Are you sure they are substantially immunocompromised? they're opening and closing their mouths and breathing through their noses on a regular basis while exposed to room air. There is no bacteria filtration like there would be with a properly configured positive pressure ventilator's circuit. The mucous membranes in the airway and nasal passages actually provide a significant amount of filtration themselves, and some circuit configurations are non-invasive which enables these natural filters to function.

There is potential for barotrauma in improperly configured devices, especially with volume-controlled ventilation, but it's possible to configure the device to ventilate safely, otherwise we wouldn't use them. Modern devices do have safety features like high pressure cutoffs and direct pressure controls which can prevent barotrauma. Some of these have to be configured correctly by the clinician for each patient.

Regarding the link to positive pressure HVAC, I'm not sure what that has to do with medical ventilation. HVAC provides a constant flow into a room, but medical ventilation cycles to an inspiratory pressure or inspiratory tidal volume repeatedly either on a patient trigger or on a set timing schedule.

I'm still really curious if there are any Respiratory Therapists or Physicians who can speak to this?