Viasys T Bird VentilatorViasys T Bird Ventilator Condition: Pre owned he T Bird VS is one of the few portable volume ventilators that is turbine driven instead of by compressor, which results in a lighter chassis which runs with less heat. Operating modes include Control, Assist Control, SIMV, and CPAP (see below for definitions). Refurbished by Bemesonline. com. Features include pressure support ventilation, automatic apnea backup ventilation when apnea is detected,