Function testing of a ventilator using an EMG or other bioelectric signal representative of the breathing of the patient to control ventilation is enabled by a simulating device for use with a breathing related device for monitoring and/or controlling a patient's breathing, the simulating device including a signal generator for providing a simulated bioelectric compound signal related to the patient's breathing function, and a contact for outputting the simulated bioelectric compound signal. The simulating device can also be used for training purposes and in the development of new ventilators.