Correlation functions for glass-forming systems

We present a simple, linear, partial-differential equation for the density-density correlation function in a glass-forming system. The equation is written down on the basis of fundamental and general considerations of linearity, symmetry, stability, thermodynamic irreversibility and consistency with the equation of continuity (i.e. , conservation of matter). The dynamical properties of the solutions show a change in behavior characteristic of the liquid-glass transition as a function of one of the parameters (temperature). The equation can be shown to lead to the simplest mode-coupling theory of glasses and provides a partial justification of this simplest theory. It provides also a method for calculating the space dependence of the correlation functions not available otherwise. The results suggest certain differences in behavior between glassy solids and glass-forming liquids which may be accessible to experiment. A brief discussion is presented of how the method can be applied to other systems such as sandpiles and vortex glasses in type II superconductors.

Plasma homocysteine is decreased in the hypothyroid rat

Recent clinical studies have indicated that plasma homocysteine was significantly increased in hypothyroid patients. Since hyperhomocysteinemia is an independent risk factor for cardiovascular disease we investigated homocysteine metabolism in hypothyroid rats. Hypothyroidism was induced in one study by addition of propylthiouracil (PTU) to the drinking water for 2 weeks. In a second study, thyroidectomized and sham-operated rats were used with thyroid hormone replacement via mini-osmotic pumps. Unlike the human hypothyroid patients, both groups of hypothyroid rats exhibited decreased total plasma homocysteine (30% in PTU rats, 50% in thyroidectomized rats) versus their respective controls. Thyroid replacement normalised homocysteine levels in the thyroidectomized rat. Increased activities of the hepatic trans-sulfuration enzymes were found in both models of hypothyroidism. These results provide a possible explanation for the decreased plasma homocysteine concentrations. The hypothyroid rat cannot be used as a model to study homocysteine metabolism in hypothyroid patients.

Regulation of homocysteine metabolism

We have used a combination of in vivo and in vitro techniques to measure factors regulating homocysteine metabolism and the plasma concentration of this atherogenic amino acid. The germane findings include: 1. Homocysteine metabolism in rat kidney proceeds predominantly through the transsulfuration pathway, whose enzymes are enriched within the proximal cells of kidney tubules. Furthermore, the rat kidney possesses significant reserve capacity to handle both acute and chronic elevations in plasma homocysteine concentrations. 2. Plasma homocysteine concentrations are lower in diabetic rats. Insulin administration corrects this perturbation. Therefore, insulin and/or one of its counter-regulatory hormones affects homocysteine metabolism, possibly through an increased flux in the hepatic transsulfuration pathway. In support of these data, glucagon administration to rats produced similar results. Further support was provided by studies with isolated rat hepatocytes, from which homocysteine export was reduced when incubated in the presence of glucagon.

Effects of streptozotocin-induced diabetes and of insulin treatment on homocysteine metabolism in the rat

An elevation in the concentration of total plasma homocysteine is known to be an independent risk factor for the development of vascular disease. Alterations in homocysteine metabolism have also been observed clinically in diabetic patients. Patients with either type 1 or type 2 diabetes who have signs of renal dysfunction tend to exhibit elevated total plasma homocysteine levels, whereas type 1 diabetic patients who have no clinical signs of renal dysfunction have lower than normal plasma homocysteine levels. The purpose of this study was to investigate homocysteine metabolism in a type 1 diabetic animal model and to examine whether insulin plays a role in its regulation. Diabetes was induced by intravenous administration of 100 mg/kg streptozotocin to Sprague-Dawley rats. We observed a 30% reduction in plasma homocysteine in the untreated diabetic rat. This decrease in homocysteine was prevented when diabetic rats received insulin. Transsulfuration and remethylation enzymes were measured in both the liver and the kidney. We observed an increase in the activities of the hepatic transsulfuration enzymes (cystathionine beta-synthase and cystathionine gamma-lyase) in the untreated diabetic rat. Insulin treatment normalized the activities of these enzymes. The renal activities of these enzymes were unchanged. These results suggest that insulin is involved in the regulation of plasma homocysteine concentrations by affecting the hepatic transsulfuration pathway, which is involved in the catabolism of homocysteine.

Improving performance through an organizational culture of employee expertise

Managers can do many things to improve organizational performance, but the accomplishments of the most skillful employees often are most important. This article makes the point that managers should be aware of employee expertise and its relationship to organizational performance. The article also describes the components of an organizational culture of employee expertise. An organizational culture of employee expertise builds on the learning organization metaphor that has frequently appeared in the management literature. How employees develop expertise to do their jobs is emerging as a critical issue for organizations, and managers will likely play a key role in that process.

Foot amputations

When presented with an ischemic limb with forefoot necrosis of varying amounts, the surgeon often categorizes the need for amputation into toe, ray, transmetatarsal, below-knee, and above-knee. Adherence to this type of algorithm ensures a primary above- or below-knee amputation rate of 10% to 20%. The utility of the more uncommon amputations advocated here is an increase of limbs deemed eligible for revascularization and limb salvage. Furthermore, delaying the amputations until the vascular supply is normalized maximizes tissue salvage and minimizes prolonged hospitalizations with multiple amputations performed as a prelude to major amputation. Although these amputations are often looked upon as an afterthought by many vascular surgeons, careful execution here is as important to effective limb salvage as any distal bypass procedure.

The fates of illustrious bones

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Increased limb salvage by the use of unconventional foot amputations

PURPOSE

Limb salvage in the presence of ischemic foot necrosis requires revascularization followed by debridement or partial foot amputation. Necrosis extending beyond the toes and metatarsal heads may require the use of unconventional types of amputations.

METHODS

Over a 15-year period 2105 ischemic limbs were treated with infrainguinal revascularization. In 98 cases, extensive foot necrosis was than managed with amputations, including 59 modified Chopart, 14 Lisfranc, 17 Pirogoff and 8 Syme amputations. Patients were not allowed to bear weight for several days to weeks.

RESULTS

Skin flap necrosis in 14 cases was managed successfully by debridement and skin grafting. Ambulation required the use of a "clamshell" prosthesis and foot spacer. The overall limb salvage rate in this group was 84% (82 of 98). In general, the modified Chopart amputation most frequently produced ambulatory limb salvage and is technically easier to perform than a Syme amputation. Patient satisfaction and long-term ambulatory function was highest with the modified Chopart.

CONCLUSION

Ischemic foot necrosis extending beyond the limits of conventional transmetatarsal amputation need not be treated with major amputation. This requires the surgeon to be well versed in the use of less common types of partial foot amputations. Acceptable limb salvage and good functional results may be attained by the motivated patient and surgeon with the use of these procedures in the revascularized limb.

Stabilization procedures of the hindfoot

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Salvage of the diabetic foot with exposed os calcis

Fifty consecutive heel ulcers were managed in three groups by debridement, split-thickness skin graft (STSG), bypass procedures, and orthotics. Group I consisted of 24 ulcers in patients with diabetes (DM) and peripheral vascular disease (PVD), 14 patients in Group II with DM only, and 12 patients with PVD only (Group III). Healing occurred in 56.5%, 64.3%, and 83.3%, respectively. An average of 2.2 procedures were performed per patient. Follow-up periods were for a minimum of two years or until amputation. Time for complete healing and the number of amputations performed were similar in all groups. Of the diabetics (combined from Groups I and II), a subgroup of 27% required partial excision of the os calcis to facilitate closure. After saline dressing changes, STSG was accomplished over thin granulation tissue. Forty percent of this subgroup healed, 30% remained open, and 30% were amputated. Aggressive management, soft-tissue coverage, and orthotic use can lead to a functional weight-bearing extremity.

Surgical arthrodesis of the neuropathic foot. A salvage procedure

Reconstructive foot and ankle surgery is a salvage procedure in the deformed neuropathic foot, despite condemnation by some authors. Clinical union and stability was achieved in 91% of the patients, and soft-tissue coverage without skin breakdown was achieved in 100% of the cases. Although one patient had moderate to severe pain in her ankle after operation and was able to do only bed-to-wheelchair transfers, she had good clinical stability, no skin ulceration, and was satisfied overall with the procedure. In addition, a significant component of her pain was believed to be from diabetic neuropathy and not pain that was directly attributable to her reconstructive surgery. All other patients were able to ambulate to some degree. More than half had unlimited use of the affected lower extremity. More than half of the patients had mild or no pain, and all patients had a functional limb. Surgical arthrodesis of the deformed neuropathic foot as a salvage procedure can preserve the limb as a stable functional unit, and create an acceptable alignment of the ankle-foot complex that will promote viability of the overlying soft-tissue structures.

Chopart amputation with percutaneous heel cord lengthening

When amputation becomes necessary in a patient with peripheral vascular disease, it is important to preserve as much tissue as possible to preserve maximum function. This is especially important because the other extremity may have similar involvement in the future. With appropriate care, an amputation at the Chopart (calcaneocuboid-talonavicular) level can give a good functional result.

Triple arthrodesis through a single lateral approach: a cadaveric experiment

Using a single lateral approach, triple arthrodesis was performed on six cadaveric feet. An attempt was made to obliterate the talocalcaneal, talonavicular, and calcaneocuboid joints. The limbs were subsequently disarticulated to allow for an inspection of the talonavicular, talocalcaneal, and calcaneocuboid joints. An estimate of cartilage and subchondral bone removed from each articular surface was made by a single observer (J.V.B.) by direct visual inspection. Results were as follows: calcaneocuboid joint, 90% of cartilage removed; talocalcaneal joint, 80% of cartilage removed; talonavicular joint, 38% of cartilage removed. Failures at the talonavicular joint were attributed to a poor appreciation of the anatomy of the talar head and poor observation. Complications involved in obliteration of the talonavicular joint from a single lateral approach included: inadvertent division of the talar neck; inadvertent division of the talar head; removal of excessive bone stock; medial skin punctures; and creation of an iatrogenic cut through the talar dome. Therefore, a triple arthrodesis through a single lateral approach, as described by Ryerson, Hoke, and Campbell, cannot be recommended. The talonavicular joint should be approached through an auxiliary medial incision, as recommended by Cracchiolo. This paper documents the experience of a beginner with this operation, and demonstrates the value of using the anatomy laboratory.

Pseudoaneurysm of the dorsalis pedis artery after Lisfranc amputation

Pseudoaneurysm formation is usually associated with laceration, fracture, or iatrogenic arterial injury. However, it may also develop as a result of blunt trauma. We report the case of a pseudoaneurysm of the dorsalis pedis artery after a Lisfranc amputation in an individual with diabetes mellitus, Charcot joint changes in the left forefoot, and atherosclerosis of the distal vessels.

Hypersensitivity pneumonitis treated with an electrostatic dust filter

A 60-year-old woman had had recurrent acute migratory pneumonias for 9 months. The results of an evaluation, which included tests for serum precipitins, a transbronchial biopsy, and a bronchial provocation, confirmed a diagnosis of hypersensitivity pneumonitis caused by an Aspergillus species. The findings from gravity air cultures in the home showed a heavy infestation of mold. The installation of electrostatic dust filters in the return ducts of the central air conditioning system resulted in the lowering of mold colony counts to normal levels. This change in the environment enabled the patient to live at home without having the signs and symptoms of hypersensitivity pneumonitis, or a need for medication. Thirty months after the electrostatic dust filters were installed, total mold colony counts were still normal, the patient remained free of the signs and symptoms of hypersensitivity pneumonitis, and serum precipitins could no longer be demonstrated. The results of a bronchial challenge to Aspergillus species, however, remained positive; these positive results suggest that long-term memory immune mechanisms may play an important role in the pathogenesis of hypersensitivity pneumonitis and lessen the importance of precipitins in establishing a diagnosis. We report that electrostatic dust filters may be an effective treatment for patients with hypersensitivity pneumonitis when avoidance of the causative antigen cannot be easily and rapidly achieved.