CPAP on Shabbos

My wife needs to use a CPAP machine to assist her breathing during sleep. The model that the doctors had her purchase – a Respironics (Philips) REMstar automatic CPAP with C-flex – is microprocessor controlled to automatically adust the level of airflow support and has a small LCD display to show status and to change system options. When powered on, the unit executes a system initialisation routine, but does not start the airflow. To begin the airflow one must either push the start button (and the airflow will begiin immediately) or one can just start breathing through the mask (and the airflow will begin after some number of breath cycles). To stop the airflow, one can again either push the start button (and the airflow immediately stops) or can remove the mask (and the airflow will stop after a short time).
1. To start the airflow – is it better to push the start button (with the back of the hand or knuckle) or to start breathing into the mask so the unit will start on its own?

2. To stop the airflow – is it better to just remove the mask so the unit will stop on its own ot must a 'shabbos' clock be used to cut off the power to the unit?

 Thank you for your time and consideration