Elastic behavior of the lungs in healthy children determined by means of an exponential function

In order to evaluate the elastic properties of the lungs in children, a new exponential sigmoid curve fitting model was developed with the function V l = Vm + ( V m /1 + b · e −K · Pst) , where V l is the lung volume, Pst the static recoil presure, V m and Vm the upper and the lower asymptotes (limits of lung volume) and K and b are specific constants. Pressure-volune (PV) data obtained from tidal breathing cycles at different inflation and deflation levels from function residual capacity (FRC) up to approximately 90% total lung capacity (TLC) in 16 healthy have been evaluated by this model. K in relation to age, calculated by the least square nonlinear regression analysis decreased during childhood, whereas 1n b increased. It seems that K (a volume-independent index of compliance and laveolar distensibility) is influenced by the increasing numbe of elastic fiber bundles, changes in the surface/volume ration and finally by changes in the composition of the surfactant. It can be seen that this model is not only restricted to higher lung volumes, the lower limb of the S-shaped curve is also represented.