Abstract: The gas mixture is fed in a circulating stream at a volume flow rate of 3-120 l/min, the mixture being cleaned and its temperature and qualitative and quantitative composition regulated. The gas mixture contains oxygen and at least one of the following gases in quantities of up to 95%: helium, argon, neon, krypton, xenon, radon, nitrogen, nitrous oxide, sulfur hexafluoride, or a mixture of these gases. Pharmaceutical preparations can also be introduced into the breathing mixture, and the level of inhaled carbon dioxide can be adjusted with the aid of the exhaled carbon dioxide. The apparatus has a circulation loop comprising connecting pipes, a respirator bag, flow booster, temperature regulator, and at least one absorption unit for absorbing the carbon dioxide, moisture, and harmful trace contamination exhaled by the patient.