title: Smallest detectable change in volume differs between mass flow sensor and pneumotachograph.
abstract: BACKGROUND
  To assess a pulmonary function change over time the mass flow sensor and the pneumotachograph are widely used in commercially available instruments. However, the smallest detectable change for both devices has never been compared. Therefore, the aim of this study is to determine the smallest detectable change in vital capacity (VC) and single-breath diffusion parameters measured by mass flow sensor and or pneumotachograph.
  
  
  METHODS
  In 28 healthy pulmonary function technicians VC, transfer factor for carbon monoxide (DLCO) and alveolar volume (VA) was repeatedly (10×) measured. The smallest detectable change was calculated by 1.96 x Standard Error of Measurement ×√2.
  
  
  RESULTS
  The mean (range) of the smallest detectable change measured by mass flow sensor and pneumotachograph respectively, were for VC (in Liter): 0.53 (0.46-0.65); 0.25 (0.17-0.36) (p = 0.04), DLCO (in mmol*kPa-1*min-1): 1.53 (1.26-1.7); 1.18 (0.84-1.39) (p = 0.07), VA (in Liter): 0.66. (0.53-0.82); 0.43 (0.34-0.53) (p = 0.04) and DLCO/VA (in mmol*kPa-1*min-1*L-1): 0.22 (0.19-0.28); 0.19 (0.14-0.22) (p = 0.79).
  
  
  CONCLUSIONS
  Smallest detectable significant change in VC and VA as measured by pneumotachograph are smaller than by mass flow sensor. Therefore, the pneumotachograph is the preferred instrument to estimate lung volume change over time in individual patients.
authors.affiliation: Department of pulmonology and institute for Cardiovascular Research (ICaR-Vu) VU University Medical Center, Amsterdam, 1007 MB, The Netherlands. h.groepenhoff@vumc.nl.
authors.forename: Herman
authors.initials: H
authors.lastname: Groepenhoff
authors.forename: Caroline B
authors.initials: CB
authors.lastname: Terwee
authors.forename: Patrick Mc
authors.initials: PM
authors.lastname: Jak
authors.forename: Anton
authors.initials: A
authors.lastname: Vonk-Noordegraaf