Baroreflex resetting of human sympathetic action potential subpopulations during exercise

Area of Science:

• Cardiovascular Physiology
• Neuroscience
• Exercise Physiology

Background:

• The baroreflex is crucial for regulating blood pressure during physiological challenges like exercise.
• During exercise, descending central commands and ascending sensory feedback from muscles interact to modulate autonomic control.
• Understanding how these signals differentially influence baroreflex resetting is key to comprehending cardiovascular adaptation.

Purpose of the Study:

• To investigate the distinct roles of descending cortical signals and ascending skeletal muscle metaboreflex signals in baroreflex resetting of sympathetic nerve activity during fatiguing exercise.
• To determine if these neural pathways exert divergent control over sympathetic action potential discharge during isometric handgrip exercise and postexercise circulatory occlusion.

Main Methods:

• Quantified baroreflex gain for sympathetic action potential (AP) clusters using peroneal microneurography and continuous wavelet transform.
• Measured AP baroreflex threshold gain as the slope of AP probability versus diastolic blood pressure during baseline, early and late isometric handgrip exercise, and postexercise circulatory occlusion.
• Analyzed data from seven healthy participants performing fatiguing isometric handgrip exercise.

Main Results:

• Isometric handgrip exercise reset baroreflex functions to higher diastolic blood pressure and AP firing probabilities, with medium-sized APs showing the most significant resetting.
• Baroreflex gain was not altered during late isometric handgrip exercise but increased significantly during postexercise circulatory occlusion, particularly for medium-sized APs.
• These differential effects on baroreflex gain were masked when analyzing the integrated muscle sympathetic nerve activity neurogram.

Conclusions:

• Descending cortical and ascending muscle metaboreceptor signals differentially influence baroreflex resetting of sympathetic postganglionic neurons during exercise.
• Postexercise circulatory occlusion uniquely enhances baroreflex gain for specific sympathetic neuron populations, an effect not observed with isometric handgrip exercise alone.
• Focusing on individual sympathetic AP clusters provides a more nuanced understanding of baroreflex control during exercise compared to analyzing integrated neurogram data.