Impaired Small-World Network Efficiency and Dynamic Functional Distribution in Patients with Cirrhosis

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome and a major complication of liver cirrhosis. Dysmetabolism of the brain, related to elevated ammonia levels, interferes with intercortical connectivity and cognitive function. For evaluation of network efficiency, a ‘small-world’ network model can quantify the effectiveness of information transfer within brain networks. This study aimed to use small-world topology to investigate abnormalities of neuronal connectivity among widely distributed brain regions in patients with liver cirrhosis using resting-state functional magnetic resonance imaging (rs-fMRI). Seventeen cirrhotic patients without HE, 9 with minimal HE, 9 with overt HE, and 35 healthy controls were compared. The interregional correlation matrix was obtained by averaging the rs-fMRI time series over all voxels in each of the 90 regions using the automated anatomical labeling model. Cost and correlation threshold values were then applied to construct the functional brain network. The absolute and relative network efficiencies were calculated; quantifying distinct aspects of the local and global topological network organization. Correlations between network topology parameters, ammonia levels, and the severity of HE were determined using linear regression and ANOVA. The local and global topological efficiencies of the functional connectivity network were significantly disrupted in HE patients; showing abnormal small-world properties. Alterations in regional characteristics, including nodal efficiency and nodal strength, occurred predominantly in the association, primary, and limbic/paralimbic regions. The degree of network organization disruption depended on the severity of HE. Ammonia levels were also significantly associated with the alterations in local network properties. Results indicated that alterations in the rs-fMRI network topology of the brain were associated with HE grade; and that focal or diffuse lesions disturbed the functional network to further alter the global topology and efficiency of the whole brain network. These findings provide insights into the functional changes in the human brain in HE

Poço de infiltração para controle de enchentes na fonte: avaliação das condições de operação e manutenção

Neste estudo foram investigados os seguintes aspectos relativos à avaliação de um poço de infiltração construído em escala real: i) tampa/filtro de entrada; ii) permeabilidade do geotêxtil interno ao poço; e iii) tempos de esvaziamento. O poço de infiltração com volume de 3,6 m³ drena área de 241,8 m². A tampa/filtro foi composta de camadas de areia, brita e geotêxtil dispostos sobre a estrutura metálica. Os anéis de concreto que compõem a estrutura lateral do poço foram revestidos com manta geotêxtil intercalada com blocos cerâmicos. O poço permaneceu em constante operação, entretanto foram simulados eventos específicos para o tempo de esvaziamento. Realizaram-se ensaios da permeabilidade de amostras de geotêxtil, do teor de materiais pulverulentos dos agregados ao poço, ou seja, a brita e a areia que compõem a tampa/filtro. O geotêxtil apresentou redução média da permeabilidade de 50,7%, 7,7% e 21,2% nas amostras do fundo, paredes e tampa do poço respectivamente. A areia do filtro da tampa reteve 34,8% de finos, enquanto a brita reteve 0,13% de finos no mesmo período. A capacidade hidráulica média do poço foi 34,7 mm/h. O coeficiente de determinação para os tempos de esvaziamento calculados e medidos foi de 0,97