An oscillatory medical ventilator comprises a ventilator duct (1) having a patient end (21) for attachment to a patient tube (22). A gas supply jet (5) is mounted in a bearing block (3) for rotation by an electric motor (10). The jet has a gas supply passage (16) to which driving or respiratory gas is supplied continuously during rotation of the jet by a gas supply chamber (15) encircling a shaft (8) of the jet and communicating with passage (16) through radially extending openings in the wall of the shaft. A cyclically varying pressure at the patient end of the ventilator duct is thus produced upon rotation of the jet to cause alternating inflation and deflation of the lungs with respiratory gas which is supplied either by the jet or by an independent source connected to the patient tube.
