Mechanical fragility of erythrocytes in normals and in patients with heart valve prostheses

Biological and environmental factors affecting ultrasound-induced hemolysis in vitro: medium tonicity

Whole human anticoagulated blood in vitro underwent controlled plasma replacement with either isotonic (0.9%) or hypotonic (0.5%) saline to 1. restore the blood to its original volume (which resulted in different hematocrits) or 2. bring the blood to a singular hematocrit (40%). The hypotonic cell MCVs were, on average, considerably larger than their isotonic counterpart by a ratio of 1.4:1. The blood samples were then subjected to two tests, one of mechanical fragility, the other to ultrasound (US)-induced hemolysis. The US exposure metrics were: 1.0-MHz center frequency, 200-micros pulse duration, 20-ms interpulse interval, exposure durations of 10 to 30 s in the presence of Albunex, as a control on blood gas nucleation, and exposure vessel rotation at 200 rpm. In all instances, the hypotonic blood displayed higher levels of hemolysis than the corresponding isotonic treatment. The highest ratio of US-induced hemolysis for the hypotonic:isotonic regimens was 2.2. In some instances, the ratio was somewhat less but appeared to be related to differences in whole blood viscosities among the regimens or other factors. The data supported the a priori hypothesis that hypotonicity will result in an increased tension on the cell membrane and render it more susceptible to shear-induced hemolysis, including exposure to US under conditions known to foster the occurrence of inertial cavitation. There was no temperature increase during the insonations of the blood.

Intravascular hemolysis in the late course of aortic valve

The degree of intravascular hemolysis was evaluated in 315 patients in the late course of aortic valve replacement. Starr-Edwards aortic ball valves of series 2300 caused significantly more hemolysis than did those of series 1200, as estimated from the serum lactate dehydrogenase levels. Smaller valves of series 2300 caused a higher degree of hemolysis than did the larger ones. Aortic disc valves induced a more moderate red cell destruction than did the ball valves, the Lillehei-Kaster significantly more than the Bjørk-Shiley prostheses. Crushing of red cells is thought to be a more important cause of hemolysis than shearing forces in turbulent blood. Hemolytic anemia represented a problem only in some patients with Starr-Edwards valve type 2300, although iron substitution was necessary also in some with other prostheses, since the hemoglobin-binding capacity of haptoglobin was exceeded in several patients. Valvular or paravalvular leakage was associated with stronger hemolysis in some patients, and should be suspected whenever the rate of red cell destruction increases. Longstanding intravascular hemolysis did not seriously affect renal function.