Central venous obstruction in the thorax.

Central venous stenosis and occlusion can occur secondary to a spectrum of conditions ranging from aggressive malignancy to benign extrinsic anatomical compression in otherwise healthy individuals. Irrespective of aetiology, significant morbidity in the acute setting and long term can occur unless prompt accurate diagnosis and appropriate management is initiated, the radiologist being central to both. The present review will provide radiologists with a thorough illustration and explanation of the range of central venous conditions in the thorax (including deep vein thrombosis, thoracic outlet syndrome, haemodialysis, and malignancy related causes), the salient imaging findings and interventional management using case examples from the authors' practice.

An optimization approach for analysing nonlinear stability with transition to turbulence in fluids as an exemplar.

This article introduces and reviews recent work using a simple optimization technique for analysing the nonlinear stability of a state in a dynamical system. The technique can be used to identify the most efficient way to disturb a system such that it transits from one stable state to another. The key idea is introduced within the framework of a finite-dimensional set of ordinary differential equations (ODEs) and then illustrated for a very simple system of two ODEs which possesses bistability. Then the transition to turbulence problem in fluid mechanics is used to show how the technique can be formulated for a spatially-extended system described by a set of partial differential equations (the well-known Navier-Stokes equations). Within that context, the optimization technique bridges the gap between (linear) optimal perturbation theory and the (nonlinear) dynamical systems approach to fluid flows. The fact that the technique has now been recently shown to work in this very high dimensional setting augurs well for its utility in other physical systems.

Genesis of streamwise-localized solutions from globally periodic traveling waves in pipe flow.

The aim in the dynamical systems approach to transitional turbulence is to construct a scaffold in phase space for the dynamics using simple invariant sets (exact solutions) and their stable and unstable manifolds. In large (realistic) domains where turbulence can coexist with laminar flow, this requires identifying exact localized solutions. In wall-bounded shear flows, the first of these has recently been found in pipe flow, but questions remain as to how they are connected to the many known streamwise-periodic solutions. Here we demonstrate that the origin of the first localized solution is in a modulational symmetry-breaking Hopf bifurcation from a known global traveling wave that has twofold rotational symmetry about the pipe axis. Similar behavior is found for a global wave of threefold rotational symmetry, this time leading to two localized relative periodic orbits. The clear implication is that many global solutions should be expected to lead to more realistic localized counterparts through such bifurcations, which provides a constructive route for their generation.

Congenital anomalies of the inferior vena cava.

Congenital anomalies of the inferior vena cava (IVC) and its tributaries are increasingly recognized in asymptomatic patients due to the more frequent use of cross-sectional imaging and computed tomography (CT) in particular. IVC development is a complex process involving formation of anastomoses between three pairs of embryonic veins in the 4th to 8th week of gestation. Various permutations occur in the basic venous plan of the abdomen and pelvis resulting in variants such as isolated left IVC, double IVC, and retroaortic left renal vein. The majority of these anomalies are asymptomatic but occasionally present clinically with thromboembolic complications. However, awareness of their existence is important to avoid important diagnostic pitfalls and in preoperative surgical and interventional radiological planning.

Experimental and theoretical progress in pipe flow transition.

There have been many investigations of the stability of Hagen-Poiseuille flow in the 125 years since Osborne Reynolds' famous experiments on the transition to turbulence in a pipe, and yet the pipe problem remains the focus of attention of much research. Here, we discuss recent results from experimental and numerical investigations obtained in this new century. Progress has been made on three fundamental issues: the threshold amplitude of disturbances required to trigger a transition to turbulence from the laminar state; the threshold Reynolds number flow below which a disturbance decays from turbulence to the laminar state, with quantitative agreement between experimental and numerical results; and understanding the relevance of recently discovered families of unstable travelling wave solutions to transitional and turbulent pipe flow.

Not a NICE CT protocol for the acutely head injured child.

AIM: To assess the impact of the introduction of the Birmingham Children's Hospital (BCH) head injury computed tomography (CT) guidelines, when compared with the National Institute of Health and Clinical Excellence (NICE) guidelines, on the number of children with head injuries referred from the Emergency Department (ED) undergoing a CT examination of the head. MATERIAL AND METHODS: All children attending BCH ED over a 6-month period with any severity of head injury were included in the study. ED case notes were reviewed and data were collected on a specifically designed proforma. Indications for a CT examination according to both NICE and BCH head injury guidelines and whether or not CT examinations were performed were recorded. RESULTS: A total of 1428 children attended the BCH ED following a head injury in the 6-month period. The median age was 4 years (range 6 days to 15 years) and 65% were boys. Four percent of children were referred for a CT using BCH guidelines and were appropriately examined. If the NICE guidelines had been strictly adhered to a further 8% of children would have undergone a CT examination of the head. All of these children were discharged without complication. The remaining 88% had no indication for CT examination by either BCH or NICE and appropriately did not undergo CT. CONCLUSIONS: Adherence to the NICE head injury guidelines would have resulted in a three-fold increase in the total number of CT examinations of the head. The BCH head injury guidelines are both safe and appropriate in the setting of a large children's hospital experienced in the management of children with head injuries.

Endothelial NO and prostanoid involvement in newborn and juvenile pig pial arteriolar vasomotor responses.

Specific cerebrovascular dilatory responses in newborn piglets are entirely prostanoid dependent, but require both nitric oxide (NO) and prostanoids in juveniles. We examined endothelial dependency and mechanisms of NO- and prostanoid-mediated cerebrovascular responses in anesthetized newborn and juvenile pigs implanted with closed cranial windows. Light/dye endothelial injury inhibited newborn and juvenile hypercapnic and bradykinin (BK) responses and inhibited dilation to acetylcholine in juveniles. Iloprost and NO act permissively in restoring light/dye inhibited newborn and juvenile responses, respectively. Differences in sensitivity to iloprost and sodium nitroprusside were not observed. Juvenile (not newborn) hypercapnic and BK cerebrovascular responses were sensitive to soluble guanylyl cyclase inhibition. Pial arteriolar diameter and cortical production of prostacyclin, cAMP, and cGMP in response to BK were measured under control conditions, after treatment with indomethacin and/or N(omega)-nitro-L-arginine methyl ester (L-NAME). Indomethacin inhibited BK responses in newborns. Juvenile responses were inhibited by L-NAME, and mildly by indomethacin. Cortical 6-keto-PGF(1 alpha), cAMP, and cGMP increased in response to BK in both age groups. Newborn cerebrovascular responses are largely NO independent, but NO becomes more important with maturation.

NO and prostanoids: age dependence of hypercapniaand histamine-induced dilations of pig pial arterioles.

Responses to hypercapnia and acetylcholine by newborn piglet pial arterioles are prostanoid dependent but appear to require both prostanoids and nitric oxide in juvenile pigs. We hypothesized that cerebrovascular dilatory responses become less prostanoid dependent and more NO dependent with development. Pial arteriolar responses to hypercapnia and histamine were recorded from alpha-chloralose-anesthetized newborn and juvenile pigs with closed cranial windows. Responses were recorded during control, after indomethacin or N(omega)-nitro-L-arginine (L-NNA), and after inhibitor plus iloprost or sodium nitroprusside. Indomethacin blocked newborn hypercapnic responses and markedly attenuated histamine dilations, but only reduced the dilations to about half in juveniles. Iloprost at subdilator concentrations restored newborn responses to hypercapnia and histamine but did not alter either response in indomethacin-treated juveniles. L-NNA attenuated juvenile, but not newborn, hypercapnia-induced dilations. Sodium nitroprusside did not restore the response. L-NNA did not alter responses to histamine in either age group. Cerebrovascular dilations to hypercapnia and histamine are prostanoid dependent and nitric oxide independent in the newborn pig, whereas nitric oxide assumes an increasing role in hypercapnic, but not histamine, responses with development.

Effect of transfusion on physiologic changes after resuscitated trauma.

BACKGROUND: The purpose of this experimental study was to test whether transfusion potentiated physiologic changes associated with fluid resuscitated trauma in controlled conditions. METHODS: Anesthetized and ventilated mongrel pigs were subjected to soft-tissue injury plus 35% hemorrhage and 1 hour shock and then were resuscitated with either autologous (shed) or heterologous (cross-transfused) fresh whole blood. Leukocyte differential counts, T-lymphocyte subsets, neutrophil adherence molecule (CD18) expression, granulocyte oxidative burst, plasma cortisol, and serum chemistries were monitored in awake animals with indwelling catheters on 3 consecutive days. Changes were referenced to preinjury baseline values and to a control group that received heterologous transfusion but no shock. To determine whether these changes might have influenced host defense, a low-dose challenge with Escherichia coli endotoxin (lipopolysaccharide [LPS]; 1 to 2 micrograms/kg for 30 minutes) was administered on day 4. RESULTS: During recovery, neutrophil counts, neutrophil CD18 expression, and granulocyte oxidative burst were generally increased, but the changes were not potentiated by transfusion. Lymphocyte subpopulations remained relatively constant. Serum enzyme markers were elevated with trauma plus shed blood or trauma plus cross-transfusion, but they remained essentially unchanged after heterologous transfusion only. Plasma cortisol, a nonspecific index of stress, peaked at 3 to 6 times higher than baseline. The increases tended to be higher and later with heterologous transfusion only, relative to trauma plus shed blood or trauma plus cross-transfusion. The delayed LPS challenge evoked profound but transient pulmonary hypertension and leukopenia, followed by subsequent hypoxemia; the time courses and magnitude of these changes were similar in all groups. CONCLUSIONS: If these measured variables before and after LPS challenge are a valid index of host defense in this species, then a 35% transfusion does not potentiate the risk for posttrauma immune dysfunction when the magnitude of injury is constant. Thus the predisposition to infection after human trauma might be due to cold storage of blood; separation of blood into components, or other transfusion-related practices rather than to transfusion per se.

External-cavity diode lasers with different devices and collimating optics.

Comparative operating characteristics of external-cavity diode lasers (ECDL's) with either a channel substrate planar device or a multi-quantum-well (MQW) device are presented. These include the output beam profile, which is significantly altered depending on the collimating lens used (either multielement or graded index), power versus injection-current characteristics, and the optical frequency and the rf spectra. The coherence lengths of the different laser diode-collimating-lens combinations in the ECDL are measured, and a new method for calculating the coupling coefficient and the coupled values of the internal quantum efficiency and the internal lumped loss is demonstrated for the MQW device.