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Biomedical subjects

R Hebel

Publications and source records attributed to R Hebel.

At least 19 recordsLinked to original sources
PubMed2001

Microscopic anatomy of the eye of the deep-diving Antarctic Weddell seal (Leptonychotes weddellii).

The microscopic anatomy of the eye of the Weddell seal was studied with various light and electron microscopic methods with a view to correlating morphological findings with the biology of this seal which is adapted to the extremes of the Antarctic environment and to extreme diving excursions into the lightless depths of the sea. In the retina an area centralis was found but no fovea centralis. The densely packed photoreceptors consist exclusively of highly differentiated rods, which in primates detect light at low intensity but have rather poor image discrimination. The ganglion cells are relatively scarce, suggesting a high degree of convergence of the light-sensitive cells on the ganglion cells. The pigment epithelium is almost devoid of pigment granules. The extensive tapetum lucidum is about 400-500 microm thick and is composed of about 30 layers of specialized cells. The cornea is 650 (center) to 800-900 (periphery) microm thick. Its structure and glycosaminoglycan histochemistry correspond to that of other mammals. The iridocorneal angle is unusually deep and pervaded by an elaborate trabecular meshwork, which together with a complex canal of Schlemm can be correlated with the ability to absorb large amounts of fluid. The ciliary muscle and its antagonist, the membrane of Bruch, are poorly developed, suggesting relatively poor abilities of accommodation. The combination of a well-developed tapetum lucidum, an unpigmented pigment epithelium, well-developed rods, and a high number of rods converging on only few ganglion cells is obviously an adaptation to an extreme light sensitivity, enabling the animals to make use of the little light available in the deep sea.

Accommodation, Ocular↗
PubMed1999

[Measurement of acetylcholine receptor antibodies in serum of patients with myasthenia gravis].

The aim of this study is the evaluation of the level of antiacetylcholine receptor antibodies in patients with different types of myasthenia (according to Osserman's classification) and establishing of correlation between the level of such antibodies and the clinical state of the patients. 63 patients with diagnosed myasthenia and 30 healthy controls without immunological diseases were evaluated. In all of them standard neurological examination was performed and the levels of antiacetylcholine receptor antibodies were measured. In 45 patients electrophysiological investigations were carried out. In 43 cases elevated levels of antiacetylcholine receptor antibodies were noted. In 20 patients the levels were within normal range. The level of antibodies showed correlation with the clinical type of myasthenia according to Osserman (the more severe was myasthenia, the higher was the level of antibodies). But the clinical state of the patient at the moment of examination did not show any clear correlation with the level of antibodies. Acetylcholine receptor antibodies measurement has significant diagnostic value in myasthenia. Nevertheless it should be interpreted with other diagnostic techniques.

Adult↗
PubMed1996

Pregnancy and the risk of stroke.

BACKGROUND: It is widely believed that pregnancy increases the risk of stroke, but there are few data available to quantify that risk. METHODS: We identified all female patients 15 through 44 years of age in central Maryland and Washington, D.C., who were discharged from any of 46 hospitals in the study area in 1988 or 1991. Two neurologists reviewed each case, using data from the women's medical records. We determined whether the women had been pregnant at the time of the stroke or up to six weeks before it occurred. For purposes of this analysis, the six-week period after pregnancy could begin with an induced or spontaneous abortion or with the delivery of a live or stillborn child. RESULTS: Seventeen cerebral infarctions and 14 intracerebral hemorrhages occurred in women who were or had recently been pregnant (pregnancy-related strokes), and there were 175 cerebral infarctions and 48 intracerebral hemorrhages that were not related to pregnancy. For cerebral infarction, the relative risk during pregnancy, adjusted age and race, was 0.7 (95 percent confidence interval, 0.3 to 1.6), but it increased to 8.7 for the postpartum period (after a live birth or stillbirth) (95 percent confidence interval, 4.6 to 16.7). For intracerebral hemorrhage, the adjusted relative risk was 2.5 during pregnancy (95 percent confidence interval, 1.0 to 6.4) but 28.3 for the postpartum period (95 percent confidence interval, 13.0 to 61.4). Overall, for either type of stroke during or within six weeks after pregnancy, the adjusted relative risk was 2.4 (95 percent confidence interval, 1.6 to 3.6), and the attributable, or excess, risk was 8.1 strokes per 100,000 pregnancies (95 percent confidence interval, 6.4 to 9.7). CONCLUSIONS: The risks of both cerebral infarction and intracerebral hemorrhage are increased in the six weeks after delivery but not during pregnancy itself.

Cerebral Hemorrhage↗
PubMed1995

Abdominal pain in an HMO.

BACKGROUND: Previous surveys have found that 14%-25% of the population report abdominal pain. Only one study examined the age-gender specific prevalence of abdominal pain in the population, and no study has examined the self-reported causes of abdominal pain. METHODS: To describe the epidemiology of abdominal pain in a large health maintenance organization population, 6,199 randomly selected members were contacted and interviewed by telephone about the occurrence of abdominal pain and related health care in the past year. RESULTS: Of those interviewed, 27% reported abdominal pain in the past year, while 38% of those individuals saw a physician for their pain. Women were more likely than men to have had pain and to have seen a physician for their pain. Fewer older individuals reported abdominal pain, but when pain occurred, they sought medical care more often than younger individuals. CONCLUSIONS: Women and younger individuals report abdominal pain more frequently. Women and older individuals are more likely to seek care for their pain.

Abdominal Pain↗
PubMed1994

Tissue characterization using intelligent adaptive filter in the diagnosis of diffuse and focal liver disease.

In ultrasonic imaging an adaptive two-dimensional filter (ATDF) can suppress randomly generated speckle using the ratio of the local variance to the local mean as the speckle recognition feature (R). The degree of smoothing depends on the difference between the recognition feature in the region to be filtered and the selected reference tissue. We have investigated the clinical application of ATDF for ultrasound B-mode images of liver abnormalities. Using the R values of normal liver as reference values, the ATDF images were displayed. Normal livers (n = 17, R = 2.19 +/- 0.14 M +/- SEM), fatty livers (N = 16, R = 1.89 +/- 0.15) and those with acute hepatitis (N = 10, R = 2.25 +/- 0.18) appeared smooth after application of the adaptive filter, but those diseases with higher R values, such as chronic hepatitis (N = 10, R = 3.04 +/- 0.30), cirrhosis (n = 16, R = 4.44 +/- 0.30), metastases (N = 16, R = 6.43 +/- 0.53) and hepatocellular carcinomas (N = 8, R = 7.92 +/- 0.85), were largely unsmoothed. In conclusion, ATDF allows differentiation of some forms of liver disease and may be helpful in the detection of microfocal echogenic textural lesions.

Adult↗
PubMed1994

Neonatal outcome in infants with evidence of fetal exposure to opiates, cocaine, and cannabinoids.

This study evaluated the neonatal outcome of infants with evidence of fetal exposure to cocaine, opiates, and cannabinoids. Subjects were from the newborn nursery of an inner-city university teaching hospital. Meconium from 141 infants admitted to the full-term nursery was analyzed for metabolites of opiates, cocaine, and cannabinoids. The population was 72% African-American; 82% had medical assistance; history of drug use was reported in the medical records in 18%; mean maternal age was 24.2 years; mean birth weight was 3,234 +/- 502 g; and neonatal abstinence syndrome was reported in 7%. Meconium analysis data showed the following: 52.5% were drug-free; cocaine was present in 31%, opiates in 18% (cocaine and/or opiates 39%), and cannabinoids in 17%. In 38 infants in whom urine toxicology was obtained for clinical indications, meconium was more sensitive than urine in detecting drug exposure (55.3% vs 31.5%). There was no significant difference between cocaine/opiate-exposed and drug-free infants in race, socioeconomic status, maternal age, birth weight, head circumference, length, and Apgar scores. Cocaine/opiate-exposed infants had greater length of stay and increased frequency of maternal sexually transmitted diseases during pregnancy, with a trend toward a higher percent with fetal distress.

Cannabinoids↗
PubMed1993

Maternal and neonatal characteristics associated with HIV infection in infants of seropositive women.

In this prospective study of infants born to human immunodeficiency virus (HIV) seropositive mothers, neonatal and maternal characteristics of infected and noninfected infants were compared to determine the factors that may be associated with or contribute to vertical transmission of HIV. Of 134 infants entered as newborns in the study, 31 have definite serological and/or clinical evidence of infection and 103 are considered noninfected (transmission rate, 23.1%). Significantly more of the infected infants had birth weights below 2,500 g (48.4% versus 22.3%), and more infected infants were found to be small for gestational age (16.2% versus 5.8%). A greater number of infected infants experienced two or more problems in the neonatal period than noninfected infants (51.6% versus 24.2%). The incidence of confirmed and suspected bacterial infections was also significantly increased in the infected group. Multiple logistic regression analysis indicated low birth weight had the strongest association with vertical transmission of HIV. There was no significant difference between the two groups in mean maternal age at first pregnancy, mother's marital status, education, type of family, or past history of type of substances abused. Mothers who transmitted HIV to their infants had a trend towards a higher frequency of clinical chorioamnionitis (16.1% versus 5.8%), reported sexually transmitted diseases during pregnancy (45.2% versus 22.3%), and continued illicit drug use (67.7% versus 49.0%). In this group of infants, low birth weight, poor intrauterine growth, neonatal infections and possibly maternal chorioamnionitis, STDs during pregnancy, and continued drug use are associated with vertical transmission of HIV.

Adult↗
PubMed1991

Lymphoproliferative responses to mitogen and antigen in HIV-infected children.

We endeavored to study lymphoproliferative responses in children with human immunodeficiency virus (HIV) infection and to compare them with normal control children. Children were grouped according to age; 6-18 months and greater than 18 months, and according to CDC classification: asymptomatic (P1), mildly symptomatic (P2A), and advanced symptoms (P2D). Absolute CD4 and CD8 numbers were compared and found to be higher in the younger age groups. The children in P1 and P2A classes demonstrated an increase in CD8+ cells; only the children with AIDS showed a significant decrease in CD4+ cells. Lymphoproliferative responses to phytohemagglutinin A (PHA) were compared to tetanus toxoid. Only the children with acquired immunodeficiency syndrome (AIDS) (P2D) in the older group and only the symptomatic children (P2A and P2D) in the younger group showed a significant decrease in proliferative responses to PHA. All classes of infected children demonstrated a significant decrease in response to tetanus toxoid. We have been able to demonstrate a loss of antigen responsiveness which precedes the loss of mitogenic responsiveness. Furthermore, we have been able to demonstrate an age related increase in lymphoproliferative responses to both PHA and tetanus in HIV-infected and control children. Therefore, we conclude that children are particularly susceptible to the immunologic effects of HIV infection. Loss of lymphoproliferative responses to antigen occurs early in infected children and precedes the loss of CD4+ helper cells and of PHA responsiveness. This increased susceptibility to the immunopathogenesis of HIV infection is due, at least in part, to the relative immunodeficiency of infancy.

Age Factors↗
PubMed1989

Natural history and serologic diagnosis of infants born to human immunodeficiency virus-infected women.

Perinatal transmission of human immunodeficiency virus is thought to occur in 25% to 50% of the offspring of infected women. Standard diagnostic methods do not permit identification of the infected newborns. To assess diagnostic methods and document the natural history of perinatal human immunodeficiency virus infection, 20 children born to human immunodeficiency virus-infected women were followed prospectively for 18 months by measuring antibody titer, Western blot profiles, and antigenemia, and the results were compared with clinical outcome. Endogenous synthesis of anti-human immunodeficiency virus IgG was demonstrated in 6 of the 8 infected children. Four children synthesized IgM against human immunodeficiency virus. Five had demonstrable p24 antigenemia. No significant differences between infected and noninfected children were noted at birth except drug withdrawal, which occurred more frequently in noninfected infants. The incidence of adenopathy, hepatomegaly, and neurologic and immunologic abnormalities in the infected children were compared with noninfected children. The distinguishing illnesses were the opportunistic infections, lobar pneumonia, and failure to thrive. Seven of the 8 infected children had human immunodeficiency virus-mediated disease by 1 year of age (Centers for Disease Control [Atlanta, Ga] P2 classification), and four had acquired immunodeficiency syndrome (Centers for Disease Control P2D). These studies offer an approach to diagnosis of human immunodeficiency virus infection in infants and document the natural history and possible outcomes of infected children.

AIDS Serodiagnosis↗
PubMed1987

Reduction of CT artifacts caused by metallic implants.

A technique to reduce metallic implant artifacts on computed tomography scans is presented. The implant boundaries are determined semiautomatically; the missing projection data are replaced by linear interpolation. The complete procedure requires 1-2 minutes per scan. Images with greatly improved quality were obtained in the presence of surgical clips and pelvic implants; success is limited in highly structured regions, such as the facial skull.

Algorithms↗
PubMed1984

Computer-aided assessment of transient ischemic attacks. A clinical evaluation.

We developed and evaluated a computer-based system to assist with the difficult problem of assessing the conditions of patients with transient ischemic attacks (TIAs). The program used criteria to classify a patient's illness localize the neurologic deficit, screen for 46 causative or mimicking disorders, recommend additional tests, and suggest management steps. We evaluated this program in 103 patients with TIAs. The TIA program's localization and classification of patients generally agreed with those made by stroke specialists at our institution, demonstrating that computer programs can reproduce the decision criteria of stroke specialists. With revisions, the TIA program or similar systems could be useful for objective disease classification in clinical trials or epidemiologic studies. In contrast, the TIA program's treatment recommendations were often found to differ significantly from the actual treatments administered by non-stroke specialists.

Computers↗
PubMed1984

Electroretinographic responses and retrograde changes of retinal morphology after intracranial optic nerve section. A quantitative analysis in the cat.

Previous experiments have shown that the ERG response to alternating gratings vanishes gradually within 4 months after transection of the optic nerve, changes begin after 2-3 weeks. The response to gratings of low spatial frequencies deteriorates earlier than the response to gratings of high spatial frequencies (Maffei and Fiorentini 1981). Quantitative analysis of ganglion cell sizes in retinal wholemounts shows that ganglion cell shrinkage and ganglion cell loss begin at three weeks in the periphery of the retina, particularly in the temporal retina. The same morphological alteration subsequently becomes apparent also in the area centralis and the nasal retina, respectively. The main and early cell loss occurs among medium sized ganglion cells, supposedly the beta-cells. Among the alpha-cells only shrinkage is observed up to two months postoperatively. Light- and electron microscopic examination of cross sections through the retina show that pathological changes are restricted to the innermost layers.

Animals↗
PubMed1983

Size and distribution of ganglion cells in the human retina.

Three human retinae have been evaluated for size and distribution of ganglion cells from a study of whole-mount Nissl preparations. With the aid of a data processing program a number of statistical data on th distribution of cell sizes has been attained. The parafoveal region is occupied by small cells. The mean cell diameter increases up to 30 degrees to 40 degrees from the fovea and then decreases further into the periphery. Histograms show homogeneous cell sizes in central retina, but greater variations towards peripheral retina. As all histograms are of a unimodal shape, differentiation of cell groups is difficult. However, the majority of ganglion cells belong to the small to medium-sized cell class, while large cells, practically absent from parafoveal retina, are almost evenly distributed in peripheral retina. The significance of our results for the alpha-, beta-, gamma-cell classification in discussed.

Adult↗
PubMed1983

[Intraoperative electrophysiological localization of the origin of sinoatrial activity and examination of the location of the sinus node using microscope anatomic studies. Animal experiment study].

Many electrophysiological and histological investigations have demonstrated that post-operative dysrhythmias which occur in children with heart disorders requiring extensive surgical treatment in the area of the right atrium, are often caused by intraoperative lesions of the sinoatrial node. Accordingly, accurate determination of that epicardial area which is closest to the primary pacemaking area of the sinoatrial node could prevent injuries and, thus, reduce the risk of postoperative arrhythmias. To localize the relevant area we developed a method which is based on the mapping technique in a series of experiments in dogs. The electrophysiological results were confirmed by histological or gross anatomical methods. After right lateral thoracotomy in the fifth intercostal space, the epicardial surface of the right atrium is subdivided into numbered fields by means of an imaginary grid. The local electrical activities are recorded as bipolar electrograms with the aid of two tripolar electrode probes, one fixed on the epicardium of the right atrial appendage and one placed onto the individual grid fields by the investigator. Intervals thus occur between those potentials derived from the mobile electrode probe and those derived from the fixed probe. Electrical activity originating from the sinoatrial node arrives earlier at the individual fields lying closer to the node than at the field of the fixed probe at the atrial appendage. Thus, the individual field associated with the longest interval between probe potentials must lie closest to the sinoatrial node. An electronic device with digital display of the interval length has been developed which enables, within three minutes, determination of the individual field with the longest interval. Comparison of the digital values with those measured from the electrograms shows good agreement. The experiments were carried out on eleven sheep dogs and large mongrels. In seven cases the location of the sinoatrial node was determined by subsequent histological examination. The assumption that the area associated with the longest interval between the probe potentials lies closest to the primary pacemaking region of the sinus node could be confirmed, since in all these cases the cranial portion of the sinoatrial node was located in the field with the greatest interval measured. In the other four cases the sinoatrial node was localized by dissection with the aid of a stereomicroscope. In three of the four cases, the cranial part of the sinoatrial node was also situated in the field associated with the longest interval.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1981

The young pregnant teenager. Impact of comprehensive prenatal care.

Pregnant teenagers under the age of 15 years are known to be at highest risk for delivering low-birth-weight infants, particularly poor black girls. Sixty-seven inner-city pregnant adolescent girls 15 years or less at the time of delivery were followed in a special Teen Obstetric Clinic staffed by an interdisciplinary team trained in adolescent and prenatal health care. Ninety-three percent of the clinic population was black. The fetal outcomes of these girls were compared with the fetal outcomes of 67 girls who attended the regular obstetric clinic. Girls were matched for age at delivery, race, socioeconomic status, and parity. Only 9.0% of the infants of the teenagers in the Teen Obstetric Clinic group weighed less than 2500 g, compared with 20.9% of the infants of the girls in the regular Obstetric Clinic group. This finding has implications for the type of prenatal care provided to young adolescents.

Adolescent↗
PubMed1980

[Morphology of the giant nerve cells in the bovine retina. Study of silver-impregnated total specimen].

Application of several silver impregnation methods on whole mounts of the bovine retina selectively elicits the giant ganglion cells of the peripheral retina. As determined by the branching pattern of their dendrites they coudl be classified in three types: 1. predominant branching in one directions; 2. branching in two opposite direction; 2. branching in two opposite directions; 3. branches radiate in all directions. Cells of the first type were mainly found in the temporal and dorsal (superior) segment; those of the second type in the nasal part; those of the third type were present in the ventral (inferior) part of the peripheral retina. The sizes of their dendritic fields differ. Another ganglion cell with a large perikaryon was found infrequently in each retina; its dendrites are located in the inner plexiform layer, ending with occasionally large knob- or clubshaped tips. An axon was never found. Evidently, they show a special topographical relationship to the blood vessels. Their function is as yet unknown.

Animals↗