An apparatus for controlling pressure of a medical gas during treatment of a patient includes is a balloon (1) that through a catheter (2) is introducable into an arterial system of the patient, and a damping bag (20), of greater volume than that of the balloon (1), adapted to be loaded with medical gas at a compliance pressure (Pc) and placed in direct fluid communication with the balloon (1). The damping bag (20) is kept in direct fluid communication with the balloon (1) for the entire duration of the treatment of the patient. The apparatus further includes fine adjusting means (30) for acting on the damping container in such a way that the compliance pressure (Pc) is maintained between the systolic pressure and the diastolic pressure of the patient when the balloon is introduced into the arterial system of the patient and during the treatment of the patient.
