A digital system for generating dynamic sinusoidal gas concentration signals.

A computer-controlled gas-mixing system is presented. It is capable of mixing four gases, the concentration of three of which will follow a path to be determined by the user. For our purposes the output O2 fraction is maintained constant and the levels of Ar and N2O vary sinusoidally and independently, with periods between 0.25 and 30 min. A fourth gas, N2 is necessary to make the sum of the individual fractions 100%. The system uses banks of between one and four solenoid valves each linked via a sonic choke to a common mixing chamber. A regime of pulse frequency modulation is employed. All calculations and timing of valve switching are performed by a dedicated microcomputer built for the purpose. The device has been used to provide respiratory gas forcing functions for a program of research in respiratory monitoring.