RESUMO

Cerebral small vessel disease (cSVD), a common cause of stroke and dementia, is traditionally considered the small vessel equivalent of large artery occlusion or rupture that leads to cortical and subcortical brain damage. Microvessel endothelial dysfunction can also contribute to it. Brain imaging, including MRI, is useful to show the presence of lesions of several types, although the association between conventional MRI measures and clinical features of cSVD is not always concordant. We assessed the additional contribution of contrast-agent-free, state-of-the-art MRI techniques such as arterial spin labeling (ASL), diffusion tensor imaging, functional MRI, and intravoxel incoherent motion (IVIM) applied to cSVD in the existing literature. We performed a review following the PICO Worksheet and Search Strategy, including original papers in English, published between 2000 and 2022. For each MRI method, we extracted information about their contributions, in addition to those established with traditional MRI methods and related information about the origins, pathology, markers, and clinical outcomes in cSVD. This paper presents the first part of the review, which includes 37 studies focusing on ASL, IVIM, and cerebrovascular reactivity (CVR) measures. In general, they have shown that, in addition to white matter hyperintensities, alterations in other neuroimaging parameters such as blood flow and CVR also indicate the presence of cSVD. Such quantitative parameters were also related to cSVD risk factors. Therefore, they are promising, noninvasive tools to explore questions that have not yet been clarified about this clinical condition. However, protocol standardization is essential to increase their clinical use.

Assuntos

Doenças de Pequenos Vasos Cerebrais , Meios de Contraste , Artérias , Doenças de Pequenos Vasos Cerebrais/diagnóstico por imagem , Imagem de Tensor de Difusão , Humanos , Imageamento por Ressonância Magnética/métodos , Marcadores de Spin

RESUMO

Cerebral autoregulation (AR) keeps cerebral blood flow constant despite fluctuations in systemic arterial pressure. The final common AR pathway is made up of vasomotor adjustments of cerebrovascular resistance mediated by arterioles. Structural and functional changes in the arteriolar wall arise with age and systemic arterial hypertension. This study evaluated whether AR is impaired in hypertensive patients and whether this impairment differs with disease control. Three groups of patients were prospectively compared: hypertensive patients under treatment with systolic blood pressure (SBP) <140 and diastolic blood pressure (DBP) <90 mm Hg (n = 54), hypertensive patients under treatment with SBP > 140 or DBP > 90 mm Hg (n = 31), and normotensive volunteers (n = 30). Simultaneous measurements of cerebral blood flow velocity (CBFV) and BP were obtained by digital plethysmography and transcranial Doppler, and the AR index (ARI) was defined according to the step response to spontaneous fluctuations in BP. Compared to the uncontrolled hypertension, the normotensive individuals were younger (age 43.42 ± 11.14, P < .05) and had a lower resistance-area product (1.17 ± 0.24, P < .05), although age and greater arteriolar stiffness did not affect the CBFV mean of hypertensive patients, whether controlled or uncontrolled (62.85 × 58.49 × 58.30 cm/s, P = .29), most likely because their ARIs were not compromised (5.54 × 5.91 × 5.88, P = .6). Hypertensive patients under treatment, regardless of their BP control, have intact AR capacity.

Assuntos

Hipertensão , Adulto , Velocidade do Fluxo Sanguíneo , Pressão Sanguínea , Circulação Cerebrovascular , Homeostase , Humanos , Hipertensão/tratamento farmacológico , Pessoa de Meia-Idade , Preparações Farmacêuticas , Ultrassonografia Doppler Transcraniana

RESUMO

OBJECTIVE: To define levels of mean arterial blood pressure (MABP) where cerebrovascular reactivity is strongest (MABPOPT) during the early transitional circulation in extremely preterm infants and to investigate the association between deviations above and below MABPOPT with intraventricular hemorrhage (IVH) and mortality. STUDY DESIGN: A total of 44 infants born at a median gestational age 25 (23-27) weeks with indwelling arterial catheter were studied at a median 5.5 (3.1-12.6) hours within the first 24 hours of life. Cerebrovascular reactivity (tissue oxygenation heart rate reactivity index) was estimated by the moving correlation coefficient between heart rate and near-infrared spectroscopy tissue oxygenation index. MABPOPT was defined as the MABP where tissue oxygenation heart rate reactivity index reaches minimum value. Deviations below or above MABPOPT values were calculated along with MABPOPT values during retrospective data analysis. RESULTS: MABPOPT was detected in all infants. The mean (SD) MABPOPT was 31.3 (±4.7) mm Hg. MABPOPT increased with increasing gestational age, R = 0.424; P = .004. Deviations below MABPOPT were greater in the IVH group (mean 2.7 mm Hg; 95% CI 2.0-3.5) compared with no-IVH (mean 1.7 mm Hg; 1.1-2.2), P = .006. In infants who died, the deviation below MABPOPT was greater (mean 3.3; 95% CI 1.9-4.8) compared with those who survived (mean 1.9 mm Hg; 95% CI 1.4-2.3), P = .015. CONCLUSIONS: Defining optimal MABP based on the strength of cerebrovascular reactivity within the first 24 hours of life is feasible and can provide an individualized approach to the care of extremely preterm infants. Deviations below MABPOPT were significantly associated with IVH and death.

Assuntos

Pressão Arterial/fisiologia , Circulação Cerebrovascular/fisiologia , Lactente Extremamente Prematuro , Oxigênio/sangue , Cateteres de Demora , Estudos de Coortes , Feminino , Idade Gestacional , Mortalidade Hospitalar , Hospitais Universitários , Humanos , Lactente , Recém-Nascido , Unidades de Terapia Intensiva Neonatal , Masculino , Monitorização Fisiológica/métodos , Prognóstico , Estudos Retrospectivos , Medição de Risco , Espectroscopia de Luz Próxima ao Infravermelho , Estatísticas não Paramétricas , Análise de Sobrevida , Fatores de Tempo , Reino Unido

RESUMO

Regional cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) in young and elderly participants were assessed using pulsed arterial spin labeling (ASL) and blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) techniques in combination with inhalation of CO2. Pulsed ASL and BOLD-MRI were acquired in seventeen asymptomatic volunteers (10 young adults, age: 30±7 years; 7 elderly adults, age: 64±8 years) with no history of diabetes, hypertension, and neurological diseases. Data from one elderly participant was excluded due to the incorrigible head motion. Average baseline CBF in gray matter was significantly reduced in elderly (46±9 mL·100 g-1·min-1) compared to young adults (57±8 mL·100 g-1·min-1; P=0.02). Decreased pulsed ASL-CVR and BOLD-CVR in gray matter were also observed in elderly (2.12±1.30 and 0.13±0.06 %/mmHg, respectively) compared to young adults (3.28±1.43 and 0.28±0.11 %/mmHg, respectively; P<0.05), suggesting some degree of vascular impairment with aging. Moreover, age-related decrease in baseline CBF was observed in different brain regions (inferior, middle and superior frontal gyri; precentral and postcentral gyri; superior temporal gyrus; cingulate gyri; insula, putamen, caudate, and supramarginal gyrus). In conclusion, CBF and CVR were successfully investigated using a protocol that causes minimal or no discomfort for the participants. Age-related decreases in baseline CBF and CVR were observed in the cerebral cortex, which may be related to the vulnerability for neurological disorders in aging.

Assuntos

Humanos , Masculino , Feminino , Adulto , Pessoa de Meia-Idade , Idoso , Adulto Jovem , Envelhecimento/fisiologia , Encéfalo/irrigação sanguínea , Encéfalo/diagnóstico por imagem , Dióxido de Carbono/metabolismo , Circulação Cerebrovascular/fisiologia , Imageamento por Ressonância Magnética/métodos , Marcadores de Spin , Fatores Etários , Análise de Variância , Mapeamento Encefálico/métodos , Oxigênio/metabolismo , Valores de Referência , Estatísticas não Paramétricas , Fatores de Tempo

RESUMO

PURPOSE: To quantify the amplitude and temporal aspects of the blood oxygenation level-dependent (BOLD) response to an auditory stimulus during normocapnia and hypercapnia in healthy subjects in order to establish which BOLD parameters are best suited to infer the cerebrovascular reactivity (CVR) in the middle cerebral artery (MCA) territory. MATERIALS AND METHODS: Twenty healthy volunteers (mean age: 23.6 ± 3.7 years, 11 women) were subjected to a functional paradigm composed of five epochs of auditory stimulus (3 sec) intercalated by six intervals of rest (21 sec). Two levels of hypercapnia were achieved by a combination of air and CO2 while the end-tidal CO2 (ETCO2 ) was continually measured. An autoregressive method was applied to analyze four parameters of the BOLD signal: onset-time, time-to-peak, full-width-at-half-maximum (FWHM), and amplitude. RESULTS: BOLD onset time (P < 0.001) and full-width at half-maximum (FWHM) (P < 0.05) increased linearly, while BOLD amplitude decreased (P < 0.001) linearly with increasing levels of hypercapnia. Test-retest for reproducibility in five subjects revealed excellent concordance for onset time and amplitude. CONCLUSION: The robust linear dependence of BOLD onset time, FWHM, and amplitude to hypercapnia suggest future application of this protocol in clinical studies aimed at evaluating CVR of the MCA territory.

Assuntos

Mapeamento Encefálico/métodos , Circulação Cerebrovascular , Hipercapnia/fisiopatologia , Interpretação de Imagem Assistida por Computador/métodos , Imageamento por Ressonância Magnética/métodos , Artéria Cerebral Média/fisiopatologia , Consumo de Oxigênio , Adulto , Velocidade do Fluxo Sanguíneo , Feminino , Humanos , Masculino , Reprodutibilidade dos Testes , Sensibilidade e Especificidade

RESUMO

Este estudo avaliou a hemodinâmica cerebral através da análise da velocidade de fluxo sangüíneo cerebral a partir da utilização do US- color Doppler (ultra-som Doppler com fluxo a cores) em crianças e adolescentes com diagnóstico de hidrocefalia e portadores de derivação liquórica ventrículo peritoneal (DVP). Testes de avaliação funcional foram realizados: teste de compressão da fontanela anterior e teste de vasoreatividade ao CO2. Conclui-se que os valores da Dopplervelocimetria encontrados neste estudo, através do acompanhamento em crianças com hidrocefalia e DVP, utilizando-se a técnica do US-Doppler, forneceram informações acerca da hemodinâmica cerebral nesses pacientes e possibilitaram a realização de testes funcionais não invasivos para avaliação da reatividade vascular e a complacência cerebral nesses pacientes.

RESUMO

Este estudo avaliou a hemodinâmica cerebral através da análise da velocidade de fluxo sangüíneo cerebral a partir da utilização do US- color Doppler (ultra-som Doppler com fluxo a cores) em crianças e adolescentes com diagnóstico de hidrocefalia e portadores de derivação liquórica ventrículo peritoneal (DVP). Testes de avaliação funcional foram realizados: teste de compressão da fontanela anterior e teste de vasoreatividade ao CO2. Conclui-se que os valores da Dopplervelocimetria encontrados neste estudo, através do acompanhamento em crianças com hidrocefalia e DVP, utilizando-se a técnica do US-Doppler, forneceram informações acerca da hemodinâmica cerebral nesses pacientes e possibilitaram a realização de testes funcionais não invasivos para avaliação da reatividade vascular e a complacência cerebral nesses pacientes.