Interaction of transthoracic ultrasound and intravenous microbubbles with cardiac mechanoreceptors

The purpose of this study was to examine the effect of transthoracic ultrasound (TTU) and intravenous microbubbles (MB) on cardiac mechanoreceptors. In 16 rabbits (eight normal and eight chronic heart failure), renal sympathetic nerve activity (RSNA), heart rate and mean arterial pressure were examined before, during and after 1 MHz TTU at different peak negative pressures (0.12 to 0.43 MPa) and duty cycles in the presence and absence of perfluorocarbon MB. TTU applications were for 10 s, and the overall duration of MB infusion was approximately 60 s for each setting. TTU without MB had no effect on any parameter. During the microbubble infusion, however, TTU at higher peak negative pressures (≥0.27 MPa) and 100% duty cycle resulted in a consistent decrease in RSNA(-41 ± 41% p < 0.001). This was accompanied by brief reflex reductions in mean arterial pressure and heart rate. The changes in RSNA induced by TTU and MB in all rabbits were abolished by vagotomy. TTU, in the presence of MB, stimulates mechanoreceptors in the heart reflexively to reduce RSNA. (E-mail: trporter@unmc.edu).