Development of viscoelasticity in heated hemoglobin solutions

Several previous studies have shown that exposure of RBC to temperatures in the range 47 to 48.8 degrees C causes an irreversible alteration of RBC rheological properties; membrane elasticity and viscosity are both increased and greater pressure is required for RBC entry into pipettes. While it has been tacitly assumed that these rheologic alterations are membrane specific, no data on heat-treated hemoglobin (Hb) solutions appear to exist. The present study was thus designed to evaluate the effects of heat-treatment (48.8 +/- 0.1 degrees C, 3 to 20 min) on the viscoelasticity of Hb solutions (30 to 45 g/100 ml) prepared from normal human RBC. Measurements of the viscous component (VC) and elastic component (EC) were made at 25 degrees C using Couette (GDM) and capillary (OCR-D) rheometers; shear rates ranged from 1 to 200 s-1. All unheated Hb solutions were Newtonian and did not exhibit elasticity. However, after 3 min of heating, an elastic component was measurable. Both VC and EC increased with heating time in a power law fashion. VC continued to exhibit Newtonian behavior, whereas the magnitude of EC was an inverse function of shear rate and directly related to Hb concentration and treatment time. A relaxation function applied to our data suggests a first order reaction. These results indicate that both cytoplasmic and membrane viscoelasticity should be considered in order to fully comprehend the rheologic behavior of heat-treated RBC.