A computer model of the artificially ventilated human respiratory system in adult intensive care

Wilson, A.J.; Murphy, C.M.; Brook, B.S.; Breen, D.; Miles, A.W.; Tilley, D.G.

doi:10.1016/j.medengphy.2009.07.009

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Volume 31, Issue 9 , Pages 1118-1133, November 2009

A computer model of the artificially ventilated human respiratory system in adult intensive care

A.J. Wilson
- Department of Physics, University of Warwick, Coventry CV4 7AL, UK
- Formerly at Department of Medical Physics and Clinical Engineering, University of Sheffield, Royal Hallamshire Hospital, Sheffield S10 2JF, UK
C.M. Murphy
- Department of Mechanical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK
- Now at Motorola Ltd., Swindon SN25 4XY, UK
B.S. Brook
- School of Mathematical Sciences, University of Nottingham, Nottingham NG7 2RD, UK
- Formerly at Department of Medical Physics and Clinical Engineering, University of Sheffield, Royal Hallamshire Hospital, Sheffield S10 2JF, UK
D. Breen
- Department of Anaesthetics, Royal Hallamshire Hospital, Sheffield S10 2JF, UK
A.W. Miles
- Department of Mechanical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK
D.G. Tilley
- Department of Mechanical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK
- Corresponding author. Tel.: +44 01225 383023.

Received 1 August 2008; received in revised form 27 April 2009; accepted 11 July 2009. published online 21 August 2009.

Abstract

A multi-technique approach to modelling artificially ventilated patients on the adult general intensive care unit (ICU) is proposed. Compartmental modelling techniques were used to describe the mechanical ventilator and the flexible hoses that connect it to the patient. 3D CFD techniques were used to model flow in the major airways and a Windkessel style balloon model was used to model the mechanical properties of the lungs. A multi-compartment model of the lung based on bifurcating tree structures representing the conducting airways and pulmonary circulation allowed lung disease to be modelled in terms of altered ratios within a lognormal distribution of values and it is from these that gas exchange was determined. A compartmental modelling tool, Bathfp, was used to integrate the different modelling techniques into a single model. The values of key parameters in the model could be obtained from measurements on patients in an ICU whilst a sensitivity analysis showed that the model was insensitive to the value of other parameters within it. Measured and modelled values for arterial blood gases and airflow parameters are compared for 46 ventilator settings obtained from 6 ventilator dependent patients. The results show correlation coefficients of 0.88 and 0.85 for the arterial partial pressures of the O₂ and CO₂, respectively (p<0.01) and of 0.99 and 0.96 for upper airway pressure and tidal volume, respectively (p<0.01). The difference between measured and modelled values was large in physiological terms, suggesting that some optimisation of the model is required.