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Intrapulmonary gas mixing studied by the closed-circuit helium technique 1 Theoretical considerations and model lung experiments

Intrapulmonary gas mixing studied by the closed-circuit helium technique 1 Theoretical considerations and model lung experiments

Australasian Ann Med: 179-186

The closed-circuit helium method of assessing regional ventilatory inequality (uneven mixing) in the lungs has been further explored by means of a model lung containing one or two chambers. A single, uniformly-ventilated chamber produces a linear fall of helium concentration when plotted on a semi-logarithmic scale, and such a result may be used as a criterion of uniform ventilation. Katharometer lag is constant throughout a mixing experiment, and the rate of fall is independent of the rate of breathing (when, the abscissa is expressed as "number of breaths"). These findings help overcome technical difficulties of analysis and to eliminate approximate "scale-up" factors. When the model lung consists of two unequally ventilated chambers, a semi-logarithmic plot of the mixing process produces a curved line. A new method of analysing this curve produces estimates of the well- and poorly-ventilated spaces which are more accurate than those obtained with previous methods of analysis of closed-circuit data. It is unlikely that more accurate information would be obtained from open circuit data. A new index of "ventilatory defect" was developed.

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Accession: 024892519

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PMID: 13584263

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