title: Simultaneous Characterization of Sympathetic and Cardiac Arms of the Baroreflex through Sequence Techniques during Incremental Head-Up Tilt.
abstract: We propose a sympathetic baroreflex (sBR) sequence method for characterizing sBR from spontaneous beat-to-beat fluctuations of muscle sympathetic nerve activity (MSNA) and diastolic arterial pressure (DAP). The method exploits a previously defined MSNA variability quantifying the fluctuations of MSNA burst rate. The method is based on the detection of MSNA and DAP sequences characterized by the contemporaneous DAP increase and MSNA decrease orvice versa. The percentage of sBR sequences (SEQ%sBR) was taken as an indication of the degree of sBR solicitation and the average slope of the regression lines in the (DAP, MSNA) plane was taken as sBR sensitivity (sBRSSEQ) and expressed in bursts.s-1.mmHg-1. sBRSSEQwas compared to a more traditional estimate based on the baroreflex threshold analysis (sBRSBTA). An incremental head-up tilt protocol, carried out in 12 young healthy subjects (age: 20-36 yr, median = 22.5 yr, 9 females) sequentially tilted at 0, 20, 30, 40, 60° table inclinations, was utilized to set the sBR sequence method parameters. Traditional sequence analysis was exploited to estimate cardiac baroreflex (cBR) sensitivity (cBRSSEQ) and percentage of cBR sequences (SEQ%cBR). The head-up tilt induced the progressive increase of SEQ%sBRand SEQ%cBRand gradual decrease of both sBRSSEQand cBRSSEQ, thus suggesting the gradual rise of the sBR and cBR solicitations and the progressive reduction of their effectiveness with the stimulus. sBRSSEQwas significantly associated with sBRSBTA. sBRSSEQand cBRSSEQwere significantly correlated as well as SEQ%sBRand SEQ%cBR, even though the correlation was not strong, thus suggesting a certain degree of independence between the baroreflex arms. The proposed sBR sequence approach provides a dynamical characterization of the sBR alternative to more traditional static pharmacological and nonpharmacological methods and fully homogenous with the cBR sequence technique.
authors.affiliation: Department of Electronics Information and Bioengineering, Politecnico di MilanoMilan, Italy; Department of Emergency and Intensive Care, San Gerardo HospitalMonza, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Marchi
authors.affiliation: Department of Biomedical Sciences for Health, University of Milan Milan, Italy.
authors.forename: Vlasta
authors.initials: V
authors.lastname: Bari
authors.affiliation: Department of Electronics Information and Bioengineering, Politecnico di MilanoMilan, Italy; IRCCS Fondazione Salvatore MaugeriMilan, Italy.
authors.forename: Beatrice
authors.initials: B
authors.lastname: De Maria
authors.affiliation: Human Neurotransmitter Laboratory, Baker IDI Heart and Diabetes Institute Melbourne, VIC, Australia.
authors.forename: Murray
authors.initials: M
authors.lastname: Esler
authors.affiliation: Human Neurotransmitter Laboratory, Baker IDI Heart and Diabetes Institute Melbourne, VIC, Australia.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Lambert
authors.affiliation: School of Electrical and Electronic Engineering, University of Adelaide Adelaide, SA, Australia.
authors.forename: Mathias
authors.initials: M
authors.lastname: Baumert
authors.affiliation: Department of Biomedical Sciences for Health, University of MilanMilan, Italy; Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San DonatoMilan, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Porta
keywords: arterial pressure variability; autonomic nervous system; cardiovascular control; heart rate variability; muscle sympathetic nerve activity