Alteration of oxygen extraction and blood flow in various organs under acute hypoxia

Abstract

To assess the compensatory mechanisms involved in maintaining aerobic metabolism in various organs during exposure to acute hypoxia, five anesthetized and paralyzed dogs were ventilated with either normoxic (FIO2: 0.21) or hypoxic gas mixture (FIO2: 0.13). Under both conditions, we examined systemic and pulmonary hemodynamic parameters, and took samples of arterial and mixed venous blood as well as venous blood from various organs including the heart, brain splanchic organs (hepatic vein) and kidney. Based on PO2, PCO2 and pH values as measured with electrodes, we calculated O2 and CO2 contents in each blood sample. The values thus obtained were then used to estimate the O2 extraction ratio (ER), gas exchange ratio (R) and difference of base excess between arterial and venous blood (avBE) in the whole body as well as in each organ. In addition, both O2 delivery (DO2) and O2 consumption (VO2) in the whole body were calculated. Although the whole body showed a decrease in DO2 and an increase in ER during hypoxic gas breathing, other parameters including R, avBE and VO2 did not change significantly. Higher ER values were found in the heart and brain than those in the splanchic organs and kidney, the qualitative trend being the same irrespective of FIO2. On the other hand, increase in ER during hypoxic gas breathing was considerably larger in the splanchic organs and kidney than that in the heart and brain. There was no significant difference in R and avBE in any of the organs between normoxic and hypoxic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)