The mammalian fetus develops cardiovascular adaptations to cope with situations like hypoxia to protect vital organs. This response is mainly based on redistribution of cardiac output and it is the result of hormonal changes and eliciting of chemoreflexes.

This study describes the changes in cardiac output distribution in response to hypoxia in the chick embryo during development.

We used fertilized eggs from 11 to 17 days of incubation. They were placed in a box which allowed for maintenance of temperature and variation of oxygen concentration. The eggs were opened at the air cell and a chorio-allantoic vein was catheterized. Different labels of 15 μ fluorescent microspheres were injected in 0.2 cc (20.000) during normoxia and after 5 minutes of hypoxia obtained by decreasing the oxygen concentration. After the injection the embryos were sacrificed and the different organs were dissected and digested for microsphere isolation and subsequent fluorescent analysis.

Redistribution in response to hypoxia (% of baseline level), in three groups of increasing incubation time. Table

Table 1
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In conclusion: The chick embryo shows a redistribution of the cardiac output in favor of the vital organs similar to the mammalian fetus during hypoxia. This response seems to develop with increasing incubation time.