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Shift of the cardiovagal baroreflex response with maintained sensitivity during head up tilt
Author(s) -
Schwartz Christopher E.,
Medow Marvin S.,
Messer Zachary,
Baugham Ila L.,
Terilli Courtney,
Tambone Robert,
Stewart Julian M.
Publication year - 2012
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.26.1_supplement.1091.27
Subject(s) - baroreflex , supine position , medicine , phenylephrine , reflex , anesthesia , blood pressure , cardiology , tilt (camera) , heart rate , mathematics , geometry
Measurement of cardiovagal baroreflex gain is often evaluated using spontaneous fluctuations in blood pressure (BP) and R‐R interval. However, spontaneous indices (SI) only provide a slope of the baroreflex curve at operating points (OP) and may not adequately identify changes in sensitivity and range of reflex function produced by the reference standard modified Oxford (mod‐Ox) technique. We hypothesize that during head up tilt (HUT) the baroreflex centering point (CP) is reset with unchanged sensitivity and response range. The mod‐Ox comprised 100 μg sodium nitroprusside, followed 1 min later by 150μg phenylephrine administered intravenously to 12 subjects (4 male) supine and again after 5 min of 70° HUT. Supine vs upright sensitivity (26±2 vs. 28±3 ms/mmHg) and response range (1104±77 vs. 1010±66 ms) were unchanged by HUT, but the CP was right and downwards shifted. Supine, the OP was near the CP; thus mod‐Ox and SI gains (21±3 vs 23±3 ms/mmHg) were similar to the reflex sensitivity (26±2, slope at CP). In contrast, the upright OP was far from the CP and thus the mod‐Ox OP gain was markedly decreased (28±3 vs 9±4 ms/mmHg) compared to the sensitivity (slope at CP) and was not different from SI gain (7.3±2). The cardiovagal baroreflex is shifted with HUT. SI estimate OP mod‐Ox gains which are similar to baroreflex sensitivity when supine but markedly reduced during HUT. Supported by NIH HL‐091948 and HL‐074873.