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Biomedical subjects

R Jacobs

Publications and source records attributed to R Jacobs.

At least 109 records · Page 6Linked to original sources
PubMed1999

Influence of inflammatory reactions vs. occlusal loading on peri-implant marginal bone level.

Plaque accumulation on abutments or implant surfaces induces an inflammatory reaction in the gingiva/alveolar mucosa just as around teeth. The longevity of oral implants can be jeopardized by either peri-implantitis and/or an occlusal overload. In the partially edentulous patient in whom pockets around teeth act as a reservoir for the colonization of the pockets around implants, the risk for inflammatory reactions of the peri-implant soft tissues seems especially more plausible than in the fully edentulous patient. This is especially true for implants with a very rough surface (e.g., plasma-sprayed), because of the positive relationship between surface roughness and supra- as well as subgingival plaque formation. Several medium-term (from 5 to 10 years) clinical studies support this hypothesis, through the observation of ongoing bone loss and subsequent decreasing success/survival percentages. Occlusal overload increases the risk for microfractures at the implant-bone interface in two-stage implants, which can result in significant marginal bone loss and even failure. There is ample evidence that occlusal factors are related to marginal angular defects around two-stage implants.

Alveolar Bone Loss↗
PubMed1999

[Preoperative planning for the placement of a single implant].

Radiography is of primary importance for the preoperative planning of oral implant placement. Depending on the indication, various techniques are available, each with its own merits and drawbacks. In general, it can be stated that the intra-oral radiography using the paralleling technique is the method of choice for a solitary tooth replacement. Panoramic radiography is indicated for implant placement in the symphyseal area of the lower jaw. Cross-sectional imaging is performed when information is needed in the bucco-lingual dimension. Conventional tomography is recommended for preoperative planning of limited edentulous areas. CT-scan imaging is required for rehabilitation of extended edentulous areas or in complex maxillofacial surgery combined with implant placement. Choosing the optimal technique can be performed by weighing the radiation dosage and the diagnostic information required.

Dental Implantation, Endosseous↗
PubMed1998

EAE TCR motifs and antigen recognition in myelin basic protein-induced anterior uveitis in Lewis rats.

T cells infiltrating the iris/ciliary body of Lewis rats with anterior uveitis (AU) that had been induced by myelin basic protein (MBP) immunization were previously found to share surface markers common to the T cells that cause experimental autoimmune encephalomyelitis (EAE). To determine whether these AU-associated T cells are in fact the same as those that infiltrate the central nervous system to cause EAE, we examined TCR V gene expression in T cells infiltrating the anterior chamber in rats with AU. As with EAE, we found a biased expression of Vbeta8.2 and Valpha2 in the iris/ciliary body and, although one would expect an influx of nonspecific inflammatory T cells, these biases were still evident at the peak of AU. An analysis of the TCR Vbeta8.2 and Valpha2 sequences derived from the iris/ciliary body demonstrated the presence of the same complementarity determining region 3 motifs found in MBP-specific T cells that are pathogenic for EAE and found in T cells derived from the central nervous system of rats with EAE. Finally, T cells isolated from the iris/ciliary body of rats with AU were found to proliferate in a specific fashion to MBP Ags. Thus, it appears that MBP-specific T cells are pathogenic for AU as well as EAE in the Lewis rat. In addition, the long-term presence of this highly restricted MBP response in the iris/ciliary body indicates that distinct immunoregulatory mechanisms exist in the environment of the eye. This provides an interesting model with which to address questions pertaining to the nature of T cells infiltrating the eye and their regulation during EAE and other systemic diseases.

Animals↗
PubMed1998

Neonatal exposure of TCR BV8S2 transgenic mice to recombinant TCR BV8S2 results in reduced T cell proliferation and elevated antibody response to BV8S2, and increased severity of EAE.

Transgenic (Tg) mouse models are unique tools for investigating regulatory mechanisms of the immune system. Mice bearing a T cell receptor (TCR) BV8S2 transgene derived from an encephalitogenic T cell clone are highly susceptible to experimental autoimmune encephalomyelitis (EAE), a T cell-mediated neurological disorder. Although the pathogenesis of EAE is not yet fully understood, TCR-specific regulatory T cells seem to play a role in its remission and/or recovery process. In previous studies, we showed that immunization of BV8S2 Tg mice with recombinant BV8S2 protein induced TCR-specific T cells and protection against EAE, clearly indicating the persistence of a functional TCR regulatory network in spite of the highly skewed T cell repertoire. To further investigate the natural regulatory role of TCR-specific T cells, we evaluated the effect on EAE of inducing neonatal tolerance to heterologous (rat) and homologous BV8S2 proteins in Tg mice. Neonatal exposure to rat BV8S2 protein induced "split" tolerance, characterized by decreased T cell proliferation but increased antibody responses to both rat and mouse BV8S2 proteins that are known to be cross-reactive. When challenged as adults with an encephalitogenic emulsion, Tg mice tolerized with rat but not mouse BV8S2 protein developed more severe EAE compared to control mice. These results demonstrate that immunity to BV8S2 determinants in BV8S2 Tg mice is naturally induced and functions to limit the severity of EAE.

Animals↗
PubMed1998

Endocrine mechanisms of stress-induced DHEA-secretion.

Acute psychological stress of a first time parachute jump stimulated DHEA and cortisol secretion in healthy volunteers. A significant shift from cortisol to DHEA occurred during this stress exposure. This effect was more pronounced in subjects receiving the beta-adrenoceptor antagonist propranolol prior to the jump. In contrast, infusion of epinephrine (0.10 microgram/kg/min) or norepinephrine (0.15 microgram/kg/min) for 20 min neither affected DHEA plasma levels nor the DHEA/cortisol ratio. However, pretreatment with propranolol resulted in a significant increase of the DHEA/cortisol ratio upon infusion of the beta-adrenoceptor agonist epinephrine. These data demonstrate that during acute psychological stress stimulation of adrenal steroid release is accompanied by a shift towards DHEA. Augmentation of this effect by beta-adrenoceptor blockade indicates a beta-adrenoceptor-dependent mechanism affecting DHEA release.

Acute Disease↗
PubMed1998

Effects of beta-adrenoceptor-blockade on stress-induced adrenocorticotrophin release in humans.

We investigated the mechanisms of stress-induced alterations in adrenocorticotrophin (ACTH) release. Tandem parachutists received either a placebo or the beta-adrenoceptor antagonist propranolol prior to a first time parachute jump. Blood samples were drawn 4 h before, immediately after, and 1 h after the jump. Cortisol and catecholamine concentrations displayed a significant stress-induced increase in both groups. The ACTH plasma concentrations significantly increased in the placebo and the propranolol group, with significantly more pronounced changes in the propranolol-treated subjects compared to the placebo group. These data demonstrated a stress-induced increase of ACTH plasma concentrations in humans that was enhanced by beta-blockade.

Adrenergic beta-Antagonists↗
PubMed1998

Oral stereognosis: a review of the literature.

Stereognosis is the ability to recognise and discriminate forms. Oral stereognostic ability has been studied in different reports. The experimental design of the test is of primary importance as both the method used and the material applied may influence the results dramatically. The form, size and surface characteristics of the test piece, the presentation order, subject-related factors and the method of scoring all have their effect on the results. With regard to subject-related factors, ageing has a negative influence on stereognostic ability; gender is considered of no importance. Another influencing factor is dental status. A healthy natural dentition offers a very good oral stereognostic ability. Edentulous subjects usually show a decreased oral stereognostic ability, depending on the rehabilitation form. A number of questions have been addressed, especially with regard to the perception itself. Receptors mainly involved in oral stereognostic ability are located in various oral structures and form perception results from an association of more than one group of receptors. The following review tries to deal with these questions and attempts to provide clear guidelines for further research on oral stereognosis.

Humans↗
PubMed1998

Stress-induced endocrine and immunological changes in psoriasis patients and healthy controls. A preliminary study.

BACKGROUND: Clinical observations suggest that psychological stress can induce exacerbation of psoriasis. It is hypothesized that these stress effects on the course and outcome of psoriasis are caused by neuroendocrine modulation of immune functions. Therefore we investigated the cardiovascular, endocrine and immunological response to a laboratory stressor in psoriasis patients and healthy controls. METHODS: Untreated (n = 7) and PUVA-treated (n = 4) psoriatics and healthy controls (n = 7) were exposed to a brief laboratory stressor (public speaking and mental arithmetic). Heart rate and blood pressure, catecholamine, cortisol, and DHEA plasma concentration, as well as distribution of T and NK lymphocytes were analyzed before, immediately after and 1 h after stress exposure. RESULTS: Heart rate and blood pressure increased in all three groups during stress exposure with the most pronounced changes in PUVA-treated patients. Psoriasis patients displayed higher adrenaline values but diminished cortisol and DHEA plasma concentrations compared to controls. NK cell numbers (CD16+, CD56+), but not T lymphocyte subsets, increased immediately after stress exposure in untreated patients and controls. This effect was significantly diminished in PUVA-treated patients. CONCLUSIONS: The data of this pilot study indicate an enhanced stress-induced autonomic response and diminished pituitary-adrenal activity in psoriasis patients. PUVA treatment seems to interfere with the cardiovascular and NK cell response to acute psychological stress. Future studies will analyze the stress-induced neuroimmunological mechanisms in psoriatics in more detail.

Adult↗
PubMed1997

Adrenergic control of natural killer cell circulation and adhesion.

Natural killer (NK) cell circulation is subject to adrenergic regulation. Exactly how NK cells are released into the circulation is unknown. In an attempt to identify some of the mechanisms, the present report focuses on aspects of adhesion regulation of NK cells. Results demonstrate that interactions between NK and endothelial cells (EC) in vitro can be reduced by beta 2-adrenoceptor stimulation for as long as the receptor stimulation occurs. The level of soluble adhesion molecules (sICAM-1, sE-selectin, sVCAM-1) in vivo remained unchanged during adrenaline infusion. In vitro analyses further reveal the requirement for Ca2+/Mg2+ in NK-EC adhesion. Blocking studies indicate the involvement of several members of the beta 1(CD29)- and beta 2(CD18)-integrin family, reducing NK cell adhesion by 28 to 39%. Stimulation of beta 2-adrenoceptors in the presence of these blocking antibodies further reduced NK adhesion by an average of 22%. Analysis of NK cell adhesion to various extracellular matrix components demonstrates significant NK cell adhesion to fibronectin but much less to laminin or collagens I and IV. NK cell adhesion to fibronectin was reduced by 50% upon beta 2-adrenoceptor stimulation, independent of the VLA-4/VLA-5 binding site on fibronectin. Together these results contribute to understanding the influences of beta-adrenoceptor stimulation on NK cell circulation and adhesion.

Cell Adhesion↗
PubMed1997

Control model of human stance using fuzzy logic.

A control model of human stance is proposed based on knowledge from behavioral experiments and physiological systems. The proposed model is based on the control of global variables specific to body orientation and alignment, rather than on the control of the body's center of mass within the base of support. Furthermore, the proposed control model is not based on purely inverted pendulum body mechanics where only motion at one joint is controlled, as for instance the ankle. In the proposed model, the degrees of freedom are controlled by using reciprocal and synergistic muscle actions at multiple joints. The control model is based on three sets of different global variables which act in parallel: (1) limb length and its derivative, (2) limb orientation and its derivative, and (3) trunk attitude and its derivative. An important feature of the control model is the use of fuzzy logic, which enables us to model experimental findings and physiological knowledge in a meaningful and explicit way using fuzzy if-then rules. In the control model, 36 fuzzy if-then rules are implemented and applied using a four-linked segment model consisting of a trunk, thigh, shank and foot. Uni- and biarticular limb muscles and trunk muscles are represented as torque actuators at each individual joint. In the model, three sets of global variables act in parallel and make corrective and coordinated responses to internal, self-induced perturbations. The data show that the use of global variables and fuzzy logic successfully enables us to model human standing with sway about a point of equilibrium. Small changes in, for example, total body sway are comparable to those seen during natural sway in human stance. The selected controllers--limb length, limb orientation and trunk attitude--seem to be appropriate for human stance control.

Fuzzy Logic↗
PubMed1997

The stereognostic ability of natural dentitions versus implant-supported fixed prostheses or overdentures.

A stereognostic ability test was performed in 60 patients. Forty patients were rehabilitated by means of osseointegrated implants. One group consisted of 20 patients with fixed prostheses on implants in both the upper and lower jaws. The other 20 patients had a maxillary denture while in the mandible an overdenture was retained by means of two implants connected by a bar. They were compared to a group of 20 subjects (controls) with a non-restored natural dentition. For the stereognostic ability test, subjects had to recognise ten different test pieces by manipulating them with two antagonistic incisor teeth, avoiding any contact with other oral structures. Both response time and percentage accuracy of recognition were evaluated. The present findings indicated that subjects with an overdenture on implants did not score significantly different from those with an implant-supported fixed prosthesis. In contrast, subjects with teeth had a significantly better stereognostic ability. The percentage of correct responses was 52% for overdentures, 56% for fixed prostheses on implants and 75% for natural dentitions. From these results, it could be concluded that the stereognostic ability is impaired in subjects rehabilitated with osseointegrated implants by about one-third to one-quarter compared to subjects with natural teeth.

Adult↗
PubMed1997

Control of a trackball by the chin for communication applications, with and without neck movements.

The overall aim was to evaluate whether a trackball could be used for communication by people who cannot speak due to severe motor impairment. The precision of trackball control by isolated jaw movements or a combination of jaw and head movements was evaluated in 18 healthy physical-education students, free of overt symptoms of craniomandibular dysfunction. The participants were asked to operate a trackball using the chin to type a standard text of four short sentences. There were two experimental situations: nine participants performed the typewriting task with their heads fixed; the other nine performed this task with free head movements. Trackball operation moved to the cursor over an alphabetical keyboard displayed on a computer screen and character selection was made by depression of the left-hand click button using the chin. Participants were asked to perform the task as quickly and accurately as possible. Result showed that those with free head movement typed the test significantly faster than those restricted to using only their jaw muscles. The mean time per character selection was 2.4 s (SD 0.3) for the group with free head movement and 2.7 s (SD 0.3) for the group using only jaw muscles. Group scores were not significantly different with regard to accuracy. It is suggested that a chin-operated trackball could be used for communication applications both with and without neck movements.

Adult↗
PubMed1997

Expression and in-vivo modulation of alpha- and beta-adrenoceptors on human natural killer (CD16+) cells.

Expression and in-vivo modulation of beta- and alpha-adrenoceptors on peripheral human natural killer (CD16+) cells was investigated. Ligand binding studies revealed that CD16+ lymphocytes express beta2, alpha1-, alpha2- but not beta1-adrenoceptors. Infusion of adrenaline, but not noradrenaline, significantly decreased beta2- and alpha1-adrenoceptor numbers on NK cells. Both catecholamines did not appreciably alter alpha2-adrenoceptor numbers. Additional analyses showed that adrenaline administration increases alpha2-adrenoceptor numbers on peripheral mononuclear blood cells (PBMC) and T-cell subsets (CD4+, CD8+) in contrast to decreased receptor numbers on CD16+ cells. These data demonstrate a specific effect of increasing levels of circulating catecholamines on beta2-adrenoceptors on NK cells.

Adrenergic Agonists↗
PubMed1997

Genetic screening--uses, potential abuses and ethical issues.

Potential uses, abuses and control of genetic screening techniques are discussed and the ethical issues arising from their use are compared with those for existing health screening practices. The main emphasis is upon issues affecting employment but more wide ranging implications are also touched upon. Although the current policy of various bodies is described, the views expressed are personal.

Advisory Committees↗
PubMed1997

Chryseobacterium meningosepticum: an emerging pathogen among immunocompromised adults. Report of 6 cases and literature review.

Chryseobacterium meningosepticum is a ubiquitous Gram-negative bacillus historically associated with meningitis in premature neonates. We report 15 positive cultures and 6 cases of infection among immunocompromised adults at our institution over a 10-year period and review the English-language literature on C. meningosepticum. Excluding the present series, there are 308 reports of positive cultures in the literature, of which 59% were determined to represent true infections. Sixty-five percent of those infected were younger than 3 months of age. Meningitis was the most common infectious syndrome among neonates, seen in 84% of cases and associated with a 57% mortality rate. Less commonly reported infections among infants included sepsis (13%) and pneumonia (3%). Pneumonia was the most frequent infection among the postneonatal group, accounting for 40% of cases, followed by sepsis (24%), meningitis (18%), endocarditis (3%), cellulitis (3%), abdominal infections (3%), eye infections (3%), and single case reports of sinusitis, bronchitis, and epididymitis. The 6 cases in our series were all adults, with a mean age of 58.7 years. Sites of C. meningosepticum infection were limited to the lungs, bloodstream, and biliary tree. Infection in our series was associated with prolonged hospitalization, prior exposure to multiple antibiotics, and host immunocompromise, particularly neutropenia. C. meningosepticum is resistant to multiple antibiotics, and disk dilution is notoriously unreliable for antibiotic sensitivity testing. Sensitivity testing on the 15 isolates from our institution revealed the most efficacious antibiotics to be minocycline (100% sensitive), rifampin (93%), trimethoprim-sulfamethoxazole (67%), and ciprofloxacin (53%). In contrast to reports in the literature, the isolates in our series displayed widespread resistance to vancomycin (100% resistant or intermediately sensitive), erythromycin (100%), and clindamycin (86%). These findings have important implications for the clinician when choosing empiric antibiotic regimens for patients with risk factors for C. meningosepticum infection.

Adult↗
PubMed1997

Infusion rates and levels of premedication in tumescent liposuction.

BACKGROUND: Tumescent liposuction has proven to be an extremely safe and effective method of liposuction. However, the infusion of tumescent anesthesia can take 1 hour or more to complete. OBJECTIVE: To document the types, dosages, and routes of administration of premedication utilized by four experienced tumescent liposuction surgeons. To determine if infusion rates for tumescent anesthesia are affected by types of premedication. METHODS: Four experienced liposuction surgeons were asked to review their most recent 100 tumescent liposuction patients with respect to types and dosages of premedication and routes of administration. Data were also provided on corresponding infusion pump settings and infusion rates. Volumes of tumescent anesthesia and corresponding volumes of fat aspirated were also collected on the same 400 patients. RESULTS: Infusion of tumescent anesthesia could be performed more rapidly in patients who were given greater amounts of premedication. Volumes of tumescent anesthesia infused were generally two or more times the volume of fat aspirated. Patients could be infused with less premedication if slow infiltration was employed. CONCLUSION: Infusion rates for tumescent anesthesia can be increased of greater amounts of premedication are given. However, this must be balanced against the safety of the premedication.

Adult↗