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Cardiovascular regulation in the period preceding vasovagal syncope in conscious humans
Open accessAbstract
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.
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The instability phase observed by Julu et al. showed heart rate and blood pressure oscillation periods ranging from 9-12 s, which could translate into slow breathing at 5-7 breaths/min.
“For example, the instability phase observed by Julu et al. (2003) showed HR and BP oscillation periods ranging from 9–12 s, which could translate into slow breathing at 5–7 breaths/min.”
From The psychophysiology of blood-injection-injury phobia: Looking beyond the diphasic response paradigm (2010) · cites this paper as Julu et al. (2003)
The Results (Phase 3: instability; page not provided) report blood-pressure oscillations, often accompanied by heart-rate oscillations, with periods of 9–12 seconds. That period is numerically equivalent to about 5–7 cycles per minute, but the paper does not establish that the oscillations translate into slow breathing. (LLM, conf=0.85)
Experimental — accuracy not yet measuredJulu et al. described four phases during tilt-table tests and lower body negative pressure: full compensation, tachycardia, instability with massive blood pressure fluctuations, and pre-syncope with blood pressure and heart rate falling below initial levels.
“They described four phases: (i) following vertical tilt, full compensation of the initial BP drop occurs within 30 s, which is followed by (ii) a tachycardia phase, subsequently followed by (iii) an instability phase with massive BP fluctuations, and finally by (iv) pre-syncope, in which BP and HR fall below initial levels (falls in BP preceded falls in HR in a majority of cases).”
From The psychophysiology of blood-injection-injury phobia: Looking beyond the diphasic response paradigm (2010) · cites this paper as Julu et al. (2003)
The Results describe the four phases in the stated order: mean BP recovered within 30 seconds of tilt, tachycardia followed, and the instability phase involved BP oscillations. In phase 4, BP and HR fell, with BP falling first in 10 of 14 subjects (71%). The Results give a pre-syncope mean arterial pressure below the supine baseline, but do not establish that HR also fell below its initial level. (LLM, conf=0.85)
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“Julu et al. (2003) administered tilt-table tests and lower body negative pressure and terminated testing when SBP fell to 80 mmHg and pre-syncopal symptoms occurred.”
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Metadata
- Authors
- Julu, P. O. O., Cooper, V. L., Hansen, S., & Hainsworth, R.
- Affiliations
- University of Leeds (GB)
- Corresponding author
- Julu, P. O. O.
- Venue
- The Journal of Physiology
- Publisher
- Wiley
- Published
- 2003-05
- Volume
- 549
- Issue
- 1
- Pages
- 299-311
- ISSN
- 0022-3751 (ISSN-L)
- 1469-7793
- PMC
- PMC2342918
- OpenAlex
- W1967961674
- Cited by
- 105
- References
- 0
- Citations by year
- 2026: 4 · 2025: 1 · 2023: 1 · 2022: 1 · 2021: 3 · 2020: 3 · 2019: 5 · 2018: 2 · 2017: 9 · 2016: 3 · 2015: 3 · 2014: 6 · 2013: 11 · 2012: 6
- FWCI
- 2.82
- Type
- journal article
- Language
- en
- Open access
- green
- www.ncbi.nlm.nih.gov
- Locations
- The Journal of Physiology (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- White Rose Research Online (University of Leeds, The University of Sheffield, University of York) (submittedVersion)
- Topics
- Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Cardiovascular Syncope and Autonomic Disorders
- Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Heart Rate Variability and Autonomic Control
- Health Sciences › Medicine › Physiology (medical) › Cardiovascular and exercise physiology
- Keywords
- vasovagal syncope, presyncope, cardiovascular regulation, cardiac vagal tone, baroreflex sensitivity, head-up tilt, lower body negative pressure, orthostatic stress, heart rate oscillations, blood pressure oscillations, autonomic nervous system, forearm blood flow, beat-to-beat analysis, tachycardia
- MeSH terms
- Adult, Blood Pressure, Consciousness, Female, Forearm, Heart Rate, Humans, Lower Body Negative Pressure, Male, Middle Aged, Periodicity, Regional Blood Flow, Tachycardia, Baroreflex, Tilt-Table Test, Syncope, Vasovagal
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