Julu, P.O.O., Cooper, V.L., Hansen, S. et al. (1 more author) (2003) Cardiovascular regulation in the period preceding vasovagal syncope in conscious humans. Journal of Physiology, 549 (1). pp. 299-311. ISSN 0022-3751
Abstract
To study cardiovascular control in the period leading to vasovagal syncope we monitored beat-to-beat blood pressure, heart rate (HR) and forearm blood flow in 14 patients with posturally related syncope, from supine through to tilt-induced pre-syncope. Signals of arterial blood pressure (BP) from a Finapres photoplethysmograph and an electrocardiograph (ECG) were fed into a NeuroScope system for continuous analysis. Non-invasive indices of cardiac vagal tone (CVT) and cardiac sensitivity to baroreflex (CSB) were derived on a beat-to-beat basis from these data. Brachial vascular resistance (VR) was assessed intermittently from brachial blood flow velocity (Doppler ultrasound) divided by mean arterial pressure (MAP). Patients underwent a progressive orthostatic stress test, which continued to pre-syncope and consisted of 20 min head-up tilt (HUT) at 60 deg, 10 min combined HUT and lower body suction (LBNP) at -20 mmHg followed by LBNP at -40 mmHg. Pre-syncope was defined as a fall in BP to below 80 mmHg systolic accompanied by symptoms. Baseline supine values were: MAP (means ± S.E.M.) 84.9 ± 3.2 mmHg; HR, 63.9 ± 3.2 beats min-1; CVT, 10.8 ± 2.6 (arbitrary units) and CSB, 8.2 ± 1.6 ms mmHg-1. HUT alone provoked pre-syncope in 30 % of the patients whilst the remaining 70 % required LBNP. The cardiovascular responses leading to pre-syncope can be described in four phases. Phase 1, full compensation: where VR increased by 70.9 ± 0.9 %, MAP was 89.2 ± 3.8 mmHg and HR was 74.8 ± 3.2 beats min-1 but CVT decreased to 3.5 ± 0.5 units and CSB to 2.7 ± 0.4 ms mmHg-1. Phase 2, tachycardia: a progressive increase in heart rate peaking at 104.2 ± 5.1 beats min-1. Phase 3, instability: characterised by oscillations in BP and also often in HR; CVT and CSB also decreased to their lowest levels. Phase 4, pre-syncope: characterised by sudden decreases in arterial blood pressure and heart rate associated with intensification of the symptoms of pre-syncope. This study has given a clearer picture of the cardiovascular events leading up to pre-syncope. However, the mechanisms behind what causes a fully compensated system suddenly to become unstable remain unknown.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2003 The Physiological Society. |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Medicine and Health (Leeds) > School of Medicine (Leeds) > Leeds Institute of Genetics, Health and Therapeutics (LIGHT) > Academic Unit of Cardiovascular Medicine (Leeds) |
Depositing User: | Repository Assistant |
Date Deposited: | 26 May 2006 |
Last Modified: | 16 Sep 2016 13:54 |
Published Version: | http://jp.physoc.org/cgi/reprint/549/1/299 |
Status: | Published |
Publisher: | Cambridge University Press |
Refereed: | Yes |
Identification Number: | 10.1113/jphysiol.2002.036715 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:1239 |