Which of the following is a thermal effect of ultrasound?

In the context of ultrasound therapy, one key thermal effect is the increase in blood flow. Ultrasound generates heat within the tissues being treated, primarily through vibration and friction of the tissues at the cellular level. This localized heating effect promotes vasodilation, or the widening of blood vessels, which enhances circulation in the area. Increased blood flow brings additional oxygen and nutrients to the tissues and aids in the removal of metabolic waste, facilitating the healing process and reducing inflammation.

While some of the other options may seem related, they do not represent direct thermal effects of ultrasound. For instance, decreased joint flexibility and decreased tissue extensibility highlight consequences of tissue changes but do not accurately reflect the thermal impact of ultrasound. Similarly, reduced nerve transmission may refer to the effects of heat on nerve conduction but does not directly correlate with the therapeutic goal of increasing blood flow in the treated area. Overall, the focus on increased circulation is a well-documented benefit of the thermal effects of ultrasound, which ultimately supports tissue healing.