This invention relates to a method for controlling a bi-level apparatus. The method includes repeatedly measuring an airflow, choosing an expiration threshold value and choosing an inspiration threshold value. Switching to an inspiration mode takes place if the airflow is greater than the expiration threshold value in a comparison with the expiration threshold value. A switching back to the expiration mode takes place if the airflow is smaller than the inspiration threshold value in a comparison with the inspiration threshold value. Moreover, the invention relates to a bi-level apparatus for performing the method.