Which of the following is NOT a thermal effect of ultrasound?

Which of the following is NOT a thermal effect of ultrasound?

• A. Alter cell membrane permeability
• B. Decreased pain
• C. Increased blood flow
• D. Increased collagen extensibility

Answer: (A)

Therapeutic ultrasound can raise tissue temperature, and when it does, several heat-driven changes occur: warmth increases blood flow by promoting vasodilation, which helps with tissue perfusion and can aid healing; heating makes collagen-containing tissues more pliable, so the tissue’s extensibility increases and movement becomes easier; and the warmth itself can help reduce pain by relaxing muscles and decreasing muscle spasm. Altering cell membrane permeability, on the other hand, is not produced by heating. That effect arises from non-thermal mechanisms of ultrasound, like acoustic microstreaming and cavitation, which can transiently influence cellular membranes independent of temperature. So the option describing changes to cell membrane permeability is the one that does not reflect a thermal effect.

Therapeutic ultrasound can raise tissue temperature, and when it does, several heat-driven changes occur: warmth increases blood flow by promoting vasodilation, which helps with tissue perfusion and can aid healing; heating makes collagen-containing tissues more pliable, so the tissue’s extensibility increases and movement becomes easier; and the warmth itself can help reduce pain by relaxing muscles and decreasing muscle spasm. Altering cell membrane permeability, on the other hand, is not produced by heating. That effect arises from non-thermal mechanisms of ultrasound, like acoustic microstreaming and cavitation, which can transiently influence cellular membranes independent of temperature. So the option describing changes to cell membrane permeability is the one that does not reflect a thermal effect.