Influence of Carotid Chemoreceptors on Cerebral Blood Flow during Normoxic Conditions
Authors: Malterer Katherine R. , Holbein Walter W. , Harvey Ronee E. , Johnson Blair D. , Joyner Michael J. 
Published: November 2023

Background

Evidence indicates that the carotid chemoreceptors play a minimal role in regulating cerebral blood flow under normoxic resting conditions. However, studies in heart failure suggest over‐active carotid chemoreceptors may decrease cerebral blood flow. With this information in mind, we hypothesized that individuals with the highest resting chemosensitivity will have the greatest increase in cerebral blood flow when the carotid chemoreceptors are desensitized with low‐dose IV dopamine.

Methods

Seven young, healthy men (33±3 y) participated in two randomized, double‐blinded study days separated by at least 4 weeks. Middle cerebral artery blood velocity (MCAv, transcranial Doppler) was measured continuously as a surrogate for cerebral blood flow. Cerebral vascular conductance index (CVCi) was calculated by normalizing MCAv for blood pressure as measured by brachial arterial catheter (MCAv/mean arterial blood pressure) and blood gasses were drawn. Subjects rested quietly in the supine position for 5‐minutes during intravenous saline infusion (saline and dopamine baseline). This was followed by a 25‐minute continuous IV infusion of either saline or dopamine. The dose of dopamine was individualized (1–2 μg/kg/min) such that it resulted in a nadir hypoxic ventilatory response. Data were analyzed from the last 5‐minutes of the infusion period (saline infusion or dopamine infusion) and compared to baseline data.

Results

Saline and dopamine infusion did not affect mean arterial blood pressure (% change saline vs dopamine day: 1.3±1.2 vs 0.9±1.3%; p>0.05) or arterial blood CO2 (% change saline vs dopamine day: −2.6±1.7 vs 1.6±1.9%; p>0.05). Dopamine infusion resulted in a significant reduction in carotid body chemosensitivity as assessed by the hypoxic ventilatory response (dopamine baseline vs infusion HVR: 0.33±0.06 vs 0.17±0.03 L/min/%SpO2; p=0.027). No changes in MCAv or CVCi were observed with saline infusion (saline baseline vs infusion: p>0.05). Dopamine did not alter MCAv (dopamine baseline vs infusion: 62±5 vs 64±5 cm/s; p>0.05). Similarly, no changes in CVCi were observed with dopamine infusion (dopamine baseline vs infusion: 0.68±0.07 vs 0.68±0.06 cm/s/mmHg; p>0.05). Although differences in group means for MCAv and CVCi were not observed with dopamine infusion, a significant negative relationship was found between baseline carotid chemosensitivity and the change in MCAv (r2=0.594, p=0.043), and CVCi (r2=0.741, p=0.013). With saline infusion, no significant relationship was found between baseline carotid chemosensitivity and the change in MCAv (r2=0.091, p>0.05), and CVCi (r2=0.089, p>0.05).

Conclusions

Blunting of the carotid chemoreceptors using IV dopamine has no group effect on MCAv or CVCi. However, contrary to our hypothesis, individuals with highest resting chemosensitivity had either a decrease or no change in cerebral blood flow after carotid body desensitization.

Support or Funding Information

W81XWH‐13‐2‐003