Muscle chemoreflex alters carotid sinus baroreflex response in humans

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Regulation
• Exercise Physiology

Background:

• The arterial baroreflex is a key regulator of blood pressure.
• The muscle chemoreflex opposes pressor responses during conditions like muscle ischemia.
• The interaction between the muscle chemoreflex and carotid sinus baroreflex (CSB) sensitivity remains incompletely understood.

Purpose of the Study:

• To quantify the effects of the muscle chemoreflex on CSB sensitivity.
• To investigate how exercise and postexercise muscle ischemia influence CSB function.
• To elucidate the combined impact of these reflexes on blood pressure control.

Main Methods:

• CSB stimulus-response (S-R) curves were generated using pulsatile neck pressure in healthy young men.
• Measurements were taken at rest, during exercise, and during postexercise recovery.
• Muscle chemoreflex was elicited by leg circulation occlusion during exercise and recovery in a separate condition.

Main Results:

• Exercise and postexercise occlusion shifted CSB S-R curves upward and rightward, indicating altered sensitivity.
• Postexercise occlusion (muscle chemoreflex) further elevated blood pressure and shifted curves above exercise-only curves.
• CSB gain increased during positive neck pressure and decreased during negative neck pressure under occlusion, showing nonlinear summation.

Conclusions:

• Muscle chemoreflex nonlinearly interacts with the CSB, affecting blood pressure regulation.
• The blood pressure-raising effect of the muscle chemoreflex enhances CSB responses to hypotension.
• Conversely, it can overpower the baroreflex's opposition to hypertension.