Modeling of forced expired volume signals with multiexponential functions

Forced expiration is a widely applied clinical test in respiratory medicine. Some patients with respiratory complaints have difficulties completing the manoeuvre. The suitability of multi-exponential models for characterizing the expired volume as a function of time was investigated. In 32 of 33 cases, the sum of two exponentials resulted in a satisfactory description of the volume time series, one time series was adequately described by a monoexponential function. Using mono- and biexponential models, forced vital capacity FVC was predicted from the first 4 s of the 33 time series. Monoexponential fits systematically overestimated FVC whereas biexponential fits provided unbiased estimations of FVC. Including the fitting procedure into the analysis of spirograms, forced expiration manoeuvres could be shortened by several seconds