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PLETHYSMOGRAPHY

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STANDARD PF PLETHYSMOGRAPH

o Spirometry Spirometryo Diffusion Capacity Diffusion Capacityo Lung Volumes Lung Volumeso MIP/MEP MIP/MEP

Thoracic Gas VolumeAirways Resistance




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MYTHS

oPlethysmography is too difficult for the patient.

oPlethysmography is too expensive

oPlethysmography is too complex and useful only as a research tool.

oMy it will be torture for my patients




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WHAT DOES IT MEASURE?

o Flow (Volume)

oMouth Pressure

oBox Pressure




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How does it measure?Mouth Pressure Xducer

Pneumotachometer (Flow)

Box Pressure Transducer




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HOW DOES IT WORK?

o As the patient pants against the closed shutter, pressure change is measured in the box and at the mouth




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ASSUMPTIONS

o Mouth Pressure (Pm) is equal to alveolar pressure (Palv)

o Abdominal gas does not effect the measurement




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HOW DOES IT WORK?

• In a fluid or gas filled circuit, pressure applied at any point is felt equally throughout the circuit

• This assumption must be true for results to be valid

Pascal’s PrincipleP1

P2 P3




WHY CALCULATE LUNG VOLUMES

o A restrictive ventilatory defect is characterized by a reduction in TLC

o below the 5th percentile of the predicted value

o Below the lower limits of normal

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ERS/ATS: The presence of a restrictive ventilatory defect may be suspected when VC is reduced.

A reduced VC by itself does not prove a restrictive ventilatory defect.

Why Determine Lung Volumes




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ERS/ATS: A reduced FVC is associated with a low TLC only 50% of the time or less.

Why Determine Lung Volumes




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• Thoracic Gas Volume (TGV) also called FRCpleth – the volume of air in the lungs at the end of a normal exhalation

• We are after Total Lung Capacity (TLC); however,

TLC is not measured directly.

Lung Volumes




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• TLC = TGV (FRC) + Inspiratory Capacity (IC)

• TLC = Residual Volume (RV) + VC

• RV = TGV - ERV

Lung Volumes




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Lung Volumes




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DETERMINATION OF FRC

oMultiple breath gas dilutiono Nitrogen Washouto Helium Dilution

o TGV via Body Plethysmographyo Imaging Techniques (radiology)

o Planimetryo CT/MRI




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o ACCP Scientific Section Recommendation:o In patients with airway obstruction the

dilution method underestimates the thoracic gas volume to the extent that depends on the severity of the obstruction. The plethysmographic method measures the total compressible gas including that of poorly ventilated areas.

Murray, Crapo, et al ,1982




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o Dilution methods measure only communicating airways and therefore can significantly underestimate true lung volume.




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FRC by Dilution = 2L FRC by Plethysmography = 2L




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Obstructed airway

FRC by Dilution = 1 L FRC by Plethysmography = 2L




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DETERMINATION OF TLC VIA SINGLE BREATH

o Single breath inert gas dilution (DLco)o Helium, Neon, Methane

o Alveolar Volume (VA) approximates TLC

o Single breath techniques further underestimate lung volume due to reduced time for equilibration.




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PLETHYSMOGRAPHY VS. DILUTION

o Decreases test time –oOne N2 washout or helium dilution can

take up to 7-8 minutes. If you have to repeat, this takes an additional 7-8 minutes after waiting for gas to clear lungs

o Plethysmography can perform several efforts in 3 minutes




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CLINICAL INDICATIONS

o To distinguish between restrictive and obstructive disease patterns, particularly in the presence of a reduced VC

o To diagnose restrictive disease patternso To provide an index of gas trapping

(plethysmography vs gas dilution)o Assess response to therapeutic intervention

AARC Clinical Practice Guideline




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TGV - HOW DOES IT WORK?

Boyle’s Law• P1V1 = P2V2

V`

P`

P

V




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TGV - HOW DOES IT WORK?

• P1V1 = P2V2

• P1 = barometric Pressure* • V1= thoracic gas volume• P2 = P1 + delta P• V2 = V1 - delta V

Solving for P1

V1 = PB • (V / P)




TESTING SEQUENCE(1ST CHOICE)

o Measure ERV after the acquisition of the FRC measurement followed by slow IVC maneuvers that are linked

o FRC reported – mean of technically acceptable FRC measurements (CV 5% = difference between highest and lowest values divided by the mean ≤ .05) linked to technically acceptable ERV and IC measurements used for calculating RV and TLC

o Acceptable IC’s CV 5% +/- 3% (obstructed)

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TESTING SEQUENCE 1ST CHOICE

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TESTING SEQUENCE 2ND CHOICE

o Perform IC immediately after the FRC measurement to TLC

o This method might work better for those who have severe COPD

o TLC = FRC + IC

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Airways Resistance(Raw)




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AIRWAYS RESISTANCE (RAW)

Airways Resistance can be thought of as how much work (driving pressure) the patient has to do simply to breath.




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• Increased Raw is the primary finding in Obstructive Airways Disease

• May be caused by bronchospasm, compression or consolidative filling

Airway Resistance (Raw)




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AIRWAYS RESISTANCE (RAW)oAirways Resistance - Pressure

cmH2O/L/secoConductance (Gaw) – Flow

L/sec/cmH20oGaw is the reciprocal of Raw

1/Raw




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AIRWAYS RESISTANCE (RAW)o Airways Resistance - Pressure

cmH2O/L/seco sRaw (Raw relative to lung volume)

Raw x Vpanto Conductance (Gaw) – Flow

L/sec/cmH20o sGaw (Gaw relative to lung volume)

Gaw/Vpant




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AIRWAYS RESISTANCE (RAW)

COPD patient -

Raw

sRaw

sGaw

Compensatory Hyperinflation




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AIRWAY RESISTANCE

Effort independent assessment of airway caliber !If pressure is constant which will conduct more

flow?




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POISEUILLE’S LAW

(Pdriving)(pi)(radius4)

Flow = ------------------------- (8)(Length)(viscosity)

Flow rate is proportional to the 4th power of a pipe’s radius.




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POISEUILLE’S LAW

You need 16 tubes to pass as much fluid as one tube twice their diameter.




AIRWAY RESISTANCE

o Since resistance is related most strongly to total cross sectional area rather than length, the majority of resistance in normal lungs resides in the larger airways

P1

P2

P3BP3A

P3A1

P3A2

P3B2

P3B1




AIRWAYS RESISTANCE

o In summary, what proportion of the total airways resistance is in the larger airways?

o What proportion of the airways resistance is in the smaller airways?

o 80% Largero 20% Smaller

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PLETH TEST MANEUVER

oDoor closed for ~1 min to allow for equilibration

oPatient sitting up straight, nose clipsoHands supporting their cheeks o Elbows at their side




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TGV TEST MANEUVER

oNormal tidal breathing until stable respiratory pattern is achieved

oAt end expiration the shutter is closedoPatient is asked to “pant” against the

closed shutter for 2 to 3 seconds.oAfter shutter reopens, perform an SVC




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THORACIC GAS VOLUME – “PANTING”

o Pant Volume: ~50cc

o Frequency: 0.5 – 1.0 Hz (30 to 60 bpm, although up to 90 is acceptable)

o Emphasize this is NOT an MVV or MIP/MEP




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THORACIC GAS VOLUME – “PANTING”

Tidal Breathing

Shutter Closure




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HOW DOES IT WORK?

Mouth Pressure vs Box Pressure

MouthPressure

Box Pressure (pleth volume)




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HOW DOES IT WORK?

MouthPressure

Box Pressure (pleth volume)

V / P is the relationship between mouth pressure and box pressure, and can be expressed as the tangent of the angle




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LINE OF “BEST FIT”




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IMPORTANCE OF “PINNED” SVC

o Trying to measure TLC

o TGV efforts can be variable

o Performing an SVC with the TGV maneuver produces more repeatable TLC values




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IMPORTANCE OF “PINNED” SVC

TGV IC TLC

3.00 1.50 4.50 L

2.50 2.00 4.50 L

3.50 1.00 4.50 L




AIRWAY RESISTANCE TESTo Open Shutter Phase

o Pant with shutter open to determine airway resistance

o Closed Shutter Phaseo Pant with shutter closed to measure lung

volume – VPant (can be used to measure TGV)




AIRWAY RESISTANCE TEST

o Patient performance criteriao Small breaths (~50)o Consistent, gentle efforts 1-1.5 efforts/sec (60 – 90

efforts/min)o Emphasize this is NOT an MVV o Provide continuous feedback on performance




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AIRWAYS RESISTANCE – “QUIET BREATHING”

o Volume: ~50cco Frequency: 0.5 cycle/sec (30 BPM)o Glottis opens and closes with each breath, causing

Raw to increaseo Most Raw predicted numbers are based on panting

efforts




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Airway Resistance Test




AIRWAY RESISTANCE

Raw =Slope (pressure/volume)

Slope (flow/volume)




AIRWAY RESISTANCE

o In the Lung:

o Flow = Pressure/ Resistance oro Resistance = Pressure/ Flow

Slope of the line is

Flow / Box PressureF

L

O

W

BOX PRESSURE




RESISTANCE

o What pressure (cmH20/L/S) does it take to create a certain flow?

o What pressure does it take to create a standardized flow of .5 L/S?

o R=Pressure/Flow

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LINE OF “BEST FIT”

o In the Lung:

o Flow = Pressure/ Resistance oro Resistance = Pressure/ Flow

F

L

O

W

BOX PRESSURE

Zero Flow 0.5 L/sec




Airway Resistance

a) Normal, b) Increased large airway Raw, c) COPD, d) Upper airway obstruction




Airway ResistanceAirway Collapse Patterns may be better represented by

separating Inspiratory and Expiratory Raw.




Airway Resistance




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AIRWAYS RESISTANCE AND AIRWAY REACTIVITY

o Airways resistance measures significant changes in airway caliber during bronchodilator and bronchoprovocation trials which might not be reflected in spirometry.

o Airways resistance explains patient’s “perceived” response in the absence of spirometric changes.




BRONCHODILATORS WITH SPIROMETRY

o Masking the response of bronchodilators

o Lung memory and the broncho-dilatory effect of deep inhalations

o Possible closure of intra-thoracic airways during forced exhalation

Blast it out!!!!

PRE POST




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o From National Jewish Medical Center in Denver:o Subjects often report subjective

benefit from bronchodilators without demonsting improvement in spirometry




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DETERMINATION OF AIRFLOW OBSTRUCTION

o Flows determined by spirometry inherently incorporate driving pressure and therefore:o are effort dependento are insensitive to early obstructive changes especially in a

young, motivated subjecto reflect true obstruction only after significant compromise

of airway radius, well beyond the development of symptoms

o Can overcome obstruction with more force




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o Determination of Airways Resistance and Conductance:o is effort independento can identify early obstructive changes throughout the

tracheobronchial treeo will identify obstructive changes, which increase work of

breathing, and cause dyspnea, that might otherwise not be identified using spirometry




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Airflow &

Artificial Resistance




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Spirometry Pred Baseline +1.5 cm/H2O/L/s

% Change

FVC 4.88 4.64 4.58 -1FEV1 3.84 3.31 3.19 -4FEV1/FVC 79 72 70 -3FEFmax 8.99 8.81 6.62 -25FEF25-75 3.78 2.46 2.28 -7




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Spirometry Pred Baseline +1.5 cm/H2O/L/s

% Change

FVC 4.88 4.64 4.58 -1FEV1 3.84 3.31 3.19 -4FEV1/FVC 79 72 70 -3FEFmax 8.99 8.81 6.62 -25FEF25-75 3.78 2.46 2.28 -7

Airway Mechanics

Raw 1.95 3.31 4.82 46Gaw 1.03 .30 .21 -30sGaw .25 .08 .05 -38




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Spirometry Pred Baseline +1.5 cm/H2O/L/

s

% Change +4.0 % Change

FVC 4.88 4.64 4.58 -1 4.59 -1FEV1 3.84 3.31 3.19 -4 3.19 -4FEV1/FVC 79 72 70 -3 69 -3FEFmax 8.99 8.81 6.62 -25 6.09 -31FEF25-75 3.78 2.46 2.28 -7 2.28 -7




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Spirometry Pred Baseline +1.5 cm/H2O/L/

s

% Change +4.0 % Change

FVC 4.88 4.64 4.58 -1 4.59 -1FEV1 3.84 3.31 3.19 -4 3.19 -4FEV1/FVC 79 72 70 -3 69 -3FEFmax 8.99 8.81 6.62 -25 6.09 -31FEF25-75 3.78 2.46 2.28 -7 2.28 -7

Airway MechanicsRaw 1.95 3.31 4.82 46 6.66 101Gaw 1.03 .30 .21 -30 0.15 -50sGaw .25 .08 .05 -38 0.04 -50




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Case Study




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Young Asthmatic Age: 16Height: 75 in Weight: 268 Sex: M

Spirometry Predicted Actual Pre % Predicted

FVC 5.54 4.70 85FEV1 4.79 3.13 65

FEV1/FVC 86 67FEF25-75% 5.27 2.08 40

FEFmax 9.46 6.27 66




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Spirometry Predicted Actual Pre % Predicted

FVC 5.54 4.70 85FEV1 4.79 3.13 65

FEV1/FVC 86 67FEF25-75% 5.27 2.08 40

FEFmax 9.46 6.27 66Airway Mechanics

Raw 1.51 7.17 474Gaw 0.66 0.14 21sGaw .019 0.02 11




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Spirometry Predicted Actual Pre % Predicted Actual Post % Change

FVC 5.54 4.70 85 4.73 1FEV1 4.79 3.13 65 3.40 9

FEV1/FVC 86 67 72 8FEF25-75% 5.27 2.08 40 2.54 22

FEFmax 9.46 6.27 66 6.32 1




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Spirometry Predicted Actual Pre % Predicted Actual Post % Change

FVC 5.54 4.70 85 4.73 1FEV1 4.79 3.13 65 3.40 9

FEV1/FVC 86 67 72 8FEF25-75% 5.27 2.08 40 2.54 22

FEFmax 9.46 6.27 66 6.32 1

Airway Mechanics

Raw 1.51 7.17 474 0.96 -87Gaw 0.66 0.14 21 1.04 643sGaw .019 0.02 11 0.25 1150




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o What is a clinically significant response?

o Raw and SRaw: 40%

o SGaw : 35-40%

Current ATS/ERS Standards use 12% and 200 ml for FVC and/or FEV1 for bronchodilator response




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IMPLICATIONS

oWithout Airways Resistance:

o Patient may not have been correctly diagnosed with reversible airway obstruction.

o Prescription of inhaler may not have been clinically justified.




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AIRWAY RESISTANCEo Spirometry alone:

o May not accurately determine the presence or absence of obstruction

o May not adequately evaluate airway response to stimuli




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“We conclude that spirometry alone fails to identify reversibility in approximately 15 percent of patients, and most of these patients can be identified by additional plethysmographic measurements…”

Smith HR, Irvin CG, Cherniak RM. The Utility of Spirometry in the Diagnosis of

Reversible Airway Obstruction. Chest 1992; 101:1577




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ASTHMA MANAGEMENT

o The use of airways resistance to diagnose and monitor the asthmatic can improve the patient’s quality of life and reduce the associated cost of care.




PLETHYSMOGRAPHY: THE BENEFITS

o Rapid, accurate functional measuremento Multiple measurements < 5 min

o Quantifies Non-Ventilated Lungo TGV-FRCo Non-Ventilated lung contributes to

• Hypoxemia (Resting/Exercise)• Dyspnea




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PLETHYSMOGRAPHY: THE BENEFITSo Enhances diagnosis and treatment of

obstructive disorders

o More accurate Lung Volumes compared to lung dilution methods

o Differential Diagnosiso Restriction/Hyperinflation is based on TLC




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PLETHYSMOGRAPHY: THE BENEFITS

o More sensitive in diagnosis of airways diseaseo Earlier detection of airways disease o More accurate evaluation of airway reactivity

(bronchodilation and bronchoprovocation) o Enhanced evaluation of upper airway lesions




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AARC Clincal Practice Guidelineshttp://www.rcjournal.com/cpgs/

ATS/ERS Guidelineshttp://www.ers-education.org/pages/

default.aspx?id=2477

http://www.rcjournal.com/cpgs/




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Thank YouPatrick G Burns

Director of MarketingMGC Diagnostics

[email protected]

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