Background: Externally applied pneumatic pressure can be helpful for rapid transfusion of red blood cells (RBCs). However, a potential disadvantage of external pressure is decreased deformability caused by increased shear stress. We hypothesized that more increased shear stress due to higher external applied pressure and aged blood may result in more decreased RBC deformability. Therefore, the primary endpoint of this study was to measure the deformability of RBC during various external pressure. The secondary endpoint was to find the effect of storage date.
Materials and methods: Two venous blood samples were obtained from two healthy human volunteers. Two blood sample was tested on 5th day after sampling, the other sample was tested on 35th days after sampling. Each blood unit was divided into four groups, then applied four different type of pressure; 150 mmHg, 200 mmHg, 250 mmHg, 300 mmHg. To measure deformability of RBC, microfluidic ektacytometer was used.
Results: The mean value of EI of fresh and aged blood at each infused time under external pneumatic pressure is summarized in table 1. Two-way ANOVA indicated there was no significant difference in EI according to pressured time under all type of external pneumatic pressure (fresh blood; pressure P = 0.900, time P = 0.934, aged blood; pressure P = 0.814, time P = 0.096 ). However, EI was significantly decreased when tested with aged blood. (P < 0.001) 
Conclusions: The deformability of fresh RBC was not influenced by external pneumatic pressure up to 300 mmHg. However, storage date of blood may significantly affect on deformability.

Determining the highest external pressure that permits rapid transfusion without hemolysis as observed using a scanning electron microscope and alteration in deformability