1. A catheter for ventilating an expiratory assisted patient, comprising an elongated member with a ventilation duct extending therethrough for alternately supplying oxygen or an oxygen-containing gas to the patient's respiratory tract and expelling exhaled gas, the ventilation duct having an open end and a connecting end for connection to feed system and has an inner diameter of not more than 4.5 mm, preferably not more than 3 mm and a length of at least 200 mm. 2. The catheter according to claim 1, wherein the elongated member has a maximum outer diameter of about 6 mm, preferably from about 1.5 to 4.5 mm. The catheter according to claim 1 or 2, wherein the delivery system is a gas flow reversing unit. The catheter according to claim 1, comprising a pressure measuring means, preferably a pressure sensor, located outside the ventilation duct for measuring pressure near the open end of the ventilation duct. The catheter according to claim 4, in which the elongated element comprises a pressure measuring channel located inside it, having one open measuring end located next to the open end of the ventilation channel, and a second closed end, the pressure measuring channel containing liquid and gas parts, and a gas part has the ability to contract as a result of moving the liquid part, and the pressure measuring channel contains a scale for measuring pressure inside this channel. 6. The catheter according to claim 4, wherein the pressure measuring means comprises at least one electronic pressure sensor with signal lines integrated inside the elongated catheter element. The catheter according to claim 4 or 6, in1. Катетер для вентиляции пациента с содействием выдоху, содержащий удлиненный элемент с проходящим внутри него вентиляционным каналом для попеременно выполняемых подачи кислорода или кислородсодержащего газа в дыхательные пути пациента и удаления из них выдыхаемого газа, причем вентиляционный канал имеет открытый конец и присоединительный конец для соединения с с
