My source, I know an engineer that works on them. First of all they are medical devices, some people can't safely sleep without them, and those people might be

My source, I know an engineer that works on them. First of all they are medical devices, some people can't safely sleep without them, and those people might be unconscious, in surgery, and/or heavily medicated. So that means audits, special testing requirements, etc. Next medical requirements are quite varied, some are just "assist", some are constant velocity but variable pressure, others are constant pressure and variable velocity, some control breaths per minute, and other setting control total volume. Various health problems, surgery recovery, etc have different requirements. There can be temperature and humidity requirements as well. So you need a pretty healthy fan to handle all the static and dynamic pressure requirements that are sometimes constant RPM or variable. Of course all the above need accurate sensors, failures could hurt someone's lungs. Good sensors require laminar flows. Laminar flows get harder with a wide range of pressures, speeds, and volumes. So it ends up quite a bit more than "a fan that blows a low pressure stream".