Microdialysis membranes (3 mm lengthx200 microm i.d.) have been used to extract volatile analytes from aqueous samples into the gas phase and interfaced with fast gas chromatography. Gas-phase extracts generated from aqueous samples reach steady-state concentrations and are transported to the detector in 5 s. The recovery of the system ranges from 1.28% for toluene to less than 0.1% for ethanol. The lowest detectable concentration without preconcentration was 5 mM for most compounds using a flame ionization detector, and as low as 0.01 mM for more volatile hydrophobic analytes. When interfaced with a fast GC system, changes in aqueous phase concentrations were monitored with a temporal resolution of 10 s.
Background
Microvascular structural alteration and dysfunction is a hallmark of arterial hypertension. So far, the visualization and the quantification of renal microcirculation in humans has been hampered by the lack of non-nephrotoxic and non-invasive radiologic techniques. Contrast-Enhanced ultrasonography (CEUS) is an alluring method to investigate renal microcirculation and has not been investigated in this setting. We aimed to compare renal microcirculation in normotensives (NT) and hypertensive (HT) participants using CEUS at rest and during a sympathetic stress test.
Methods
We measured the renal perfusion index (PI, primary outcome), the renal resistive index (RRI), beat-to-beat systemic hemodynamics and plasma catecholamines before and during a 2-minute cold pressor test (CPT) in NT and HT participants. Linear mixed model analysis was used to compare the effect of the CPT on the variables of interest.
Results
73 participants (32 HT) with normal kidney function were included. HT participants had a lower baseline PI compared to NT participants [1476(959–2155) arbitrary unit (a.u.) vs 2062(1438–3318) a.u., p < 0.001]. The CPT increased blood pressure, heart rate and catecholamines in all participants. The increase in PI observed in NT during the CPT was blunted in HT (+504(117–920) a.u. vs + 1159(678–2352) a.u in NT, interaction p = 0.013). Age, sex and body mass index did not modify these results.
Conclusions
HT patients had a lower basal renal cortical perfusion. During the cold pressor test, HT participants had a smaller increase in the PI, suggesting that renal cortical flow reserve is impaired.
We study the problem of online graph exploration on undirected graphs, where a searcher has to visit every vertex and return to the origin. Once a new vertex is visited, the searcher learns of all neighboring vertices and the connecting edge weights. The goal such an exploration is to minimize its total cost, where each edge traversal incurs a cost of the corresponding edge weight.We investigate the problem on tadpole graphs (also known as dragons, kites), which consist of a cycle with an attached path. Miyazaki et al. (The online graph exploration problem on restricted graphs, IEICE Transactions 92-D (9), 2009) showed that every online algorithm on these graphs must have a competitive ratio of 2 − ε, but did not provide upper bounds for non-unit edge weights. We show via amortized analysis that a greedy approach yields a matching competitive ratio of 2 on tadpole graphs, for arbitrary non-negative edge weights.
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