Submaximal blood flow and blood viscosity in newborn infants.

In newborn infants with varying hematocrit values the submaximal blood flow has been studied by the use of strain gauge plethysmography under standardized conditions. Submaximal flow was defined as the flow obtained after 4 minutes of suprasystolic occlusion. With increasing hematocrit there was a decreasing maximal flow. Capillary filtration coefficient seemed to decrease with increasing hematocrit. The relation between circulatory failure in newborns due to abnormally high hematocrit and low capacity to increase blood flow upon demand has been discussed.