Premium
Modulation of the control of muscle sympathetic nerve activity during severe orthostatic stress
Author(s) -
Ichinose Masashi,
Saito Mitsuru,
Fujii Naoto,
Kondo Narihiko,
Nishiyasu Takeshi
Publication year - 2006
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2006.117507
Subject(s) - presyncope , baroreflex , medicine , supine position , orthostatic intolerance , orthostatic vital signs , blood pressure , microneurography , anesthesia , cardiology , heart rate
We tested the hypothesis that arterial baroreflex (ABR)‐mediated beat‐to‐beat control over muscle sympathetic nerve activity (MSNA) is progressively modulated as orthostatic stress increases in humans, but that this control becomes impaired just before the onset of orthostatic syncope. In 17 healthy subjects, the ABR control over MSNA (burst incidence, burst strength and total MSNA) was evaluated by analysing the relationship between beat‐to‐beat spontaneous variations in diastolic blood pressure (DAP) and MSNA during supine rest (control) and during progressive, stepwise increases in lower body negative pressure (LBNP) that were incremented by −10 mmHg every 5 min until presyncope (nine subjects) or −60 mmHg was reached. (1) The linear relationships between DAP and burst strength and between DAP and total MSNA were shifted progressively upward as LBNP increased until the level at which syncope occurred. The relationship between DAP and burst incidence, however, gradually shifted upward from control only to LBNP =−30 mmHg; there was no further upward shift at higher LBNPs. (2) Although the slope of the relationship between DAP and burst strength and between DAP and total MSNA remained constant at all LBNPs tested, except at the level where syncope occurred, the slope of the relationship between DAP and burst incidence was reduced at LBNPs of −40 mmHg and higher ( versus control). (3) In syncopal subjects, the slopes of the relationships between DAP and burst incidence, burst strength, and total MSNA were all substantially reduced during the 1–2 min period prior to the onset of syncope. Taken together, these results suggest baroreflex control over MSNA is progressively modulated as orthostatic stress increases, so that its sensitivity is substantially reduced during the period immediately preceding the severe hypotension associated with orthostatic syncope.