Acute physiological effects of ultrasonic vibrations on nervous tissue

We investigated the acute effects of ultrasonically induced lesions on action potential conduction and blood flow in nervous tissues. A Cavitron ultrasonic surgical aspirator (CUSA) was used to emulsify small areas of cat thoracic spinal cord while hydrogen clearance, somatosensory evoked potentials, and vestibulospinal evoked potentials were monitored. In addition, we examined the effect of direct and indirect application of the vibrating probe on rat sciatic nerves. The CUSA created localized lesions of the spinal cord, sparing the function and blood flow of immediately adjacent white structures. Histological studies revealed a sharp demarcation of the lesion sites with little morphological evidence of tissue injury beyond the borders of the lesions. The rat sciatic nerve experiments showed that, as long as the probe tip did not touch the nerve, ultrasonic vibrations had little effect on the nerve. These results suggest that the destructive effects of the ultrasonic vibrating probe are limited to a small volume at the probe tip. We conclude that, at low power levels sufficient to cause tissue emulsification at the probe tip, the CUSA does not acutely affect the function of nearby white matter. However, our results may not be extendable to higher intensity levels and do not rule out chronic effects.