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Modulation of the control of muscle sympathetic nerve activity during severe orthostatic stress in humans
Author(s) -
Ichinose Masashi,
Saito Mitsuru,
Kondo Narihiko,
Nishiyasu Takeshi
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a1427-a
We aimed at investigating whether arterial baroreflex (ABR) control of muscle sympathetic nerve activity (MSNA) is progressively modulated with increasing orthostatic stress, and ABR‐mediated MSNA control becomes impaired before the onset of orthostatic syncope. In 17 healthy subjects, ABR control of MSNA [burst incidence (BI) and strength (BS), and total activity (TA)] were evaluated by analyzing the relationship between spontaneous variations in diastolic blood pressure (DAP) and MSNA during supine rest and at each stage of progressive lower body negative pressure (LBNP) in increments of −10 mmHg every 5min until presyncope (nine subjects) or −60 mmHg was reached. (a) The linear relationships between DAP and BS and TA shifted progressively upward with increasing levels of LBNP until the last stage. The relationship between DAP and BI, however, gradually shifted upward from the control to −30 mmHg, but there was no further significant upward shift from the −30 mmHg and higher stages. (b) The sensitivity of the BS and TA controls did not changed in any situation except in the stages where syncope occurred, but the sensitivity of the BI control was decreased at the −40 mmHg and higher stages. (c) In syncopal subjects, the sensitivity of BI, BS, and TA controls were all largely decreased during a 1–2 min period before the onset of syncope. These results suggest that 1) ABR control of MSNA is progressively modulated with increasing orthostatic stress and, 2) the sensitivity of ABR control of MSNA is reduced during the development of orthostatic syncope. This study was supported by grants from COE projects and the Ministry of Education, Science, and Culture of Japan.