Theoretical Analysis of Factors Influencing Recovery of Ventilation Distributions from Inert Gas Washout Data
For the quantitative analysis of intraregional ventilation inhomogeneities, one classically applies the inert gas washout method [7,24] in which an inert gas of negligible solubility in blood and tissue is washed into the lungs. After washin is complete, the inspiratory inert gas fraction is set to a smaller value and the time course of the mixed endexpiratory inert gas fraction during the subsequent inert gas washout is recorded. The determinants of this time course are: The endexpiratory alveolar volume at the instant of change in inspiratory inert gas fraction, the anatomical dead space, the gas exchange ratio, the respiratory frequency, the in- and expiratory tidal volumes, and the inhomogeneous distribution of the tidal volume among the alveolar space. For determining this distribution from the time course of mixed endexpiratory inert gas fractions, several methods have been described which may be grouped into two classes: The depeeling methods and mathematically more advanced methods for assessing continuous distributions.
KeywordsTidal Volume Dead Space Conducting Airway Alveolar Volume Ventilation Distribution
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