The objective of the thesis was to evaluate the possibility to calculate the unloading distribution between a ventilator and a patient using a new mathematical modelling of the breathing patterns. The modelling used today is considered to lack sufficient precision for clinical use, and is a somewhat simplified model. To evaluate the possibility of a new model, a volunteer test was carried out - recording data such as Edi, pressure, volume and flow. Using this data, and by using a more complex model, tidal volume was estimated and compared to the measured data. The results did not imply any improvement compared to the simpler model regarding the accuracy and the variability. However, more work should be done in this area, as time deficiency prevented further analysis.