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Point and Counterpoint |

Rebuttal From Dr EnrightRebuttal From Dr Enright FREE TO VIEW

Paul L. Enright, MD
Author and Funding Information

From the University of Arizona (retired).

CORRESPONDENCE TO: Paul L. Enright, MD, PO Box 675, Mount Lemmon, AZ 85619; e-mail: lungguy@gmail.com


CONFLICT OF INTEREST: P. L. E. has been reimbursed for travel expenses by professional societies during the past 3 years for giving talks at international meetings about pulmonary function testing. These societies were often given funding for these talks by ndd Medical Technologies, Inc, which does not make a forced oscillation technique instrument.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;148(5):1138-1139. doi:10.1378/chest.15-1039
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Several years ago while working with Drs Berger, Goldring, and Oppenheimer evaluating people who were exposed to World Trade Center (WTC) dust and fumes, I found them to be excellent pulmonary physiologists, and I appreciate the high quality of their research using pulmonary function tests, such as forced oscillometry technique (FOT). Studies showing that an FOT index is abnormal more often than spirometry in smokers or people exposed to respiratory hazards in the workplace may merely mean that the false positive rate for oscillometry is higher than that for spirometry. An up-to-date review referenced by Dr Berger and colleagues1 regarding the diagnostic value of FOT concluded that “it is unclear whether any of these measures of airway resistance contribute clinically important information to the traditional measures derived from spirometry (FEV1, FVC, and FEV1/FVC).”2

Obesity is very common (eg, one-half of WTC responders were obese at their initial examination), and obesity often causes dyspnea on exertion. A study of 100 obese patients (37% of whom reported dyspnea) noted that oscillometric abnormalities “were evident in essentially all subjects, thus confounding the ability of oscillometry to detect associated respiratory dysfunction independent of the effects of mass loading.”3 Spirometry and specific airway conductance (measured by body plethysmography) were normal. Thus, although it is easy to identify obesity in a patient, an abnormal FOT result in overweight patients may be falsely attributed to small airways disease causing their dyspnea. Note that in the pie charts Dr Berger and colleagues1 present, 50% of the symptomatic cases had abnormal oscillometry (but normal spirometry), but so did 22% of the control subjects. This suggests that about one-half of the abnormal oscillometry interpretations were false positive findings.

Community members enrolled in the WTC Registry had relatively short exposures to the ground zero dust and fumes compared with the responders (including firefighters) who worked intensively at the ground zero site for many days. This may explain why exposure indexes as well as chronic respiratory symptoms were significantly associated with abnormal spirometry results in the workers4 but not in the community members.

Regarding the use of oscillometry for methacholine challenge testing, it would be a mistake to stop the test and call the findings positive for bronchial hyperresponsiveness when an FOT index increases before the FEV1 falls by 20%. A very large body of literature exists that allows interpretation of the provocative concentration of methacholine causing a 20% fall in FEV1 or dose of methacholine producing a 20% fall in FEV1 to alter the pretest probability of bronchial hyperresponsiveness.5,6 This is not true for changes in FOT indexes that are not accompanied by a > 20% fall in FEV1. In addition, it is safe to proceed by giving an additional dose of methacholine when the FEV1 has not fallen by > 20%.

In summary, oscillometry is easier for patients to perform compared with spirometry but more difficult for technologists to obtain reliable results and pulmonologists to understand them. The apparently enhanced sensitivity of oscillometry when used to screen for airway disease is accompanied by a reduction in specificity and positive predictive value.

References

Berger KI, Goldring RM, Oppenheimer BW. Point: should oscillometry be used to screen for airway disease? Yes. Chest. 2015;148(5):1131-1135.
 
Kaminsky DA. What does airway resistance tell us about lung function? Respir Care. 2012;57(1):85-96. [CrossRef] [PubMed]
 
Oppenheimer BW, Berger KI, Segal LN, et al. Airway dysfunction in obesity: response to voluntary restoration of end expiratory lung volume. PLoS One. 2014;9(2):e88015. [CrossRef] [PubMed]
 
Udasin I, Schechter C, Crowley L, et al. Respiratory symptoms were associated with lower spirometry results during the first examination of WTC responders. J Occup Environ Med. 2011;53(1):49-54. [CrossRef] [PubMed]
 
Crapo RO, Casaburi R, Coates AL, et al. Guidelines for methacholine and exercise challenge testing—1999. Am J Respir Crit Care Med. 2000;161(1):309-329. [CrossRef] [PubMed]
 
Cockcroft DW. Direct challenge tests: airway hyperresponsiveness in asthma: its measurement and clinical significance. Chest. 2010;138(2_suppl):18S-24S. [CrossRef] [PubMed]
 

Figures

Tables

References

Berger KI, Goldring RM, Oppenheimer BW. Point: should oscillometry be used to screen for airway disease? Yes. Chest. 2015;148(5):1131-1135.
 
Kaminsky DA. What does airway resistance tell us about lung function? Respir Care. 2012;57(1):85-96. [CrossRef] [PubMed]
 
Oppenheimer BW, Berger KI, Segal LN, et al. Airway dysfunction in obesity: response to voluntary restoration of end expiratory lung volume. PLoS One. 2014;9(2):e88015. [CrossRef] [PubMed]
 
Udasin I, Schechter C, Crowley L, et al. Respiratory symptoms were associated with lower spirometry results during the first examination of WTC responders. J Occup Environ Med. 2011;53(1):49-54. [CrossRef] [PubMed]
 
Crapo RO, Casaburi R, Coates AL, et al. Guidelines for methacholine and exercise challenge testing—1999. Am J Respir Crit Care Med. 2000;161(1):309-329. [CrossRef] [PubMed]
 
Cockcroft DW. Direct challenge tests: airway hyperresponsiveness in asthma: its measurement and clinical significance. Chest. 2010;138(2_suppl):18S-24S. [CrossRef] [PubMed]
 
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