Compensation of two important non-linearities in the globally linear mechanical behavior of the human lung

A mathematical model has been developed that describes the mechanical behavior of the human ventilatory system in healthy subjects under plethysmograph test conditions. We have shown that the introduction of the non-linear gas compression law into the mechanical model of the lung, while assuming air resistance to be a constant, leads to erroneous plethysmographic curves. When "volume-resistance" dependence is introduced, however, plethysmographic curves will then form the same shape as those usually recorded in healthy subjects. It is therefore evident that the semblance of linearity does not correspond with the more complex reality of the global behavior of the lung in which some non-linearities may offset each other.