Chest
Volume 130, Issue 6, December 2006, Pages 1650-1656
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Original Research: Lung Function
A Statistical Rationale for the Use of Forced Expired Volume in 6 s

https://doi.org/10.1378/chest.130.6.1650Get rights and content

The purpose of the study was to determine the best surrogate for FVC when performing spirometry to detect obstruction or restriction. Volume-time curves from 3,539 participants in the Family Heart Study with acceptable quality test sessions were analyzed. An index of the variability of each timed volume (FEVx) from 1 to 12 s was determined for each subject. The least within-test session variability was seen for forced expired volume in 6 s (FEV6) and forced expired volume in 7 s (for both, mean range was 95 mL). The sensitivity and specificity for detecting obstruction and restriction when substituting the FEV6 for the FVC were then determined before and after allowing for measurement errors of 50 mL (approximately the lower limit of spirometers ability to detect volume). Sensitivity was 76% before the 50-mL error analysis and 95% after. Specificity was 98% before the 50-mL error analysis and 99.5% after. We conclude that use of FEV6 to replace the FVC for spirometry testing will result in improved reproducibility, with no significant loss of sensitivity or specificity, after allowing a 50-mL measurement error, for detecting obstruction or restriction.

Section snippets

Materials and Methods

Spirometry was performed in 4,827 subjects recruited for the FHS, a community-based, multicenter study5 of genetic and nongenetic determinants of coronary heart disease. Data were collected at four field centers (Framingham, MA; Minneapolis, MN; Forsyth County, NC; and Salt Lake City, UT). Spirometric data were obtained by trained technicians using the 1987 ATS standards.6 Each participant performed five to eight spirometric maneuvers using a water-sealed spirometer connected to a linear

Results

There were 4,827 FHS participants; 3,539 subjects were entered into group 1 to analyze the FEVx variability. Group 1 contained spirometry tests for all individuals who completed at least three maneuvers with at least 10 s of exhalation, and data were analyzed up to 12 s. Some of the tests did not meet the ATS reproducibility requirement of 200 mL (n = 141) but were included so that no systemic bias was introduced in the estimates of the FEVx variability. Average spirometric data for these

Discussion

Reference value comparisons require both biological and technical comparability between the person being tested and the reference values.10 Reducing intraindividual variation in spirometry measures will create closer alignment between reference populations and should decrease errors in clinical classification: first, by ensuring that each measured value more precisely represents the individual being tested; second, by more accurately placing an individual’s measurements above or below the LLN.

References (20)

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Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).

The authors have no conflicts of interest to disclose.

The Family Heart Study is a National Institutes of Health-funded multicenter study.

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