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Contributions of cardiac output and total peripheral resistance to vasovagal syncope during orthostasis in humans
Author(s) -
Fu Qi,
VanGundy Tiffany B,
Shibata Shigeki,
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.611.7
Subject(s) - presyncope , vasovagal syncope , medicine , heart rate , blood pressure , cardiac output , cardiac index , cardiology , stroke volume , hemodynamics , mean arterial pressure , anesthesia , syncope (phonology)
Mean arterial pressure is determined by cardiac output (CO) and total peripheral resistance (TPR). However, the contribution of CO and TPR to blood pressure (BP) drop during vasovagal syncope in humans is uncertain. We studied retrospectively 26 subjects (4 men and 22 women, age range 16‐50) who had no previous history of syncope but had presyncopal episodes during 45 min 60° upright tilt in our lab in the past 4 years. Muscle sympathetic nerve activity (MSNA), heart rate (HR), and BP were recorded continuously, while beat‐to‐beat hemodynamics were derived from the Modelflow method calibrated by the acetylene rebreathing technique. Systolic BP decreased progressively and then rapidly 100 and 20 s prior to presyncope, while diastolic BP started to decrease 40 s before presyncope. Fifteen of them (58%, Group A) had falls in both CO and TPR, while 11 (42%, Group B) had only a fall in CO 60 s prior to presyncope. Cardiac index, calculated as CO divided by body surface area, was lower [2.10±0.39 (SD) L/min/m 2 vs 2.50±0.53, P =0.0498], while TPR was greater (1.30±0.83 MU vs 0.87±0.16, P =0.0572) in Group B than Group A at presyncope. The steeper fall in CO in Group B was due to a decrease in HR rather than stroke volume. MSNA decreased rapidly 20 s prior to presyncope in both groups. These results suggest that both CO and TPR are determinant factors for the drop in arterial pressure. A marked decrease in CO alone or a modest decrease in CO accompanied by a modest systemic vasodilation contributes to syncope during orthostasis in humans.