Systemic vascular effects of acute electrical baroreflex stimulation

Abstract

Burgoyne S, Georgakopoulos D, Belenkie I, Tyberg JV. Systemic vascular effects of acute electrical baroreflex stimulation. Am J Physiol Heart Circ Physiol 307: H236 -H241, 2014. First published May 9, 2014; doi:10.1152/ajpheart.00422.2013.-We intended to determine if acute baroreflex activation therapy (BAT) increases venous capacitance and aortic conductance. BAT is effective in resistant hypertension, but its effect on the systemic vasculature is poorly understood. Left ventricular (LV) and aortic pressures and subdiaphragmatic aortic and caval flows (ultrasonic) were measured in six anesthetized dogs. Changes in abdominal blood volume (V abdominal) were estimated as the integrated difference in abdominal aortic inflow and caval outflow. An electrode was implanted on the right carotid sinus. Data were measured during control and BAT. Next, sodium nitroprusside (SNP) was infused and BAT was subsequently added. Finally, angiotensin II (ANG II) was infused, and three increased BAT currents were added. We found that BAT decreased mean aortic pressure (P Ao) by 22.5 Ϯ 1.3 mmHg (P Ͻ 0.001) and increased aortic conductance by 16.2 Ϯ 4.9% (P Ͻ 0.01) and V abdominal at a rate of 2.2 Ϯ 0.6 ml·kg Ϫ1 ·min Ϫ1 (P Ͻ 0.01). SNP decreased PAo by 17.4 Ϯ 0.7 mmHg (P Ͻ 0.001) and increased V abdominal at a rate of 2.2 Ϯ 0.7 ml·kg Ϫ1 ·min Ϫ1 (P Ͻ 0.05). During the SNP infusion, BAT decreased P Ao further, by 26.0 Ϯ 2.1 mmHg (P Ͻ 0.001). ANG II increased PAo by 40.4 Ϯ 3.5 mmHg (P ϭ 0.001). When an increased BAT current was added, P Ao decreased to baseline (P Ͻ 0.01) while aortic conductance increased from 62.3 Ϯ 5.2% to 80.2 Ϯ 3.3% (P Ͻ 0.05) of control. V abdominal increased at a rate of 1.8 Ϯ 0.9 ml·kg Ϫ1 ·min Ϫ1(P Ͻ 0.01), reversing the ANG II effects. In conclusion, BAT increases arterial conductance, decreases P Ao, and increases venous capacitance even in the presence of powerful vasoactive drugs. Increasing venous capacitance may be an important effect of BAT in hypertension.baroreceptors; venous capacitance; aortic conductance ELECTRICAL BARORECEPTOR activation therapy (BAT) can be achieved with an implantable medical device (CVRx Inc.) and has been used to treat resistant hypertension (27). There is also potential for this approach to be useful in heart failure (11). While the effects of BAT on cardiac function (i.e., heart rate, contractility, and cardiac output) have been established (11), the effects on the peripheral circulation (i.e., arterial conductance and venous capacitance) have not been defined. Control of venous capacitance is important in the maintenance of cardiovascular homeostasis and cardiac output (35). Modulation of venous capacitance by sympathetic outflow has been demonstrated with studies during electrical stimulation, including splanchnic and hepatic nerves (5, 7), changes in carotid artery pressure (31), and pharmacological manipulation of sympathetic activity (23). The control of vascular capacitance by the carotid baroreflex has been well-investigated and demonstrated (30). While the effects of ...

Baroreflex Activation Therapy Lowers Arterial Pressure Without Apparent Stimulation of the Carotid Bodies

“…23,24 Our data demonstrate that the acute BP decrease during BAT is mainly achieved by changes in the vasculature and not so much to the heart. A recent study by Burgoyne et al 25 demonstrated an increase in arterial conductance and venous capacitance with acute BAT, which is consistent with our results and is consistent with the view that a drop in sympathetic activity is responsible for the cardiovascular effects.…”

“…23,24 Estos datos demuestran que la disminución aguda de la PA durante el BAT se logra principalmente mediante cambios en la vasculatura y no tanto en el corazón. Un estudio reciente realizado por Burgoyne et al 25 demostró un aumento de la conductividad arterial y capacidad venosa con el BAT agudo, lo que concuerda con nuestros resultados y con la perspectiva de que la disminución de la actividad simpática es responsable de los efectos cardiovasculares.…”

Baroreflex Activation Therapy in Congestive Heart Failure: Novel Findings and Future Insights

“…It was thus hypothesized that the sympathoinhibition triggered by the stimulation of carotid baroreceptors would lead to an improvement in arterial function. However, at variance from what already reported in animal models of heart failure [22,23], no significant improvement of carotid-femoral pulse wave velocity and augmentation index, calculated from central blood pressure analysis, was observed following a 3-month follow-up [27]. These findings are in contrast with the evidence collected in resistant hypertensive patients demonstrating a favorable effect of the baroreflex activation therapy on the main functional features of the large arteries [28•], which have been shown to be under sympathetic and reflex influences [29,30].…”

“…Acutely, carotid baroreceptor stimulation in healthy dogs significantly increases stroke volume and reduces heart rate while preserving cardiac output as well as renal perfusion [21,22]. This is achieved by reducing systemic vascular resistance and arterial stiffness [23]. The reduced myocardial oxygen demand, the increased cardiac reserve, as well as the preserved tissue perfusion allow to improve functional capacity and protect against the arrhythmogenic effects of myocardial ischemia.…”

“…The reduced myocardial oxygen demand, the increased cardiac reserve, as well as the preserved tissue perfusion allow to improve functional capacity and protect against the arrhythmogenic effects of myocardial ischemia. In addition to the arterial effects, carotid baroreceptor stimulation modulates the venous system increasing venous capacitance via a transfer of blood volume from the arterial to the venous circulation [23]. The intervention exerts also important electrophysiological effects at myocardial level, by enhancing refractory period and action potentials duration of the myocardial cells and reducing the incidence of ventricular arrhythmias [24].…”