Sympathetic action potential synchronicity and blood pressure regulation in healthy young adults

This study investigated sympathetic neural blood pressure regulation in humans by quantifying synchronous and asynchronous action potential (AP) discharge. Muscle sympathetic AP discharge was measured (microneurography; continuous wavelet transform) in twenty-one healthy young adults. Baroreflex functions (central baroreflex component) and diastolic blood pressure (DBP) transduction (peripheral baroreflex component) were quantified for synchronous and asynchronous AP discharge. Analyses were stratified by falling and rising blood pressures to examine hysteresis. Medium-sized synchronous APs exhibited the greatest discharge frequencies ( p<0.001) and baroreflex threshold gains ( p<0.001). Asynchronous AP discharge exhibited weak baroreflex regulation ( p=0.999). Central baroreflex regulation of medium-sized synchronous APs exhibited hysteresis. Medium-sized synchronous APs expressed stronger baroreflex threshold gains (Sympathetic AP Cluster 3: DBP Fall slope: -5.48±3.07%/mmHg, DBP Rise slope: -4.71±2.91%/mmHg; p<0.001) and greater discharge frequencies (Sympathetic AP Cluster 3: DBP Fall: 0.29±0.15Hz, DBP Rise: 0.25±0.13Hz; p<0.001) during falling compared to rising blood pressures. The peripheral baroreflex component exhibited hysteresis. Transduction responses to synchronous AP discharge were larger during rising compared to falling blood pressures (DBP Fall peak: 2.67±1.02mmHg, DBP Rise peak: 3.14±1.29mmHg; p=0.009). Asynchronous AP discharge was associated with attenuated blood pressure reductions compared to cardiac cycles with no AP activity, and more so during rising compared to falling blood pressures (DBP Fall nadir: -2.17±1.09mmHg, DBP Rise nadir: -1.43±0.68mmHg; p<0.001). These data suggest that homeostatic blood pressure regulation is achieved via distinct subpopulations of synchronous and asynchronous APs that receive different central baroreflex and non-baroreflex inputs. Central and peripheral baroreflex hysteresis may reflect a moment-to-moment compensatory strategy for blood pressure regulation.