title: Longitudinal validity of spirometers--a challenge in longitudinal studies.
abstract: OBJECTIVE
  Pulmonary function testing (PFT) in longitudinal studies involves the repeated use of spirometers over long time periods. We assess the comparability of PFT results taken under biologic field conditions using thirteen certified devices of various technology and age. Comparability of measurements across devices and over time is relevant both in clinical and epidemiological research.
  
  
  METHODS
  Forced Vital Capacity (FVC), Forced Expiratory Volume in the first second (FEV1) and Forced Expiratory Flow 50% (FEF50) were compared before and after the data collection of the Swiss Study on Air Pollution and Lung Diseases in Adults (SAPALDIA) and the European Community Respiratory Health Survey (ECRHS) cohort studies. Three test series were conducted with 46, 50 and 56 volunteers using various combinations of spirometers to compare the eight flow-sensing spirometers (Sensormedics 2200) used in the SAPALDIA cross-sectional and follow-up, two new flow-sensing instruments (Sensormedics Vmax) and three volume displacement spirometers (two Biomedin/Baires and one Sensormedics 2400).
  
  
  RESULTS
  The initial comparison (1999/2000) of eight Sensormedics 2200 and the follow-up comparison (2003) of the same devices revealed a maximal variation of up to 2.6% for FVC, 2.4% for FEV1 and 2.8% for FEF50 across devices with no indication of systematic differences between spirometers. Results were also reproducible between Biomedin, Sensormedics 2200 and 2400. The new generation of Sensormedics (Vmax) gave systematically lower results.
  
  
  CONCLUSIONS
  The study demonstrates the need to conduct spirometer comparison tests with humans. For follow-up studies we strongly recommend the use of the same spirometers.
authors.affiliation: Keck School of Medicine, University of Southern California, Los Angeles 90033-9013, USA. kuenzli@usc.edu
authors.forename: Nino
authors.initials: N
authors.lastname: Künzli
authors.forename: Birgit
authors.initials: B
authors.lastname: Kuna-Dibbert
authors.forename: Dirk
authors.initials: D
authors.lastname: Keidel
authors.forename: Roland
authors.initials: R
authors.lastname: Keller
authors.forename: Otto
authors.initials: O
authors.lastname: Brändli
authors.forename: Christian
authors.initials: C
authors.lastname: Schindler
authors.forename: Karl-Manfred
authors.initials: KM
authors.lastname: Schweinzer
authors.forename: Philippe
authors.initials: P
authors.lastname: Leuenberger
authors.forename: Ursula
authors.initials: U
authors.lastname: Ackermann-Liebrich
mesh_terms: D000293:Adolescent; D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D005540:Forced Expiratory Flow Rates / Q000502:physiology*; D005541:Forced Expiratory Volume / Q000502:physiology*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results; D013147:Spirometry; D014797:Vital Capacity / Q000502:physiology*