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

Abstract

Abstract-Carotid baroreflex activation therapy produces a sustained fall in blood pressure in patients with resistant hypertension. Because the activation electrodes are implanted at the level of the carotid sinus, it is conceivable that the nearby located carotid body chemoreceptors are stimulated as well. Physiological stimulation of the carotid chemoreceptors not only stimulates respiration but also increases sympathetic activity, which may counteract the effects of baroreflex activation. The aim of this exploratory study is to investigate whether there is concomitant carotid chemoreflex activation during baroreflex activation therapy. Fifteen participants with the Rheos system were included in this single-center study. At arrival at the clinic, the device was switched off for 2 hours while patients were at rest. Subsequently, the device was switched on at 6 electric settings of high and low frequencies and amplitudes. Respiration and blood pressure measurements were performed during all device activation settings. Multilevel statistical models were adjusted for age, sex, body mass index, antihypertensive therapeutic index, sleep apnea, coronary artery disease, systolic blood pressure, and heart rate. There was no change in end-tidal carbon dioxide, partial pressure of carbon dioxide, breath duration, and breathing frequency during any of the electric settings with the device. Nevertheless, mean arterial pressure showed a highly significant decrease during electric activation (P<0.001). Carotid baroreflex activation therapy using the Rheos system did not stimulate respiration at several electric device activation energies, which suggests that there is no appreciable coactivation of carotid body chemoreceptors during device therapy.

Role of Chemoreceptor Activation in Hemodynamic Responses to Electrical Stimulation of the Carotid Sinus in Conscious Rats

“…These authors concluded that carotid BAT using the Rheos system involved no appreciable attendant activation of carotid body chemoreceptors during the device therapy. 16 Certainly, this is not the case concerning the approach employed in the current study in conscious rats, which deserves a thorough investigation of the respiratory changes due to the direct activation of the carotid chemoreflex.…”

“…Using this experimental model, the present study shows that combined electrical stimulation of the carotid sinus and the carotid sinus nerve concomitantly activates both carotid baroreceptors and chemoreceptors, indicating that attendant carotid chemoreceptor activation blunted the hypotensive response in conscious rats. Nevertheless, it is of note that recent study of Alnima and colleagues 16 indicates no relevant carotid body coactivation with Rheos system in patients with resistant hypertension, probably because their pulse generator is implanted at the surface of each carotid sinus wall without reaching the nearby located carotid body chemoreceptors. 16 …”

“…Nevertheless, Alnima and colleagues 16 demonstrated that a short-term (2 to 4 min) protocol for carotid BAT in patients with resistant hypertension caused no change in end-tidal carbon dioxide, partial pressure of carbon dioxide, breath duration, and breathing frequency, combined with highly significant decrease in mean arterial pressure during electric activation. These authors concluded that carotid BAT using the Rheos system involved no appreciable attendant activation of carotid body chemoreceptors during the device therapy.…”

“…15 . Of note, the recent study from Alnima and colleagues, 16 using short-term electric activation settings of 2 and 4 min, provided remarkable information for BAT using the Rheos system. These authors observed that this electroceutical therapy in patients with resistant hypertension did not stimulate respiration at several electric device activation parameters suggesting that there is no attendant activation of carotid body chemoreceptors during device therapy.…”

“…These authors observed that this electroceutical therapy in patients with resistant hypertension did not stimulate respiration at several electric device activation parameters suggesting that there is no attendant activation of carotid body chemoreceptors during device therapy. 16 …”