title: Calibrated variability of muscle sympathetic nerve activity during graded head-up tilt in humans and its link with noradrenaline data and cardiovascular rhythms.
abstract: Muscle sympathetic nerve activity (MSNA) variability is traditionally computed through a low-pass filtering procedure that requires normalization. We proposed a new beat-to-beat MSNA variability computation that preserves dimensionality typical of an integrated neural discharge (i.e., bursts per unit of time). The calibrated MSNA (cMSNA) variability technique is contrasted with the traditional uncalibrated MSNA (ucMSNA) version. The powers of cMSNA and ucMSNA variabilities in the low-frequency (LF, from 0.04 to 0.15 Hz) band were computed with those of the heart period (HP) of systolic and diastolic arterial pressure (SAP and DAP, respectively) in seven healthy subjects (age, 20-28 years; median, 22 years; 5 women) during a graded head-up tilt. Subjects were sequentially tilted at 0°, 20°, 30°, 40°, and 60° table inclinations. The LF powers of ucMSNA and HP variabilities were expressed in normalized units (LFnu), whereas all remaining spectral markers were expressed in absolute units. We found that 1) the LF power of cMSNA variability was positively correlated with tilt angle, whereas the LFnu power of the ucMSNA series was uncorrelated; 2) the LF power of cMSNA variability was correlated with LF powers of SAP and DAP, LFnu power of HP and noradrenaline concentration, whereas the relationship of the LFnu power of ucMSNA variability to LF powers of SAP and DAP was weaker and that to LFnu power of HP was absent; and 3) the stronger relationship of cMSNA variability to SAP and DAP spectral markers compared with the ucMSNA series was confirmed individually. The cMSNA variability appears to be more suitable in describing sympathetic control in humans than traditional ucMSNA variability.
authors.affiliation: Department of Electronics Information and Bioengineering, Politecnico di Milano, Milan, Italy; Department of Emergency and Intensive Care, San Gerardo Hospital, Monza, Italy;
authors.forename: Andrea
authors.initials: A
authors.lastname: Marchi
authors.affiliation: Department of Biomedical Sciences for Health, University of Milan, Italy;
authors.forename: Vlasta
authors.initials: V
authors.lastname: Bari
authors.affiliation: IRCCS Fondazione Salvatore Maugeri, Milan, Italy;
authors.forename: Beatrice
authors.initials: B
authors.lastname: De Maria
authors.affiliation: Human Neurotransmitter Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, Australia;
authors.forename: Murray
authors.initials: M
authors.lastname: Esler
authors.affiliation: Human Neurotransmitter Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, Australia;
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Lambert
authors.affiliation: School of Electrical and Electronic Engineering, University of Adelaide, Australia; and.
authors.forename: Mathias
authors.identifier: 0000-0003-2984-2167
authors.initials: M
authors.lastname: Baumert
authors.affiliation: Department of Biomedical Sciences for Health, University of Milan, Italy; Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, Milan, Italy alberto.porta@unimi.it.
authors.forename: Alberto
authors.identifier: 0000-0002-6720-9824
authors.initials: A
authors.lastname: Porta
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000502:physiology; D001683:Biological Clocks / Q000502:physiology*; D002138:Calibration; D003935:Diagnostic Techniques, Cardiovascular / Q000592:standards; D003943:Diagnostic Techniques, Neurological / Q000592:standards; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009638:Norepinephrine / Q000097:blood*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013564:Sympathetic Nervous System / Q000502:physiology*; D018667:Tilt-Table Test / Q000592:standards*
chemical_list: D009638:Norepinephrine
keywords: MSNA; arterial pressure variability; autonomic nervous system; cardiovascular control; catecholamines; heart rate variability