In imaging of the chest or abdomen, motion artifact is an unavoidable problem. In the radiation treatment, motion of organs is caused by the respiratory activity. This creates the unavoidable problem for implementation of the safe and effective cancer treatment with preserving the healthy tissue. Computation of the estimated respiratory signal is necessary to irradiate corresponding dose during the inspiration or expiration. This study is focused on the review of various mathematical models for the respiratory modelling, which provides the basis for the most clinically applied methods of computing the estimated respiratory signals. In this article, we compared the most popular methods for modeling the estimated respiratory wave, the results of our modeling are presented in the resulting table (including the correlation coefficient R).