Comprehensive study on the light shielding potential of thermotropic layers for the development of new materials.

In recent years thermotropic overheating protection glazings have been the focus for both solar thermal collector technology and architecture. A thermotropic glazing changes its light transmittance from highly transparent to light diffusing upon reaching a certain threshold temperature autonomously and reversibly. In thermotropic systems with fixed domains (TSFD) the scattering domains are embedded in a polymer matrix, which exhibits a sudden change of the refractive index upon reaching a threshold temperature. The aim of the present study was to comprehensively investigate the light shielding characteristics and potential of TSFD materials by applying simulation of light scattering in particle-filled layers. In random walk simulations a variety of parameters were varied systematically, and the effect on the light transmission behavior of TSFD was studied. The calculation steps of the simulation process are shown in detail. The simulations demonstrate that there is great potential for the production of functional materials with high overheating protection efficiency.

Modeling the absorption behavior of solar thermal collector coatings utilizing graded alpha-C:H/TiC layers.

Wavelength selective coatings are of common use in order to enhance the efficiency of devices heated by radiation such as solar thermal collectors. The use of suitable materials and the optimization of coating layer thicknesses are advisable ways to maximize the absorption. Further improvement is achievable by embedding particles in certain layers in order to modify material properties. We focus on optimizing the absorption behavior of a solar collector setup using copper as substrate, a layer of amorphous hydrogenated carbon with embedded titanium carbide particles (a-C:H/TiC), and an antireflection coating of amorphous silicon dioxide (aSiO(2)). For the setup utilizing homogeneous particle distribution, a relative absorption of 90.98% was found, while inhomogeneous particle embedding yielded 98.29%. These results are particularly interesting since until now, absorption of more than 95% was found only by using embedded Cr but not by using the more biocompatible Ti.

Intraspinal extradural meningeal cyst demonstrating ball-valve mechanism of formation. Case report.

A diverse collection of unverified theories as to the etiology of extradural meningeal cysts have been previously proposed. One case of intraspinal extradural meningeal cyst of the thoracolumbar region is presented in which a ball-valve mechanism involving an idiopathic dural rent and a herniated segment of an underlying dorsal rootlet was suggested by the operative findings. Closure of the dural rent with marsupialization of the meningeal cyst obliterated this extradural lesion. The ball-valve mechanism of formation and other previously proposed theories are discussed.

Transpalatal approach for the extracranial surgical repair of transsphenoidal cephaloceles in children.

The surgical treatment of transsphenoidal cephaloceles in children is controversial. Reduction and repair via a transcranial approach are associated with high postoperative rates of morbidity, mortality, and hypothalamic dysfunction. In this study, four patients, aged 3 to 35 months at surgery, underwent successful transpalatal repair of two encephaloceles and two meningoceles. Two patients presented with nasal obstruction in infancy, one presented with unexplained meningitis, and in one patient the lesion was found incidentally during evaluation for seizures. Two children had median cleft face syndrome, another had an associated Arnold-Chiari type I malformation, and the fourth had no other cranial abnormalities. All patients underwent preoperative evaluation including magnetic resonance (MR) imaging. Auditory, ophthalmological, genetic, endocrinological, or other evaluation was undertaken as indicated. Lesions were approached through the median raphe of the hard and soft palates. All cephaloceles were easily visualized and dissected after division of the nasal palatal mucosa. The dural sac and its contents were reduced by surface coagulation after division and dissection of the overlying mucosa. Once reduced, the bone defect was obliterated in three of four patients. The dura was not opened and anomalous neural elements were not resected. At follow-up evaluation, all patients demonstrated resolution of preoperative symptoms without evidence of infection or lasting morbidity. Follow-up MR imaging showed reduction in all cases. The authors conclude that this transpalatal approach is safe and reliable for the treatment of transsphenoidal cephaloceles in young children.

A comparison between endovascular and surgical management of basilar artery apex aneurysms.

OBJECT: The goal of this retrospective study was to evaluate endovascular treatment by means of Guglielmi detachable coils (GDCs) compared with surgical management for basilar artery (BA) apex aneurysms. METHODS: Forty-one patients presented with saccular BA apex aneurysms with angiographically definable necks that were judged suitable for either treatment. Of 20 patients who underwent surgery and 21 who underwent GDC embolization, 15 (75%) and 11 (52%), respectively, were treated in the acute phase after subarachnoid hemorrhage (SAH). Twenty-four (92%) of the 26 patients presenting with an SAH had a Hunt and Hess Grade III or better. Fifteen patients with unruptured or ruptured aneurysms more than 14 days post-SAH were treated electively. Patients in the endovascular and surgical treatment groups had aneurysms with comparable dimensions and configurations. Overall, 15 (75%) of the surgical patients and 20 (95%) of the patients in whom GDC embolization was performed had a good outcome (Glasgow Outcome Scale score of 4 or 5). Among those patients treated in the acute stage post-SAH, 11 (73%) of the surgical group and 10 (91%) of the endovascular group did well. Fourteen patients treated electively (93%) had good outcomes. There were two deaths (10%) in the surgical group and none in the endovascular group. Patients treated surgically were hospitalized twice as long and incurred twice the expenses of patients who underwent endovascular treatment (p<0.001). CONCLUSIONS: Endovascular GDC embolization of select BA apex aneurysms may be a competitive alternative to direct surgical clipping. Long-term follow up is needed to better define the natural history of the endovascularly treated aneurysm and to further evaluate the accuracy of these preliminary results.

Endoscopic washout: a new technique for treating chronic subdural hematomas in infants.

Chronic hematomas are a common problem during infancy and usually occur as the consequence of trauma. They tend to enlarge and are often managed successfully with repeated subdural taps. In patients with collections that fail to respond to percutaneous drainage, the choice of operative management, including burr hole evacuation, shunting, or craniotomy, remains controversial. A new technique, called endoscopic washout, was successfully used in 7 children under the age of 2 years who presented with irritability, vomiting, seizures, and rapid head growth. Preoperative computerized tomography (CT) scans demonstrated enlarging, bilateral, chronic subdural collections; these failed to respond to repeated percutaneous taps over 10 days. With the patient positioned supine, bilateral linear incisions were made anterior to the coronal suture in the midpupillary lines and burr holes were placed. After the dura and outer membrane were opened and coagulated with bipolar cautery, a 4-mm steerable fiberscope was introduced into the subdural space to visualize the collections, evacuate any residual clot, and continuously irrigate the space with lactated Ringer's solution warmed to physiologic temperature. No bridging vessels or synechiae were violated; nitrous oxide and hyperventilation were discontinued before removing the fiberscope. The subdural space was irrigated again prior to closure. At follow-up (range 18 months to 8 years), CT scans showed reexpansion of the brain and no reaccumulation of the hematomas. We conclude that the endoscopic washout is a safe, uncomplicated treatment for chronic subdural hematomas in infants; is more effective than treatment with conventional burr holes alone, and eliminates the need for shunting or craniotomy.

Hypertonic saline attenuates the hormonal response to injury.

We reported previously in a randomized double-blinded study in 20 postoperative coronary bypass patients that hypertonic saline (1.8% NaCl, HS) provides early hemodynamic benefits, increased osmolality and net negative fluid balance compared to 0.9% NaCl (NS). To investigate the effects of HS on the hormonal response to injury, we measured ACTH, cortisol, angiotensin II (AII), aldosterone, vasopressin (AVP), and atrial natriuretic factor (ANF) in these patients. ACTH and cortisol concentrations increased in the NS group but were suppressed in the HS group (p less than 0.05). Aldosterone increased in NS patients, but was suppressed in HS patients (HS: delta Aldosterone 13.0 +/- 3.0 vs. NS: delta Aldosterone 26.0 +/- 7.0 ng/dl, p less than 0.05). The AII response was suppressed at six and eight hours (p less than 0.05) in patients receiving HS but did not change in patients receiving NS. ANF did not change significantly for either group. The significant increases in AVP were similar in both groups (p less than 0.05), but correlated with increases in osmolality only in the NS group (r = 0.8, p less than 0.009). Other than AVP, HS suppressed the responses of some of the hormones that normally increase in response to injury, relative to NS. Attenuation of the neuroendocrine response and other previously reported effects of HS suggest that HS may be an efficacious solution for resuscitation in the postoperative and postinjury period.

Hypertonic saline fluid therapy following surgery: a prospective study.

Successful resuscitation of the injured may be achieved more rapidly and with less fluid using hypertonic crystalloid solutions than with isotonic solutions. This randomized, double-blind study compared 0.9% normal saline (NS) to 1.8% hypertonic saline (HS) in 20 postoperative coronary artery bypass patients suffering uniform injury. Study solutions were administered to maintain physiologic endpoints: heart rate, blood pressure, and pulmonary capillary wedge pressure. The groups were similar with respect to age, body surface area, operative procedure, intraoperative fluid status, and intraoperative and postoperative red cell transfusion requirements. HS patients required 30% less fluid than NS patients and were in negative fluid balance during the study (-1,715 +/- 732 ml/24 hr, HS, vs. +266 +/- 825 ml/24 hr, NS; p less than 0.01). In contrast, NS patients were in positive fluid balance after 8 hours. Moreover, HS patients experienced less chest tube drainage than NS patients (981 +/- 88 ml, HS, vs. 1,700 +/- 285 ml, NS; p less than 0.01). Systemic and pulmonary hemodynamic measurements, oxygen delivery, oxygen consumption, and shunt fraction did not differ between the two groups. Serum sodium and osmolality increased in the HS group and peaked at 12 hours (145.4 +/- 1.4 mEq/L and 308.7 +/- 2.0 mOsm/kg, respectively) and correlated with the volume of HS infused (correlation coefficient = 0.81). No deaths occurred and no complication was attributed the hypertonicity of the solution. We conclude that 1.8% hypertonic saline is a safe alternative to isotonic crystalloid therapy in the fluid management of postoperative patients. Decreased third-space losses may occur with HS as suggested by the lower thoracic losses in the HS group; 1.8% NaCl may be the preferred solution in situations where excess free water administration is not desired, and where interstitial edema is detrimental to function and/or survival.