Disclosed is apparatus for breathing with hypoxic gaseous mixtures. The apparatus comprises of: a supporting frame； a respiratory reservoir equipped with an inspiration valve, a first sensor of oxygen content and an absorber of CO2 and H2O； a controllable compressor connected via puffing valve to the respiratory reservoir； and a chamber for sampling and accumulation of aliquots of expired gaseous mixtures equipped with a second sensor of oxygen content, controllable adjusting valve and controllable ejector. The apparatus also includes means for attachment to a user, such as a mask； an inspiration line comprising controllable centre valve and first inspiratory rate flowmeter； a tee fitting； main expiration line that is equipped with first air blower and connects said attachment with said reservoir； additional expiration line that is equipped with second flowmeter measuring volume of sampling aliquots and second air blower and connects said attachment with said chamber； and a supplementary sensor complex and program control unit. This apparatus provides for the estimation of minute oxygen consumption and, accordingly, efficiency of regulation of breathing with hypoxic gaseous mixtures.
