Biomedical subjects

L Kramer

Publications and source records attributed to L Kramer.

At least 37 records · Page 2Linked to original sources

PubMed2003

Dynamics of cholesteric structures in an electric field.

Motivated by Lehmann-like rotation phenomena in cholesteric drops we study the transverse drift of two types of cholesteric fingers, which form rotating spirals in thin layers of cholesteric liquid crystal in an ac or dc electric field. We show that electrohydrodynamic effects induced by Carr-Helfrich charge separation or flexoelectric charge generation can describe the drift of cholesteric fingers. We argue that the observed Lehmann-like phenomena can be understood on the same basis.

Journal Article↗

PubMed2003

Modulated structures in electroconvection in nematic liquid crystals.

Motivated by experiments in electroconvection in nematic liquid crystals with homeotropic alignment we study the coupled amplitude equations describing the formation of a stationary roll pattern in the presence of a weakly damped mode that breaks isotropy. The equations can be generalized to describe the planarly aligned case if the orienting effect of the boundaries is small, which can be achieved by a destabilizing magnetic field. The slow mode represents the in-plane director at the center of the cell. The simplest uniform states are normal rolls, which may undergo a pitchfork bifurcation to abnormal rolls with a misaligned in-plane director. We present a new class of defect-free solutions with spatial modulations perpendicular to the rolls. In a parameter range where the zigzag instability is not relevant these solutions are stable attractors, as observed in experiments. We also present two-dimensionally modulated states with and without defects which result from the destabilization of the one-dimensionally modulated structures. Finally, for no (or very small) damping, and away from the rotationally symmetric case, we find static chevrons made up of a periodic arrangement of defect chains (or bands of defects) separating homogeneous regions of oblique rolls with very small amplitude. These states may provide a model for a class of poorly understood stationary structures observed in various highly conducting materials ("prechevrons" or "broad domains").

Journal Article↗

PubMed2003

Electrophysiological assessment of the afferent sensory pathway in cardiac arrest survivors.

BACKGROUND: Hypoxic-ischaemic brain damage in cardiac arrest survivors is global, but postmortem histology could identify parts of the brain that are selectively vulnerable to ischaemia, comprising the thalamus and cortex. We hypothesized that hypoxic-ischaemic brain damage increases along the afferent sensory pathway with a stepwise decrease of detectable somatosensory evoked potential peaks. METHODS: Somatosensory evoked potentials were recorded within 72 h after cardiac arrest in 305 comatose patients after cardiopulmonary resuscitation. We measured the short latency SEP peaks N9, P15, N20, P25 (reflecting the peripheral-thalamo-cortical pathway) and the long latency SEP peaks N35 and N70 (reflecting complex cortico-cortical interactions). Patients with a Cerebral Performance Category score > 2 at 1 year were defined as patients with hypoxic-ischaemic brain damage. RESULTS: Patients with hypoxic-ischaemic brain damage (n = 232) showed a statistically significant decrease of detectable peaks (P < 0.05) along the thalamo-cortical afferent pathway: N13, P15, N20, P25 and N70 peaks were detectable in 99%, 63%, 59%, 55% and 44% patients, respectively. In patients without hypoxic-ischaemic brain damage (n = 73) the N13, P15, N20, P25 peaks were detectable in all, and the N35 and N70 peaks in 98%. Furthermore, in patients with hypoxic-ischaemic brain damage and detectable SEP peaks, P15, N20, P25, N35 and N70, peak latencies were prolonged (P < 0.05) and N20 and N70 amplitudes were decreased (P < 0.05) compared with patients without hypoxic-ischaemic brain damage. CONCLUSION: Extent of hypoxic-ischaemic brain damage in cardiac arrest survivors increases along the afferent sensory pathway, with pronounced vulnerability of thalamic and cortical brain regions.

Adolescent↗

PubMed2003

Benign paroxysmal positioning vertigo in multiple sclerosis: diagnosis, pathophysiology and therapeutic techniques.

OBJECTIVE: To report on the most common causes of vertigo in patients with multiple sclerosis (MS) and emphasize appropriate diagnostic techniques and treatment interventions. BACKGROUND: True vertigo is estimated to occur in about 20% of MS patients. Lesions within the vestibular nuclei and in the root entry zone of cranial nerve VIII represent the most common locations where demyelinating activity can provoke vertigo in patients with MS. However, other causes of vertigo should be explored in MS patients in order to avoid unnecessary treatment with corticosteroids and vestibular suppressants. Recently, we reviewed our four-year experience with new onset vertigo in our university-based MS population and found that benign paroxysmal positioning vertigo (BPPV) to be the most common cause. All patients diagnosed with BPPV were treated successfully with particle repositioning maneuvers. The remaining patients were treated with conventional therapies appropriate for the specific diagnosis. CONCLUSIONS: Empiric treatments with corticosteroids and/or vestibular suppressants should not be employed until all MS patients undergo a careful bedside examination, which includes diagnostic positional and, if indicated, particle repositioning maneuvers. Here we emphasize the pathophysiology of BPPV and illustrate the proper techniques for the diagnostic and therapeutic maneuvers.

Humans↗

PubMed2003

Ultrastructural evidence of the degenerative events occurring during embryogenesis of the filarial nematode Brugia pahangi after tetracycline treatment.

Intracellular bacteria belonging to the genus Wolbachia have been described in filarial nematodes and these microorganisms appear to have evolved an obligatory mutualistic association with their filarial hosts. In fact, antibiotic treatment leads to the clearance of bacteria from worms resulting in a block in embryogenesis and, eventually, death of adult filariae. Currently, the antifilarial action of antibiotic treatment is interpreted as a secondary consequence of the bacteriostatic activity against Wolbachia endosymbionts. Here, we demonstrate by transmission electron microscopy the degenerative events occurring during embryogenesis of Brugia pahangi after tetracycline treatment. After 56 days of treatment the cytoplasm of hypodermal cords was totally void of Wolbachia and numerous vacuoles, residual of cytolitic activity, were observed. In the ovary, the morphology of the oocytes was well conserved 33 days after treatment, but the texture of symbiotic bacteria appeared altered. After 56 days of treatment embryogenesis was dramatically affected and the terminal portion of the ovary appeared totally empty. The authors suggest that the symbiotic bacteria play a direct role in worm metabolism and a long-term bacteriostatic effect may block bacterial activity involved in the active control of cytolysis. As a consequence, the bacteriophorous vacuole is transformed into a digestive vacuole and the whole symbiotic population is disrupted.

Animals↗

PubMed2002

Electroconvection in nematic liquid crystals with positive dielectric and negative conductivity anisotropy.

Electroconvection in an unusual nematic compound with strongly positive dielectric anisotropy and negative anisotropy of the conductivity is investigated. For homeotropic alignment, where one has a direct transition to rolls or squares depending on the frequency of the applied voltage, we present a quantitative theory. From the comparison we infer values for some viscosities, which are rather unusual, but not unreasonable in view of the vicinity of the nematic-smectic transition. For planar alignment, electroconvection sets in above a splay Freedericksz transition with "parallel rolls," which is also captured by the theory.

Journal Article↗

PubMed2002

Teaching of veterinary parasitology: the Italian perspective.

The curriculum in veterinary medicine in Italy is undergoing important changes, as in the rest of Europe. The 2001 fall semester will mark the beginning of a new format for the degree in veterinary medicine and these changes will obviously affect the teaching of veterinary parasitology. In Italy, veterinary parasitology is usually taught in the third year with a disciplinary approach, similar to that described by Euzéby [Vet. Parasitol. 64 (1996) 21] and Eckert [Vet. Parasitol. 88 (2000) 117]. Approximately 90 h of lectures and 40 h of laboratory are offered and are usually divided into parasitology, followed by parasitic diseases. A more problem-oriented approach to parasitology is offered to fifth-year students within several professional routes (large animal medicine, small animal medicine, hygiene and food safety, etc.), amounting to approximately 15-60 h per student. Indeed, in the last year of study, there are less students and it is possible to present clinical cases and orient the students towards team work and critical discussion. This new curriculum guarantees a reduction in the number of lecture hours and an increase in both laboratory work and personal study, as suggested by the guidelines of the European association of establishment for veterinary education (EAEVE).

Animals↗

PubMed2002

Pattern-forming instability induced by light in pure and dye-doped nematic liquid crystals.

We study theoretically the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle on a thin layer of homeotropically oriented nematic liquid crystal with special emphasis on the dye-doped case. The spatially periodic Hopf bifurcation that occurs as the secondary instability after the stationary Freedericksz transition is analyzed.

Journal Article↗

PubMed2002

Feline heartworm infection: serological survey of asymptomatic cats living in northern Italy.

Heartworm infection is now recognized as a potential cause of serious disease in cats. Epidemiological studies indicate that in locations where the infection is endemic in the dog, cats are at risk. The aim of this work was to carry out a serological survey for the presence of anti-Dirofilaria immitis antibodies in privately owned, predominantly asymptomatic cats living in different areas of northern Italy in order to determine the distribution of the parasite and the risk of infection in this species. Serum samples from 1045 cats were evaluated using a commercial antibody (Ab) detection kit (Heska Solo Step Filariosi Felina, Heska Corporation) and results were analyzed together with information obtained by questionnaire. Results showed that 16% of all tested cats were positive for anti-D. immitis antibodies, with values ranging from 9 to 27%, depending on location. Male cats and outdoor cats appeared to be at greater risk, with a significantly higher number of positive antibody tests. The results of this study suggest that the risk of exposure with D. immitis in cats is high in northern Italy and suggest that the use of preventive drugs would be advisable in this area endemic for canine heartworm disease.

Age Factors↗

PubMed2002

Priorities and satisfaction on the help needed and provided in a first episode of psychosis. A survey in five European Family Associations.

In the case of a first episode of psychosis among members of different associations of families of mentally ill people, little is known about their priorities and how satisfied they are with the help provided to them. A survey was conducted in five European family associations. Respondents emphasized the need for early (ambulant) intervention through outreach with very practical goals directed at creating stability and social functioning. About one-third of the respondents are unsatisfied or very unsatisfied. The highest percentage of unsatisfied respondents was in the following five areas of care: advice on how to handle specific problems; help with preserving or regaining social functioning; help with regaining structure and routine; information; prompt assistance preferably in patients own environment. The agreement of these findings with findings from earlier studies underlines the importance of suggesting specific changes in the delivery of care.

Adult↗

PubMed2002

Influence of hydroxy ethyl starch infusion on serum bilirubin levels in cirrhotic patients treated with artificial liver support.

Serum bilirubin levels are commonly used to assess extracorporeal detoxification by liver support systems. We tested the hypothesis that intravenous colloids administered before liver support treatment could confound bilirubin values. Eight cirrhotic patients received an infusion of a 6% hydroxy ethyl starch solution (10 ml/kg, 30 minutes) before detoxification using a liver support system (FPSA). Bilirubin was measured before and 1 hour after infusion, and after FPSA treatment (7 hours). Infusion of hydroxy ethyl starch was associated with a drop in bilirubin values (mean, 18%, range, 1-44%, p=0.03 versus baseline values). Bilirubin levels were further reduced during FPSA treatment (mean, 27%, range, 22-34%; p=0.02 versus pretreatment values). In conclusion, hydroxy ethyl starch solution may decrease bilirubin levels in hyperbilirubinemic cirrhotic patients receiving extracorporeal detoxification. The role of potentially confounding factors in liver support studies is discussed further.

Bilirubin↗

PubMed2002

Effects of sorbent suspension dialysis on plasma amino acid levels in cirrhotic patients with refractory hepatic encephalopathy.

In cirrhotic patients, plasma amino acid levels are severely deranged. A decreased ratio of branched-chain to aromatic amino acids (Fischer ratio) has been implicated in the pathogenesis of hepatic encephalopathy. In this prospective study, we investigated the effects of extracorporeal detoxification on amino acid levels using a sorbent suspension dialysis system. Twenty patients with documented cirrhosis and hepatic encephalopathy grade II-III not responding to standard treatment were randomized to receive either six hours of sorbent dialysis and standardized conventional medical treatment or ongoing medical treatment alone. In contrast to previous uncontrolled studies, no significant effect on amino acid levels, Fischer ratio or clinical grade of hepatic encephalopathy was detected in either treatment group. In conclusion, a 6-hour treatment with sorbent dialysis did not significantly influence plasma levels of amino acids and did not ameliorate the clinical grade of hepatic encephalopathy.

Adult↗

PubMed2002

Extracorporeal treatment in fulminant hepatic failure: pathophysiologic considerations.

Fulminant hepatic failure is a life-threatening clinical syndrome following severe hepatic injury leading to cerebral edema and brainstem herniation. Excessive mortality can be currently reduced only by timely orthotopic liver transplantation. Due to the shortage of donor organs, a considerable proportion of patients develop irreversible neurological damage, multiorgan failure or death while waiting for transplantation. Consequently, alternatives to orthotopic liver transplantation and methods of stabilizing patients on the waiting list including extracorporeal detoxification treatment are currently investigated. Recent advances in the pathophysiology of cerebral edema have challenged some of the traditional assumptions on which many blood detoxification systems are based. This article aims to integrate pathophysiology of hepatic encephalopathy and cerebral edema into a proposed future concept of liver support.

Ammonia↗

PubMed2001

Oxcarbazepine (Trileptal) as monotherapy in patients with partial seizures.

OBJECTIVE: To evaluate the efficacy and safety of oxcarbazepine (OXC) as monotherapy for patients with uncontrolled partial seizures. METHODS: A multicenter, double-blind, randomized, parallel-group, dose-controlled monotherapy trial compared OXC at 2400 mg/day with OXC at 300 mg/day in patients with uncontrolled partial-onset seizures previously receiving carbamazepine (CBZ) monotherapy. During a 28-day open-label conversion phase, patients were tapered off CBZ and titrated to OXC 2400 mg/day. After a 56-day open-label baseline phase on OXC 2400 mg/day, patients entered a 126-day double-blind treatment phase in which they were randomized to continue OXC at 2400 mg/day or were down titrated over 6 weeks to OXC at 300 mg/day. Patients met the efficacy endpoint by completing the double-blind treatment phase or by meeting one of four predefined exit criteria. The primary efficacy variable was time to meeting one of the exit criteria. The secondary efficacy variable was the percentage of patients meeting one of the exit criteria in each of the two treatment groups. RESULTS: Of the 143 patients enrolled, 96 were randomized in the double-blind treatment phase. Time to meeting an exit criterion was significantly in favor of the OXC 2400 mg/day group (p = 0.0001). The median time to meeting an exit criterion was 68 days for the OXC 2400 mg/day Group and 28 days for the OXC 300 mg/day Group. In addition, the percentage of patients meeting one of the exit criteria was significantly lower for the OXC 2400 mg/day Group (p = 0.0001). Overall, OXC was well tolerated with the most common adverse events consisting of fatigue, nausea, ataxia, and headache. CONCLUSION: This trial demonstrated that OXC at 2400 mg/day is well tolerated and efficacious when administered as monotherapy in patients with uncontrolled partial onset seizures.

Adolescent↗

PubMed2001

Numerical investigation of optically induced director oscillations in nematic liquid crystals.

We present a theoretical study of the effects induced by the passage of a linearly polarized light beam through a thin cell of homeotropic nematic liquid crystal. The light is incident at a slightly oblique angle and is polarized perpendicular to the plane of incidence. Experiments in this geometry have revealed a rich variety of complex, time dependent director motion. We solve numerically the director equations for the nematic and compare the results with existing experimental findings.

Journal Article↗

PubMed2001

Dynamics of the 16O(e, e'p) reaction at high missing energies.

We measured the cross section and response functions for the quasielastic 16O(e,e'p) reaction for missing energies 25< or =E(m)< or =120 MeV at missing momenta P(m)< or =340 MeV/c. For 25<E(m)<50 MeV and P(m) approximately 60 MeV/c, the reaction is dominated by a single 1s(1/2) proton knockout. At larger P(m), the single-particle aspects are increasingly masked by more complicated processes. Calculations which include pion exchange currents, isobar currents, and short-range correlations account for the shape and the transversity, but for only half of the magnitude of the measured cross section.

Journal Article↗

PubMed2001

Time-dependency of sensory evoked potentials in comatose cardiac arrest survivors.

OBJECTIVE: To assess the validity of early sensory evoked potential (SEP) recording for reliable outcome prediction in comatose cardiac arrest survivors within 48 h after restoration of spontaneous circulation (ROSC). DESIGN AND SETTING: Prospective cohort study in a medical intensive care unit of a university hospital. PATIENTS: Twenty-five comatose, mechanically ventilated patients following cardiopulmonary resuscitation MEASUREMENTS AND RESULTS: Median nerve short- and long-latency SEP were recorded 4, 12, 24, and 48 h after ROSC. Cortical N20 peak latency and cervicomedullary conduction time decreased (improved) significantly between 4, 12, and 24 h after resuscitation in 22 of the enrolled patients. There was no further change in short-latency SEP at 48 h. The cortical N70 peak was initially detectable in seven patients. The number of patients with increased N70 peak increased to 11 at 12 h and 14 at 24 h; there was no further change at 48 h. Specificity of the N70 peak latency (critical cutoff 130 ms) increased from 0.43 at 4 h to 1.0 at 24 h after ROSC. Sensitivity decreased from 1.0 at 4 h to 0.83 at 24 h after ROSC. CONCLUSION: Within 24 h after ROSC there was a significant improvement in SEP. Therefore we recommend allowing a period of at least 24 h after cardiopulmonary resuscitation for obtaining a reliable prognosis based on SEP.

Adult↗

PubMed2001

Molecular and clinical characterisation of homocystinuria in two Austrian families with cystathionine beta-synthase deficiency.

The influence of the genotype on the phenotypic expression of homocystinuria due to cystathionine beta-synthase (CBS) deficiency is frequently unclear. We therefore investigated the genotype and the phenotype of CBS deficiency in two Austrian families also considering genetic polymorphisms with a putative association with vascular disease (MTHFR 677C-->T, MTHFR 1298A-->C, F5 1691G-->A, F2 20210G-->A) and response to therapy. We identified the CBS 833T-->C/1058C-->T and CBS 828ins104/1358del134 compound heterozygous genotype in our index patients. Both patients showed mental retardation and ectopia lentis. CBS 833T-->C/1058C-->T was associated with severe vascular complications, which was not the case for CBS 828ins104/1358del134. The patient with CBS 828ins104/1358del134 was negative for F5 1691G-->A, F2 20210G-->A, MTHFR 677C-->T, and MTHFR 1298A-->C, while the patient with CBS 833T-->C/1058C-->T was heterozygous for MTHFR 1298A-->C. A combination therapy including pyridoxine, folic acid, hydroxycobalamin, and betaine failed to lower total homocysteine plasma levels below 50 mumol/L in both patients. In summary, our study demonstrates that the CBS 833C/1058T-MTHFR 1298AC genotype can be related to severe vascular disease, while the CBS 828ins104/1358del134-MTHFR 1298AA genotype presents with a somewhat milder clinical phenotype. Both genotypes do not allow for normalisation of total homocysteine plasma levels following vitamin therapy.

Adult↗