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A Pilot Study of Thermal Effect of Low-intensity Focused Ultrasound on Blood Pressure Modulation

Our recent study showed that low-intensity focused ultrasound stimulation (FUS) of the vagus nerve is capable of lowering blood pressure (BP). However, it remains unknown that what is the underlying mechanisms of BP modulation with FUS. In our preliminary experiments, we noticed that there was temperature elevation accompanied the FUS. Thus, to verify whether the thermal effect of ultrasound contributes in the BP-lowering effect, this study compared the BP response under the FUS (with thermal effect and mechanical effect) and the alternative heating source treatment (AHST) (with thermal effect only) of left vagus nerve. Six Sprague Dawley rats were randomly divided into two groups (FUS, n=3 and AHST, n=3). In vivo temperature measurements were conducted to evaluate the heating performance of the FUS and the AHST. Blood pressure (BP) waveform was continuously recorded from the right common artery and was used for analyzing systolic BP (SBP), diastolic BP (DBP), mean BP (MBP), and heart rate (HR). The results showed that the SBP, DBP, MBP and HR decreased during the 15-min FUS. However, most of the SBP, DBP, MBP and HR increased during the 15-min AHST, which had the approximate temperature elevation of the FUS. Thus, the thermal effect of ultrasound probably does not contribute in the BP-lowering effect induced by low-intensity FUS of the vagus nerve.