Neural blockade during exercise augments central command's contribution to carotid baroreflex resetting

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology
• Autonomic Nervous System Regulation

Background:

• The carotid baroreflex (CBR) is crucial for regulating blood pressure.
• Understanding how central command influences CBR during exercise is vital for cardiovascular health.
• Exercise can alter autonomic nervous system responses, including baroreflex sensitivity.

Purpose of the Study:

• To investigate the role of central command in the resetting of the carotid baroreflex during dynamic and static exercise.
• To differentiate the effects of central command on the cardiac and vasomotor components of the CBR.

Main Methods:

• Nine healthy subjects performed static and rhythmic handgrip exercise at varying intensities (30-40% MVC).
• Carotid baroreflex stimulus-response curves were generated using neck pressure-neck suction before and after axillary neural blockade.
• Heart rate (HR) and ratings of perceived exertion (RPE) were monitored as indicators of central command.

Main Results:

• Neural blockade reduced maximal voluntary contraction (MVC) and increased HR and RPE during exercise, indicating heightened central command.
• Carotid baroreflex curves demonstrated vertical resetting during exercise, with further parallel resetting after neural blockade.
• The operating point of the CBR shifted to align with the curve's centering point during exercise.

Conclusions:

• Central command is a primary driver of carotid baroreflex resetting during exercise.
• Central command appears to modulate the carotid-cardiac reflex to a greater extent than the carotid-vasomotor reflex.
• These findings elucidate the complex interplay between central motor commands and autonomic cardiovascular regulation during physical activity.