The effect of microaggregates in stored blood on canine pulmonary vascular resistance

Microaggregates have been implicated as a contributory cause of respiratory distress syndrome. Blood flow and resistance changes are compared between the right and left lungs following the selective administration of stored autologous heparinized blood into the left pulmonary artery. Eight dogs were bled 1,160 +/- 47 c.c. over 3 days. Following storage for 5 days the volume, number and size of microaggregates were measured by multichannel particle size analyzer and compared to 14-day-old human blood. Distribution of blood flow and resistance were calculated from data derived from injection of radioactively tagged microspheres into the right atrium and determination of cardiac output and pulmonary artery and wedge pressures. These measurements were made during a control period, following resuscitation from a 2 hour hemorrhagic shock period with the stored blood and 3 hours after resuscitation. Despite the administration of stored blood with massive amounts of microaggregates into the left pulmonary artery, the distribution of blood flow immediately and 3 hours following resuscitation was the same as in the control period. The pulmonary vascular resistance increased across both lungs but the increase was the same on the left as the right. These data suggest that microaggregates may not be important in the development of the respiratory distress syndrome.