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Carbon dioxide, critical closing pressure and cerebral haemodynamics prior to vasovagal syncope in humans
Abstract
The cerebrovascular changes that occur prior to vasovagal syncope (VVS) are unclear, with both increases and decreases in cerebrovascular resistance being reported during pre-syncope. This study assessed the cerebrovascular responses, and their potential underlying mechanisms, that occurred before VVS induced by head-up tilt (HUT). Groups of 65 normal subjects with no previous history of syncope and of 16 patients with recurrent VVS were subjected to 70 degrees HUT for up to 30 min. Bilateral middle cerebral artery (MCA) cerebral blood flow velocities (CBFVs) were measured using transcranial Doppler ultrasound, along with simultaneous measures of MCA blood pressure, heart rate, and end-tidal and transcutaneous carbon dioxide concentrations. All 16 patients and 14 of the control subjects developed VVS during HUT. During pre-syncope, mean CBFV declined, due predominantly to a decrease in diastolic rather than systolic CBFV (decreases of 44.5+/-19.8% and 6.3+/-12.9% respectively; P<0.0001). CO(2) levels and indices of cerebrovascular resistance decreased during pre-syncope, while critical closing pressure (CrCP) increased to levels approaching MCA diastolic blood pressure before decreasing precipitously on syncope. Pre-syncopal changes were similar in syncopal patients and syncopal controls. CrCP, therefore, rises during pre-syncope, possibly related to progressive hypocapnia, and may account for the relatively greater fall in diastolic CBFV. Falls in cerebrovascular resistance,…
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Carey et al. found on average small reductions (−3.8 mmHg) in end-tidal PCO2 in 7 patients with neurally mediated syncope and healthy controls before syncope.
“Carey et al. (2001) found on average small reductions (−3.8 mmHg) in end-tidal PCO2 in 7 patients with neurally mediated syncope and healthy controls before syncope”
From The psychophysiology of blood-injection-injury phobia: Looking beyond the diphasic response paradigm (2010) · cites this paper as Carey et al. (2001)
In patients with recurrent vasovagal syncope, hyperventilation appears to change the pressure threshold at which blood flow in cerebral vessels ceases and vessel walls start collapsing, in that higher pressures than are present under normocapnia are sufficient to induce this state.
“In patients with recurrent vasovagal syncope, hyperventilation appears to change the pressure threshold at which the blood flow in cerebral vessels ceases and vessel walls start collapsing (critical closing pressure), in that higher pressures than are present under normocapnia are sufficient to induce this state (Carey et al., 2001).”
From The psychophysiology of blood-injection-injury phobia: Looking beyond the diphasic response paradigm (2010) · cites this paper as Carey et al., 2001
Carey et al. concluded that hypocapnia due to an increase in respiratory amplitude forms an intrinsic part of the pathophysiology of vasovagal syncope.
“Carey at al. (2001) concluded that “it would appear that hypocapnia due to an increase in respiratory amplitude forms an intrinsic part of the pathophysiology of vasovagal syncope” (p. 356).”
From The psychophysiology of blood-injection-injury phobia: Looking beyond the diphasic response paradigm (2010) · cites this paper as Carey at al. (2001)
CO2-rebreathing has been used to counteract hypocapnia-induced reductions in cerebral blood flow in vasovagal syncope and has been recommended for further scrutiny as an intervention technique.
“Indeed, CO2-rebreathing has been used to counteract hypocapnia-induced reductions in CBF in vasovagal syncope (Novak et al., 1998) and has been recommended for further scrutiny as an intervention technique (Carey et al., 2001).”
From The psychophysiology of blood-injection-injury phobia: Looking beyond the diphasic response paradigm (2010) · cites this paper as Carey et al., 2001
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The psychophysiology of blood-injection-injury phobia: Looking beyond the diphasic response paradigm
Ritz, T., Meuret, A. E., & Ayala, E. S. (2010) · International Journal of Psychophysiology · doi:10.1016/j.ijpsycho.2010.05.007 · Cited by 74
Metadata
- Authors
- CAREY, B. J., EAMES, P. J., PANERAI, R. B., & POTTER, J. F.
- Affiliations
- University of Leicester (GB)
- Venue
- Clinical Science
- Publisher
- Portland Press Ltd.
- Published
- 2001-10-01
- Volume
- 101
- Issue
- 4
- Pages
- 351
- ISSN
- 0143-5221 (ISSN-L)
- OpenAlex
- W1984379267
- Cited by
- 79
- References
- 0
- Citations by year
- 2025: 3 · 2024: 3 · 2023: 2 · 2022: 3 · 2020: 1 · 2019: 2 · 2018: 1 · 2017: 3 · 2016: 3 · 2015: 3 · 2014: 6 · 2013: 6 · 2012: 5
- FWCI
- 3.64
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Clinical Science (publishedVersion)
- PubMed (publishedVersion)
- Leicester Research Archive (University of Leicester) (submittedVersion)
- Funders
- Stroke Association
- Coral Reef Conservation Program
- 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
- Life Sciences › Neuroscience › Neurology › Vestibular and auditory disorders
- Keywords
- vasovagal syncope, presyncope, cerebral blood flow velocity, middle cerebral artery, cerebrovascular resistance, critical closing pressure, hypocapnia, carbon dioxide, head-up tilt, cerebral hemodynamics, diastolic blood pressure
- MeSH terms
- Adolescent, Adult, Aged, Aged, 80 and over, Blood Pressure, Carbon Dioxide, Cerebral Arteries, Cerebrovascular Circulation, Female, Hemodynamics, Homeostasis, Humans, Male, Middle Aged, Recurrence, Vascular Resistance, Ultrasonography, Doppler, Transcranial, Syncope, Vasovagal
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