The Forced Oscillation Technique The Future of Pulmonary Function Testing?

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The Forced Oscillation TechniqueThe Future of
Pulmonary Function Testing?

• Alexander S. Niven, MD
• Clinical Assistant Professor, University of
  Washington
• Director, Respiratory Care Services
• Madigan Army Medical Center

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Conflict of Interest Disclosure

• Equipment loan from Viasys Inc.

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Why Look for New Techniques?
72 yo with bronchiectasis, MAC
21 yo with VCD, possible asthma
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Disadvantages of Spirometry

• Requires maximal,
• reproducible efforts
• Flow limiting segment (FLS)
• Central to peripheral airways
• Maximal expiratory flow
• (MEF) is dependent on
• Lung recoil pressure
• Dynamic airway resistance
• Airway properties at FLS

Pride NB. Clin Chest Med 2001 22(4) 599-622
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Evaluation of Obstructive Lung Disease

• Spirometry, bronchoprovocation testing
• Cannot reliably differentiate these patients
• Insensitive to early airway changes

Lapperre TS et al. Am J Respir Crit Care Med
2004 170 449-504 Fabbri LM et al. Am J Respir
Crit Care Med 2003 167 418-424
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Forced Oscillation Technique

• Superimposed external pressure signals on
  spontaneous tidal breathing
• Effort independent assessment of mechanics
• Significant pediatric literature
• Increasing interest in adult lung function testing

Dubois AB. J Appl Physiol 1956 8 587-94 Smith
HJ. Eur Respir Mon 2005 31 1-34
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DuBois AB, Brody AW, Lewis DH, Burgess BF.
Oscillation mechanics of lungs and chest in man.
J Appl Physiol 1956 8 587-94
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Loudspeaker
Resistor
Pneumotach
Transducer
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Methodology

• Mono or multi frequency
• 2-4 Hz to 30-35 Hz
• Continuous
• Pseudo-random noise (PRN)
• Time discrete
• Impulse oscillation (IOS)

Modified from Smith HJ et al.
Smith HJ et al. Eur Respir Mon 2005 31 1-34
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Impulse Oscillometry Testing

• Seated
• Head in neutral position
• Tidal breathing
• 20 90 seconds
• Cheek support when necessary

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Niven A et al. Am J Respir Crit Care Med 2003
167(7) A419
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Large Airways
Small Airways
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Total Respiratory Impedance (Zrs)
Small Airways
Large Airways
Goldman MD. Pulm Pharmacol Ther 2001 14(5)
341-350
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Resistance (Rrs)
Small Airways
Large Airways
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Rrs
Normal
Baseline
Frequency Dependence
Post Bronchodilator
COPD
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Reactance (Xrs)
Small Airways
Large Airways
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Resonant Frequency (frs)
0
Reactance Area (AX)
Smith HJ et al. Eur Respir Mon 2005 31 1-34
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Normal
frs
COPD
AX
Post Bronchodilator
frs 18 Hz
Baseline
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http//sunsite.unc.edu/dave/drfun.html
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Clinical Applications

• Screening
• Upper airway obstruction
• Obstructive lung disease
• Bronchoprovocation testing
• Bronchodilator response
• Respiratory Mechanics
• Obstructive sleep apnea

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Screening

• 96 iron workers at 9/11 clean up site
• 53 noted new respiratory symptoms
• Cough, dyspnea, wheezing, sinus complaints

p lt 0.01
Adapted from Skloot G. Chest 2004 125 1248-1255
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Large Airway Resistance

• Large particles deposit in central airways
• Increased resistance causes impulse shadow

Large Airways (increased resistance)
Measurement reflects large airways only
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Central (Large Airway) Obstruction Reactive
airways at Ground Zero
Baseline

Pre-BD
Post Bronchodilator
Courtesy of MD Goldman
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Vocal Cord Dysfunction

• Pathologic adduction of vocal cords
• 10-15 of young dyspnea patients
• More common in females
• Perfectionism, psychiatric conditions
• Etiology may be multifactorial
• Conversion disorder
• Post-nasal drip syndrome, GERD

Morris M et al. Chest 1999 116 1676-1682 Newman
K et al. Semin Respir Crit Care Med 1994 15
162-167 Christopher KL et al. N Engl J Med
19833081566-1570
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Vocal Cord Dysfunction
Inspiration
Expiration
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Inspiratory impedance spikes due to variable
extrathoracic obstruction from VCD
Red Impedance (H2O/L/s) Blue Volume (L)
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Bronchoprovocation Testing

• Oscillometry consistently more sensitive in the
  detection of small airway changes
• Greater magnitude of change
• Lower dose of challenge agent
• Histamine, methacholine
• Eucapneic voluntary hyperventilation, cold air

Hnatiuk OW et al. Chest 2000 118(4) 198S Evans
TM et al. J Asthma 2006 43(1) 49-55 Rundell KW
et al. Can Respir J 2005 12(5) 257-63 Evans TM
et al. Chest 2005 128(4) 2412-9
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Bronchoprovocation Testing

Courtesy of MD Goldman
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Bronchoprovocation Testing
Courtesy of MD Goldman
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Lung Allograft Rejection

• IOS in 22 bilateral lung allograft recipients
• 5 acute rejection, 7 bronchiolitis obliterans
• Abnormalities in R5 (9), R5-15 (10), frs (12), AX
  (12)

Goldman MD et al. Respir Physiol Neurobiol 2005
148 179-194 Ross D et al. J Heart Lung
Transplant 2004 23 S131
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Bronchodilator Response
Coefficient of Variation () Test Day sGaw
9.3 7.8 frs 5.0 7.4 R5 8.4 13.5 FEV1
3.3 3.5 IC 3.2 6.6
sGaw
frs
R5
FEV1

• Gaw, frs, R5 more sensitive to airway changes
  but demonstrate greater variability than FEV1

Borrill ZL et al. Br J Clin Pharmacol 2005 59
379-384
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CPAP Titration
Navajas D et al. Am J Respir Crit Care Med 1998
157 1524-1530
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Impact of Uvulopharyngoplasty
Lin CC et al. Eur Arch Otolaryngol 2006 263
241-7
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Standardization of Spirometry

• Acceptable and reproducible data
• Reference standards
• Diverse demographics
• Interpretation strategies
• Clinical significance of measurements

Adapted from Brusasco V et al, eds. Eur Respir J
2005 26 319-338
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Data Collection Criteria

• Minimum data acquisition ( gt 20 seconds)
• Multiple tests
• Artifacts
• Swallow, cough
• Circuit leak
• Tongue, cheeks
• Data coherence
• measurements

Tongue Artifact
Goldman MD et al. Respir Physiol Neurobiol 2005
148 179-194
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Reference Values
Adapted from Oostveen E. Eur Respir J 2003 22
1026-1041
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Age and Ethnic Variation
Guo YF et al. Eur Respir J 2005 26
602-608 Shitoa S et a. Respirology 2005 10
310-315 Haymore BR et al. Am J Respir Crit Care
Med 2005 2 A32
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Which Small Airways?

• Airflow obstruction in COPD correlates to
  pathologic airway changes (lt 2 mm)
• Small airway resistance using FOT
• Airway resistance
• Tissue impedance
• Respiratory compliance
• Tissue resistance
• Concomitant lung volume measurements may aid
  physiologic interpretation

Hogg JC. N Engl J Med 2004 350
2645-2653 Marchal F. Eur Respir J 1996 9 253-261
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Conclusions

• Promising tool in pulmonary testing
• Minimal cooperation, no maneuvers
• Unique tool to evaluate central airways
• Sensitive to peripheral airway changes and
  respiratory mechanics
• Further standardization is needed

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The Future of Pulmonary Function Testing?
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COPD and Plethysmography

• Increased interest in inspiratory capacity
• Indirect measurement of small airways
• Influenced by
• Patient effort
• Respiratory muscle strength

Gibson GJ. Clin Chest Med 2001 22(4)
623-635 Sutherland RE et al. NEJM 2004 350
2689-97
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