Theoretical Analysis of Gas Exchange in a Lung Model

Abstract

A mathematical model, derived from physiological data, is presented
to represent gas exchange in the lung during steady state and, for the
first time, unsteady state conditions, The model is used to simulate
functional defects that can occur in the diseased lung. From a review
of available literature four types of defect are recognised, namely, regional
inequalities of ventilation, regional inequalities of blood flow, series
inequalities and direct pulmonary blood shunts. The effects of changing
minute volume, cardiac output and inspired oxygen concentration upon
overall gas exchange are studied for each defect when oxygen uptake and
carbon dioxide output are held constant at normal values in the steady state.
The unsteady state condition is examined during the uptake and elimination
of four hypothetical inert gases having differing blood solubilities,

The model is used to assess how well certain pulmonary function
tests discriminate between the various defects considered, and from
information gained a new protocol for defining lung function is proposed.

Utilising a more elaborate version of the model, the influence of
nitrous oxide induction and excretion upon overall gas exchange is
evaluated, The effect of blood recirculation time, minute volume,
cardiac output, lung volume and inspired N,0 concentration upon arterial
PO2 and PCO2. are examined during the unsteady state. The change in FRC
occasioned when inspired and expired volumes are kept constant, are
discussed as an alternative to the general case in which FRC is held
constant and expired volume varied, A comparison between the model
prediction of expired gas tensions with values obtained from three normal
subjects during N,0 induction is also included,

Date of Award	1973
Original language	English