A A l la ab bo or ra at to or ry y c co om mp pa ar ri is so on n o of f f fo ou ur r p po os si it ti iv ve e p pr re es ss su ur re e v ve en nt ti il la at to or rs s u us se ed d i in n t th he e h ho om me e I.E. Smith, J.M. Shneerson These results show that distinct brands of ventilator respond to changes in the patient and patient circuit in different ways, which are not always predictable from a simple description of their operating principles. This should be borne in mind when choosing a positive pressure ventilator for noninvasive ventilation.