Rapid Changes in Cerebrovascular Compliance During Vasovagal Syncope
Notice bibliographique
Résumé
Background: The rapid reduction in arterial blood pressure (ABP) during vasovagal syncope (VVS) is associated with a characteristic decline in diastolic cerebral blood velocity (CBV) and maintained systolic CBV as measured by transcranial Doppler. This increased pulsatility was originally considered to be indicative of a “dysfunctional” increase in cerebrovascular resistance (CVR). Conversely, it may be due to increased cerebrovascular compliance (Ci) that partially attenuates the cerebral effects of rapid hypotension. We tested the hypothesis that Ci supports CBV during pre-syncope in VVS. Method: Finger ABP and right middle cerebral artery blood velocity (MCAv) were recorded from 15 otherwise healthy patients (n = 11 female, 40 ± 16 years, 24.9 ± 4.0 kg/m 2 ) at rest and during head-up tilt (80°, 5 to 28 min). Individual ABP and CBV waveforms of every second heartbeat during VVS were input into a modified Windkessel model to calculate Ci and CVR. MCAv pulsatility was determined as pulse amplitude (systolic MCAv-diastolic MCAv) and Pulsatility Index (Pi; pulse amplitude/mean MCAv). Linear mixed models assessed the contribution of Ci to changes in CBV and Pi. Within-subject mediation analysis investigated the possibility of Ci mediating the relation between blood pressure (i.e., mean ABP and pulse pressure, PP) and cerebrovascular pulsatility. Results: Diastolic and systolic ABP decreased progressively during presyncope, resulting in a nadir reduction of mean ABP of Δ24 ± 9 mmHg at end-tilt (all p ≤ 0.04 vs mid-tilt). Mean MCAv decreased by 22 ± 12% prior to end-tilt (p < 0.01 vs mid-tilt). CVR decreased progressively for 10s prior to end-tilt (p ≤ 0.04 vs mid-tilt). Pi increased significantly, with peak increases occurring at 4 s prior to end-tilt (77 ± 50%, p < 0.01 vs mid-tilt). The increase in Ci (307 ± 223%, p < 0.01 vs mid-tilt) significantly contributed to changes in MCAv (χ 2 =10.6, p < 0.01) and Pi (χ 2 = 4.9, p = 0.03). Correlations of PP and ABP with Pi were not significant. However, PP was related to MCAv pulse amplitude (total effect: b = 1.57) and Ci ( b = -0.01, both p < 0.01). Ci partially mediated (indirect effect: b = -0.78, p < 0.01) the direct relation between PP and MCAv pulse amplitude ( b = 0.79, p = 0.01). Conclusion: These data provide evidence that Ci attenuates the fall in CBV under conditions of falling PP. Cerebrovascular regulation in VVS appears to be functioning as in healthy populations. However, this regulation is not suffcient to preserve flow in the presence of such extreme and rapid reductions in ABP. USRI — Western University, Natural Sciences and Engineering Research Council of Canada (NSERC, Grant No. RGPIN-2018-06255). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,001 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».