Abstract
Summary
1) The chromium 51 red cell tagged dilution method is valid for measuring red cell mass in the presence of hypovolemic shock as no difference was found in red cell mass measured in tourniquet shocked animals when 15, 30 and 60 minutes were allowed for mixing of tagged cells, or between these values and those of control animals. 2) The response of blood volume compartments and plasma proteins to acute withdrawal of 50% of circulating blood volume has been determined at 2, 4, and 8 hours after hemorrhage. Plasma volume is restored to 100% of the control within 4 hours and is 108% at 8 hours post-hemorrhage. Despite the elevated plasma volume, total blood volume remains well below the control, due to persistent red cell mass deficit. Changes in hematocrit inversely reflect plasma volume changes. Plasma protein concentration is restored to 87% of control by 8 hours. Protein replacement seems to occur in 2 stages. An immediate response is evident within the first 2 hours and a delayed response begins at 4 hours after blood withdrawal and extends over a 48 hour period.
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