A pneumatically-powered automatic cycling machine intended to provide automated, alveolar ventilatory support for patients during interhospital or intrahospital transport, and in emergency situations. It is used to assist or control alveolar ventilation using a frequency that is considerably higher than the physiological breathing rate and a tidal volume less than or equal to the anatomic dead space (percussive ventilation). It is typically a compact, lightweight, rugged device powered either by institutional gas supply or on-board compressor systems, with manually-operated user interface. It is used in conjunction with an endotracheal (ET) tube, tracheostomy cannula, or mask.