Method for analysing multiple-breath bitrogen washouts

  • B. A. Sjöqvist
  • K. Sandberg
  • O. Hajalmarson
  • T. Olsson


A method of analysing multiple-breath nitrogen washouts is described and discussed. The method is objective and introduces no weighting into the results. The necessary raw data are obtained from a computer-assisted nitrogen washout test. During the analysis, objective parameters which characterise the alveolar ventilation in terms of nitrogen elimination pattern and gas-mixing efficiency are calculated, together with estimates of functional residual capacity (FRC), tidal volume, dead space, and effective part of the tidal volume. The elimination pattern is described through linear fitting of exponential models to the obtained washout course and is performed by using the z-transform. The dead space and the effective part of the tidal volume are estimated from a gas-mixing model. The applied estimation procedure difines a dead space which is larger than the corresponding single-breath dead space and has been designated ‘effective dead space’. The gas-mixing efficiency is described by two indices, one describing the efficiency within an idealised breath and the other the overall efficiency of the lungs. The calculation algorithms are fast and the results are easy to interpret, which makes the method suitable for clinical online applications. The method has been evaluated in a group of 24 healthy newborns at about 26 hours of age, but the application is not restricted to this category of patient.


Computer analysis Dead space calculation Distribution of ventilation Gas mixing Linear estimation of exponentials Multiple breath nitrogen washout Nitrogen elimination pattern Ventilatory efficiency z-transform 


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Copyright information

© International Federation for Medical & Biological Engineering 1986

Authors and Affiliations

  • B. A. Sjöqvist
    • 1
  • K. Sandberg
    • 2
  • O. Hajalmarson
    • 2
  • T. Olsson
    • 1
  1. 1.Research Laboratory of Medical ElectronicsChalmers University of TechnologyGöteborgSweden
  2. 2.Department of Pediatrics 1University of GöteborgGöteborgSweden

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