Efficacy of Electrical Baroreflex Activation Is Independent of Peripheral Chemoreceptor Modulation.

Arterial baroreflex activation through electrical carotid sinus stimulation has been developed for the treatment of resistant hypertension. Previous studies suggested that the peripheral chemoreflex is tonically active in hypertensive patients and may inhibit baroreflex responses. We hypothesized that peripheral chemoreflex activation attenuates baroreflex efficacy evoked by electrical carotid sinus stimulation. We screened 35 patients with an implanted electrical carotid sinus stimulator. Of those, 11 patients with consistent acute depressor response were selected (7 men/4 women, age: 67 +/- 8 years, body mass index: 31.6 +/- 5.2 kg/m(2), 6 +/- 2 antihypertensive drug classes). We assessed responses to electrical baroreflex stimulation during normoxia, isocapnic hypoxia (SpO(2): 79.0 +/- 1.5%), and hyperoxia (40% end-tidal O-2 fraction) by measuring heart rate, blood pressure, ventilation, oxygen saturation, end-tidal CO2 and O-2 fractions, and muscle sympathetic nerve activity. During normoxia, baroreflex activation reduced systolic blood pressure from 164 +/- 27 to 151 +/- 25 mm Hg (mean +/- SD, P<0.001), heart rate from 64 +/- 13 to 61 +/- 13 bpm (P=0.002), and muscle sympathetic nerve activity from 42 +/- 12 to 36 +/- 12 bursts/min (P=0.004). Hypoxia increased systolic blood pressure 8 +/- 12 mm Hg (P=0.057), heart rate 10 +/- 6 bpm (P<0.001), muscle sympathetic nerve activity 7 +/- 7 bursts/min (P=0.031), and ventilation 10 +/- 7 L/min (P=0.002). However, responses to electrical carotid sinus stimulation did not differ between hypoxic and hyperoxic conditions: systolic blood pressure: -15 +/- 7 versus -14 +/- 8 mm Hg (P=0.938), heart rate: -2 +/- 3 versus -2 +/- 2 bpm (P=0.701), and muscle sympathetic nerve activity: -6 +/- 4 versus -4 +/- 3 bursts/min (P=0.531). We conclude that moderate peripheral chemoreflex activation does not attenuate acute responses to electrical baroreflex activation therapy in patients with resistant hypertension. These patients provided insight into human baroreflex-chemoreflex interactions that could not be gained otherwise.