A breathing apparatus provides high frequency oscillatory ventilation [HFO] to a patient by supplying breathing gas to the patient according to an oscillating pressure profile oscillating between a positive pressure and a negative pressure. The breathing apparatus has a patient circuit including an inspiratory line for conveying breathing gas to the patient and an expiratory line for conveying gas away from the patient, and an inspiration valve for regulating a flow of pressurised breathing gas into the inspiration line, and a control computer that controls the inspiration valve. The control computer operates to cause the oscillating pressure profile by controlling the inspiration valve to oscillate between a top flow position in which the flow of breathing gas through the inspiration valve assumes a top flow value, and a minimum flow position in which the flow through the inspiration valve assumes a minimum flow value.
