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Open AccessArticle

Cardiac and Vascular Sympathetic Baroreflex Control during Orthostatic Pre-Syncope

1
Department of Internal Medicine, Humanitas Clinical and Research Center, IRCCS, Humanitas University, 20089 Rozzano, Italy
2
Institute of Aerospace Medicine, German Aerospace Center (DLR), 51147 Cologne, Germany
3
Department of Biomedical Sciences for Health, University of Milan, 20122 Milan, Italy
4
Chair of Aerospace Medicine, University of Cologne, 51147 Cologne, Germany
5
Autonomic Dysfunction Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA
6
Departamento de Kinesiología, Universidad Católica del Maule, 3530000 Talca, Maule, Chile
7
Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico di San Donato, 20097 San Donato Milanese, Italy
*
Author to whom correspondence should be addressed.
J. Clin. Med. 2019, 8(9), 1434; https://doi.org/10.3390/jcm8091434
Received: 1 August 2019 / Revised: 4 September 2019 / Accepted: 5 September 2019 / Published: 10 September 2019
(This article belongs to the Special Issue Autonomic Nervous System: From Bench to Bedside)
We hypothesized that sympathetic baroreflex mediated uncoupling between neural sympathetic discharge pattern and arterial pressure (AP) fluctuations at 0.1 Hz during baroreceptor unloading might promote orthostatic pre-syncope. Ten volunteers (32 ± 6 years) underwent electrocardiogram, beat-to-beat AP, respiratory activity and muscle sympathetic nerve activity (MSNA) recordings while supine (REST) and during 80° head-up tilt (HUT) followed by −10 mmHg stepwise increase of lower body negative pressure until pre-syncope. Cardiac and sympathetic baroreflex sensitivity were quantified. Spectrum analysis of systolic and diastolic AP (SAP and DAP) and calibrated MSNA (cMSNA) variability assessed the low frequency fluctuations (LF, ~0.1 Hz) of SAP, DAP and cMSNA variability. The squared coherence function (K2) quantified the coupling between cMSNA and DAP in the LF band. Analyses were performed while supine, during asymptomatic HUT (T1) and at pre-syncope onset (T2). During T2 we found that: (1) sympathetic baroreceptor modulation was virtually abolished compared to T1; (2) a progressive decrease in AP was accompanied by a persistent but chaotic sympathetic firing; (3) coupling between cMSNA and AP series at 0.1 Hz was reduced compared to T1. A negligible sympathetic baroreceptor modulation during pre-syncope might disrupt sympathetic discharge pattern impairing the capability of vessels to constrict and promote pre-syncope. View Full-Text
Keywords: syncope; vasovagal; baroreceptors; muscle sympathetic nerve activity; power spectrum analysis; heart rate variability; blood pressure variability; MSNA variability syncope; vasovagal; baroreceptors; muscle sympathetic nerve activity; power spectrum analysis; heart rate variability; blood pressure variability; MSNA variability
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Furlan, R.; Heusser, K.; Minonzio, M.; Shiffer, D.; Cairo, B.; Tank, J.; Jordan, J.; Diedrich, A.; Gauger, P.; Zamuner, A.R.; Dipaola, F.; Porta, A.; Barbic, F. Cardiac and Vascular Sympathetic Baroreflex Control during Orthostatic Pre-Syncope. J. Clin. Med. 2019, 8, 1434.

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