Cell density dependence of the ultrasonic degassing of fixed erythrocyte suspensions

Ultrasonic cell lysis in vitro shows a strong dependence on the cell density of the suspensions. The major determinant in this phenomenon appears to be the suspended particle density per se. Reported are the results of experiments designed to test the hypothesis that the majority of the cell density effect arises as a consequence of the cell density-dependent formation of cellular aggregates around oscillating bubbles in an ultrasound field (Nyborg and Miller 1982), which in turn diminishes the potential for the occurrence and sustenance of destructive cavitational events in the bulk suspension fluid. The hypothesis was tested indirectly using manometric methods to measure ultrasound-induced release of dissolved gas from saline solutions and fixed erythrocyte suspensions. Ultrasonic degassing of the fluids in excess of that attributable to thermal effects was observed, and was suppressed by the presence of fixed erythrocytes when the cell density was greater than 5 x 10(6) cells/mL. At higher cell densities, the inhibition of ultrasonic degassing by fixed cells increased monotonically with increasing cell density, attaining complete suppression at a cell density of 5 x 10(8) cells/mL. The data thus support the hypothesis.