MAPLESON A (MAGILL) BREATHING SYSTEM CONWAY, C.M.
British journal of anaesthesia : BJA,
February 1986, 1986-02, 1986-02-00, Letnik:
58, Številka:
2
Journal Article
A model has been constructed of a subject breathing from a circle system. The subject model is based on the circulation-time model of anaesthetic uptake described by Mapleson. This is a ...multi-compartmental model of body tissues in which gas exchange in each compartment is calculated at each heart beat. The lung compartment of Mapleson’s model has been modified to allow for an unlimited number of gases to be present in the inspired gas mixture. The circle system model assumes total absorption of all expired carbon dioxide and full mixing of all gases within the system. The volume of gas in the system and its composition is calculated for each respiratory cycle. The subject model can be considered as being either attached to a non-rebreathing system, when inspired gas composition is under the control of the operator, or attached to the circle system, when the operator has control of fresh gas flow and composition. The model has been realized as a computer program written in Pascal.
A mathematical model of a subject breathing from a circle system has been used to follow the course of anaesthetic uptake during the simulated administration of 60% nitrous oxide, 2% halothane and 2% ...methoxyflurane, under non-rebreathing conditions and with fresh gas flows to the circle system of between 8 and 0.25 litre min-1. Compared with the non-rebreathing state, the use of a circle system reduced the initial rate of increase of alveolar towards fresh gas anaesthetic concentration, and the rate of increase in body anaesthetic content. The degree of reduction became more marked as fresh gas flow was reduced, and as agents of increasing blood solubility were used. These effects of a circle system were influenced by the volume of the circle system and the composition of gas initially present within the system. When the circle system was in use there were increases in the magnitude of both the concentration effect and the second gas effect which were related to the magnitude of fresh gas flow. The use of a circle system augmented the effects of changes in cardiac output and reduced the effects of changes in ventilation on the alveolar concentrations of the anaesthetic. These influences of a circle system were also dependent on the magnitude of fresh gas flow. The degree of augmentation of the effects of cardiac output decreased with increasing blood solubility of the agent in use, whilst the limitation of the effects of ventilation was greatest with the agent of highest blood solubility. Both under non-rebreathing conditions and with the circle system in use, the effects of cardiac output and ventilation were greater with 2% nitrous oxide than with 60% nitrous oxide, and were also greater when gases were given separately than when administered in combination.
The performance of a model of a subject breathing from a circle system has been examined in relation to nitrogen and helium. The ability of the model to maintain a nitrogen steady-state breathing ...air, the attainment of a new steady-state after perturbation of an existing nitrogen equilibrium, the washout of nitrogen from the subject model on breathing oxygen, and the estimation of functional residual capacity using a rebreathing method with helium as an indicator have been assessed. The predictable and accurate performance of the model in these studies, together with its ability to reproduce the results of a number of previously published studies in man, suggest that the model can be used to predict the behaviour of circle systems when used with inhaled anaesthetic agents.
Product select multiplier Conway, C.M.; Swartzlander, E.E.
Proceedings of 1994 28th Asilomar Conference on Signals, Systems and Computers,
1994, Letnik:
2
Conference Proceeding
The Booth (1951) multiplier represents an efficient and simple way to multiply signed binary numbers. This paper describes an improvement to the standard implementation of a Booth multiplier at any ...radix. More specifically, it compares VHDL implementations of conventional radix 2, 4, 8, 16, and 32 Booth multipliers against multipliers with the product select circuitry added. VHDL models of the multipliers are analyzed and conclusions are drawn. Estimates of area gain and speedup indicate that this multiplier scheme has significant advantages at lower radices and, at higher radices, still maintains a relative advantage over the radix 2 implementation.< >
Expressions have been derived to show the dependence of alveolar oxygen and anaesthetic concentrations on fresh gas flow to a circle system, the composition of fresh gas, ventilation and gas uptake. ...The form of these expressions is influenced by the degree of mixing of fresh and expired gases within the circle system. These expressions assume an equilibrium state within the circle system and the rate at which equilibrium will be approached has been quantified in terms of the time-constants of change of composition of gas within the system. Time-constants approach infinity as fresh gas flow approaches values which just satisfy gas uptake. Whilst simplifying assumptions made in the derivation of the various alveolar gas equations limits their accuracy, the expression can serve as a guide to the likely behaviour of circle systems under any given conditions of use.
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