Systemic hemodynamic phenomenon accounting for advantageous oxygen supply to, and asymmetry of, the brain.

In experiments with anesthetized rabbits we found that blood in various branches of the aortic arch has unequal content of red cells. The blood flowing via the carotid arteries to the head contained significantly greater red cell concentration and hematocrit than that flowing via the abdominal aorta to the hind legs. Furthermore, the blood flowing via the right brachial artery to the corresponding foreleg showed a significantly higher red cell concentration and hematocrit than the blood carried via the left brachial artery to the respective foreleg. This phenomenon of unequal distribution of red cells from the aorta to various arterial branches results in that the brain is supplied with blood containing a higher number of oxygen carriers, i.e. red cells, than caudal parts of the body. On the other hand, the higher red cell content of the blood in the right foreleg, as compared to the left one, might in a certain way contribute to asymmetry of the forelegs, and thence of the brain, in the evolutionary process of vertebrates. A possible mechanism of the described hemodynamic phenomenon is discussed.