Simulating respiratory loads and tuning of closed-circuit underwater breathing apparatus.

An experimental apparatus for simulating respiratory loads in closed-circuit underwater breathing systems comprises a partly submerged vertical tube having a dual path exit on the submerged end of the tube. One path is controlled by a valve that alters the inertance of the system, changes the natural frequency, and provides the tuning. The vertical tube provides elastic loading to simulate a counterlung or breathing bag in an underwater breathing apparatus (UBA). The experimental apparatus was connected to a breathing machine controlled by a signal generator to simulate a diver's breathing. The benefits of reactance tuning of this apparatus are demonstrated. A mathematical model describes both the simulator and UBA. The simulator can be used with human subjects to study respiratory response to changes in impedance.