Abstract: A portable apparatus for supplying dosages of an oxygen-containing gas to the respiratory tract of a person in synchronization with the inhalation phase of the respiratory cycle of said person comprising: (a) a low voltage step control relay with an inlet port for connecting to a source of oxygen-containing gas having a gas proportion regulator; (b) a low voltage microbridge mass gas flow sensor connected to a gas outlet for connection to the respiratory tract of the person said gas flow sensor sensing the duration of oxygen containing gas flow during each inhalation phase of the respiratory cycle of the person and transmitting corresponding information to a microcontroller; (c) a programmed low voltage microcontroller for receiving electrical signals from the gas flow sensor upon detection by the gas flow sensor of the beginning or termination of inhalation by the person; (d) a portable low voltage electrical power supply for operating the low voltage gas flow sensor, the low voltage microcontroller, and the