For skin transplants to “take root”, it needs to be ensured that the patient’s tissue is properly irrigated with blood. Low-frequency ultrasound can promote this effect. Researchers have developed the first device that permits variable control of the ultrasound frequency.
Minor skin wounds might hurt a lot, but they usually heal within a matter of days. For diabetics, the slightest scratch can have more serious consequences. In many cases the wound takes a long time to heal and spreads to the entire lower leg: Specialists refer to this as an “open leg ulcer”. The main reason is poor circulation, which causes insufficient oxygen and other nutrients to be transported to the wound. In many cases, the only solution is a skin transplant of healthy tissue.
To ensure that the transplant is accepted, the surgeon has to clean the wound and artificially stimulate the blood flow in the surrounding tissue – often using low-frequency ultrasound. Unlike the ultrasound used in prenatal examinations, which operates at frequencies of several hundred kilohertz, the frequencies used here are measured in tens of kilohertz. Devices operating at fixed frequencies are already available. But what effect does the treatment have on the patient’s circulation? The only empirical data that exists at present is based on patient surveys.
Researchers at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Dresden teamed up with colleagues from IMM Ingenieurbüro Mittweida and Smart Material GmbH Dresden to carry out a systematic study of this method. How often, for how long, and at what frequencies do wounds have to be treated to prepare them optimally for transplantation?
“We have developed a device that permits the frequency of the ultrasound waves to be varied between 20 and 120 kilohertz, and also has an output regulator,” says IWU team leader Dr. Gunther Naumann. “To stimulate the blood flow in the deeper epidermal layers, we need a lower frequency than that required to clean the wound in the subcutaneous zone.”
Another unique feature of the new ultrasound device is that it is equipped with a measuring system that directs light into the wound using special probes. The red region of the color spectrum of the reflected light indicates the concentration of oxygen in the blood – which in turn reveals how efficiently the tissue is being irrigated.
“Our observations have shown that the oxygen concentration continues to rise for 30 minutes after treatment. But we need to conduct further investigations to determine whether a sustained higher level can be reached after repeated treatment,” Naumann reports.
A prototype of the new device has been installed for use in clinical trials in the Department of Dermatology and Allergology at the academic teaching hospital in Dresden-Friedrichstadt. Ten patients have been treated so far. The study is to be continued in 2008.
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