Sound Agents

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Last modified 22/05/2015

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Chapter 46 Sound Agents

46.1 Therapeutic Ultrasound

OVERVIEW.

Therapeutic ultrasound is a physical agent that emits high frequency oscillations or sound waves (0.7 to 3.3 MHz frequency range) that penetrates tissue and produces deep heat. The clinical aim is to promote healing by softening scar tissue, increasing cell metabolism, and promoting nutrition. The agent has both a thermal and mechanical effect.¹ Because therapeutic ultrasound produces heat, tissues need to be capable of dissipating heat via adequate blood circulation.

SUMMARY: CONTRAINDICATIONS AND PRECAUTIONS.

Eight sources cited a total of 37 concerns for therapeutic US. Concerns ranged from 7 to 23 per source with a physician citing the largest number and an OT citing the fewest number. The greatest percentage of concerns related to vulnerable tissue (e.g., over reproductive tissue, eyes, heart, or neural tissue). The most frequently cited concerns were neoplasm, pregnancy, and over the eye (cited by all 8 sources).

While not formally listed under contraindications, sources generally recommended the procedure of moving the sound head (i.e., avoid stationary transducers) to avoid increasing the risk of hot spots, unstable cavitation, blood cell stasis, or blood vessel damage to the endothelial cells. Pain from a stationary technique may suggest periosteal heating. In an in vivo 1974 study, Dyson ² describes blood cell stasis (temporary blood flow arrest) and endothelial damage (permanent) in the blood vessels of a chick embryo treated with US using a stationary technique (minimum intensity <0.5 W/cm²; 3 MHz).²

In a case series, Gnatz ³ reported transient radicular symptoms in 36-year-old and 37-year-old females with lumbar disc herniations a few minutes following US treatment to lumbar paraspinals at 1.5-1.75 W/cm². The incidences were postulated to be due to heat-induced edema accumulation within a confined space.

Note: Several sources incorporates general thermotherapy concerns into their US guidelines.