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(Hypertension. 2000;36:1029.)
© 2000 American Heart Association, Inc.

Scientific Contributions

Effects of Spinal Section and of Positive-Feedback Excitatory Reflex on Sympathetic and Heart Rate Variability

Nicola Montano; Chiara Cogliati; Valdo Jose Dias da Silva; Tomaso Gnecchi-Ruscone; Marcello Massimini; Alberto Porta; Alberto Malliani

From Centro Ricerche Cardiovascolari CNR, Dipartimento di Scienze Precliniche LITA di Vialba, Medicina Interna II, Ospedale L. Sacco, Universita’ degli Studi di Milano, Milano, Italy (N.M., C.C., V.J.D.d.S., M.M., A.P., A.M.); and Cardiologia, Ospedale S.L. Mandic, Merate, Italy (T.G.-R.).

Correspondence to Alberto Malliani, MD, Medicina Interna II, Ospedale L. Sacco, via GB Grassi 74, 20157 Milano, Italy. E-mail albertom{at}fisiopat.sacco.unimi.it

Abstract—The sympathetic outflow appears to be capable of displaying a rhythmicity synchronous with cardiovascular Mayer’s waves even after spinal section. To test the hypothesis that spinal sympathetic low frequency (LF) oscillation can be enhanced during sympathetic excitation, we recorded cardiac sympathetic nerve activity (SNA), R-R interval, arterial pressure, and ventilation in 9 unanesthetized decerebrate-vagotomized cats before and after C1 spinal section. LF and high frequency (HF) components were detected in the variability of SNA, R-R interval, and systolic arterial pressure both before and after spinal section. In this latter condition, a significant coherence between LF_SNA and LF_R-R was present in 5 animals, whereas HF_SNA and HF_R-R were correlated in 4 animals. During an excitatory sympathetic spinal reflex elicited by aortic constriction, the efferent sympathetic firing was markedly enhanced (from 7±2 to 33±7 spikes/s); concomitantly, the powers of both LF_SNA and HF_SNA were also increased. Coherence between LF_SNA and LF_R-R became significant in all cases, whereas HF_SNA and HF_R-R became correlated in 6 animals. In 3 animals, the reflex sympathetic excitation was no longer elicitable after interrupting a vast contingent of sympathetic afferents by means of thoracic dorsal root section. We report for the first time that LF and HF oscillations are detectable in SNA, R-R interval, and systolic arterial pressure variabilities of decerebrate-vagotomized spinal cats and that an excitatory spinal reflex is capable of increasing the power of both SNA spectral components.

Key Words: autonomic nervous system • sympathetic nervous system • heart • reflex

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