The influence of variations in biophysical conditions on hemolysis near ultrasonically activated gas-filled micropores.

Hemolysis induced by 1.9-MHz ultrasound in 0.5% suspensions of canine erythrocytes with 3.7-microns-diam micropore-trapped gas bodies was investigated for a variety of biophysical conditions. For isotonic media, hemolysis increased with exposure duration (4-64 min) but did not greatly change with exposure temperature (15, 25, 37, and 48 degrees C), or prior heat treatment (48 or 50 degrees C for 30 min). The temperature results were especially interesting because increased temperatures might have been expected to increase the sensitivity of the cells to the ultrasonically activated gas bodies. Variations in osmolarity (180, 290, or 580 mOsm) had little influence on the results. Increasing the viscosity (0.7, 2.2, 2.3, or 4.2 cP) of the medium decreased the effect, and this did not seem to depend on the molecular weight of the dextran additive (9400 or 250,000). A medium with elevated mass density (1.12 g/cm3) seemed to increase the effectiveness of the exposures. This condition eliminated the density difference between the cells and the medium, and might have been expected to reduce the effectiveness of the exposures, because the radiation force, which theoretically gathers cells to the gas bodies, is minimized for such conditions. This information should aid in developing refinements to the theoretical understanding of low-intensity ultrasonic bioeffects.