361 research outputs found
Virtual lines, a deadlock-free and real-time routing mechanism for ATM networks
In this paper, we present a routing mechanism and buffer allocation mechanism for an ATM switching fabric. Since the fabric will be used to transfer multimedia traffic, it should provide a guaranteed throughput and a bounded latency. We focus on the design of a suitable routing mechanism that is capable of fulfilling these requirements and is free of deadlocks. We will describe two basic concepts that can be used to implement deadlock-free routing. Routing of messages is closely related to buffering. We have organized the buffers into parallel FIFO's, each representing a virtual line. In this way, we not only have solved the problem of head of line blocking, but we can also give real-time guarantees. We will show that for local high-speed networks, it is more advantageous to have a proper flow control than to have large buffers. Although the virtual line concept can have a low buffer utilization, the transfer efficiency can be higher. The virtual line concept allows adaptive routing. The total throughput of the network can be improved by using alternative routes. Adaptive routing is attractive in networks where alternative routes are not much longer than the initial route(s). The network of the switching fabric is built up from switching elements interconnected in a Kautz topology
Virtual lines, a deadlock free and real-time routing mechanism for ATM networks
In this paper we present a routing mechanism and buffer allocation mechanism for an ATM switching fabric. Since the fabric will be used to transfer multimedia traffic it should provide a guaranteed throughput and a bounded latency. We focus on the design of a suitable routing mechanism that is capable to fulfil these requirements and is free of deadlocks. We will describe two basic concepts that can be used to implement deadlock free routing. Routing of messages is closely related to buffering. We have organized the buffers into parallel fifos, each representing a virtual line. In this way we not only have solved the problem of Head Of Line blocking, but we can also give real-time guarantees. We will show that for local high-speed networks it is more advantageous to have a proper flow control than to have large buffers. Although the virtual line concept can have a low buffer utilization, the transfer efficiency can be higher. The virtual lines concept allows adaptive routing. The total throughput of the network can be improved by using alternative routes. Adaptive routing is attractive in networks where alternative routes are not much longer than the initial route(s). The network of the switching fabric is built up from switching elements interconnected in a Kautz topology
Prostanoids in bronchoalveolar lavage fluid do not predict outcome in congenital diaphragmatic hernia patients
Vasoactive prostanoids may be involved in persistent pulmonary hypertension (PPH) in infants with a congenital diaphragmatic hernia (CDH). We hypothesized that increased levels of prostanoids in bronchoalveolar lavage (BAL) fluid would predict clinical outcome. We measured the concentrations of 6-keto-prostaglandin F1α (6-keto-PGF1α), thromboxane B2 (TxB2), protein, albumin, total cell count, and elastase-α1-proteinase-inhibitor complex in BAL fluid of 18 CDH patients and of 13 control subjects without PPH. We found different concentrations of prostanoids in BAL fluid of CDH patients with PPH: infants with a poor prognosis had either high levels of both 6-keto-PGF1α and TxB2 compared to controls, or high levels of
6-keto-PGF1α only. TxB2 levels showed a large variability in all CDH patients irrespective of outcome. We conclude that prostanoid levels in BAL fluid do not predict clinical outcome in CDH patients
Assessment and significance of long-term outcomes in pediatric surgery
Treatment modalities for newborns with anatomical congenital anomalies have greatly improved over the past decades, with a concomitant increase in survival. This review will briefly discuss specific long-term outcomes to illustrate, which domains deserve to be considered in long-term follow-up of patients with anatomical congenital anomalies. Apart from having disease-specific morbidities these children are at risk for impaired neurodevelopmental problems and school failure, which may affect participation in society in later life. There is every reason to offer them long-term multidisciplinary follow-up programs. We further provide an overview of the methodology of long-term follow-up, its significance and discuss ways to improve care for newborns with anatomical congenital anomalies from childhood into adulthood. Future initiatives should focus on transition of care, risk stratification, and multicenter collaboration
Pulmonary neuroendocrine cells in neonatal rats with congenital diaphragmatic hernia
Lung hypoplasia and persistent pulmonary hypertension are the principal causes of high mortality and morbidity in infants with congenital diaphragmatic hernia (CDH). Amine-and peptide-producing pulmonary neuroendocrine cells (PNEC), widely distributed throughout the airway mucosa, are thought to play an important role in both pulmonary development and regulation of pulmonary vascular tone. Furthermore, recent studies show increased levels of calcitonin gene-related peptide (CGRP), a pulmonary vasodilator produced by PNEC, during chronic hypoxia. The article reports data on morphometric analysis of CGRP immunoreactive PNEC clusters (neuroepithelial bodies, NEB) in a rat model of CDH. CDH was induced in neonatal Sprague Dawley rats by oral administration of 2,4-dichloro-phenyl- p-nitro-phenylether (Nitrofen; Rohm Haas, Philadelphia, PA) to the mother at 10 days of gestation. Sections of lungs from term neonatal rats with and without CDH and controls were immunostained for CGRP (marker of NEB) with specific antibody against rat CGRP. NEB size and number of NEB/area of lung were assessed using a semiautomatic image analysis system. In lungs of neonatal rats with CDH, the number of NEB per surface area of lung parenchyma was significantly increased compared with the age-matched controls. Although the mean size of NEB was larger in CDH, the differences were not significant. This is the first study of PNEC in CDH. Whether the phenomenon observed in this study results in altered NEB function including imbalance in vasoactive mediators requires further studies, especially in the human being
Calcitonin gene-related peptide expression is altered in pulmonary neuroendocrine cells in developing lungs of rats with congenital diaphragmatic hernia
Congenital diaphragmatic hernia (CDH) is associated with high neonatal
mortality from lung hypoplasia and persistent pulmonary hypertension.
Pulmonary neuroendocrine cells (PNEC) produce calcitonin gene-related
peptide (CGRP), a potent vasodilator. We previously reported altered
distribution of CGRP-positive PNEC in full-term rats with CDH, that may
lead to an imbalance in vasoactive mediators. In the present study we
examined the expression of CGRP-positive PNEC during lung development in
rats with CDH induced by 2,4-dichlorophenyl-p-nitrophenylether (Nitrofen).
Cesarean sections were performed on Days 16, 18, 20, or 22, and the lungs
were immunostained for CGRP and immunoreactive cells were quantitated
through image analysis. On Day 16, CGRP-immunoreactive staining was
negative; on Day 18, CGRP-immunoreactive cells were found in all controls
(not exposed to Nitrofen), whereas in CDH pups, CGRP-positive cells were
present in only four of six cases. On Day 20, CGRP immunoreactivity was
similar in CDH pups, Nitrofen-exposed pups without CDH, and controls. On
Day 22 (term), significantly more CGRP-positive cells (i.e., number of
positive cells per surface area [mm2] or lung volume [mm3]) were found in
ipsilateral lungs of CDH pups than in controls (P < 0.05). The difference
was even more striking in contralateral lungs of CDH pups (P < 0.001),
ruling out nonspecific effects of Nitrofen. In CDH lungs, the proportion
of immunostained epithelium and the size of the neuroendocrine cell
clusters (neuroepithelial bodies [NEB]) were not significantly different
from those of controls. On Day 22, supraoptimal dilution
immunocytochemistry yielded similar results in CDH pups and controls. We
conclude that in CDH, CGRP expression in PNEC and NEB is delayed during
early stages of lung development. Because CGRP also exhibits growth
factor-like properties for endothelium and epithelial cells, the lack of
this factor during a crucial developmental stage (canalicular period) may
be causally related to lung hypoplasia
Attention for future reward
When stimuli are consistently paired with reward, attention toward these stimuli becomes biased (e.g., Abrahamse, Braem, Notebaert & Verguts, et al., Psychological Bulletin 142:693â728, 2016, https://doi.org/10.1037/bul0000047). An important premise is that participants need to repeatedly experience stimulusâreward pairings to obtain these effects (e.g., Awh, Belopolsky & Theeuwes, Trends in Cognitive Sciences 16:437â443, 2012, https://doi.org/10.1016/j.tics.2012.06.010). This idea is based on associative learning theories (e.g., Pearce & Bouton, Annual Review of Psychology 52:111â139, 2001) that suggest that exposure to stimulusâreward pairings leads to the formation of stimulusâreward associations, and a transfer of salience of the reward to the neutral stimulus. However, novel learning theories (e.g., De Houwer, Learning and Motivation 53:7â23, 2009, https://doi.org/10.1016/j.lmot.2015.11.001) suggest such effects are not necessarily the result of associative learning, but can be caused by complex knowledge and expectancies as well. In the current experiment, we first instructed participants that a correct response to one centrally presented stimulus would be followed by a high reward, whereas a correct response to another centrally presented stimulus would be paired with a low reward. Before participants executed this task, they performed a visual probe task in which these stimuli were presented as distractors. We found that attention was drawn automatically toward high-reward stimuli relative to low-reward stimuli. This implies that complex inferences and expectancies can cause automatic attentional bias, challenging associative learning models of attentional control (Abrahamse et al., 2016; Awh et al., 2012)
Long-term pulmonary sequelae in children with congenital diaphragmatic hernia.
Neonates with congenital diaphragmatic hernia (CDH) often suffer from respiratory
insufficiency due to lung hypoplasia and pulmonary hypertension. Artificial
ventilation is frequently required, and this leads to a high incidence of
bronchopulmonary dysplasia. Long-term follow-up studies have shown persisting
airway obstruction. To evaluate the long-term pulmonary sequelae in CDH, we
studied 40 CDH patients of age 7 to 18 yr (median 11.7 yr) and 65 age-matched
controls without CDH and lung hypoplasia who underwent similar neonatal
treatment. Mild airway obstruction was found in both groups with more peripheral
airway obstruction in CDH patients than in control subjects. Both groups had
normal TLC and single-breath carbon monoxide diffusion capacity (DLCO). CDH
patients had increased residual volume (RV) and RV/TLC compared with controls.
Increased airway responsiveness to methacholine (MCH) was common but
bronchoconstriction to inhaled metabisulfite (MBS) was rare both in CDH and
control subjects. We conclude that this group of CDH patients has minor residual
lung function impairment. Mild airway obstruction and increased airway
responsiveness to inhaled MCH but not to MBS suggest that structural changes in
distal airways are involved and not autonomic nerve dysfunction. Both artificial
ventilation in the neonatal period and residual lung hypoplasia seem important
determinants of persistent lung function abnormalities in CDH patients
Lung eicosanoids in perinatal rats with congenital diaphragmatic hernia
Abnormal levels of pulmonary eicosanoids have been reported in infants with persistent pulmonary hypertension (PPH) and congenital diaphragmatic hernia (CDH). We hypothesized that a dysbalance of vasoconstrictive and vasodilatory eicosanoids is involved in PPH in CDH patients. The levels of several eicosanoids in lung homogenates and in bronchoalveolar lavage fluid of controls and rats with CDH were measured after caesarean section or spontaneous birth. In controls the concentration of the stable metabolite of prostacyclin (6-keto-PGF1α), thromboxane
A2 (TxB2), prostaglandin E2 (PGE2), and leukotriene B4 (LTB4) decreased after spontaneous birth. CDH pups showed respiratory insufficiency directly after birth. Their lungs had higher levels of 6- keto-PGF1α, reflecting the pulmonary vasodilator prostacyclin
(PGI2), than those of controls. We conclude that in CDH abnormal lung eicosanoid levels are present perinatally. The elevated levels of 6-keto-PGF1α in CDH may reflect a compensation mechanism for increased vascular resistance
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