Temperatures Produced in Tissues by Ultrasound: Experimental Study Using Various Technics

Abstract

Nerves and bones are heated selectively in situ by ultrasound. The temps. produced in these tissues are significantly higher than the temps. of neighboring tissues. Nerves may be blocked by ultrasound. The same results may be obtained also by heating the nerve directly. The possibility of using sound or heat for reversible blocking of nerves seems impractical when the technics described in this report are used, because the margin of safety between conditions for irreversible and reversible block is too narrow. A differential study of the changes in the action potentials of the A, B, and C fibers of the sciatic nerve of the frog did not lend support for an explanation of the apparent analgesic effects of ultrasound. The effects of direct heat on nerves are strikingly similar to the effects of ultrasound. A clear-cut distinction was not observed under the conditions of the experimental studies. The high temps. produced in bone by a stationary source of continuous ultrasonic waves can be reduced to levels acceptable for therapy by either pulsing the stationary ultrasonic energy or by a to-and-fro movement of the continuous ultrasonic energy over the selected region. Data on the temps. developed by these various technics are presented.