Studies on Hemorrhagic Hypotension in Domestic Fowl

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Abstract
White Leghorn hens were Wed at a constant rate to a mean arterial pressure of 50 mm Hg and maintained at this pressure by further hemorrhage. Average duration of hypotension tolerated by mature hens anesthetized with paraldehyde was about 5 h, and the bleeding volume during this interval was almost three-quarters of the initial measured blood volume. Younger chickens and those anesthetized with barbiturate responded similarly, but died somewhat earlier, apparently because of respiratory difficulties. The response to hemorrhage was characterized by a large, rapid fall in mean arterial pressure after a relatively small loss of blood, and by a large influx of protein-poor fluid into the vascular space. The latter was at least twice as rapid as and four times the volume of maximal extravascular fluid mobilization by dogs. In contrast to dogs, no phase of decompensation and hemoconcentration was demonstrable in these experiments, and may not occur in chickens. This was associated with absence of "irreversibility to transfusion"; reinfusion of the shed blood even at the time of terminal circulatory collapse produced a stable cardiovascular state. Comparison of the present observations on chickens with the published results of similar experiments on dogs indicates that homeostatic mechanisms operate predominantly to maintain the blood volume in the former and the blood pressure in the latter.

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