A pneumatically-powered automatic cycling machine designed for static use and intended 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. The device will typically function independently or may be used in conjunction with an intensive care ventilator to superimpose its high frequency percussive ventilation on top of a normal ventilation frequency. It is typically used in critical care situations on patients with respiratory disease requiring ventilatory assistance, typically through an artificial airway [e.g., endotracheal (ET) tube or tracheostomy].