Effect of Carotid Body Chemoreceptor Inhibition on Cardiac Baroreflex Sensitivity in Resting Humans

Activation or inhibition of the carotid body chemoreceptors (CBCs) may impact cardiac baroreflex sensitivity (cBRS). The purpose of this study was to test the hypothesis that inhibition of the CBCs will elicit a change in cBRS when compared to normal resting conditions. Young, healthy subjects (n=16, 31±2, 6 women) were given IV saline and a range of IV dopamine (DA) (1‐4 µg/kg/min) for 15 minutes prior to and throughout five hypoxic ventilatory response (HVR) tests. Subjects were initially infused with IV saline. After each HVR, the DA infusion rate was increased by 1 µg/kg/min. A 3‐lead EKG and beat‐by‐beat blood pressure (NexFin) were used to determine cBRS. Data were analyzed from the 5 minutes prior to the HVR associated with the DA dose that elicited the greatest attenuation of the HVR when compared to saline. Heart rate was not significantly different during saline vs. DA (62±3 vs. 65±3, p=0.25). Diastolic blood pressure (77±2 vs. 72±1 mmHg), mean arterial pressure (98±2 vs. 92±2 mmHg), and cBRS “up” sequence (38±7 vs. 21±3 ms/mmHg) were significantly lower during saline vs. DA (p<0.05 for all). cBRS values from the RRI spectrum were not statistically distinguishable between saline and DA (26±4 vs. 21.1±3, p=0.06). In summary, inhibiting the CBCs via DA infusion in young, healthy subjects results in a fall in blood pressure and a reduction in cBRS in response to a rise in blood pressure. These data suggest the CBCs contribute to cBRS and play an important role in modulating parasympathetic control of blood pressure.