Effect of polycythemia on gastrointestinal blood flow and oxygenation in piglets.

Gastrointestinal blood flow and oxygenation were measured before and after the induction of polycythemia in newborn piglets. Sixty minutes after exchange transfusion with age-matched packed red blood cells, hematocrit and in vitro whole blood viscosity increased, while 51Cr-measured blood volume did not change. Cardiac output and total gastrointestinal blood flow (the sum of stomach, jejunum, ileum, and colon blood flows) decreased a similar degree after exchange transfusion, although the reduction in total gastrointestinal blood flow was not uniform in all regions of the gastrointestinal tract. Specifically, blood flow to the stomach and mucosa-submucosa layer of the small bowel decreased, whereas that to the colon and muscularis-serosa layer of the small bowel remained unchanged. Gastrointestinal O2 delivery increased after exchange transfusion because of the increase in arterial O2 content consequent to polycythemia. The arteriovenous O2 content difference remained unchanged following exchange transfusion, and gastrointestinal O2 consumption thus decreased 49 +/- 2%. After a test meal, postprandial values for gastrointestinal blood flow and oxygenation in polycythemic piglets increased to levels similar to postprandial values reported previously in normal newborn piglets.