Moderate hypoxia (5% O2) and moderate hypoxia + hypercapnea (5% O2 + 2% CO2) administered to Hamilton-Hamburger stage-17 (60-h) chick embryos produced significant frequencies of brain, eye, and limb malformations, as observed grossly, and cardiovascular malformations, as found in serial sections. Hypoxia + hypercapnea was more lethal (survival rate, 49%) than hypoxia alone (mean survival rate, 65%) but the frequencies of malformations produced by both procedures were in the same range. When moderate hypoxia + hypercapnea was utilized hemorrhages, heart and blood vessel distention, bradycardia, and the disappearance of blood flow patterns occurred. Such changes were previously found to be produced by moderate hypoxia alone. Since cardiovascular malformations were produced under conditions known to affect hemodynamics, it is postulated that these events are related.
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