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Biomedical subjects

S Schendel

Publications and source records attributed to S Schendel.

12 recordsLinked to original sources
PubMed2001

Virtual reality based surgical assistance and training system for long duration space missions.

Access to medical care during long duration space missions is extremely important. Numerous unanticipated medical problems will need to be addressed promptly and efficiently. Although telemedicine provides a convenient tool for remote diagnosis and treatment, it is impractical due to the long delay between data transmission and reception to Earth. While a well-trained surgeon-internist-astronaut would be an essential addition to the crew, the vast number of potential medical problems necessitate instant access to computerized, skill-enhancing and diagnostic tools. A functional prototype of a virtual reality based surgical training and assistance tool was created at our center, using low-power, small, lightweight components that would be easy to transport on a space mission. The system consists of a tracked, head-mounted display, a computer system, and a number of tracked surgical instruments. The software provides a real-time surgical simulation system with integrated monitoring and information retrieval and a voice input/output subsystem. Initial medical content for the system has been created, comprising craniofacial, hand, inner ear, and general anatomy, as well as information on a number of surgical procedures and techniques. One surgical specialty in particular, microsurgery, was provided as a full simulation due to its long training requirements, significant impact on result due to experience, and likelihood for need. However, the system is easily adapted to realistically simulate a large number of other surgical procedures. By providing a general system for surgical simulation and assistance, the astronaut-surgeon can maintain their skills, acquire new specialty skills, and use tools for computer-based surgical planning and assistance to minimize overall crew and mission risk.

Aerospace Medicine↗
PubMed2000

Development and application of a virtual environment for reconstructive surgery.

OBJECTIVE: This paper details the development and application of a Virtual Environment for Reconstructive Surgery (VERS). It addresses the technical and user-interface challenges in developing such a system, and the lessons learned during application of the system in the case of a 17-year-old boy with a severe facial defect arising from the removal of a soft-tissue sarcoma. MATERIALS AND METHODS: Computed tomography (CT) scans were segmented into bone and soft-tissue classifications using traditional and novel algorithms, a surface mesh was generated, and imaging artifacts were removed, yielding a mesh suitable for visualization. This patient-specific mesh was then used in a virtual environment by the surgeons for preoperative visualization of the defect, planning of the surgery, and production of a custom surgical template to aid in repairing the defect. RESULTS: This system was successfully used to plan the surgery of the patient and to produce a custom, patient-specific template that was used to harvest bone from a donor site in order to reconstruct the defect. CONCLUSION: Despite technical challenges, virtual-environment surgical planning is useful as a clinical tool for preoperative visualization, cephalometric analysis, and surgical intervention. It can provide a more precise surgical result than would otherwise be realized using traditional methods.

Adolescent↗
PubMed1998

Acidic pH promotes dimerization of Bcl-2 family proteins.

Several members of the apoptosis-regulating Bcl-2 family of proteins can homo- or heterodimerize with each other at neutral pH and can also form ion channels in synthetic membranes at low pH. The effects of low pH on dimerization among these proteins, however, have not heretofore been examined. Surface plasmon resonance was used to examine the kinetics of dimerization as a function of pH between the anti-apoptotic protein Bcl-XL (applied in the mobile phase) and three other members of the Bcl-2 family: Bcl-2, Bax, and Bid (immobilized on biosensor chips). In all cases, the relative affinity of dimerization was substantially increased at pH 4.0 compared to pH 7.0-7.4, ranging from a approximately 10-fold enhancement for Bcl-XL/Bcl-XL homodimers to >60-fold for Bcl-XL/Bid heterodimers. Comparison of the apparent association (ka) and dissociation (kd) rates at neutral and acidic pH revealed that the major contributor to increased affinity at low pH was a decreased rate of dimer dissociation. Thus, low pH stabilizes homo- and heterodimeric complexes comprised of Bcl-XL and these other Bcl-2 family proteins. At pH 4.0, the circular dichroism spectra of Bcl-XL and Bax were essentially unchanged relative to pH 7.0-7.4, indicating a complete retention of alpha-helical secondary structure at low pH and excluding gross denaturation of the proteins. Size-exclusion chromatography and bisANS (4,4'-dianilino-1, 1'-binaphthyl-5,5'-disulfonic acid) labeling studies provided indirect evidence that Bcl-XL may undergo conformational changes at low pH. The findings are discussed with respect to the mechanisms of ion-channel formation by Bcl-2 family proteins and the putative molten globule state that has been proposed for these and structurally similar proteins.

Amino Acid Sequence↗
PubMed1998

Apert's syndrome correlates with low fibroblast growth factor receptor activity in stenosed cranial sutures.

Recent genetic studies have shown that Apert's syndrome results from mutations of the fibroblast growth factor (FGF) receptor 2 gene. We were interested in investigating the expression of FGF receptor 2 at the tissue level in children with Apert's syndrome. We studied FGF receptor activity in cranial sutures of children with Apert's syndrome and nonsyndromic, isolated craniosynostosis. Fourteen children between the ages of 6 months and 12 months were studied. Five of these children had Apert's syndrome with coronal suture stenosis. Nine children had an isolated, nonsyndromic coronal stenosis. Stenosed and nonstenosed cranial sutures were removed at the time of cranioplasty, fixed, decalcified, and paraffinized. Immunohistochemistry was performed with labeled, specific anti-FGR receptor 2 antibodies. We found lower levels of FGF receptor 2 staining in both stenosed and unstenosed sutures of children with Apert's syndrome compared with those from children with a nonsyndromic suture stenosis. Furthermore, fused sutures from children with Apert's syndrome demonstrated lower levels of FGF receptor 2 staining than unfused sutures from the same sample. The findings suggest that Apert's syndrome correlates with low FGF receptor 2 activity in cranial sutures. These results are consistent with and similar to our findings in Crouzon's syndrome, and support genetic studies showing localized mutational changes occurring at the FGF receptor 2 gene for both Apert's and Crouzon's syndromes. Furthermore, the findings suggest the possibility that variable expression of FGF receptor 2 occurs at the tissue level in patients with Apert's syndrome.

Acrocephalosyndactylia↗
PubMed1997

Preliminary report: a ceramic containing crosslinked collagen as a new cranial onlay and inlay material.

Simple ceramic bone graft materials have demonstrated significant limitations for use in craniomaxillary reconstruction. We investigated a new, alloplastic composite bone grafting material containing particulate hydroxyapatite and crosslinked collagen in a time-sequence study. Five rabbits underwent surgical placement of high-loading and low-loading composite onlay and inlay grafts in the parietal region of the skull. Animals were sacrificed at either 1, 2, 4, or 6 months postoperatively. All rabbits demonstrated tissue continuity and healing of both onlay and inlay grafts to the outer table of the skull. Bony ingrowth was shown in both onlays and inlays with bone proliferation and vascularization. Bony ingrowth was seen as early as 1 month postoperatively. Inlay grafts healed flush to the outer table, while onlay grafts maintained at least 80% of graft volume at 6 months postoperatively. We conclude that a composite bone grafting material containing a ceramic and collagenous matrix may offer significant advantages to the reconstructive surgeon. The material appears to be easy to handle and carve, is biologically tolerated, and is able to maintain graft volume. Further studies of this new composite material are warranted.

Animals↗
PubMed1995

Crouzon's disease correlates with low fibroblastic growth factor receptor activity in stenosed cranial sutures.

Reports have demonstrated that Crouzon's disease is associated with a gene on chromosome 10 coding for the fibroblastic growth factor (FGF) receptor 2. The purpose of this investigation was to evaluate the FGF receptor 2 levels in cranial sutures of children with Crouzon's disease and nonsyndromic, isolated craniosynostosis. Twelve children between the ages of 6 and 24 months were studied. Four patients had Crouzon's disease with coronal suture stenosis. The 8 remaining had a nonsyndromic, isolated coronal stenosis. Stenosed and adjacent nonstenosed cranial sutures were removed at cranioplasty and promptly fixed, decalcified, and embedded in paraffin. Immunohistochemical analysis of cranial sutures was performed with labeled, specific anti-FGF receptor 2 antibodies. In children with Crouzon's disease, we found significantly lower levels of FGF receptor 2 staining in stenosed sutures compared with nonstenosed sutures. In addition, sutures from children with Crouzon's disease demonstrated lower levels of FGF receptor 2 activity in both stenosed and nonstenosed sutures compared with children with a nonsyndromic, isolated coronal stenosis. However, there were no significant differences in FGF receptor 2 staining between stenosed and nonstenosed sutures in children with a nonsyndromic, isolated coronal stenosis. These findings suggest that low FGF receptor 2 activity in cranial sutures correlates with Crouzon's disease. This work supports genetic studies and yet shows that patients with Crouzon's disease have low FGF receptor 2 activity in cranial sutures. The findings also suggest that there may be etiological differences between syndrome- and nonsyndrome-associated craniosynostoses in children.

Child, Preschool↗
PubMed1992

Dynamic properties of the colicin E1 ion channel.

The mechanism of channel formation and action of channel-forming colicins is a paradigm for the study of dynamic aspects of membrane-protein interactions. The following experimental results concerning interaction of the colicin E1 channel domain with target membranes, in vitro and in vivo, are discussed: (1) the nature of the translocation-competent state of the channel-forming domain; (2) unfolding of the colicin channel peptide during in vitro binding and anchoring of the channel to liposome membranes at acidic pH; (3) reversal of channel peptide binding to liposomes by an alkaline-directed pH shift; (4) voltage-driven translocation and gating of the ion channel, discussed in the context of a four-helix model for a monomeric channel; (5) rescue of colicin-treated cells by high levels of external K+; (6) trypsin rescue of cells depolarized by the colicin ion channel; and (7) interaction of the channel domain with its immunity protein.

Amino Acid Sequence↗
PubMed1989

Submental-submandibular suction lipectomy: indications and surgical technique.

The submental and submandibular regions play an essential role in the overall harmony of facial aesthetics. The appearance of the cervicomental area may be the result of many factors, including mandibular hypoplasia, localized lipodystrophy, a low-positioned hyoid bone, platysmal deformity, soft tissue laxity, or a combination of any of these. Although much attention has been directed toward correction of bony contour deformities of the mandible and chin, minimal emphasis has been placed on evaluation and correction of soft tissue disharmonies in the submental-submandibular areas. This article discusses the indications and contraindications, patient examination, surgical technique, and potential complications of suction-assisted lipectomy of the cervicomental region. Select cases are presented to illustrate the concepts and techniques discussed herein.

Chin↗
PubMed1989

Nasal anatomy and maxillary surgery. II. Unfavorable nasolabial esthetics following the Le Fort I osteotomy.

The Le Fort I osteotomy is among the most commonly performed orthognathic surgical procedures for correction of skeletal dysplasias. Numerous authors have described unfavorable nasal and labial changes following maxillary surgery, such as widening of the alar bases of the nose, upturning of the nasal tip, flattening and thinning of the upper lip, and downturning of the commissures of the mouth. These postoperative changes in nasolabial morphology are secondary to alterations in the regional anatomy following skeletal repositioning, cartilaginous resectioning, muscular retraction, and the resultant effects of these procedures on the overlying skin and subcutaneous tissues. In part I of this series a systematic method of evaluation and a detailed anatomic description of the nasolabial region were presented. This paper presents a series of cases with unfavorable nasal changes following Le Fort I osteotomies, analyzes each case in detail, and discusses the possible etiologies. Part III of this series will present techniques for handling of the skeletal, cartilaginous, and musculofascial components of the nasomaxillary region during the Le Fort I procedure to improve nasofacial esthetics and avoid unfavorable results.

Adolescent↗
PubMed1989

Nasal anatomy and maxillary surgery. I. Esthetic and anatomic principles.

The LeFort I osteotomy is commonly performed to correct maxillary dentofacial deformities. Secondary changes in the nasolabial region that have occurred following this procedure include widening of the alar bases of the nose, upturning of the nasal tip, flattening and thinning of the upper lip, and downturning of the commissures of the mouth. Surgical techniques can modify undesirable secondary changes. Applying these surgical techniques and achieving the desired results require an understanding of the underlying anatomy. This paper will present a thorough review of the nasolabial anatomy (both external and internal) as it pertains to the patient undergoing maxillary surgery.

Esthetics, Dental↗
PubMed1978

Mandibular deficiency syndrome. I. Clinical delineation and therapeutic significance.

The mandibular deficiency syndrome is a constellation of abnormalities, including a spectrum of skeletal, neuromuscular, occlusal, and esthetic conditions. The extremes of this syndrome exhibit different skeletal and esthetic morphology and growth patterns. Different orthodontic and surgical approaches must be considered for optimal functional and esthetic correction in the three different facial types. Differentiation between cases with low, medium, and high mandibular plane angles and knowledge of the growth tendencies will permit different surgical and orthodontic considerations for each of the three basic morphologic types. Predictable functional and esthetic results can then be expected.

Adolescent↗