2007 pfts the forced oscillation technique
TRANSCRIPT
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The Forced Oscillation TechniqueThe Future of Pulmonary Function Testing?
Alexander S. Niven, MDClinical Assistant Professor, University of Washington
Director, Respiratory Care ServicesMadigan 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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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
Evaluation of Obstructive Lung Disease
• Spirometry, bronchoprovocation testing– Cannot reliably differentiate these patients – Insensitive to early airway changes
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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
Transducer
Resistor
Pneumotach
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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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Small Airways Large Airways
Total Respiratory Impedance (Zrs)
Goldman MD. Pulm Pharmacol Ther 2001; 14(5): 341-350
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Resistance (Rrs)
Small Airways Large Airways
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Normal
COPD
Baseline
Post Bronchodilator
Rrs
Frequency Dependence
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Reactance (Xrs)
Small Airways Large Airways
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Reactance Area (AX)
Smith HJ et al. Eur Respir Mon 2005; 31: 1-34
Resonant Frequency (frs)
0
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Normalfrs
frs = 18 Hz
COPD
Post Bronchodilator
Baseline
AX
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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
Smokers Nonsmokers
FVC,% pred 100 + 14 99 + 10
FEV1, % pred 97 + 15 99 + 13
FEV1/FVC 0.78 + 0.08 0.82 + 0.07
R5, cm H2O/L/s 3.9 + 0.9 3.5 + 0.8
R20, cm H2O/L/s 3.1 + 0.6 3.1 + 0.7
R5-R20, cm H2O/L/s 0.8 + 0.5* 0.5 + 0.3
AX, cm H2O/L/s 3.9 + 0.3* 1.8 + 0.1* p < 0.01Adapted 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”
Pre-BD
Post Bronchodilator
Baseline
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: 1676-1682Newman K et al. Semin Respir Crit Care Med 1994; 15: 162-167Christopher KL et al. N Engl J Med 1983;308:1566-1570
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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): 198SEvans TM et al. J Asthma 2006; 43(1): 49-55Rundell KW et al. Can Respir J 2005; 12(5): 257-63Evans 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
Gaw, frs, R5 more sensitive to airway changes but demonstrate greater variability than FEV1
sGaw
frs
R5
FEV1
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
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 ( > 20 seconds)• Multiple tests• Artifacts
– Swallow, cough– Circuit leak– Tongue, cheeks
• Data coherence
measurementsTongue Artifact
Goldman MD et al. Respir Physiol Neurobiol 2005; 148: 179-194
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Reference ValuesHz Male Female
Rrs (cmH20/L/s)
n Age (yrs)
Rrs (cmH20/L/s)
n Age (yrs)
Landser, 1982 4 - 24 2.5 (0.6) 224 26 (10)
Clement, 1983 8 - 24 ~ 2.6 442 29
Gimeno, 1992 10 2.9 (0.8) 102 50
Pasker, 1994 6 - 24 2.6 (0.6) 126 33 (12) 3.0 (0.6) 100 29 (12)
Govaerts, 1994 10 - 32 2.6 (0.7) 32 48 (15) 3.4 (0.7) 28 55 (13)
Pasker 1996 6 - 24 2.5 (0.5) 137 53 (14) 3.1 (0.7) 140 58 (14)
Adapted from Oostveen E. Eur Respir J 2003; 22: 1026-1041
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Age and Ethnic Variation
Age > 65 Japanese African American
n 223 166 13
Age (SD) 83 (8) 39 (17) 35 (6)
Rrs (SD) (cmH20/L/s) 2.2 (0.6) M
2.6 (0.7) F
2.8 (0.5)
R5 (SD) (cmH20/L/s) 2.8 (0.7) 3.1 (0.5)
R20 (SD) (cmH20/L/s) 2.4 (0.6) 2.4 (0.4)
R5-R20 (SD) (cmH20/L/s) 0.8 (0.3)
AX (SD) (cmH20/L/s) 4.8 (2.1)
Guo YF et al. Eur Respir J 2005; 26: 602-608Shitoa S et a. Respirology 2005; 10: 310-315Haymore 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 (< 2 mm)
• “Small airway resistance” using FOT– Airway resistance– Tissue impedance
• Respiratory compliance• Tissue resistance
• Concomitant lung volume measurements may aid physiologic interpretationHogg 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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