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

• Published in: British journal of anaesthesia : BJA Vol. 97; no. 5; pp. 718 - 731
• Main Authors: Yem, J.S., Turner, M.J., Baker, A.B., Young, I.H., Crawford, A.B.H.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.11.2006; Oxford University Press; Oxford Publishing Limited (England)
• Subjects: Adult; Anesthesia; Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Biological and medical sciences; Breath Tests; Humans; Male; Medical sciences; modelling; Models, Biological; Pulmonary Alveoli - physiopathology; Pulmonary Embolism - physiopathology; Pulmonary Emphysema - physiopathology; Pulmonary Gas Exchange; Solubility; ventilation inhomogeneity; Ventilation-Perfusion Ratio; ventilation/perfusion distribution; ventilation inhomogeneity; modelling; ventilation/perfusion distribution; Short term; Human; Dynamic response; Lung disease; Nitrogen washout; Shunt; Respiratory disease; Carbon dioxide; Steady state; Embolism; Inert gas; Lung volume; Bronchus disease; Anesthesia; Obstructive pulmonary disease; Gas exchange; Emphysema
• ISSN: 0007-0912; 1471-6771
• DOI: 10.1093/bja/ael216

To simulate the short-term dynamics of soluble gas exchange (e.g. CO2 rebreathing), model structure, ventilation–perfusion ( V˙A/ Q˙) and ventilation–volume ( V˙A/VA) parameters must be selected correctly. Some diseases affect mainly the V˙A/ Q˙ distribution while others affect both V˙A/ Q˙ and V˙A/VA distributions. Results from the multiple inert gas elimination technique (MIGET) and multiple breath nitrogen washout (MBNW) can be used to select V˙A/ Q˙ and V˙A/VA parameters, but no method exists for combining V˙A/ Q˙ and V˙A/VA parameters in a multicompartment lung model. 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 V˙A/ Q˙ distributions and normalized MBNWs obtained from similar subjects. Normal lungs and representative cases of emphysema and embolism are studied. The normal, emphysematous and embolism models simplify to one, three and two alveolar compartments, respectively. The models reproduce their respective MIGET and MBNW patient results well, and predict disease-specific steady-state and dynamic soluble and insoluble gas responses.