An apparatus for feeding gas mixtures to a compressor comprising a tubular mixing pipe connected with the compressor intake, first and second gas intake devices injecting into the mixing pipe gas received from a Helium source and an Oxygen source respectively, two sensors measuring the Oxygen percentage of the gas mixture, a first servo-controlled throttling valve interposed between the first gas intake device and the Helium source, a second servo-controlled throttling valve interposed between the second gas intake device and the Oxygen source, and a control unit configured to manage the throttling valves depending on the Oxygen percentages of the gas mixture measured by the sensors. The apparatus includes first and second auxiliary pressure regulators, electrically connected with the control unit, interposed respectively between the first servo-controlled valve and a manual regulator of the Helium source and between the second servo-controlled valve and a manual regulator of the Oxygen source.