Advantage of Recording Single-Unit Muscle Sympathetic Nerve Activity in Heart Failure

Hisayoshi Murai,Shuichi Kaneko,Masayuki Takamura

doi:10.3389/fphys.2012.00109

Abstract

Elevated sympathetic activation is a characteristic feature of heart failure (HF). Excessive sympathetic activation under resting conditions has been shown to increase from the early stages of the disease, and is related to prognosis. Direct recording of multiunit efferent muscle sympathetic nerve activity (MSNA) by microneurography is the best method for quantifying sympathetic nerve activity in humans. To date, this technique has been used to evaluate the actual central sympathetic outflow to the periphery in HF patients at rest and during exercise; however, because the firing occurrence of sympathetic activation is mainly synchronized by pulse pressure, multiunit MSNA, expressed as burst frequency (bursts/min) and burst incidence (bursts/100 heartbeats), may have limitations for the quantification of sympathetic nerve activity. In HF, multiunit MSNA is near the maximum level, and cannot increase further than the heartbeat. Single-unit MSNA analysis in humans is technically demanding, but provides more detailed information regarding central sympathetic firing. Although a great deal is known about the response of multiunit MSNA to stress, little information is available regarding the responses of single-unit MSNA to physiological stress and disease. The purposes of this review are to describe the differences between multiunit and single-unit MSNA during stress and to discuss the advantages of single-unit MSNA recording in improving our understanding the pathology of increased sympathetic activity in HF.

Highlights

Augmented sympathetic nerve activity is a characteristic feature of heart failure (HF)
We demonstrated that singleunit muscle sympathetic nerve activity (MSNA) can be recorded during periods of physiological stress [e.g., handgrip (HG) exercise and the Valsalva maneuver] and that reflex sympathoexcitation could be attributed to changes in the frequency of single-unit spike firing within each multiunit sympathetic burst in healthy subjects
These results suggest that an instantaneous increase in the frequency of single-unit firing during one cardiac interval provides additional and accurate information on efferent sympathetic firing, which cannot be determined by multiunit MSNA analysis

Summary

INTRODUCTION

Augmented sympathetic nerve activity is a characteristic feature of heart failure (HF). Lambert et al (2011) reported that the incidence of multiple firing was positively correlated to cardiac norepinephrine spillover in humans These results suggest that an instantaneous increase in the frequency of single-unit firing during one cardiac interval provides additional and accurate information on efferent sympathetic firing, which cannot be determined by multiunit MSNA analysis. In HF at rest, despite the elevated level of multiunit MSNA, the incidence of multiple firing of single-unit sympathetic spikes was not different, but the firing frequency of single-unit MSNA was significantly increased compared to healthy subjects (Macefield et al, 1999). We recently demonstrated that the percentage of multiple single-unit spikes within one cardiac interval was increased during HG exercise in chronic HF patients compared to healthy subjects, the response of multiunit MSNA was not significantly different between the two groups (Murai et al, 2009; Figure 3). ASSESSMENT OF MUSCLE SYMPATHETIC NERVE ACTIVITY DURING IRREGULAR VENTRICULAR RESPONSES IN HF

LIMITATIONS

Findings

CONCLUSION