Spin-spin interactions in organic magnetoresistance probed by angle-dependent measurements.

The dependence of organic magnetoresistance (OMAR) on the orientation of the magnetic field has been investigated. In contrast with previous claims, a finite and systematic change in magnitude is observed when the orientation of the field is changed with respect to the sample. It is demonstrated that, to explain these effects, spin-spin interactions have to be included in the models previously suggested for OMAR. Dipole coupling and exchange coupling are introduced in combination with either an anisotropy of the orientation of the spin pairs or an anisotropy in the hyperfine fields.

Sign inversion of magnetoresistance in space-charge limited organic devices.

In this Letter, we explain the puzzling sign change of organic magnetoresistance in space-charge limited devices by device physics. We prove analytically and numerically that in the case of bipolar conduction with an Ohmic majority carrier and an injection limited minority carrier contact, a decrease in minority carrier mobility may give rise to an increase in the device current. It is shown that when the magnetic field acts to decrease the mobility of both carriers, a sign change in the magnetoconductivity as a function of applied bias may result. This behavior is in agreement with experimental observations.

Extremely large magnetoresistance in boron-doped silicon.

Boron-doped Si-SiO2-Al structures are fabricated to study extremely large magnetoresistance (MR) effects. Current-voltage characteristics show a nonlinear behavior, dominated by an autocatalytic process of impact ionization. At low temperatures, the magnetic field postpones the onset of impact ionization to higher electric fields. This results in a symmetric positive MR of over 10,000% at 400 kA/m. Applying a magnetic field leads to an increase of the acceptor level compared to the valence band as deduced by admittance spectroscopy. A macroscopic transport model is introduced to describe how the MR is controlled by voltage, electrode spacing, and oxide thickness.

Separating positive and negative magnetoresistance in organic semiconductor devices.

We study the transition between positive and negative organic magnetoresistance (OMAR) in tris-(8 hydroxyquinoline) aluminium (Alq_{3}), in order to identify the elementary mechanisms governing this phenomenon. We show how the sign of OMAR changes as function of the applied voltage and temperature. The transition from negative to positive magnetoresistance (MR) is found to be accompanied by an increase in slope of log(I) versus log(V). ac admittance measurements show this transition coincides with the onset of minority charge (hole) injection in the device. All these observations are consistent with two simultaneous contributions with opposite sign of MR, which may be assigned to holes and electrons having different magnetic field responses.

Cimetidine (Tagamet) combined with steroids and H1 antihistamines for the prevention of serious radiographic contrast material reactions.

Cimetidine has recently proved useful in the prophylaxis of certain allergic and other histamine-mediated reactions. We have encountered a patient who had a serious cutaneous and respiratory reaction to Renografin-76 during cardiac catheterization. For the four days preceding his second catheterization, the patient was treated with prednisone, 30 mg daily, diphenhydramine, 25 mg orally, three times a day, intravenous diphenhydramine, 25 mg, three times a day, and Solu-Cortef, 500 mg, intravenously, every six hours. Despite this preparation, he developed an intense reaction to Renografin-76, which did not respond to further doses of Solu-Cortef and diphenhydramine in the catheterization laboratory. Cimetidine, 300 mg, in 100 ml of D5W over 15 minutes, rapidly reversed the entire cutaneous and respiratory phenomenon. In the future, strong consideration should be given to using cimetidine, in its intravenous form, as a routine medication in angiographic laboratories where radiographic contrast materials (RCM) are used. It may be helpful as a pretreatment for recognized RCM reactive patients when catheterization is essential.

Spirometric comparison of carbuterol and isoproterenol aerosol therapy in bronchial asthma. A double blind, matched-pair study of 28 adults and a double blind crossover study of 18 children.

Two adrenergic aerosols were compared in a double blind, matched-pair study of 6 months' duration in 28 adult patients with chronic bronchial asthma, and in a double blind, crossover, short-term study in 18 children with severe asthma. In the adult study, one member of each pair was given either 150 mug of isoproterenol or 200 mug of carbuterol 4 times per day, by inhalation, for 6 months. In the childhood study, 18 children, 6 to 12 years of age, with moderate to severe asthma were studied in a double blind, crossover therapeutic trial in which high or low doses of aerosolized carbuterol or isoproterenol were given 4 times daily for 5 days each. Treatment results were evaluated by measuring forced vital capacity, 1-sec forced expiratory volume, and maximal mid-expiratory flow (FEF25-75%) at regulat intervals before and after administration of the respective test drugs. In the adult study, there was a significant difference between carbuterol and isoproterenol for forced vital capacity (P less than 0.02), for 1-sec forced expiratory volume (P less than 0.02), and for FEF25-75% (P less than 0.01) in favor of carbuterol. In the pediatric study, the difference between carbuterol and isoproterenol was significant (P less than 0.05) only for the FEF25-75% on the fifth day of treatment with the high dose administration of carbuterol. There was no associated toxicity of either drug with respect to electrocardiogram, blood chemistry, or subjective complaints. Tachyphylaxis (tolerance with time) to isoproterenol appeared to develop in one patient.

Theophylline bioavailability following oral administration of six sustained-release preparations.

Plasma theophylline concentrations were measured in 20 adults after single doses of 8 mg/kg of each of six oral sustained-release theophylline preparations. Twelve subjects were studied in a multiple-dose trial. Comparison of bioavailability and absorption characteristics suggest usefulness of some of these products for the purpose of maintaining safe and effective blood levels with twice-a-day dosing.

Use of barbiturate therapy in severe perinatal asphyxia: a randomized controlled trial.

The possible cerebral sparing effect of thiopental was evaluated in 32 severely asphyxiated neonates randomly assigned to either a thiopental treatment or control group. All infants had neurologic manifestations of asphyxia and required assisted ventilation. Thiopental was begun at a mean age of 2.3 hours and was given as a constant infusion that delivered 30 mg/kg over 2 hours. Treatment was continued at a lower dose for 24 hours. Seizure activity occurred in 76% of infants given thiopental and 73% of control infants at a mean age of 1.5 and 2.5 hours, respectively. Although initial arterial blood pressure was similar in both groups, hypotension occurred in 88% of treated and 60% of control infants. The amount of blood pressure support required was significantly greater (P less than 0.005) in the thiopental treatment group. Three infants died in the control group, and five in the treatment group. Developmental assessment was performed at a minimum of 12 months of age in 22 infants. There were no significant differences in neurologic, cognitive, or motor outcome between groups. Deteriorating performance over time was a consistent trend in both groups. These findings indicate that treatment of severe perinatal asphyxia with thiopental does not appear to have a cerebral sparing effect and may be associated with significant arterial hypotension.

Flunisolide aerosol in the treatment of perennial allergic rhinitis.

A double-blind, crossover study was performed with a new topical aerosol steroid, flunisolide, administered every 12 hours over a period of eight weeks to 36 adult patients with perennial allergic rhinitis. During the treatment period the majority of patients had significant relief of symptoms as compared with the placebo period. Most prominent improvement occurred with the symptoms of nasal stuffiness, sneezing, rhinorrhea and the number of times patients had to blow their noses. Best results were obtained in patients with higher degrees of atopy. Side effects were minimal and limited to nasal irritation in some patients. Criteria for optimal patient selection are discussed and an explanation for the lack of systemic effects of aerosolized use of the newer corticosteroids is given.

Treatment of perennial allergic rhinitis with cromolyn sodium. Double-blind study on 34 adult patients.

A double-blind crossover study was performed on 34 adult patients with perennial allergic rhinitis, using an aqueous solution of 4% cromolyn sodium or a placebo substance six times daily over a 4-wk period with daily documentation of both symptoms and use of symptomatic medications. All patients had markedly positive skin test reactions to at least one antigen. Chemistry screens and IgE serum levels were determined. Significant reductions occurred in the symptom-scores for runny nose, stuffy nose, sneezing, and nose blowing while patients were on cromolyn treatment (p less than 0.005). Likewise, while on treatment, there was a significant reduction in the consumption of antihistamines. In an attempt to differentiate between good and poor cromolyn responders by clinical and laboratory parameters, we found that (1) patients with high IgE levels responded better than those with low IgE levels, (2) patients with markedly positive skin test reactions to epidermoids and to foods responded better than those with pollen allergy, and (3) females appeared to have a significantly better drug response than males. Age did not play a role in drug response, nor did drug sequence (placebo-active or active-placebo).

Acquired immunodeficiency syndrome in infants.

Fourteen infants with clinical and laboratory features of an acquired immunodeficiency syndrome were identified in a single metropolitan area from November 1980 to July 1983. Patients were predominantly of Haitian parentage, although two cases occurred in offspring of non-Haitian intravenous drug abusers. Only one patient had received a blood transfusion before the development of clinical findings. The predominant clinical findings included failure to thrive, persistent infection of the oral mucosa by Candida albicans, chronic pulmonary infiltrates, hepatosplenomegaly, lymphadenopathy, and diarrhea. Immunologic studies showed most of the infants to have inverted ratios of T-cell subsets, greatly increased immunoglobulin levels, and circulating immune complexes. Lymphopenia was not common, as it is in adult patients. Infectious agents responsible for opportunistic infections in this series included Pneumocystis carinii, herpesviruses, particularly cytomegalovirus, and C. albicans. Bacterial infections were common, and gram-negative sepsis was the major cause of death in the seven infants who have died. At autopsy, two infants had disseminated lymphadenopathic Kaposi's sarcoma. These observations suggest the likelihood of transplacental, perinatal, or postnatal transmission of an as yet unidentified infectious agent that causes this disease.