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Muscle sympathetic nerve activity is dependent on stroke volume via carotid artery distortion during orthostatic stress
Author(s) -
Hastings Jeff,
Shibata Shigeki,
Shook Robin,
Okazaki Kazunobu,
Conner Colin,
Palmer M. Dean,
Fu Qi,
Levine Benjamin
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.21.6.a878-c
Sympathetic nerve activity (SNA) increases during upright posture, even though blood pressure does not change or may increase. If the increase in SNA is baroreflex mediated, then some other stimulus must be involved. We hypothesized that SV alters carotid distortion, thereby influencing baroreflex stimulation. Common carotid dimensions, muscle SNA (MSNA), and stroke volume (SV) were measured during graded head‐up tilt (HUT) in 9 healthy young subjects. Carotid measurements were made with ultrasonography (ATL HDI 5000, SonoCT). SV was derived from heart rate and cardiac output via C2H2 rebreathing. An index of carotid distortion was calculated by ΔP·Δr/t avg (ΔP = hydrostatically corrected pulse pressure, Δr = radius change from systole to diastole, and t = average wall thickness). SV decreased during graded HUT (mean ±SD: 102±23ml supine vs 82±26 and 66±22 at 30° and 60°, P=0.006,) as did carotid distortion (9.9±4.6 mmHg; 7.7±2.9, and 6.6±4.5, P=0.039). Carotid distortion was positively correlated to SV (R = 0.675, P < 0.001). MSNA increased during graded HUT (12.4±7.0 bursts/min, 20.2±7.9, and 30.9±5.8; P<0.01). There was a close linear correlation between mean values of MSNA and carotid distortion (R=0.945) CONCLUSIONS: Changes in carotid distortion due to alterations in stroke volume directly affect changes in sympathetic baroreflex output during orthostatic stress in healthy humans. Support:NIH K23 (HL0752 83) and GCRC grant (RR00633).