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Neither gender nor the menstrual cycle affects sympathetic baroreflex sensitivity during orthostasis in humans
Author(s) -
Fu Qi,
Shibata Shigeki,
VanGundy Tiffany B,
Okazaki Kazunobu,
Galbreath M Melyn,
Levine Benjamin D
Publication year - 2009
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.23.1_supplement.786.6
Subject(s) - baroreflex , supine position , medicine , menstrual cycle , heart rate , blood pressure , diastole , hemodynamics , luteal phase , cardiology , follicular phase , hormone
We tested the hypothesis that baroreflex control of muscle sympathetic nerve activity (MSNA) during orthostasis is impaired in women and can be affected by the menstrual cycle. MSNA and hemodynamics were measured supine and during a graded upright tilt (30º and 60º, 6 min each) in 11 young men and 11 women during the early follicular (EFP) and mid‐luteal phase (MLP) of the menstrual cycle. Sympathetic baroreflex sensitivity was quantified using the slope of the linear correlation between MSNA and diastolic pressure during spontaneous breathing. It was further assessed as the relation between MSNA and stroke index (SI), with SI derived from cardiac output (CO, C 2 H 2 rebrathing), heart rate and body surface area. MSNA increased during tilting, and the responses were similar between genders and phases. Sympathetic baroreflex sensitivity did not differ between genders and phases supine [?280±151 (SD) units/beat/mmHg in men vs ?252±172 in EFP and ?272±131 in MLP in women, P =0.679 and 0.890], and at 30º (?648±429 vs ?610±262 and ?486±312, P =0.781 and 0.264) and 60º tilt (?792±447 vs ?831±305 and ?814±471, P =0.814 and 0.912); the sensitivity was not affected by the menstrual cycle. Changes in MSNA were associated with changes in SI, while the slope of the line was not different between genders and phases. These results suggest that neither gender nor the menstrual cycle affects sympathetic baroreflex sensitivity. Other factors rather than neural mechanisms contribute to gender differences in orthostatic tolerance in humans. 1