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.

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ASSESSMENT OF RAW DATA

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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.

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APPLICATION OF RAW

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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

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126

AIRWAYS OBSTRUCTION

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RESTRICTIVE LUNG DISEASE

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EXTRATHORACIC AIRFLOW PROBLEM

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AIRWAY COLLAPSE

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BEYOND THE ROUTINE

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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

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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

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GAS COMPRESSION

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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

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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

CONTACT & CONSULTANCY

Adrian.Kendrick@UHBristol.nhs.uk

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