Human baroreflex rhythms persist during handgrip and muscle ischaemia

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Regulation
• Exercise Physiology

Background:

• The vagal baroreflex is crucial for maintaining blood pressure homeostasis.
• Rhythmic fluctuations in baroreflex gain are known to exist during rest.
• The persistence of these rhythms during physiological stress like exercise is not well understood.

Purpose of the Study:

• To investigate if physiological, rhythmic fluctuations of vagal baroreflex gain persist during exercise, post-exercise ischemia, and recovery.
• To characterize the behavior of these rhythmic fluctuations under different physiological conditions.

Main Methods:

• Healthy participants (6 men, 1 woman) underwent a protocol including rest, handgrip exercise, post-exercise ischemia, and recovery.
• Measurements included electrocardiographic R-R intervals, finger arterial pressures, and muscle sympathetic nerve activity.
• Vagal baroreflex gains were calculated using a sliding window transfer function analysis of systolic pressure and R-R intervals (0.04-0.15 Hz).

Main Results:

• Vagal baroreflex gain exhibited oscillations at a near-constant frequency (approx. 0.06 Hz) throughout the entire protocol.
• During exercise, these oscillations predominantly occurred at low-gain levels.
• During post-exercise ischemia and recovery, oscillations shifted to predominantly high-gain levels.

Conclusions:

• Physiological rhythms of vagal baroreflex gain are not abolished by exercise.
• These rhythms are also not overwhelmed during the post-exercise ischemia and recovery phases.
• The findings suggest a continuous, albeit modulated, rhythmic regulation by the vagal baroreflex under stress.