Forced expiratory time was moderately useful for diagnosing obstructive airways disease
ACP J Club. 1994 Mar-April;120:43. doi:10.7326/ACPJC-1994-120-2-043
Schapira RM, Schapira MM, Funahashi A, McAuliffe TL, Varkey B. The value of the forced expiratory time in the physical diagnosis of obstructive airways disease. JAMA. 1993 Aug 11;270:731-6.
To evaluate the characteristics of the forced expiratory time (FET) in diagnosing obstructive airways disease (OAD).
2 blinded studies comparing FET with spirometry in diagnosing OAD and evaluating the inter-rater agreement of the FET measurement.
A pulmonary function laboratory in a tertiary care hospital.
A consecutive sample of 500 referred patients: 400 to evaluate the FET and 100 to assess inter-rater agreement.
Description of test and diagnostic standard
FET was measured by auscultation over the trachea with a stethoscope and timed with a stopwatch. Immediately after FET measurement, pulmonary function testing was done. Forced expiratory volume at 1 second (FEV1), forced vital capacity (FVC), FEV1/FVC(%), and total lung capacity (TLC) were obtained. Physician examiners were blinded to the results of FET and spirometry. A pure obstructive defect was defined as FEV1/FVC(%) < 70 and FVC or TLC ≥ 80% predicted; combined obstructive and restrictive defect as FEV1/FVC(%) < 70 and TLC < 80% predicted; restrictive defect as FEV1/FVC(%) ≥ 70 and FVC or TLC < 80% predicted; and normal pulmonary function as FEV1/FVC(%) ≥ 70 and FVC or TLC ≥ 80% predicted.
Main outcome measures
A receiver operating characteristic (ROC) curve was created, and positive likelihood ratios (LRs) were calculated.
The kappa statistic for inter-rater agreement for FET was 0.7, which showed substantial agreement. 4% of patients were excluded, 49% had a pure obstructive defect, 5% had combined obstructive and restrictive defects, 19% had a pure restrictive defect, and 26% had normal lung function. The positive LRs for FET in patients ≥ 60 years of age are in the Table. At a cutoff of 6 seconds, the sensitivity and specificity for OAD for all patients were 74% and 75%, respectively, and the area under the ROC curve was 0.63. The FET provided less diagnostic information in patients younger than 60 years (LR for FET < 2 s 0.36, LR for ≥ 8 s 2.32).
Forced expiratory time was moderately useful in the diagnosis of obstructive airways disease. There was substantial agreement among raters.
Source of funding: Not funded.
For article reprint: Dr. R.M. Schapira, Pulmonary Medicine/111-E, Zablocki Veterans Affairs Medical Center, 5000 West National Avenue, Milwaukee, WI 53295-1000, USA. FAX 414-383-8010.
Table. Positive likelihood ratios for forced expiratory time in diagnosing obstructive airways disease in patients ≥ 60 years of age
|Timing cut point||+LR* (95% CI)|
|< 2 seconds||0.15 (0.05 to 0.41)|
|≥ 2 to < 4 seconds||0.32 (0.19 to 0.52)|
|≥ 4 to < 6 seconds||0.42 (0.24 to 0.73)|
|≥ 6 to < 8 seconds||2.19 (1.02 to 4.80)|
|≥ 8 seconds||4.08 (2.52 to 6.79)|
*LR defined in Glossary
The elements of the history and physical examination should receive the same dissection and study as other diagnostic tests (1). In this context, 2 questions can be asked of the study by Schapira and colleagues. First, does the FET point to a diagnosis of OAD? Second, are other signs and symptoms better?
For the first question, the authors found the FET to be "moderately" helpful in the diagnosis of OAD when blinded observers evaluated this single sign. The study was large, carefully conducted, and agreed reasonably well with a previous study (2). Therefore, the FET does appear to be useful in the diagnosis of OAD.
What about the second question? This study was not really designed to provide the answer. A recent study, however, applying multivariate analysis to 92 patients with a self-reported history of cigarette smoking or OAD, concluded that the best variables for diagnosing OAD are diminished breath sounds and a smoking history of 70 or more pack-years (3). For moderate OAD, the FET appeared to add little.
The authors recommend measuring FET when other signs and symptoms do not point to a clear diagnosis and when spirometry is unavailable. Based on their data and the literature, this recommendation seems quite reasonable.
Richard A. Robbins, MD
University of Nebraska Medical CenterOmaha, Nebraska, USA