Comparison of alveolar and arterial concentrations of 85Kr and 133Xe infused intravenously in man

Abstract

Intravenous infusion of poorly soluble inert tracer gases into 15 supine men with normal or nearly normal lungs produced steady blood and gas concentrations after 10 min. The average ratio of arterial tracer concentration (CaT) in gas equivalent units to end-tidal tracer concentration (CAT) was 1. 39 for 85Kr and 1. 16 for 133Xe, while the ratio of arterial to end-tidal CO, tensions was 1. 04. Calculation of alveolar ventilations based on arterial tracer concentrations yielded values much lower using 85Kr, and somewhat lower using 133Xe, than those obtained from PaCO2. Corresponding calculations using end-tidal tracer concentrations improved the agreement with the alveolar ventilation calculated from PACO2. Theoretical analysis shows that CaT CAT for any tracer increases as the distribution of ventilation-perfusion ratios around the average ratio becomes wider, and that for a given distribution of ventilation-perfusion ratios, CaT/CAT is greatest for the least soluble tracer. Thus, the observed data are appropriate to the solubilities of the gases.