Carotid baroreflex activation therapy (BAT) by the Rheos® system produces a sustained fall in blood pressure in patients with resistant hypertension. Since 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 carotid chemoreceptors not only raises respiration, but it also increases sympathetic activity which may in part counteract the effects of BAT. The aim of the present study is to investigate whether there is evidence for concomitant carotid chemoreflex activation during BAT. We hypothesized that there is no clinically relevant co-activation of the carotid body chemoreceptors during BAT in patients with resistant hypertension.

Inclusion Criteria:

• Be currently implanted with Rheos system and have completed the 13-month follow-up period.
• Be on stable anti-hypertensive therapy for at least 4 weeks prior to inclusion, where stable is defined as no changes in medications or dosage of medications.
• Have at least one functional carotid baroreflex activation electrode.
• Have signed and approved informed consent form for participation in this study.

Exclusion Criteria:

• Myocardial infarction (MI) or cerebral vascular accident (CVA) within the past 90 days, or subject is still unstable from a prior MI or CVA that occurred more than 90 days ago.
• Are unable or unwilling to comply with the protocol requirements of this study.
• Diagnosed with severe chronic obstructive lung disease (COPD/asthma GOLD stadium III and IV).

Subjects implanted with a BAT system will be invited to participate in this study. These are patients who were enrolled in the DEBuT-HET and Rheos Pivotal Trial and have given their permission to be approached for follow-up studies. Subjects are all >21 years of age and were all known with a blood pressure ≥160/90 mmHg despite optimal antihypertensive therapy before receiving BAT. It is essential to have the Rheos® device implanted to enable participation in this study, as we want to investigate the effect of electrical carotid sinus activation on the carotid body chemoreflex.