1Department of Obstetrics and Gynecology, Tokyo University, 2Chemistry Laboratory, Tokyo University of Marine Sciences
Body fluid, Cavitation, Free radical, OH radical, Safety of ultrasound
We used the spin trapping method with DMPO to measure free radicals in distilled water, human follicular fluid, amniotic fluid, and plasma that had been exposed to ultrasound with bubbling Ar gas. Ultrasound was produced by an ultrasonic cleaner and pulsed ultrasound-producing equipment. The ultrasonic intensity of the cleaner was about 10-1∼1 W/cm2 of SATA. The characteristics of the pulsed ultrasound were as follows: frequency; 2 MHz, pulse repetition frequency; 1 KHz, pulse duration; 10 μsec, SPTA; 4 W/cm2, negative maximum pressure; 3 MPa. Significant findings are as follows. First, DMPO-OH radical spectrum was obtained in distilled water with ultrasound produced by the ultrasonic cleaner. Second, in follicular fluid, amniotic fluid, and blood plasma, the common radical spectrum (aN=1.52 mT, aH=1.89 mT), and no DMPO-OH spectrum, was obtained with ultrasound produced by the ultrasonic cleaner. Third, follicular fluid was diluted with distilled water in 1:3, 1:1, and 3:1 ratios and exposed to ultrasound produced by the ultrasonic cleaner. When ratio of body fluid was high, the amplitude of DMPO-OH was low, and that of the common radical spectrum described above was high. Fourth, no spectrum was obtained in distilled water sonicated for 10 minutes by the pulsed ultrasound-producing equipment. And fifth, no spectrum was obtained in follicular fluid, amniotic fluid, or blood plasma sonicated for 10 minutes by pulsed ultrasound-producing equipment. In body fluid, very little or no OH radical is formed by ultrasound with similar power as that used for diagnostic purposes. Even if the OH radical were formed, moreover, it would be quickly neutralized by chemical reaction. We thus conclude that the possibility of any direct effect of OH radical on cells is very low.