Mechanical damage of red blood cells by rotary blood pumps: selective destruction of aged red blood cells and subhemolytic trauma.

In this study, mean cell volume (MCV), mean cell hemoglobin concentration (MCHC), and mean cell hemoglobin (MCH) were measured to quantify RBC damage by rotary blood pumps. Six-hour hemolysis tests were conducted with a Bio-pump BPX-80, a Sarns 15200 roller pump, and a prototype mag-lev centrifugal pump (MedTech Heart) using fresh porcine blood circulated at 5 L/min against a 100 mm Hg head pressure. The temperature of the test and noncirculated control blood was maintained at 37 degrees C. The normalized index of hemolysis (NIH) of each pump was determined by measuring the plasma-free hemoglobin level. The MCV was measured with a Coulter counter, and MCHC was derived from total hemoglobin and hematocrit. MCH was derived from MCV and MCHC. A multivariance statistical analysis (ANOVA) revealed statistically significant differences (n = 15, P < 0.05) in MCV, MCHC, and MCH between the blood sheared by the rotary blood pumps and the nonsheared control blood. Normalized to the control blood, the Bio-pump BPX-80 showed an MCV of 1.04 +/- 0.03, an MCHC of 0.95 +/- 0.04, and an MCH of 0.98 +/- 0.02; the mag-lev MedTech Heart had an MCV of 1.02 +/- 0.02, an MCHC of 0.97 +/- 0.02, and an MCH of 0.99 +/- 0.01; and the roller pump exhibited an MCV of 1.03 +/- 0.03, an MCHC of 0.96 +/- 0.03, and an MCH of 0.99 +/- 0.01. Per 0.01 increase in NIH, the BPX-80 showed a normalized MCV change of +10.1% and a normalized MCHC change of -14.0%; the MedTech Heart demonstrated a +6.9% MCV and -9.5% MCHC change; and the roller pump had a +0.5% MCV and -0.6% MCHC change. Due to shear in the pump circuits, the RBC increased while the MCHC decreased. The likely mechanism is that older RBCs with smaller size and higher hemoglobin concentration were destroyed fast by the shear, leaving younger RBCs with larger size and lower hemoglobin concentration. Subhemolytic trauma caused the intracellular hemoglobin to decrease due to gradual hemoglobin leakage through the micropores formed in the thinned membrane. In conclusion, the rate of change in MCV and MCHC with respect to NIH change provides useful information relating to selective destruction of RBCs, while the MCH level reflects subhemolytic damage.