Model-based approach to estimate dFRC in the ICU using measured lung dynamics

Ankit N. Mishra, Yeong Shiong Chiew, Geoffrey M. Shaw, J. Geoffrey Chase

Research output: Chapter in Book/Report/Conference proceedingConference PaperOther


Acute Respiratory Distress Syndrome (ARDS) is characterized by inflammation, filling of the lung with fluid and collapsed lung unit. Mechanical ventilation (MV) is used to treat ARDS/ALI using positive end expiratory pressure (PEEP) to recruit and retain lung units, thus increasing pulmonary volume and dynamic functional residual capacity (dFRC) at the end of expiration. However, simple methods to measure dFRC at the bedside currently do not exist and other methods are invasive and impractical to carry out on a regular basis. Stress-strain theory is used to estimate ΔdFRC, which represents the extra pulmonary volume due to PEEP, utilizing readily available patient data from a single breath. The model uses commonly controlled or measured parameters (lung compliance, plateau airway pressure, PV data) to identify a parameter β1 as a function of PEEP and tidal volume. A median β1 value is calculated for each PEEP level over a cohort and is hypothesised as a constant throughout the population for the particular PEEP. Estimated ΔdFRC values are then compared to measured values to assess accuracy of the model. δdFRC was calculated for 9 patients and compared to the measured values. The median percentage error was 40.29% [IQR: 14.20-55.39] for PEEP = 5cmH2O, 31.12% [IQR: 10.53-192.71] for PEEP = 10cmH 2O, 20.8% [IQR: 7.51-81.06] for PEEP = 15cmH2O, 15.44% [IQR: 11.92-36.18] for PEEP = 20cmH2O, 19.7% [IQR: 4.79-20.76] for PEEP = 25cmH2O and 11.78% [IQR: 2.99-27.5] for PEEP = 30cmH 2O. Linear regression between estimated and measured ΔdFRC produced R2 = 0.862. The model-based approach offers a simple and non-invasive method which does not require interruption of MV to estimate dFRC. The clinical accuracy of the model is limited but was able to track the impact of changes in PEEP and tidal volume on dFRC, on a breath-by-breath basis for each PEEP.

Original languageEnglish
Title of host publicationProceedings of the 8th IFAC Symposium on Biological and Medical Systems, BMS 2012
PublisherElsevier - International Federation of Automatic Control (IFAC)
Number of pages6
ISBN (Print)9783902823106
Publication statusPublished - 2012
Externally publishedYes
EventIFAC Symposium on Biological and Medical Systems 2012 - Budapest, Hungary
Duration: 29 Aug 201231 Aug 2012
Conference number: 8th (Proceedings)

Publication series

NameIFAC Proceedings Volumes (IFAC-PapersOnline)
ISSN (Print)1474-6670


ConferenceIFAC Symposium on Biological and Medical Systems 2012
Abbreviated titleBMS 2012
Internet address


  • ARDS
  • DFRC
  • FRC
  • Functional residual capacity
  • ICU
  • Intensive care
  • Model
  • Pulmonary

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