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Biomedical subjects

D Cohen

Publications and source records attributed to D Cohen.

At least 73 records · Page 4Linked to original sources
PubMed2001

Parametric evolution for a deformed cavity.

We consider a classically chaotic system that is described by a Hamiltonian H(Q,P;x), where (Q,P) describes a particle moving inside a cavity, and x controls a deformation of the boundary. The quantum eigenstates of the system are /n(x)>. We describe how the parametric kernel P(n/m)=/ /(2), also known as the local density of states, evolves as a function of deltax=x-x(0). We illuminate the nonunitary nature of this parametric evolution, the emergence of nonperturbative features, the final nonuniversal saturation, and the limitations of random-wave considerations. The parametric evolution is demonstrated numerically for two distinct representative deformation processes.

Journal Article↗
PubMed2001

Parametric dependent Hamiltonians, wave functions, random matrix theory, and quantal-classical correspondence.

We study a classically chaotic system that is described by a Hamiltonian H(Q,P;x), where (Q,P) are the canonical coordinates of a particle in a two-dimensional well, and x is a parameter. By changing x we can deform the "shape" of the well. The quantum eigenstates of the system are /n(x)>. We analyze numerically how the parametric kernel P(n/m)=/ /(2) evolves as a function of delta(x)[triple bond](x-x(0)). This kernel, regarded as a function of n-m, characterizes the shape of the wave functions, and it also can be interpreted as the local density of states. The kernel P(n/m) has a well-defined classical limit, and the study addresses the issue of quantum-classical correspondence. Both the perturbative and the nonperturbative regimes are explored. The limitations of the random matrix theory approach are demonstrated.

Journal Article↗
PubMed2001

Cryptosporidium infection in Bedouin infants assessed by prospective evaluation of anticryptosporidial antibodies and stool examination.

An enzyme-linked immunosorbent assay system using oocyst lysate as antigen was used to detect serum- specific antibody responses to Cryptosporidium parvum between 1989 and 1994 in consecutive sera obtained at birth, and at the age of 6, 12, and 23 months, from 52 infants living in a Bedouin town located in the south of Israel. The serologic tests revealed high levels of immunoglobulin G anti-Cryptosporidium at birth that dropped significantly by the age of 6 months and then rose continuously to a geometric mean titer of 481 at age 23 months. The serum immunoglobulin M Cryptosporidium antibodies rose continuously from nearly undetectable levels at birth to a geometric mean titer of 471 (157-fold increase) at age 23 months. All the subjects already showed at 6 months a significant rise in immunoglobulin M. A significant rise in immunoglobulin A titers was detected in 48% and 91% of subjects at 6 and 23 months, respectively. By monthly surveillance, microscopy using the modified Ziehl-Neelsen method and confirmed by indirect immunofluorescence assay detected Cryptosporidium antigens in only 11% at age 6 months and 48% at age 23 months. The extent of exposure to Cryptosporidium immediately after birth as detected by serology is much higher than that predicted by frequent prospective assessment of stool samples.

Adult↗
PubMed2001

Laser myringotomy in different age groups.

OBJECTIVE: To study the qualities of laser myringotomy (LM) as a treatment for middle ear ventilation problems. DESIGN: Prospective study and follow-up of consecutive cases of adults, children, and infants. Patients were observed for up to 2 years. SETTING: Children underwent LM, with or without adenoidectomy, under general anesthesia in the operating room. Adults and infants underwent LM under topical anesthesia, as an outpatient procedure. PATIENTS: All consecutive patients with either secretory otitis media (SOM) (adults and children) or acute otitis media (AOM) (infants) who agreed to participate were included without selection. INTERVENTION: Myringotomy was performed using new laser equipment, enabling a 0.1-second ablation with changeable diameter. OUTCOME MEASURES: Close follow-up, with microscopic examination of all ears. Findings were noted on the medical charts. RESULTS: Among all age groups, 136 ears were followed up. Perforation lasted a mean 22 days in adults, 17 days in children, and 11 days in infants. Patient age was found to be a significant determining factor for duration of perforation (P =.002). Laser myringotomy in the anterior and inferior areas lasted longer than posterior LM (P<.001). In patients with SOM, during the time the LM was patent, all ears were ventilated. In children, 38% of SOM cases resolved after a single LM treatment. All infants with AOM recovered promptly without antibiotic treatment. CONCLUSIONS: Laser myringotomy is a convenient, quick procedure that can be performed in the medical office with the use of topical anesthesia and is suitable for patients with AOM or for those who need short-term ventilation for SOM. It was found to be a safe alternative to ventilation tubes in these patients. In AOM, it was used instead of antibiotics and gave prompt relief from symptoms and cure of the AOM.

Adolescent↗
PubMed2001

A novel transgenic marker for migrating limb muscle precursors and for vascular smooth muscle cells.

A unique pattern of LacZ expression was found in a transgenic mouse line, likely due to regulatory elements at the site of integration. Two new genes flanking the transgene were identified. At early stages of development, the transgene is transiently expressed in ventro-lateral demomyotomal cells migrating from the somites into the limb buds. At late developmental stages and in the adult, lacZ staining marks vascular smooth muscle cells throughout the vascular bed, with the exception of the major elastic arteries, and in pericytes. No expression was detected in skeletal and smooth muscles. Different patterns of expression in vascular smooth muscles was observed at distinct levels of the vascular tree, in arteries as well as in veins. Vessel injury, resulting in stimulation of smooth muscle cells proliferation and migration, is associated with transgene down-regulation. After the formation of neointima thickening, it is reactivated. This transgenic insertion may therefore be used as a useful marker to identify novel physiological cues or genetic elements involved in the regulation of the vascular smooth muscle phenotype(s). It may also provide an experimental tool for studying vasculature and the involvement of pericytes in regulating microvascular homeostasis.

Animals↗
PubMed2001

Loss of chromosome arms 3p and 9p and inactivation of P16 (INK4a) in normal epithelium of patients with primary lung cancer.

The accumulation of genetic alterations in the respiratory epithelium may give rise to cancer and often is accompanied by a series of histologic alterations over a period of several years. Recent studies have identified some molecular alterations in histologically normal-appearing epithelium among patients with lung cancer. To extend these observations, we investigated clonal genetic alterations by using fluorescence in situ hybridization (FISH) analysis and immunohistochemistry in 69 biopsy samples of histologically normal-appearing bronchial epithelium from 22 patients with or without lung cancer. Thirty-seven biopsy specimens from 13 patients were examined for loss of 3p14, and 48 biopsy specimens from 18 patients were examined for loss at 9p21 by FISH. P16(INK4a) expression was analyzed in 54 biopsy samples from 19 patients. In at least one biopsy specimen from five of the 13 patients with primary lung cancer, FISH or immunohistochemistry detected loss of the 3p14 or 9p21 region. In contrast, no alterations were detected for the same regions in the nine patients without primary lung cancer. Our results support the concept that the normal epithelial surface of large bronchi of patients with lung cancer has molecular changes suggestive of the outgrowth of numerous clonal foci.

Bronchi↗
PubMed2001

Techniques for long-term multisite neuronal ensemble recordings in behaving animals.

Advances in our understanding of neural systems will go hand in hand with improvements in the experimental techniques used to study these systems. This article describes a series of methodological developments aimed at enhancing the power of the methods needed to record simultaneously from populations of neurons over broad regions of the brain in awake, behaving animals. First, our laboratory has made many advances in electrode design, including movable bundle and array electrodes and smaller electrode assemblies. Second, to perform longer and more complex multielectrode implantation surgeries in primates, we have modified our surgical procedures by employing comprehensive physiological monitoring akin to human neuroanesthesia. We have also developed surgical implantation techniques aimed at minimizing brain tissue damage and facilitating penetration of the cortical surface. Third, we have integrated new technologies into our neural ensemble, stimulus and behavioral recording experiments to provide more detailed measurements of experimental variables. Finally, new data analytical techniques are being used in the laboratory to analyze increasingly large quantities of data.

Animals↗
PubMed2001

Prospective cohort studies of shigellosis during military field training.

Epidemiological and clinical features of shigellosis occurring among cohorts of Israeli recruits followed-up for 3-6 months during the summer field training of years 1993-1997 were studied. The incidence rate of culture-proven shigellosis was the highest (78 cases per 1,000 recruits) in 1996 and the lowest (13 cases per 1,000 recruits) in 1995. Shigella sonnei (152 isolates) and Shigella flexneri (151 isolates) were the most common species. Fifty percent of the patients with shigellosis had fever (>37.5 degrees C), compared to only 18% of the subjects with other diarrheal diseases (P < 0.001). The duration of illness was longer among subjects with shigellosis than among those with other diarrheal diseases (P < 0.001). Illness due to Shigella flexneri was more severe than illness caused by Shigella sonnei.

Adolescent↗
PubMed2001

The future of genetic case-control studies.

The case-control study design has been a veritable workhorse in epidemiological research since its inception and acceptance as a valid and valued field of inquiry. The reasons for this owe to the simplicity of the required sampling and the (potential) ease of analysis and interpretation of results. Unfortunately, there are a number of problems that plague the use of the case-control design in assessing relationships between genetic variation and disease susceptibility in the population at large. Many of these problems are entirely analogous to problems that inhere in applications of the case-control design in nongenetic settings. These problems include stratification, the assessment of statistical significance, heterogeneity, and the interpretation of multiple outcomes or phenotypic information. In this chapter we describe 10 problems thought to plague genetic case-control studies and offer potential solutions to each. Many of our proposed solutions require the use of multiple DNA markers to accommodate the genetic background of the individuals sampled as cases and controls. It is hoped that our discussions and proposals will spark further debate about the analysis and ultimate utility of the case-control study in genetic epidemiology research.

Case-Control Studies↗
PubMed2001

Acute mastoiditis--the antibiotic era: a multicenter study.

OBJECTIVES: To evaluate the clinical course and identify the causative organisms of acute mastoiditis in a community where most of the patients who develop acute otitis media are treated with antibiotics. METHODS: A multicenter retrospective review of a series of 223 consecutive cases of acute mastoiditis. SETTING: Nine secondary or tertiary academic or non-academic referral centers. RESULTS: Prior to the diagnosis of acute mastoiditis, 121 of the patients (54.3%) had been receiving oral antibiotic treatment for acute otitis media for periods ranging from 1 to 21 days (mean 5.3 days). Samples for bacterial culture were obtained from 152 patients. Cultures were negative in 60 patients. The organisms isolated in the 92 positive cultures were: Streptococcus pneumoniae (15 patients), Streptococcus pyogenes (14 patients), Staphylococcus aureus (13 patients), Staphylococcus coagulase negative (three patients), Pseudomonas aeruginosa (eight patients), Haemophilus influenzae (four patients), Proteus mirabilis (two patients), Escherichia coli (two patients), Klebsiella pneumoniae (one patient), Enterobacter (one patient), Acinetobacter (one patient), anaerobic gram-negative bacilli (one patient), and fungi (two patients). Ten patients had mixed flora. Sixteen patients presented with complications (cerebellar abscess, perisinus empyema, subdural abscess or empyema, extradural abscess, cavernous sinus thrombosis, lateral sinus thrombosis, bacterial meningitis, labyrinthitis, petrositis, or facial nerve palsy). CONCLUSIONS: Antibiotic treatment cannot be considered an absolute safeguard against the development of acute mastoiditis. Early myringotomy for acute otitis media seems to decrease the incidence of complications. The distribution of causative organisms in acute mastoiditis differs from that in acute otitis media. Intracranial complications in acute mastoiditis are not rare. Because of the diversity of causative organisms in acute mastoiditis and the growing resistance of bacteria to the various antibiotics, all means to obtain a sample for culture prior to antibiotic treatment, including general anesthesia.

Acute Disease↗
PubMed2001

[Giant cell tenosynovial tumor, spread in the forearm soft tissues. A case report].

Giant cell tumor of the tendon sheath (GCTTS), tenosynovial giant cell tumor are a group of rare proliferative disorders which involves synovial joints and tendon sheaths. Considerable confusion exists about the surgical treatment and diagnosis of these disorders. We report an exceptional case of a tenosynovial giant cell tumor of the forearm. It concerns a 23 years old woman presenting multiple tumors of the forearm and wrist. Result of the primary biopsy concluded to an eosinophilic granuloma. Magnetic resonance imaging demonstrated a richly vascularized tissular lesion involving the extensor carpi radialis and extensor pollicis longus. Surgical excision of the tumor was performed. Macroscopic, histologic and immunohistochimic findings confirmed the diagnosis of tenosynovial giant cell tumor. This diffused form is rare compared with the nodular one involving fingers. Optimal treatment is surgical resection. The only risk is recurrence.

Adult↗
PubMed2001

[Vaginal hysterectomy:apropos of a series of 1008 interventions].

STUDY AIM: The aim of this study was to analyse our vaginal hysterectomies performed for prolapsed uterus and non prolapsed uterus with benign disease. For the latter indication, a comparison was made with abdominal hysterectomy. PATIENTS AND METHODS: From february 1986 to december 1998, 1008 vaginal hysterectomies were performed in our department: 219 for prolapsed uterus and 789 for non prolapsed uterus with benign disease. During the same time, 217 abdominal hysterectomies were performed for non prolapsed uterus with benign disease. RESULTS: Intra-operative and post-operative complications had the same rates in the two groups. Owing to the low number of abdominal hysterectomies, we cannot draw a valuable conclusion. The study of the literature shows in this field an advantage for the vaginal hysterectomy; mean time hospitalization was shorter in the vaginal group. CONCLUSION: Advantages of vaginal hysterectomy are multiple: aesthetic, shorter hospitalization, quicker recovery. The low rate of vaginal hysterectomy on non prolapsed uterus with non malignant disease is linked with the lack in training of surgeons for the vaginal approach. In these cases, a rate of 70% is a realistic one in a well trained hospital center.

Adult↗
PubMed2001

Selective control of basolateral membrane protein polarity by cdc42.

The rho GTPase cdc42 is implicated in several aspects of cell polarity. A recent study (Kroschewski R, Hall A, Mellman I. Nat Cell Biol 1999;1:8-13) demonstrated that a dominant negative mutant of cdc42 abolishes the polarity of basolateral membrane proteins in MDCK cells, but did not elucidate whether this effect was selective for basolateral proteins or nonselective for all secreted proteins. To answer this question, we analyzed the polarity of newly synthesized membrane and soluble proteins in MDCK cell lines previously induced to overexpress mutant forms of cdc42. GTPase-deficient and dominant negative cdc42 did not affect the apical targeting of a newly synthesized apical membrane protein, but reversed to apical the distribution of two exogenous basolateral membrane proteins. In striking contrast, GTPase-deficient cdc42 did not affect polarized exocytosis of endogenous soluble proteins, either apical or basolateral. The exquisitely selective regulation of polarized protein targeting by cdc42 may allow cells to fine-tune their membrane composition in response to extracellular signals during development, migration and in response to injury.

Adenosine Triphosphatases↗
PubMed2001

Cultural variation: considerations and implications.

Cultural systems vary widely across the world. Partly this is due to different cultures' occupying different ecological and environmental niches. But partly it is due to similar circumstances giving rise to multiple stable equilibriums, each with a distinct cultural form. Using insights and examples from various fields, this article illustrates the way that multiple equilibriums can emerge and the forces that push a culture toward one equilibrium point or another. Considerations of game theory principles, mutual interdependence, historical circumstance, dependence on initial conditions, and crucial choice points are highlighted in discussing the ways humans create and re-create their culture. Cultural traits develop within physical, social, intracultural, and intercultural niches, and implications of this for how culture might be studied and the benefits of combining an "equilibrium" perspective and a "meaning" perspective are discussed.

Cultural Characteristics↗
PubMed2001

General health management and long-term care of the renal transplant recipient.

The steady improvement in short-term success rates in renal transplant patients has translated into better long-term success rates and a large number of patients with long-functioning renal transplants. The necessity for the lifelong administration of immunosuppressive medications to prevent rejection, coupled with the presence in many patients of a variety of other medical problems dating from the period of renal insufficiency prior to the time of renal transplantation, has created a large group of patients with a unique and complex set of long-term medical care needs. Due to the constraints of managed care, considerations of geography, or patient preference, the long-term care of an increasing number of renal transplant recipients has shifted away from the transplant center to the community-based nephrologist or internist. For optimal care to be delivered, it is important that the physicians managing these patients be cognizant of the complex and interacting medical issues involved in their care. Appropriate management can significantly prolong the life of the allograft as well as that of the patient. Guidelines for understanding and managing some of the more important and common general medical problems facing the long-term renal transplant recipient (eg, infectious complications, cardiovascular disease, hypertension, diabetes, hyperlipidemia, malignancy, pregnancy, bone disease, dental care, preventive care) are addressed in this section.

Ambulatory Care↗
PubMed2001

Long-term results in patients treated with thrombolysis, thoracic inlet decompression, and subclavian vein stenting for Paget-Schroetter syndrome.

PURPOSE: In an effort to minimize long-term disability related to effort thrombosis of the subclavian vein, selected patients were treated with thrombolysis, thoracic inlet decompression, percutaneous transluminal angioplasty (PTA), and subclavian vein stenting. We evaluated the long-term outcomes of patients treated with this algorithm. METHODS: Between 1994 and 2000, 23 patients were evaluated with effort thrombosis of the subclavian vein. Thrombolysis was instituted on an average of 9.4 days (range, 1-30 days) after initial onset of symptoms. Average time to clot lysis was 34 hours (range, 12-72 hours). After immediate supraclavicular thoracic inlet decompression, all patients underwent PTA. Fourteen patients with residual vein stenosis (>50%) after PTA underwent stenting of the subclavian vein. Complications in this series included three wound hematomas that required drainage in two patients and one subpleural hematoma that required thoracotomy for decompression. RESULTS: All patients who underwent PTA are patent, with a mean follow-up of 4 years (range, 2-6 years). In the veins treated with stents, 9 of 14 veins are patent, with a mean follow-up of 3.5 years (range, 1-6 years). Two veins had early occlusions (2 days); two veins occluded at 1 year; and seven veins occluded at 3 years. Three of the patients (including those patients who experienced the early failed procedures) were later identified with factor V Leiden. Early failures also had clot extending into the brachial vein. CONCLUSION: Patients with short-segment venous strictures after successful lysis and thoracic outlet decompression may safely be treated with subclavian venous stents and can expect long-term patency.

Activated Protein C Resistance↗