Auscultated forced expiratory time as a clinical and epidemiologic test of airway obstruction

Our plain-English summary of Auscultated forced expiratory time as a clinical and epidemiologic test of airway obstruction, by D.G. Kern, S.R. Patel (Chest, 1991).

The study

• Authors: D.G. Kern, S.R. Patel
• Journal: Chest
• Published: 1991;100(3):636-9
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004926).

Abstract

Objective: Seeking an inexpensive, readily available, clinical, screening, and field surveillance test of airway obstruction, we determined the validity of current dogma that forced expiratory time (FET) is a good clinical test of airway obstruction yet is of no epidemiologic use given excessive intrasubject variability.

Subjects And Methods: Two hundred twenty-nine white male plumbers and pipefitters were evaluated by spirometry, chest roentgenography, and a standardized respiratory questionnaire during a union-sponsored asbestos screening program. Subjects were classified as having large airway obstruction (LAO), small airway obstruction (SAO) alone, or no obstruction, on the basis of standard spirometric prediction equations. Two physicians, blinded to clinical and spirometric data, independently measured FET while auscultating the trachea with a stethoscope. The FET was defined as the time taken for an individual to forcefully exhale through an open mouth from total lung capacity until airflow became inaudible. Five such times were recorded for each subject. The mean of the three times having the narrowest range was deemed the FET for calculating test sensitivity and specificity. Based on previous literature, an FET greater than or equal to 6 s was considered abnormally prolonged.

Results: Two hundred five subjects completed both spirometry and FET testing; 67 had LAO, 5 SAO, and 133 no obstruction. A total of 83 percent had three FETs reproducible within a range of less than or equal to 1 s. The sensitivity and specificity of FET for LAO were 92 and 43 percent, respectively, while for SAO alone, 60 and 44 percent, respectively. Overall, FET misclassified 56 percent of nonobstructed subjects. Adjusting the normal-abnormal cutoff points for both FET and SAO minimally improved the performance of FET.

Conclusion: Although FET is a simple, inexpensive, sensitive, and fairly reproducible clinical test of LAO, it cannot be recommended as a clinical or an epidemiologic tool because of its extremely low specificity.

In plain English

The study tested whether auscultated forced expiratory time (FET) could detect airway obstruction. A stopwatch timed it from the first sound of forceful exhalation until airflow was no longer audible through a stethoscope. Subjects were 229 white male plumbers and pipefitters at a 1985 to 1986 Rhode Island asbestos screening. Of these, 205 completed both FET and spirometry. No asbestos disease findings were reported. An FET of 6 seconds or more counted as abnormal. Of the 205 men, one hundred seventy-one (83 percent) gave three FET times within 1 second. For large airway obstruction, FET caught 92 percent of affected men but correctly cleared only 43 percent of others. For small airway obstruction alone, seen in only five men, the figures were 60 and 44 percent. Overall, 56 percent of men without obstruction had an abnormal FET. The authors wrote that other cutoffs minimally affected accuracy, though at 12 seconds accuracy for large airway obstruction rose from 60 to 73 percent while sensitivity fell to 55 percent. The authors concluded that FET cannot be recommended as a clinical or epidemiologic test because of its extremely low specificity.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Diagnostic test evaluation (cross-sectional): sensitivity, specificity and reproducibility of auscultated FET compared against spirometry
• Who was studied: Active and retired union plumbers and pipefitters in Rhode Island were offered screening for asbestos-related disease on June 22 to 23, 1985, and January 25 to 26, 1986. Of the 561 offered screening, 229 white men took part, and 205 were analyzed.
• Exposure: Asbestos exposure was not measured or analyzed; it was only the reason for the screening program. The study examined the auscultated FET. A stopwatch measured the time from the first sound of forced expiratory flow, heard with a stethoscope over the trachea, until airflow was no longer audible. An FET of 6 seconds or more counted as abnormally prolonged.
• Main results:
  • Of the 229 subjects, 24 did not complete both FET testing and spirometry and were excluded, leaving 205. Of these, 67 had large airway obstruction, 5 had small airway obstruction alone, 8 had restriction and 125 had normal spirometry.
  • One hundred seventy-one of the 205 subjects (83 percent) reproduced three FET measurements within a 1-second range.
  • At a 6-second cutoff, FET sensitivity was 92 percent and specificity 43 percent for large airway obstruction. For small airway obstruction alone, sensitivity was 60 percent and specificity 44 percent.
  • Overall, 56 percent of subjects without spirometrically defined obstruction had an abnormally prolonged FET (75 of 133 in Table 1).
  • The authors wrote that changing the FET cutoff from 6 seconds to 5, 7, 8 or 12 seconds minimally affected overall test accuracy. Their Table 3 shows the trade-off. For large airway obstruction, accuracy went from 60 percent at 6 seconds to 73 percent at 12 seconds; sensitivity fell from 92 to 55 percent and specificity rose from 43 to 82 percent. For small airway obstruction, accuracy went from 44 to 80 percent and sensitivity fell from 60 to 20 percent.
  • Under a less restrictive definition of small airway obstruction (FEF25-75% less than 75 percent of predicted), 39 subjects had small airway obstruction and 99 had no obstruction. FET specificity improved only negligibly. Table 4 gives 48 percent specificity and 69 percent sensitivity at the 6-second cutoff.
• The authors' conclusion: The authors concluded that auscultated FET is a simple, inexpensive, sensitive and fairly reproducible test of large airway obstruction. However, they also concluded that it cannot be recommended as a clinical or epidemiologic test because of its extremely low specificity.
• Limitations the authors state:
  • The authors stated that their choice of spirometric gold standard for small airway obstruction was a likely contributor to the low specificity of FET.
  • Only five subjects were classified as having small airway obstruction. The authors said this made the estimate of FET sensitivity for small airway obstruction unstable.

Topics

Medical terms in this study, explained in our Lexicon: Pipefitter, Spirometry, Total Lung Capacity (TLC).

Related studies

• The relative importance of clinical, radiological and pulmonary function variables in evaluating asbestosis and chronic obstructive airway disease in asbestos workers — G.M. Regan, B. Tagg, et al. (1971)
• Expiratory and inspiratory forced vital capacity and one-second forced volume in asymptomatic never-smokers in Norway — A. Gulsvik, T. Tosteson, et al. (2001)
• Asbestos exposure and airways obstruction — M.G. Pearson (1991)
• Vital capacity and one-second forced expiratory volume in Australian male asbestos cement workers — L.N. Balaam, S.F. McCullagh (1975)
• Association between increased small airway obstruction and asbestos exposure in patients with asbestosis — X. Yang, Y. Yan, et al. (2018)
• Airway obstruction in asbestos-exposed shipyard workers: with and without irregular opacities — K.H. Kilburn, R.H. Warshaw (1990)

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