Modelling mixing within the dead space of the lung improves predictions of functional residual capacity

Chris D. Harrison, Phi Anh Phan, Cathy Zhang, Daniel Geer, Andrew D. Farmery

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)
38 Downloads (Pure)


Routine estimation of functional residual capacity (FRC) in ventilated patients has been a long held goal, with many methods previously proposed, but none have been used in routine clinical practice. This paper proposes three models for determining FRC using the nitrous oxide concentration from the entire expired breath in order to improve the precision of the estimate. Of the three models proposed, a dead space with two mixing compartments provided the best results, reducing the mean limits of agreement with the FRC measured by whole body plethysmography by up to 41%. This moves away from traditional lung models, which do not account for mixing within the dead space. Compared to literature values for FRC, the results are similar to those obtained using helium dilution and better than the LUFU device (Dräger Medical, Lubeck, Germany), with significantly better limits of agreement compared to plethysmography.
Original languageEnglish
JournalRespiratory Physiology and Neurobiology
Early online date18 Mar 2017
Publication statusPublished - 31 Aug 2017


  • lung function
  • functional residual capacity
  • mathematical modeling
  • parameter estimation
  • alveolar volume
  • airway dead space
  • nitrous oxide
  • mechanical ventilation


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