Determination of the Avogadro constant by counting the atoms in a 28Si crystal.

The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determination by counting the atoms in 1 kg single-crystal spheres, which are highly enriched with the 28Si isotope. It enabled isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, NA = 6.022,140,78(18) × 10(23) mol(-1), is the most accurate input datum for a new definition of the kilogram.

Evidence for an early free radical-mediated reperfusion injury in frostbite.

Frostbite is characterized by acute tissue injury induced by freezing and thawing. Initial complete ischemia is followed by reperfusion and later, tissue necrosis. These vascular events support the hypothesis that free radical-mediated reperfusion injury at thawing might contribute to tissue necrosis after frostbite in a manner similar to that seen after normothermic ischemia. To test this hypothesis, rabbit ears were frozen at -21 degrees C for 30, 60, 90, or 120 s and rewarmed at room temperature (22 degrees C). Rabbits were treated "blindly" with saline alone, highly purified, pharmaceutical grade superoxide dismutase (SOD), allopurinol, or deferoxamine. The area of ear necrosis was determined 3 weeks after frostbite by "blinded" morphometry. The administration of SOD at the time of thawing significantly improved viability in ears frozen for 60 and 90 s, but not in those frozen for 30 or 120 s. Deferoxamine also improved viability in ears frozen for 60 s. Allopurinol did not significantly affect ear survival. Electron micrographs showed the appearance of severe endothelial cell injury beginning during freezing and extending through early reperfusion. Later, neutrophil adhesion, erythrocyte aggregation, and microvascular stasis were seen. These findings suggest that free radical-mediated reperfusion injury has a role in frostbite, and quantitate the proportion of the injury that is due to this mechanism.

Biologic response to passive dissolution of titanium craniofacial microplates.

The effect of anodization on passive dissolution of titanium was studied by measuring titanium levels in peritoneal leukocytes and tissues of laboratory animals with titanium plates implanted into the peritoneal cavity. Fifteen Sprague-Dawley rats were assigned randomly to three treatment groups of five animals. One group served as controls, the other two groups had an anodized or an unanodized implant placed in the left paracolic gutter. Peritoneal lavage samples and blood samples, organ tissues and tissue surrounding the implants, were removed for histologic examination and titanium levels. Titanium was not detected in any distant organs or in the peritoneal lavage fluid. The capsular tissues surrounding the implants contained titanium at levels ranging from 2610 to 16786 ng/g for unanodized plates, and 888-5933 ng/g for anodized plates. The titanium levels within the peritoneal leukocytes of animals with unanodized implants were significantly elevated (P = 0.01) over time, as compared with controls. The level of titanium in the peritoneal leukocytes of animals with anodized implants was not significantly elevated when compared with controls. Titanium levels in the trace range, as measured in the capsular tissues, are likely a result of corrosion. Surface treatment of titanium by anodization reduces passive dissolution.

Impaired wound healing in Cushing's syndrome: the role of heat shock proteins.

BACKGROUND: Glucocorticoids impair wound healing and cause surgical morbidity. Heat shock proteins are essential to cellular stress tolerance and are associated with glucocorticoids. The adrenal heat shock protein response is under hypothalmic-pituitary-adrenal-axis control, whereas the vascular response is associated with alpha-1 receptors. Because heat shock proteins affect cellular stress responses and are under hypothalmic-pituitary-adrenal-axis control in other tissues, we postulated an association between heat shock proteins and glucocorticoids in healing wounds. METHODS: Modified Hunt-Schilling wound chambers were implanted subcutaneously in rats. They received subcutaneous time-release dexamethasone (25 mg) or placebo pellets. Wound chamber heat shock protein 25 and heat shock protein 72/73 were serially assayed for 21 days with western analysis and immunocytochemistry. RESULTS: Dexamethasone caused Cushing's syndrome with approximately 10% weekly weight-loss and adrenal atrophy. Total wound tissue decreased 90% with profound differences in molecular wound responses manifested by decreased heat shock protein 25, 72, and 73 in animals treated with dexamethasone despite equal protein loads. Furthermore, dexamethasone caused heat shock protein 72 redistribution by immunocytochemistry. CONCLUSIONS: This study represents the first description of heat shock proteins in a wound healing model and demonstrates tissue-specific decrease of heat shock proteins with glucocorticoid therapy. Thus the heat shock protein response is intimately associated with normal wound healing and is profoundly altered in subjects with Cushing's syndrome. Manipulation of this response may have clinical importance in wound healing.

Improved survival in free skin flap transfers in rats.

We have demonstrated previously that oxygen-derived free radicals are important mediators of tissue injury in experimental island skin flaps that have been subjected to prolonged ischemia (vascular occlusion) followed by reperfusion. In this study the role of oxygen free radicals in ischemia/reperfusion injury has been investigated in free flap transfers. Groin skin flaps were harvested, stored at room temperature for 21 to 24 hours, and transplanted to the contralateral groin. These free flap transfers normally exhibit a high incidence of complete necrosis. Treatment before the onset of reperfusion with a single dose of superoxide dismutase (SOD), a scavenger of superoxide radicals, increased the survival rate of these skin flaps from 38% in the control group to 76% (p less than 0.025). Tissue levels of SOD were measured before ischemia, after ischemia but before reperfusion, and 30 minutes after reperfusion: untreated flap tissues, which were destined to undergo necrosis, exhibited a significant decrease in SOD activity after reperfusion, whereas SOD-treated flap tissues, destined to survive, demonstrated increased enzyme activity. High levels of tissue SOD activity thus appeared to be associated with improved flap survival. The results have significant clinical implications with regard to organ preservation and transplantation.

The effects of hyperbaric oxygen on free flaps in rats.

The effects of hyperbaric oxygen on survival were investigated in free flaps and island flaps. Skin flaps transplanted following 18, 21, and 24 hours of preservation at 24 degrees C demonstrated survival rates of 20%, 10%, and 0%, respectively. Treatment with hyperbaric 100% oxygen improved the survival rates to 66%, 67%, and 40%. A preservation time of 21 to 24 hours at room temperature appears to be the threshold of irreversible ischemic damage. In acute island flaps, flap survival was improved significantly from 35% to 53% and 64% of the random flap area by preoperative or postoperative treatment, respectively. Prolonged preoperative and postoperative treatment improved survival to 66%.

Pathophysiology of sea nettle (Chrysaora quinquecirrha), envenomation in a rat model and the effects of hyperbaric oxygen and verapamil treatment.

The effect of lethal sea nettle envenomation on the morphology and blood flow in various rat organs was characterized and the influence of two antidotes (hyperbaric oxygen and verapamil) was compared. Either antidote slightly prolonged survival, but the protective effects were not statistically significant. The venom caused no histologic alterations in brain, heart, or lungs but induced hepatic and renal necrosis. Hepatocytes in mid-zonal regions and renal tubular epithelium were the cell types predominantly affected. Hyperbaric oxygen and verapamil did not decrease the hepatic injury. The venom did not influence central hemodynamics until preterminally and it diminished blood flow to brain, but not to liver or kidney. Hyperbaric oxygenation protected against venom-induced decreases in blood flow to the brain. These results add toxic hepatic and renal necrosis and cerebral ischemia to the pathophysiology of envenomation in this model.

Anterior resection for adenocarcinoma. Lahey Clinic experience from 1963 through 1969.

The results of anterior resection for adenocarcinoma of the rectum and rectosigmoid are reported with respect to survival rates and complications. Anastomotic recurrence is related to low lying, ulcerated, and less well differentiated tumors that have penetrated the bowel wall. The incidence of recurrent disease at the anastomosis increases with decreases in the margin of resection. Distal margins of at least 6 cm offer significant protection from recurrence. This study shows that anastomotic septic and fistulous complications are related to advanced age, diabetes, anemia, atherosclerotic disease, construction of the anastomosis below the peritoneal reflection, perforated bowel, obstructed bowel, and the use of drains. The determination of those factors that correlate with the development of anastomotic complications can be accomplished with pre- and intraoperative examinations. The role of these factors in operative decision-making and patient management is emphasized.

High-energy ballistic and avulsive injuries. A management protocol for the next millennium.

This article discusses high-energy ballistic and avulsive injuries, which are a formidable challenge to the reconstructive surgeon. Management protocols are provided for the next millennium.

Facial bone healing and bone grafts. A review of clinical physiology.

The physiology of bone healing, regeneration, and bone transfer is discussed from the dual perspectives of basic physiology and the application to clinical situations of bone transfer. Recommendations are made regarding clinical applications for the site, orientation, and fixation of grated materials. Rationale for the use of vascularized transfers is presented.

Nasoethmoid orbital fractures. Current concepts and management principles.

The proper management of nasoethmoid orbital fractures relies upon early accurate diagnosis and treatment. A surgical plan must be established after careful review of the physical examination and CT scans. Identification of the extent and type of fracture pattern determines the operative approach. Extended (wide) exposure, using craniofacial techniques, facilitates precise reduction and rigid fixation of all bone fragments. Transnasal reduction of the canthus-bearing central segment (medial orbital rim) is the critical operative maneuver required to achieve normal intercanthal distance. Immediate bone grafting replaces severely comminuted or missing bone fragments. The skin overlying the nasoethmoid area is carefully redraped by gentle pressure from padded external compression bolsters. These principles form the basis for superior aesthetic and functional results.

Panfacial fractures: organization of treatment.

Recent advances in facial trauma management have enabled the surgeon to perceive and successfully reconstruct complex panfacial injuries. Restoration of both preinjury facial aesthetics and function is now the goal. An organized approach to these injuries begins at the maxillary and mandibular arches with progression to the vertical mandible. The nasoorbital ethmoidal complex is stabilized to the cranium and bone grafted when indicated. The zygomatic complex is related medially, and orbital reconstruction performed. The facial architectural restoration is completed at the Lefort I level. Adherence to this protocol enables the surgeon to obtain reproducibly good results, even with the most extensive facial dislocations.

Cheek reconstruction with laterally based flaps.

Laterally based cervicofacial advancement flaps that follow the borders of facial aesthetic subunits provide a more aesthetic solution to the reconstruction of anterior cheek defects than do standard cervicofacial flaps or skin grafts. The circulation in these laterally and inferiorly based flaps is improved, because the transverse facial artery is spared. These flaps also provide better contour and possess more aesthetic scar placement than do anteriorly and inferiorly based flaps.

Anesthesia in head and neck surgery. Head and neck cancer surgery and maxillofacial trauma.

Safe anesthetic management of head and neck surgery and maxillofacial trauma depends on an accurate identification of ancillary problems, precise intraoperative monitoring, and treatment. Protocols facilitate thorough management, and a discussion is provided.

Deep orbital reconstruction for correction of post-traumatic enophthalmos.

Post-traumatic enophthalmos is a complex orbital deformity resulting from an injury disrupting orbital bone and ligament support, allowing displacement and a change in shape of the orbital soft-tissue contents. Clinically, this is manifested by inferior and posterior displacement of the globe, pseudoptosis, and deepening of the supratarsal fold. Soft-tissue changes such as canthal malposition and shortening of the horizontal dimension of the palpebral fissure are present when unreduced nasoethmoidal orbital fractures exist. The essential principles of surgical correction include full dissection of the bony orbital soft tissues including the posterior orbit with restoration of bony orbital volume by the judicious insertion of bone grafts to correct the vertical as well as the anteroposterior position of the ocular globe. The combination of techniques of craniofacial exposure, osteotomy, and bone grafting allow the condition of post-traumatic enophthalmos to be greatly improved with minimal complications.

Early and late complications of orbital fractures.

Complications, unfortunately, arise as a result of traumatic or iatrogenic injuries. The sequelae can range from the most insignificant to the most debilitating. The most common complications noted in the diagnosis and treatment of orbital fractures are outlined as well as discussed as appropriate to their appearance during the healing process. With better understanding and better management, complications can be prevented.

Nasoethmoidal and orbital fractures.

It is helpful to consider fractures of the orbit both in terms of their location and fracture pattern. CT scanning is an invaluable aid to the diagnosis and treatment of all orbital fractures. Early operative intervention, wide exposure, and accurate and stable fixation accompanied by immediate bone grafting provide the most successful treatment of fractures of the orbit.

Strategies for the treatment of enophthalmos.

The surgical correction of post-traumatic enophthalmos is among the most challenging problems for the surgeon. A thorough understanding of orbital anatomy and the purposed mechanisms of enophthalmos is crucial to the ultimate success or failure of the procedures. The successful orbital reconstruction begins with a careful physical examination of the patient that is attentive to ocular function, soft-tissue position, and visible or palpable defects of the facial skeleton. The physical examination combined with thin section CT scanning in the axial and coronal planes provides the basis of the operative plan. The anatomy of the deformity should dictate the anatomy and shape in the surgical correction. In many cases, multiple surgical incisions will be required; therefore, care must be taken to maximize exposure and minimize the cosmetic problems associated with large incisions. We advocate a step-wise approach consisting of mobilization of the soft tissues in the area of the fracture, repositioning of the anterior and middle sections of the bony orbit, and reattachment of the soft tissue to the bone at the proper location. The approach to reconstruction of the bony orbit that we advocate is to first sequentially reposition each segment of the rim, carefully examining each articulation. Once rim reconstruction is complete, reconstruction of the internal wall is performed. Recall that the largest source of error is in inadequate reduction of the orbital rim, owing to the fact that this error is "squared" (according to the model) in the computation of the orbital volume. Through the application of these principles, the cosmetic and functional sequelae of post-traumatic enophthalmos can be improved greatly with minimal complications.

A variation in the appearance of melanoma-in-situ (Clark's level I malignant melanoma).

Recently two cases of atypical melanoma-in-situ have been treated. The role of assessing this lesion, its clinical presentation, and margins of resection is reviewed. Early diagnosis and biopsy are essential.

Numbness after blepharoplasty: the relation of the upper orbital fat to sensory nerves.

Numbness after blepharoplasty was infrequent complication (less than 1 percent). It represents nerve injury to terminal branches of the ophthalmic division division of the trigeminal nerve which are found superior and superomedial to fat in the upper orbital fat compartments. Nerve injury has multiple mechanisms and can be avoided by recognition of the proximity of sensory nerve fibers to orbital fat and by awareness of the mechanism of injury.