O’Brien; Satoshi Furukawa; Anne Marie Kuzma; Francis Cordova; Gerard J. Criner. CHEST 1999; 115:75–84
112
Normally it accounts for about 25% of TLC.
Limited by chest wall compression
RV increased
in airway narrowing with air trapping (Asthma)
in loss of elastic recoil (Emphysema).
RV decreased
Increased elastic recoil (pulmonary fibrosis)
RESIDUAL VOLUME (RV)
TIDAL VOLUME (TV)
Equates to about 7ml/kg
400-700 ml
TV increased
Severe AWO + reduced breathing frequency
TV decreased
in severe RLD, + increase in breathing frequency
113
TOTAL LUNG CAPACITY (TLC)
114
It is the total volume of air within the lung after
maximum inspiration.
TLC is limited by lung compliance
TLC Increased
in airway narrowing with air trapping (Asthma)
in loss of elastic recoil (emphysema).
TLC Decreased
in ILD, muscle weakness, Obesity etc
EXPIRATORY RESERVE VOLUME
ERV reduced
Obesity (BMI > 35 kg.m-2)
ILD
115
116
INSPIRATORY CAPACITY (IC)
It is the maximal volume of air inspired from resting
expiratory level
Useful marker of de-hyperinflation after BD’s
FUNCTIONAL RESIDUAL CAPACITY (FRC)
117
It is the volume of air remaining in the lungs at the end
of resting (normal) expiration.
Balance of chest wall and lung compliances
FRC Increased (>+1.65 SR) in
Emphysema (decreased elastic recoil)
Asthma
Bronchiolar obstruction (air trapping)
FRC decreased (< 1.65 SR) in
intrinsic ILD
by upward movement of diaphragm (obesity, painful
thoracic or abdominal wound)
VITAL CAPACITY
118
volume of gas measured on complete expiration
after complete inspiration without effort
Decreased in
Obstructive Lung Disease
ILD, Muscle weakness, Obesity etc
Note
If VC < 15 ml/kg and VT < 5ml/kg, patient needs
ABG’s and overnight oximetry as this indicates likely
need for non-invasive ventilation
AWO RLD (Lung) RLD (non-Lung)
FEV1 N or N or
FVC or N
FEV1/FVC N or N or
RV N
TLC N or
RV/TLC N N
VC
FRC
FRC/TLC N or N or
FEV1/TLC N N
119
INTERPRETATION OF AIRWAYS
RESISTANCE
120
INDICATION FOR R AW MEASUREMENT
Further evaluation of airflow limitation beyond spirometry
Determining the response to B.D.
Determination of bronchial hyper-reactivity
The commonly used limit for bronchial provocation 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.
Difference between types of obstructive lung disease having similar spirometry pattern.
Following the course of the disease and response to treatment.
121
ASSESSMENT OF RAW DATA
122
PARAMETER OF AIRWAY RESISTANCE
sReff (specific effective airway resistance) which reflects
the larger central airways
sRtot (specific total airway resistance) which reflects the
smaller peripheral airways
The parameter of sR0.5 reflects the behavior of larger ,
more proximal airways with much less sensitivity to
peripheral airways.
123
APPLICATION OF RAW
124
DEFINITION OF ABNORMAL LUNG FUNCTION
USING RAW ETC
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
Bronchial hyper-responsiveness
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 2-5 yrs
125
126
AIRWAYS OBSTRUCTION
127
RESTRICTIVE LUNG DISEASE
128
EXTRATHORACIC AIRFLOW PROBLEM
129
AIRWAY COLLAPSE
130
BEYOND THE ROUTINE
131
OBESITY AND LUNG VOLUMES
132 Small differences in TLC and VC over range of BMI’s
OBESITY AND LUNG VOLUMES
133 Big differences in FRC and especially ERV over range of BMI’s
OBESITY AND LUNG VOLUMES
134
135
BRONCHODILATOR RESPONSE
Where FEV1 does not significantly improve, patients often state they feel symptomatically better
Changes have occurred in the degree of hyperinflation, so work of breathing is reduced.
Raw decreases
FRC decreases
RV decreases
IC increases
Demonstrated for 2-agonists, combination drugs and anticholinergic drugs
Relate changes in static lung volumes and Raw pre and post treatment to symptomatic improvement (VAS score) and to 6MWT
136
137
138
GAS COMPRESSION
139
TRACHEAL STENTING
Assess airway function by use of airways resistance
measurements before and after stenting and to follow
progress of patient over time
Raw is more comfortable for the patient to perform
Stent should Raw as radius of airway is greater.
FEV1 should also increase and shape of F-V curve
should be more normalized
140
PNEUMOTHORAX AND PLEURAL EFFUSION
Possible to make measurements of He dilution and
TGV from body plethysmograph to demonstrate
differences between total volume of the chest and
actual accessible lung volume
TLCpleth – TLCHe equates to difference in accessible
gas exchange volume. 141
SUMMARY
Body plethysmography provides a more accurate
reflection of the true size of the lungs at RV, FRC and
TLC than gas dilution techniques, especially in AWO.
Airways resistance provides a useful measure of airway
dysfunction and can be used in relation to dynamic lung
volumes to further assess airway dysfunction
Body plethysmography is recommended in the
assessment of patients undergoing LVRS and may be
used to assess other disorders including spinal cord
injury etc.
Body plethysmography can be used beyond the simple
static lung volume measurements 142