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Acute diffuse alveolar hypoxia which is similar to the early stage of acute respiratory failure was induced using 15% and 10% oxygen in balance nitrogen in 7 mongrel dogs. The changes of cardiopulmonary hemodynamics and oxygenation were evaluated and compared to the value obtained in 21% oxygen in balance nitrogen as follows: 1) The concentration of oxygen which increase pulmonary arterial pressure(PAP) by 25% and 50%(ED25 and ED50) during hypoxic challenges were 4.47% and 12.74%, respectively. 2) Cardiac output(CO) and heart rate(HR) were only apparently increased in 10% oxygen by 18.8% and 6.0% respectively. But the most remarkable changes were noticed in pulmonary arterial pressures which were increased by 11.9% in 15% oxygen and 33.0% in 10% oxygen. Pulmonary vascular resistance(PVR) tended to increase by 47.1% and 68.0% in 15% and 10% oxygen. Both PVR and pulmonary perfusion pressure(PPP) were increased proportionally to the increases in PAP. 3) Not only arterial and mixed venous oxygen tension(PaO2 and PvO2) were markedly decreased by 36.1% and 14.7% in 15% oxygen and by 57.4% and 41.3% in 10% oxygen. but also arterial and mixed venous oxygen saturation(SaP2 and SvO2) were significantly decreased, which were 91% and 71% in 15% oxygen, and 72% and 48% in 10% oxygen, but 97% and 80% in the control group, respectively. 4) Oxygen consumption(VO2) was decreased proportionally to the decrease in oxygen flux and inversely proportional to PvO2. Oxygen extraction ration(O2ER) tended to increase by increasing the degree of hypoxic stimull and proportional to the increase in Vo2. 5) Depping the hypoxia resulted in proportional increase in pulmonary shunt ration(Qs/Qt) from 1.9% in control group to 22.7% and 51.9% in 15% and 10% oxygen, respectively. In conclusion, acute diffuse alveolar hypoxia in dogs showed increases in PAP, PVR and Qs/Qt, and decreases in PaO2, SaO2, PvO2 and SvO2, which resemble the early findings in acute respiratory failure. So it should be considered that reversal of the above mentioned parameters might be the therapeutic aim for acute respiratory failure.
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