Quantitative Thermal Stimulation Using Therapeutic Ultrasound to Improve Cerebral Blood Flow and Reduce Vascular Stiffness

It is important to improve cerebrovascular health before the occurrence of cerebrovascular disease, as it has various aftereffects and a high recurrence rate, even with appropriate treatment. Various medical recommendations for preventing cerebrovascular diseases have been introduced, including smoking cessation, exercise, and diet. However, the effectiveness of these methods varies greatly from person to person, and their effects cannot be confirmed unless they are practiced over a long period. Therefore, there is a growing need to develop more quantitative methods that are applicable to the public to promote cerebrovascular health. Thus, in this study, we aimed to develop noninvasive and quantitative thermal stimulation techniques using ultrasound to improve cerebrovascular health and prevent cerebrovascular diseases. This study included 27 healthy adults in their 20s (14 males, 13 females). Thermal stimulation using therapeutic ultrasound at a frequency of 3 MHz was applied to the right sternocleidomastoid muscle in the supine posture for 2 min at four intensities (2.4, 5.1, 7.2, and 10.2 W/cm(2)). Diagnostic ultrasound was used to measure the peak systolic velocity (PSV), heart rate (HR), and pulse wave velocity (PWV) in the right common carotid artery (CCA), and the physiological changes were compared between intervention intensities. Compared to pre-intervention (preI), the PSV showed a significant increase during intervention (durI) at intensities of 7.2 W/cm(2) and 10.2 W/cm(2) (p = 0.010 and p = 0.021, respectively). Additionally, PWV showed a significant decrease for post-intervention (postI) at 7.2 W/cm(2) and 10.2 W/cm(2) (p = 0.036 and p = 0.035, respectively). However, the HR showed no significant differences at any of the intensities. The results demonstrate that an intervention at 3 MHz with an intensity of 7.2 W/cm(2) or more can substantially increase cerebral blood flow and reduce arterial stiffness. Therefore, the use of therapeutic ultrasound of appropriate intensity is expected to improve the cerebral blood flow and reduce vascular stiffness to maintain cerebral blood flow at a certain level, which is closely related to the prevention and treatment of cerebrovascular diseases, thereby improving cerebrovascular health.