Steady state measurement of regional ventilation to perfusion ratios in normal man.

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Abstract
A method is described whereby the ratio of alveolar ventilation to perfusion (Va/Q) is individual lung zones may be measured during normal steady state conditions. Regional count rates were recorded during a 5-min. period of constant intravenous infusion of Xenonl33 dissolved in saline, and during a similar period of Xenonl33 rebreathing into a closed circuit. Theoretical considerations and experimental measurements have indicated that, for practical purposes a steady-state is achieved within these time limits in normal subjects. Similar patterns of regional Va/Q were recorded during quiet tidal breathing in 4 normal subjects seated upright. It was possible to correct these data to allow for the influence of reinspired dead space gas, and to compute regional Ve/Q, where Ve represented total gas exchanging ventilation. Regional respiratory gas concentrations were calculated from such Ve/Q measurements and appeared to show less regional variation than previously reported. Limitations of the technique are discussed.