A medical respirator having switching means to control flow of patient gas from a pressure source through a control means into a variable volume during an expiration period of the respirator and from the variable volume to the patient through restrictive means during an inspiration period. The gas container is divided into two volumes by a movable member, the first volume being variable and the ratio of volumes varying with the position of the movable member. Gas for the patient is expelled from the first volume during part of the inspiration period by decrease of the capacity of the first volume as a result of the movement of the movable member caused by the pressure of the patient gas in the second volume.
