Lateralization of expression of neural sympathetic activity to the vessels and effects of carotid baroreceptor stimulation

Abstract

Furlan R. Lateralization of expression of neural sympathetic activity to the vessels and effects of carotid baroreceptor stimulation. Am J Physiol Heart Circ Physiol 296: H1758 -H1765, 2009. First published April 10, 2009 doi:10.1152/ajpheart.01045.2008.-Human studies suggest that cardiovascular neural sympathetic control is predominantly modulated by the right cerebral hemisphere. It is unknown whether post-ganglionic sympathetic activity [muscle sympathetic nerve activity (MSNA)] shows any functional asymmetry. Eight right-handed volunteers (3 women and 5 men, 32 Ϯ 2 yr of age) underwent ECG, beat-by-beat blood pressure, respiratory activity, and simultaneous right and left MSNA recordings during spontaneous and controlled breathing (CB, 15 breaths/min, 0.25 Hz). Dynamic carotid baroreceptor stimulation was obtained by 0.1-Hz sinusoidal suction, from 0 to Ϫ50 mmHg, randomly applied to the right, left, and combined right and left sides of the neck during CB. Laterality was assessed by changes in the MSNA burst rate (in bursts/min, and bursts/100 beats), strength [amplitude (A) and area (AA)], and the oscillatory component at 0.1 Hz during baroreceptor stimulation. Amplitude parameters were normalized by CB burst mean amplitude and area of the same side. At rest, the right and left MSNA burst rate and total MSNA activity were similar. Conversely, the right MSNA normalized burst AN (1.36 Ϯ 0.18) and AAN (1.31 Ϯ 0.16) were larger than the left MSNA AN (1.04 Ϯ 0.09) and AAN (1.02 Ϯ 0.08). Unilateral and bilateral carotid baroreflex stimulation abolished the right prevalence of AN and AAN. In conclusion, the right lateralization of sympathetic activity to the vessels is indicated by normalized burst strength parameters of bilateral MSNA recordings at rest during spontaneous breathing. Carotid baroreceptor stimulation disrupted such expression of MSNA lateralization possibly by disturbing the synchronizing action of right cerebral hemisphere. sympathetic control of circulation; muscle sympathetic nerve activity recording; burst amplitude; area; laterality SEVERAL HUMAN STUDIES support the concept that the neural sympathetic activity regulating the cardiovascular system undergoes a predominant modulation exerted by the right cerebral hemisphere (2, 4, 10, 17-19, 33, 34). The right side of the medulla was also found to be involved in cardioacceleration in vagotomized animals (16). However, it has to be pointed out that the large majority of these investigations focused on functional modifications of the sympathetic target organs, i.e., on changes of heart rate and blood pressure and their variability, and did not focus on a direct measure of right and left efferent sympathetic activity.Two studies (27, 28) addressed the problem of the potential dissimilarity between the right and left neural efferent sympathetic activity by recording simultaneously muscle sympathetic nerve activity (MSNA) in both peroneal nerves in humans. Sundlof and Wallin (27) focused on burst rate, which was found to be similar in the right and le...

Electrical Carotid Sinus Stimulation: Chances and Challenges in the Management of Treatment Resistant Arterial Hypertension

“…Moreover, the response appears to be variable and some patients may not respond stimulation exhibited better blood pressure control compared with patients with unilateral left-sided stimulation. This observation would support the idea that baroreflex regulation is asymmetric as suggested based on human physiological experiments using neck suction [31][32][33]. However, all these findings have to be interpreted with great caution because comparisons between stimulation settings were not conducted in a systematical fashion.…”

Bilateral or Unilateral Stimulation for Baroreflex Activation Therapy

“…Because sinusoidal baroreflex activation is able to abolish the difference, the data also suggest that this is a functional rather than an anatomically related phenomenon. 8 In a study on 12 volunteers, Furlan et al 9 also found greater effects of neck suction on the right side than on the left one. All these studies, however, focused on changes in heart rate and blood pressure variability and not on blood pressure alterations per se.…”

“…Further observations indicated that during spontaneous breathing there is a rightsided predominance in strength of muscle sympathetic activity at rest but that this right-left difference disappears during carotid baroreflex stimulation, regardless of whether unilateral or bilateral stimulation is applied. 8 In other words, it seems that sympathetic activity at rest is stronger in the right part of the body. Because sinusoidal baroreflex activation is able to abolish the difference, the data also suggest that this is a functional rather than an anatomically related phenomenon.…”

“…They suggested that the functional asymmetry could be related to differences in central ipsilateral projection of the carotid baroreceptor afferents to the nuclei tractus solitarii. Later on, Diedrich et al 8 described that under conditions of controlled respiratory rate, right-sided and bilateral baroreflex loading by 0.1-Hz sinusoidal neck suction were more effective in modulating heart rate and systolic blood pressure variability than leftsided loading. There was, however, no asymmetry in muscle sympathetic nerve discharge responses.…”

Carotid baroreflex activation therapy for resistant hypertension

“…These data are consistent with animal studies indicating right-sided predominance of the carotid baroreflex; 93 studies in humans using the neck suction device are inconclusive. [94][95][96] Future trials of carotid baroreflex activation therapy for resistant hypertension should be designed to overcome the limitations of this first phase III trial. Meanwhile, a s econd-generation miniaturized device-Barostim neo™-for unilateral pacing has been designed to reduce surgical procedure time and facial nerve complications and to improve efficacy.…”