2007 pfts the forced oscillation technique

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

Conflict of Interest Disclosure

Equipment loan from Viasys Inc.

Why Look for New Techniques?

72 yo with bronchiectasis, MAC 21 yo with VCD, possible asthma

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

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

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

DuBois AB, Brody AW, Lewis DH, Burgess BF. Oscillation mechanics of lungs and chest in man. J Appl Physiol 1956; 8: 587-94

Loudspeaker

Transducer

Resistor

Pneumotach

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

Impulse Oscillometry Testing

• Seated• Head in neutral

position• Tidal breathing• 20 – 90 seconds• Cheek support

when necessary

Niven A et al. Am J Respir Crit Care Med 2003; 167(7): A419

Large Airways Small Airways

Small Airways Large Airways

Total Respiratory Impedance (Zrs)

Goldman MD. Pulm Pharmacol Ther 2001; 14(5): 341-350

Resistance (Rrs)

Small Airways Large Airways

Normal

COPD

Baseline

Post Bronchodilator

Rrs

Frequency Dependence

Reactance (Xrs)

Small Airways Large Airways

Reactance Area (AX)

Smith HJ et al. Eur Respir Mon 2005; 31: 1-34

Resonant Frequency (frs)

0

Normalfrs

frs = 18 Hz

COPD

Post Bronchodilator

Baseline

AX

http://sunsite.unc.edu/dave/drfun.html

Clinical Applications

• Screening

• Upper airway obstruction

• Obstructive lung disease– Bronchoprovocation testing– Bronchodilator response

• Respiratory Mechanics– Obstructive sleep apnea

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

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

Large Airways (increased resistance)

Measurement reflects large airways only

Central (Large Airway) Obstruction

Reactive airways at “Ground Zero”

Pre-BD

Post Bronchodilator

Baseline

Courtesy of MD Goldman

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

Vocal Cord Dysfunction

Inspiration Expiration

Inspiratory impedance “spikes” due to variable extrathoracic obstruction from VCD

Red = Impedance (H2O/L/s)

Blue = Volume (L)

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

Bronchoprovocation Testing

Courtesy of MD Goldman

Bronchoprovocation Testing

Courtesy of MD Goldman

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

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

CPAP Titration

Navajas D et al. Am J Respir Crit Care Med 1998; 157: 1524-1530

Impact of Uvulopharyngoplasty

Lin CC et al. Eur Arch Otolaryngol 2006; 263: 241-7

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

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

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

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

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

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

The Future of Pulmonary Function Testing?

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