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Open Access Short Report

Smallest detectable change in volume differs between mass flow sensor and pneumotachograph

Herman Groepenhoff1*, Caroline B Terwee2, Patrick MC Jak1 and Anton Vonk-Noordegraaf1

Author Affiliations

1 Department of pulmonology and institute for Cardiovascular Research (ICaR-Vu) VU University Medical Center, Amsterdam, 1007 MB, The Netherlands

2 Department of Epidemiology and Biostatistics and the EMGO Institute for Health and Care Research. VU University Medical Center, Amsterdam, 1007 MB, The Netherlands

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BMC Research Notes 2011, 4:23  doi:10.1186/1756-0500-4-23

Published: 28 January 2011



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.


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.


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).


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.