Respiratory Fluctuations of Oxygen Pressure in Alveolar Gas and Blood of the Dog

Moment-to-moment variation of effective alveolar Poi (Рлеоз) during the respiratory cycle was calculated based on a two-alveolar lung model in dogs anesthetized and pump-ventilated under various conditions induced by continuous infusion of sympathomimetics. Under fixed ventilation the amplitude of respiratory fluctuation of ΡΑ6ΟΙ(Δ Рлеог) increased with огСД Рлеог = 0.774· Voi + 1.862; p<0.001) while Δ Рлеог did not show any correlation with VD/VT or with the fraction of effective alveoli. Ideal alveolar P02 (РАІ02) in the same situation was near the peak of fluctuating Рлеоі, thus higher than mean effective alveolar P02 (Рлеоі) by about 4 to 5 mm Hg. This difference of Рліоз and Рлеог might be attributed to the difference in respiratory pattern, i.e., constant one-way flow as against periodic ventilation. Alveolar oxygen tension Sympathomimetics Oxygen fluctuations (respiratory) Dog Artificial ventilation Respiratory fluctuations of Pcoi and P02 have been calculated by several authors (for CO2: DuBois et ai, 1952; Chilton and Stacy, 1952; Yamamoto, 1960; Lamb et ai, 1965; for O2: Chilton et al., 1954; for both gases: Nye, 1970; Gumming and Lin, 1971 ; Suwa and Bendixen, 1972). Lamb et al. (1965) combined this sort of calculation with experiments and demonstrated changes of the amplitude of the alveolar Pco2 variations during exercise. Previous calculations of the alveolar P02 oscillations were based on assumptions of ventilatory pattern and alveolar ventilation different from those presumed for the concept of ideal alveolar P02 by Riley and Cournand (1949) and also from real volume changes. Recently Nye (1970) and Knelson et al. (1970) showed the importance of respiratory pattern for the computed mean effective alveolar P02 by theoretical analysis and by experimental studies, respectively. It may be pre­ sumed that ideal alveolar P02 based on constant flow ventilation should not be the same as mean effective alveolar P02 calculated from periodic ventilation. In this paper we present data on the comparison between ideal and mean effective alveolar P02 as well as variations of the amplitude of effective alveolar P02 in various metabolic, circulatory, and respiratory conditions induced by infusion of sympathomimetics.