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PubMed · 6802916

A flexible system for closed-loop ventilator development.

W I Marsh·W D Smith
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Abstract

The feasibility of using a microcomputer to regulate the delivery of artificial ventilation was investigated experimentally. To carry out this study, a sampled-data proportional, integral, derivative feedback controller was implemented on a commercial microcomputer and interfaced with a digital/analogue model of a prototype ventilator and two-compartment patient. The microcomputer sampled end-tidal CO2 and calculated a new frequency of ventilation from the difference of end-tidal CO2 and a desired set point value. Use of a microcomputer programmable in BASIC allowed easy manipulation of feedback structure. With the proper choice of feedback constants, the microcomputer was able to maintain end-tidal CO2 at a desired set point.

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Carbon DioxideComputersFeedbackHumansMicrocomputersVentilators, MechanicalJournal Article

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W I Marsh, W D Smith. 1982. A flexible system for closed-loop ventilator development.. https://doi.org/10.1007/bf00994120

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It is often argued that substantially more carbon dioxide and water were degassed from the martian interior than can be found at present in the atmosphere, polar caps and regolith. Calculations have shown that atmospheric escape cannot account for all of the missing volatiles. Suggestions that carbon dioxide is stored as marine or lacustrine deposits, are challenged by Earth-based and spacecraft remote-sensing data. Moreover, recent modelling of the martian atmosphere suggests that rainfall or open bodies of water are in any case unlikely to have persisted for extended periods of time. Hydrothermal carbonates therefore provide a possible solution to this dilemma. Using an accessible terrestrial system (Iceland) as a guide to the underlying processes, and a host rock composition inferred from the least-altered martian meteorite, we present a geochemical model for the formation of carbonates in possible martian hydrothermal systems. Our results suggest that an extensive reservoir of carbonate minerals--equivalent to an atmospheric pressure of carbon dioxide of at least one bar--could have been sequestered beneath the surface by widespread hydrothermal activity in the martian past.

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