Lung Function in Growth and Aging
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Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general US population. Am J Respir Crit Care Med 1999; 159: 179-187.

Methods

Spirometry was performed in 20,627 survey participants (16,484 adults and 4,143 youths) as part of NHANES III. The NHANES III is the most recent in a series of studies designed to assess the health and nutrition status of adults and children in the United States through interviews and direct physical examinations. The sample design of the NHANES III is a stratified multistage probability sample of the U.S. population. The survey was conducted by the National Center for Health Statistics (NCHS) beginning in 1988 and continuing until 1994. Detailed description of the survey design and data collection methodology have been published by NCHS (12, 13). The participants (for children a proxy - ideally a parent or guardian) also completed a detailed administered questionnaire that gathered information on sex, race, ethnicity, health, and limited occupational history. Body measurements were also taken, including standing height, weight, and sitting height. Standing height was measured without shoes with the subject’s back to a vertical backboard. Both heels were placed together, touching the base of the vertical board.

After an explanation of the test procedure, each subject attempted to perform at least five FVC maneuvers, with an additional goal of meeting the 1987-ATS acceptability and reproducibility criteria. Forced exhaled volumes were measured using a dry rolling-seal spirometer. The spirometer used a digital shaft encoder to measure volume with a volume resolution of 2.6 ml and a sampling interval of 10 ms. All of the digital volume-time curves were saved on digital tape (as much as 20 s of exhalation), allowing recalculation of all parameters and test performance with regard to ATS acceptability and reproducibility criteria. The spirometry system has been independently tested (14) and found to exceed the ATS spirometry equipment recommendations.

During the performance of the FVC maneuver, real-time displays of flow-volume and volume-time curves were provided to the technicians with an indication of when 6 s of exhalation had been achieved. At the completion of each maneuver, a display was provided of all the flow-volume curves, the FVC, FEV1, PEF, and expiratory time, and the percentage difference between each value of FVC, FEV1, and PEF and the corresponding largest value. The computer also determined whether the last maneuver was unacceptable (cough, excessive extrapolated volume, and late peak flow) and whether additional maneuvers were needed to meet the ATS acceptability and reproducibility criteria. The technicians were instructed to obtain a minimum of five maneuvers and a maximum of eight, ensuring that the subject produced the highest possible peak flows, and that maximum exhalation continued for at least 6 s and until there was a plateau in the volume-time curve: no change in volume (40 mL) for at least 2 s. For Spanish-speaking subjects, a Spanish-speaking technician administered the test or an interpreter was provided. The test was performed in the standing position and noseclips were worn unless there was a valid reason these conditions could not be met.

A more detailed description of the study and spirometry procedures is available (13) and a more detailed description of the results of applying the ATS acceptability and reproducibility criteria in this study has been reported by Hankinson and Bang (15). Quality control of the spirometry data was conducted by the National Institute for Occupational Safety and Health (NIOSH), Morgantown, West Virginia, which served as the quality control center. In addition to formal initial training of at least 1 wk and a pilot study of 820 subjects (data not included), the technicians were continuously monitored during the entire study by a senior quality control technician who periodically traveled to the field to observe and provide additional instructions. At the completion of each study location (approximately 300 subjects per location), a quality control report evaluating each technician’s performance was used to determine whether additional training or monitoring was warranted. In addition, the raw flow-volume and volume-time curves were reviewed by a senior technician and the subject’s performance was graded. Those subjects whose performance was judged to be unacceptable by two senior technicians (less than two acceptable curves) were excluded from this analysis.
In 1994, the ATS approved a new statement on spirometry (11) that changed the reproducibility criteria to a constant 200 ml and the extrapolated volume lower limit from 100 to 150 mL. The ATS also recommended that three acceptable and reproducible maneuvers be performed, in contrast to the minimum of five maneuvers used in the NHANES III data collection protocol. To determine the impact of strictly following the 1994 ATS spirometry recommendations, the raw volume-time curves were reanalyzed to provide new values of FVC, FEV1, etc., which would have been obtained if the 1994 ATS recommendations had been in place during the NHANES III survey period. Specifically, each raw volume-time curve was reprocessed in the order that it was obtained (including unacceptable maneuvers). When the 1994 ATS minimum criteria were met (three acceptable maneuvers with a reproducible FVC and FEV1), no additional curves were used in the recalculation of this new set of spirometric parameters. In addition, when all curves were used, the 1994 acceptability and reproducibility criteria were used.  This analysis showed when averaged over all the subjects, the mean differences between the FVC and FEV1 using all curves compared with ATS-min were 62.5 and 52 mL, respectively.

For use in the development of reference values, only asymptomatic, lifelong nonsmoking subjects with at least two acceptable maneuvers were included in our analysis. Applying these criteria eliminated 13,198 of the 20,627 study participants who performed spirometry, leaving 7,429 subjects (see Tables 1 and 2).

When compared to other reference values, the FEV1, and particularly the FVC, appear to be larger than those observed in other studies.  There are several explanations for these expected differences:
  1. As described above, the NHANES III study required a minimum of five maneuvers, regardless of whether the minimum ATS-criteria (3-acceptable curves and a repeatable test) had been obtained.
  2. Also as described above, there was a quality control program in place with feedback to the technicians.  This feedback resulted in better coaching, with a corresponding increase in the number of acceptable curves and repeatable tests.
  3. The end of test was not limited to 15-seconds and for some older normal subject, multiple exhalations as long as 20 seconds were obtained.
  4. A fixed BTPS factor was used to correct the FVC and FEV1 to BTPS conditions.  With a dry-rolling-sealed spirometer, the air in the spirometer is not typically at the final spirometer temperature when the FEV1 measurement is obtained.  Therefore when the constant BTPS factor, based on the assumption of instantaneous cooling, was used a slight over-estimation of the FEV1 can occur (about 2%) [Hankinson JL, Viola JO: Dynamic BTPS correction factors for spirometric data. J Appl Physiol Respir Environ Exercise Physiol 44:1354, 1983.], [Hankinson JL, Castellan RM, Kinsley KB, Keimig DG: Effects of spirometer temperature over FEV1 shift changes. J Occup Med 28:1222-125, 1986.].

References

11. American Thoracic Society. 1995. Standardization of spirometry: 1994 Update. ATS Statement. Am J Respir Crit Care Med 152:1107–1136.
12. National Center for Health Statistics. 1994. Plan and operation of the Third National Health and Nutrition Examination Survey, 1988–1994. U.S. Government Printing Office, Washington, DC. DHHS Publication No. (PHS) 94-1308.
13. National Center for Health Statistics. 1996. NHANES III Reference Manuals and Reports. Data Dissemination Branch, Hyattsville, MD. CD-ROM No. 6-0178 (1096).
14. Nelson, S. B., R. M. Gardner, R. O. Crapo, and R. L. Jensen. 1990. Performance evaluation of contemporary spirometers. Chest 97:288–297.
15. Hankinson, J. L., and K. M. Bang. 1991. Acceptability and reproducibility criteria of the American Thoracic Society as observed in a sample of the general population. Am Rev Respir Dis 143:516–521.
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