Transmissivity of Coupling Agents Used to Deliver Ultrasound Through Indirect Methods

Brian Klucinec, Matthias Scheidler, Craig R. Denegar, Elizabeth Domholdt, Sharon Burgess

Ultrasound continues to be a popular modality among physical therapists and athletic trainers. Whether the intent of the ultrasound treatment is for thermal or nonthermal effects, it can be difficult to deliver an effective treatment over an irregular surface. Thermal ultrasound treatments are typically used to decrease muscle spasms, treat pain, increase circulation, and increase tissue extensibility. Draper and Prentice describe the “direct” technique of ultrasound as involving "actual contact between the applicator and the skin, with a thin film of couplant between." Although the direct technique has been recommended when therapeutic heating is desired, several authors discuss alternate, indirect techniques for performing thermal ultrasound treatments over irregular surfaces, thereby promoting a more uniform energy distribution during treatment. These indirect techniques have included water bath immersion, use of a commercial gel pad, and use of gel- or water-filled bladders. The effectiveness of water bath immersion as a method of delivering acoustic energy for purposes of tissue heating has, over the past years, yielded inconsistent results. Water has been found to be a good conductor, a poor conductor, and equivalent to other coupling agents when used to transmit ultrasound. Despite this conflicting evidence, authors continue to present the water bath technique as an appropriate indirect treatment alternative. It is our observation that clinicians continue to utilize this method in the athletic training room and physical therapy clinic. Research regarding the transmissivity of gel pads, bladder techniques, and water bath immersion are inconclusive and warrant investigation. The purpose of this in vitro study was to examine the relative transmissivity of a commercial gel pad, bladder techniques, and water bath immersion in the transmission of therapeutic ultrasound.

J Orthop Sports Phys Ther. 2000;30(5):263-269.

Key Words: thermal, nonthermal, water bath, gel pad, conductor

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