Exercise causes an increase in sympathetic activity which helps to redistribute blood flow while maintaining blood pressure. The exact mechanisms that regulate sympathetic activity and blood flow during exercise are not completely understood. By modulating the activity of a specific chemical receptor (the carotid chemoreceptor), we showed that this receptor contributes to the regulation of blood flow during exercise in healthy subjects. These findings demonstrate the importance of the carotid chemoreceptor in the regulation of blood flow during exercise in health.
Carotid chemoreceptor (CC) inhibition reduces sympathetic nervous outflow in exercising dogs and humans. We sought to determine if CC suppression increases muscle blood flow in humans during exercise and hypoxia. Healthy subjects (N= 13) were evaluated at rest and during constant–work leg extension exercise while exposed to either normoxia or hypoxia (inspired O2 tension, Symbol, ≈ 0.12, target arterial O2 saturation = 85%). Subjects breathed hyperoxic gas (Symbol≈ 1.0) and/or received intravenous dopamine to inhibit the CC while femoral arterial blood flow data were obtained continuously with pulsed Doppler ultrasound. Exercise increased heart rate, mean arterial pressure, femoral blood flow and conductance compared to rest. Transient hyperoxia had no significant effect on blood flow at rest, but increased femoral blood flow and conductance transiently during exercise without changing blood pressure. Similarly, dopamine had no effect on steady–state blood flow at rest, but increased femoral blood flow and conductance during exercise. The transient vasodilatory response observed by CC inhibition with hyperoxia during exercise could be blocked with simultaneous CC inhibition with dopamine. Despite evidence of dopamine reducing ventilation during hypoxia, no effect on femoral blood flow, conductance or mean arterial pressure was observed either at rest or during exercise with CC inhibition with dopamine while breathing hypoxia. These findings indicate that the carotid chemoreceptor contributes to skeletal muscle blood flow regulation during normoxic exercise in healthy humans, but that the influence of the CC on blood flow regulation in hypoxia is limited.