Decrease in cardiac output and muscle sympathetic activity during vasovagal syncope

Departments of 1  General Medicine, 2  Cardiology, and 3  Medicine, Christchurch Hospital, Christchurch, New Zealand The importance of cardiac output (CO) to blood pressure level during vasovagal syncope is unknown. We measured thermodilution CO, mean blood pressure (MBP), and leg muscle mean sympat...

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Bibliographic Details
Published in:American journal of physiology. Heart and circulatory physiology 2002-05, Vol.282 (5), p.H1804-H1809
Main Authors: Jardine, D. L, Melton, I. C, Crozier, I. G, English, S, Bennett, S. I, Frampton, C. M, Ikram, H
Format: Article
Language:English
Subjects:
Adult
Aged
Blood Pressure
Cardiac Output
Electrocardiography
Female
Heart Rate
Humans
Leg
Male
Middle Aged
Muscle, Skeletal - innervation
Oxygen - blood
Oxygen Consumption
Posture
Sex Characteristics
Space life sciences
Sympathetic Nervous System - physiopathology
Syncope, Vasovagal - physiopathology
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Summary:Departments of 1  General Medicine, 2  Cardiology, and 3  Medicine, Christchurch Hospital, Christchurch, New Zealand The importance of cardiac output (CO) to blood pressure level during vasovagal syncope is unknown. We measured thermodilution CO, mean blood pressure (MBP), and leg muscle mean sympathetic nerve activity (MSNA) each minute during 60° head-up tilt in 26   patients with recurrent syncope. Eight patients tolerated tilt (TT) for 45 min (mean age 60 ± 5 yr) and 15 patients developed syncope during tilt (TS) (mean age 58 ± 4 yr, mean tilt time 15.4   ± 2 min). In TT patients, CO decreased during the first minute of tilt (from 3.2 ± 0.2 to 2.5 ± 0.3 l · min 1 · m 2 , P  = 0.001) and thereafter remained stable between 2.5 ± 0.3   ( P  = 0.001) and 2.4 ± 0.2 l · min 1 · m 2 ( P  = 0.004) at 5 and 45 min, respectively. In TS patients, CO decreased during the first minute (from 3.3 ± 0.2 to 2.7 ± 0.1   l · min 1 · m 2 , P  = 0.02) and was stable until 7 min before syncope, falling to 2.0 ± 0.2 at syncope ( P  = 0.001). Regression slopes for CO versus time during tilt were 0.01 min 1 in TT versus 0.1 l · min 1 · m 2 · min 1 in TS ( P  = 0.001). However, MBP was more closely correlated to total peripheral resistance ( R  = 0.56,  P  = 0.001) and MSNA ( R   = 0.58,  P  = 0.001) than CO ( R  = 0.32,  P  = 0.001). In vasovagal reactions, a progressive decline in CO may contribute to hypotension some minutes before syncope occurs. tilt test; neurocardiogenic syncope; vasodilatation
ISSN:0363-6135
1522-1539
DOI:10.1152/ajpheart.00640.2001