Abstract
Biological effects of ultraound are classified as 1) thermal effects, 2)non-thermal cavitational effects, and 3)non-thermal and non-cavitational effects. First, the chemical effects of ultrasound in aqueous solutions are due to acoustic cavitation which refers to the formation, growth and collapse of small gas bubbles in liquid. The very high temperatures and pressures of collapsing gas bubbles lead to the thermal dissociation of water vapor into OH radicals and H atoms which are the same as observed in radiation chemistry. There is evidence for free radical formation in aqueous solutions and biological fluids, produced in vitro by exposure to continuous waves, tone-burst, and microsecond pulses of ultrasound at acoustic pressures similar to those which may be encountered during medical applications. Although there is evidence that free radicals produced by ultrasound are associated with cell killing in vitro, the extent of their role has not been established. Acoustic cavitation induced by ultrasound is of interest because of the wide use of diagnostic imaging and therapeutic application of safety considerations for posible deleterious effects due to physical and chemical effects of cavitation. Here, the role of cavitation in the induction of apoptosis and the change of gene expression is discussed.
