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BJA Advance Access published online on August 21, 2006
British Journal of Anaesthesia, doi:10.1093/bja/ael216
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© The Board of Management and Trustees of the British Journal of Anaesthesia 2006. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
Accepted May 19, 2006

Laboratory Investigation

A tidally breathing model of ventilation, perfusion and volume in normal and diseased lungs

J. S. Yem 1, M. J. Turner 1 *, A. B. Baker 1, I. H. Young 2, and A. B. H. Crawford 3

1 Department of Anaesthetics, The University of Sydney, Royal Prince Alfred Hospital, Missenden Road, Camperdown, NSW 2050, Australia
2 Department of Respiratory Medicine, The University of Sydney, Royal Prince Alfred Hospital, Missenden Road, Camperdown, NSW 2050, Australia
3 Department of Respiratory Medicine, Westmead Hospital, Westmead, NSW 2145, Australia

* To whom correspondence should be addressed.
M. J. Turner, E-mail: mjturner{at}usyd.edu.au


  Abstract

Background. To simulate the short-term dynamics of soluble gas exchange (e.g. CO2 rebreathing), model structure, ventilation-perfusion ({Vdot}A/{Qdot}) and ventilation-volume ({Vdot}A/VA) parameters must be selected correctly. Some diseases affect mainly the {Vdot}A/{Qdot} distribution while others affect both {Vdot}A/{Qdot} and {Vdot}A/VA distributions. Results from the multiple inert gas elimination technique (MIGET) and multiple breath nitrogen washout (MBNW) can be used to select {Vdot}A/{Qdot} and {Vdot}A/VA parameters, but no method exists for combining {Vdot}A/{Qdot} and {Vdot}A/VA parameters in a multicompartment lung model.

Methods. We define a tidally breathing lung model containing shunt and up to eight alveolar compartments. Quantitative and qualitative understanding of the diseases is used to reduce the number of model compartments to achieve a unique solution. The reduced model is fitted simultaneously to inert gas retentions calculated from published {Vdot}A/{Qdot} distributions and normalized MBNWs obtained from similar subjects. Normal lungs and representative cases of emphysema and embolism are studied.

Results. The normal, emphysematous and embolism models simplify to one, three and two alveolar compartments, respectively.

Conclusions. The models reproduce their respective MIGET and MBNW patient results well, and predict disease-specific steady-state and dynamic soluble and insoluble gas responses.

Keywords: modelling, ventilation/perfusion distribution, ventilation inhomogeneity.
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