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A mathematical model of the human respiratory system is being developed in order to simulate manned diving operations using various types of breathing equipment. A simulation study is presented of a human diving to a depth of 50 m, using a semi-closed re-breathing system with two different oxygen flow settings. A gas supply with 32.5 per cent oxygen concentration results in a safe dive whereas a 60 per cent setting indicates a dangerous diving condition. Typical respiratory model input data are illustrated for the lung, together with dimensional details for the re-breathing counterlung. The simulation results show variations in alveolar and pleural pressures, gas concentrations and partial pressures in the equipment and in the human respiratory system.

This paper addresses the operational performance of a fixed-displacement pump controlled by an unloading valve to provide a fluctuating flow source. This approach should be cheaper and more efficient than the use of a variable-displacement unit. Computer simulation is used to predict the performance of the system and act as a guide in optimizing the control system. An experimental rig has been constructed to examine the practicalities of these ideas. Some experimental results are presented. Future work will be concerned with noise and efficiency studies.

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