An entrainment port regulates the flow of gas and/or medicine into an inspiratory limb of a high frequency oscillatory ventilator (H0FOV) to improve the oxygen content of the air entering a patient. The entrainment port is connected to an oxygen source and uses entrained oxygen therefrom to enter the inspiratory limb. Medication and/or admixtures of medication, gas and/or humidification can be introduced through the entrainment port. The flow of entrained oxygen and the mean airway pressure is regulated by a plug valve. A check valve is calibrated to a pre-defined cracking pressure to open and allow the entrained oxygen into the inspiratory limb when negative pressure is asserted in the HFOV circuit by operation of the expiratory cycle of the HFOV.
