title: Low-frequency oscillation of sympathetic nerve activity decreases during development of tilt-induced syncope preceding sympathetic withdrawal and bradycardia.
abstract: Sympathetic activation during orthostatic stress is accompanied by a marked increase in low-frequency (LF, approximately 0.1-Hz) oscillation of sympathetic nerve activity (SNA) when arterial pressure (AP) is well maintained. However, LF oscillation of SNA during development of orthostatic neurally mediated syncope remains unknown. Ten healthy subjects who developed head-up tilt (HUT)-induced syncope and 10 age-matched nonsyncopal controls were studied. Nonstationary time-dependent changes in calf muscle SNA (MSNA, microneurography), R-R interval, and AP (finger photoplethysmography) variability during a 15-min 60 degrees HUT test were assessed using complex demodulation. In both groups, HUT during the first 5 min increased heart rate, magnitude of MSNA, LF and respiratory high-frequency (HF) amplitudes of MSNA variability, and LF and HF amplitudes of AP variability but decreased HF amplitude of R-R interval variability (index of cardiac vagal nerve activity). In the nonsyncopal group, these changes were sustained throughout HUT. In the syncopal group, systolic AP decreased from 100 to 60 s before onset of syncope; LF amplitude of MSNA variability decreased, whereas magnitude of MSNA and LF amplitude of AP variability remained elevated. From 60 s before onset of syncope, MSNA and heart rate decreased, index of cardiac vagal nerve activity increased, and AP further decreased to the level at syncope. LF oscillation of MSNA variability decreased during development of orthostatic neurally mediated syncope, preceding sympathetic withdrawal, bradycardia, and severe hypotension, to the level at syncope.
authors.affiliation: Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, 5-7-1 Hujishirodai, Suita, Osaka 565-8565, Japan. kamiya@ri.ncvc.go.jp
authors.forename: Atsunori
authors.initials: A
authors.lastname: Kamiya
authors.forename: Junichiro
authors.initials: J
authors.lastname: Hayano
authors.forename: Toru
authors.initials: T
authors.lastname: Kawada
authors.forename: Daisaku
authors.initials: D
authors.lastname: Michikami
authors.forename: Kenta
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Hideto
authors.initials: H
authors.lastname: Ariumi
authors.forename: Syuji
authors.initials: S
authors.lastname: Shimizu
authors.forename: Kazunori
authors.initials: K
authors.lastname: Uemura
authors.forename: Tadayoshi
authors.initials: T
authors.lastname: Miyamoto
authors.forename: Takeshi
authors.initials: T
authors.lastname: Aiba
authors.forename: Kenji
authors.initials: K
authors.lastname: Sunagawa
authors.forename: Masaru
authors.initials: M
authors.lastname: Sugimachi
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001919:Bradycardia / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007024:Hypotension, Orthostatic / Q000503:physiopathology*; D008297:Male; D008955:Models, Cardiovascular; D010507:Periodicity; D011187:Posture; D013564:Sympathetic Nervous System / Q000502:physiology*; D013575:Syncope / Q000503:physiopathology*; D014630:Vagus Nerve / Q000502:physiology