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Biomedical subjects

F Alvarez

Publications and source records attributed to F Alvarez.

At least 91 records · Page 5Linked to original sources
PubMed1997

Single neuron model with recurrent excitation: response to slow periodic modulation.

The influence of a recurrent excitatory connection on the response of three neuron models to slow periodic modulation is analyzed. The models are the graded response model and the threshold model with and without adaptation. Lissajous displays of the system's output (discharge rate) as a function of the instantaneous input value show hysteresis in all three models. Hence, the outputs are different depending on whether the input is increasing or decreasing. Recurrent excitation increases the width of the hysteresis with (i) the frequency of the periodic modulation, (ii) the transmission delay of the recurrent connection, and (iii) the connection strength.

Action Potentials↗
PubMed1997

Levonorgestrel concentrations during use of levonorgestrel rod (LNG ROD) implants.

In a three-year randomized trial that included 398 women, blood samples were collected for the purpose of assaying levonorgestrel concentrations in women using a new two-rod contraceptive implant system or an earlier implant formulation, Norplant-2 implants. Sample collection was at 1, 3, 6, 9, and 12 months after placement and semiannually thereafter through three years. Resulting assays and analyses showed that levonorgestrel concentrations of each implant formulation decreased significantly with time after placement, with increasing body weight, and with ponderal index. In the third year, several measures indicated that concentrations of the contraceptive drug were higher in women using the LNG ROD implants than in users of the original formulation. No pregnancies occurred among women in either group in the three years. This study provides evidence that the minimum levonorgestrel concentration needed to protect against pregnancy is below 200 pg/ml, and possibly is below 175 pg/ml.

Adolescent↗
PubMed1997

Contraceptives for lactating women: a comparative trial of a progesterone-releasing vaginal ring and the copper T 380A IUD.

From approximately one week before normal ovulation resumes, lactating women require protection against pregnancy by a contraceptive that is safe for both infant and mother in a multicenter one-year study, the natural hormone, progesterone, delivered vaginally by a sequence of four contraceptive rings designed for continuous use, was evaluated as a contraceptive for nursing mothers in comparison with the Copper T 380A IUD. Individual rings release in effective average dose of 10 mg day for a 3 month period. Evaluation included measures of lactational performance as well as of contraceptive efficacy and safety to mother and child. Nine participating clinics enrolled 802 ring users and 734 IUD acceptors between postpartum days 29 and 63. Life table analyses were performed with parallel decrements for ring and IUD subjects. Continuation in the study and analysis required that subjects not stop breastfeeding. The ring, with a one-year pregnancy rate of 1.5 per 100, did not differ significantly from the IUD with respect to contraceptive effectiveness (p > 0.05). More than half of the ring subjects were continuing at 6 months post admission and a quarter (23.5 per hundred) were still using the ring and breastfeeding one year after admission. Women with the IUD, however, had higher continuation rates (p < 0.001) at both time points. The largest single decrement for each method was that for weaning. Ring users had more complaints of vaginal problems but had fewer vaginal disorders on examination. At 12 months postpartum, 46 per 100 continuing ring users remained in amenorrhea. Lactation performance and the health and weight gain of the infants were similar among users of either regimen.

Administration, Intravaginal↗
PubMed1997

First week drug concentrations in women with levonorgestrel rod or Norplant capsule implants.

Forty-two healthy women volunteered to have blood samples drawn at 2, 4, 8, 24, 48, and 168 h (7 days) following placement of levonorgestrel-releasing rod (LNG rod) or of Norplant capsule implants to permit measurement of drug concentrations. Three clinics recruited 10 women each, half of whom used each type of implant. Twelve additional subjects were later enrolled at one site to provide greater detail for the capsule implants. Throughout the week, women with Norplant implants had apparently higher mean drug concentrations than did women with LNG rod implants, but the differences were significant only in the first 48 h after placement (p < 0.05). Maximum levels for capsule implants were found at the 24-h sample (mean, 1358 to 1474 pg/mL) and for the LNG rod implants at 48 h (772 pg/mL). Body weight was negatively correlated with levonorgestrel concentrations at all times (p < 0.05). For several sampling times, differences between clinics in mean concentrations were statistically significant after weight adjustment. Despite differences by implant type, weight, or clinic location, drug concentrations compatible with contraceptive effect were attained within 24 h in users of LNG rod or of Norplant implants, insofar as all women had levonorgestrel concentrations above 250 pg/mL at the 24-h sample.

Adolescent↗
PubMed1997

Colposcopic evaluation of a vaginal gel formulation of iota-carrageenan.

There is an urgent need to develop safe, effective, and acceptable vaginal products for the prevention of sexually transmitted infections. Preliminary in vitro results suggest that vaginal formulations of sulfated polysaccharides, including iota-carrageenan, have the potential to block mucosal transmission of human immunodeficiency virus (HIV). Twenty-five women in five sites participated in Phase I trials to evaluate the safety of a formulation containing iota-carrageenan (PC 213). The results of this study indicate that a 5 mL 2% gel formulation of iota-carrageenan is not associated with significant irritation of the female reproductive tract when administered once daily in the absence of sexual intercourse. Given the small number of participants in this initial study, careful observation for potential irritation must also be included in larger studies of this and other vaginal formulations.

Administration, Intravaginal↗
PubMed1997

Brain tumor and pregnancy.

OBJECTIVE: To establish the indications for surgical intervention, at the appropriate gestational duration, for brain tumors in pregnant women, and to evaluate any association pregnancy hormones may have with the rate of growth or development of complications of brain tumors. METHODS: We observed seven women with brain tumors associated with pregnancy in a series of 126,413 pregnancies from 1983 to 1995. One woman presented with symptoms of intracranial hypertension, and neurologic signs were the first symptoms in two other women. One woman presented with a sudden hemorrhagic lesion, and three had focal seizures. All were evaluated with computed tomography, magnetic resonance imaging, or both. RESULTS: Six of the seven women had surgery; the seventh was treated with radiotherapy because the neuroradiologic studies suggested a quickly growing brainstem glioma. Diagnoses were confirmed on histology in six women: two with meningiomas, two with ependymomas, and two with low-grade astrocytomas (one of these had multiple astrocytomas). Estrogen and progesterone receptors were studied in two cases (one meningioma and one astrocytoma) and were present in both. CONCLUSION: Management of brain tumors should be tailored to the individual patient. There may be a relation between pregnancy hormones and the rate of brain tumor growth mediated through specific intracellular receptors.

Adult↗
PubMed1997

A comparison of "U" and standard techniques for Norplant removal.

OBJECTIVE: To evaluate the "U" technique versus the manufacturer-recommended technique for Norplant removal. METHODS: We conducted a randomized comparison of the manufacturer-recommended method of removal and the "U" technique. The latter involves an incision between and parallel to the third and fourth implants and uses a modified vasectomy clamp to remove the implants by pulling perpendicular to the implant's axis. RESULTS: Twenty-one physicians (three experienced, 18 inexperienced) performed 200 Norplant removals. Inexperienced physicians took significantly less time for removal using the "U" technique than the standard technique (7.9 versus 10.5 minutes), even after controlling for other factors. Experienced physicians also required less time for removal using the "U" technique (3.1 versus 3.7 minutes), but the difference was not statistically significant after controlling for other factors. Both experienced and inexperienced physicians broke implants more frequently using the standard technique, although the difference was significant only for experienced physicians (relative risk 3.6, 95% confidence interval 1.2, 10.8). No differences were noted between the techniques with respect to tissue damage or patient reports of pain during or after removal. CONCLUSIONS: These results suggest that the "U" technique is an improvement over the standard technique, particularly for personnel who are not highly experienced in Norplant removal.

Adult↗
PubMed1997

Subfulminant hepatic failure in autoimmune hepatitis type 1: an unusual form of presentation.

Autoimmune hepatitis type 1 is known to progress insidiously and in many cases cirrhosis is already established at the first presentation of symptoms. It affects mostly females, with peaks of incidence around 10 and 50 years of age. Subfulminant hepatic failure is an unusual initial form of presentation of AIH type 1 and it was observed in three post-pubertal female patients. Rapid disease evolution or no response to immunosuppressive therapy led to liver transplantation in all patients. Two did not have cirrhosis, and the third had focal cirrhosis. The occurrence of the unusual subfulminant form of autoimmune hepatitis in three latepubertal girls (Tanner V) suggests that estrogen may play a role in the severity of the disease.

Adolescent↗
PubMed1997

Use of interferon-alpha in laryngeal papillomatosis: eight years of the Cuban national programme.

Laryngeal papillomatosis is one of the first diseases where interferon (IFN) was found to be effective. In 1983, a programme for the treatment of all such cases started in Cuba. Up to December 1991, 125 patients (92 children, 33 adults) have been treated: 102 with leucocyte IFN-alpha, 12 with recombinant IFN-alpha-2b, and 11 have received both preparations. Case management consisted of surgical removal of the lesions followed by an IFN schedule starting with 10(5) IU/kg of weight in children or 6 x 10(6) IU in adults, i.m. daily. The dose was progressively reduced, as long as no relapses occurred. At the end of the one-year schedule the doses were reduced to 5 x 10(4) IU/kg in children or 3 x 10(6) IU in adults, weekly. If there was a relapse, it was removed surgically and the patient returned to a higher dose level. Most cases (89; 71 per cent) have not relapsed after the treatment; 60 of them have been followed for more than three years. In those with relapses, the frequency of recurrence decreased in all but four patients. The treatment seemed to be more effective if initiated less than three months after the disease onset. The tracheostomy could be removed in five out of seven patients who needed it before the IFN treatment and was necessary in only three new cases during IFN treatment. In two of these, decannulation was possible later on. In a total of 14 patients relapses persisted after several cycles of IFN treatment. They were considered resistant to such treatment. No severe side effects were reported. The most frequent ones were fever, drowsiness, increased bronchial secretion, chills and headache. The establishment of this programme has maintained the disease under control in Cuba.

Adolescent↗
PubMed1997

A new approach to cytochrome CYP2D6 antibody detection in autoimmune hepatitis type-2 (AIH-2) and chronic hepatitis C virus (HCV) infection: a sensitive and quantitative radioligand assay.

Antibodies specific for cytochrome CYP2D6, formally known as liver-kidney-microsome type-1 antibodies (LKM-1), are characteristically found in a subgroup of patients presenting autoimmune hepatitis. They are also found in some patients with chronic HCV infection. These autoantibodies are usually detected by indirect immunofluorescence, immunoblotting and ELISA tests. In an attempt to set up a more sensitive detection assay we developed a quantitative immunoprecipitation radioligand assay using a 35S-methionine-labelled CYP2D6 antigen obtained by in vitro transcription and translation synthesis. All 16 sera from AIH-2 patients strongly bound to this CYP2D6 antigen. Two of the nine sera (22%) from AIH-2 patients that presented only liver cytosol-1 antibodies also bound to CYP2D6. All 24 sera from HCV patients that were positive for LKM-1 antibodies by indirect immunofluorescence were also positive using this CYP2D6 radioligand assay. Lastly, all 15 sera from HCV patients negative for LKM-1 antibodies were negative by this test. The present results support the view that this quantitative radioligand assay is more sensitive than immunoblotting and ELISA CYP2D6 assays, and that it could be used in combination with indirect immunofluorescence assay.

Adolescent↗
PubMed1997

Detection of Pneumocystis carinii in tracheal aspirates of intubated patients using calcofluor-white (Fungi-Fluor) and immunofluorescence antibody (Genetic Systems) stains.

OBJECTIVE: To compare the detection rate of Pneumocystis carinii in endotracheal aspirates with that rate in bronchoalveolar lavage fluid, using calcofluor-white (Fungi-Fluor) and immunofluorescence antibody (Genetic Systems) staining methods. DESIGN: Prospective, consecutive cases. SETTING: Medical intensive care unit at Ben Taub General Hospital. PATIENTS: Thirty-one intubated patients admitted with respiratory failure and suspected P. carinii pneumonia. INTERVENTIONS: An endotracheal aspirate specimen was obtained after maximally advancing a closed-system suction catheter, instilling aliquot portions of saline, and suctioning the lavage fluid. This procedure was followed within 30 mins by fiberoptic bronchoscopy and bronchoalveolar lavage. MEASUREMENTS AND MAIN RESULTS: Endotracheal aspirate and bronchoalveolar lavage specimens from each patient were mixed with Saccomano's fixative, blended, and centrifuged. Using a modified method for P. carinii cysts, the sediment was stained with the test calcofluor-white stain Solution A and the test antibody stain. The test antibody stain on the bronchoalveolar lavage specimens was positive for P. carinii for 13 patients and was used as the standard for comparison. In the endotracheal aspirate specimens, the test antibody stain detected 12 (92%) P. carinii-positive patients while the test calcofluor-white stain detected ten (77%) P. carinii-positive patients. CONCLUSIONS: We described a simple method for obtaining, processing, and staining endotracheal aspirate specimens for P. carinii. Obtaining an endotracheal aspirate specimen did not require specially trained personnel or a specialized and more expensive catheter, and was not associated with any complications.

Benzenesulfonates↗
PubMed1997

Comparison of pressure support ventilation and assist-control ventilation in the treatment of respiratory failure.

STUDY OBJECTIVE: To assess whether pressure support ventilation (PSV) could be used as an alternative ventilatory mode to assist-control (A/C) ventilation in the treatment of respiratory failure. DESIGN: A short-term (4-h) prospective study in which the beneficial effect of PSV on respiratory mechanics, gas exchange, arterial oxygenation, cardiovascular hemodynamics, and oxygen consumption was compared with A/C ventilation. SETTING: ICU of a community hospital. PATIENTS: Forty-five patients (mean age, 62.8 [11.8] years) with respiratory failure secondary to COPD, restrictive disorders, or neuromuscular disease requiring mechanical ventilatory support in the ICU were selected for study. INTERVENTIONS: The mean duration of mechanical ventilation before the study was 7.16 (8.64) days. Patients were switched to the PSV mode of the mechanical ventilator for a period of 4 h after which conventional A/C ventilation was resumed. RESULTS: Patients supported with PSV compared with A/C ventilation showed significantly higher tidal volume, minute ventilation, and inspiratory time in association with significantly lower pressure in the airway and I:E ratio. With regard to gas exchange data, an increase in dead space/tidal volume ratio (VD/VT), decrease in PaO2, and statistically but not clinically significant alteration of arterial oxygenation indexes were noted. However, when patients with COPD, restrictive disorders, and neuromuscular disease were compared, significant changes in arterial oxygenation parameters were found only in patients with restrictive disorders. There were significant decreases in heart rate, systolic pulmonary artery pressure, and pulmonary capillary wedge pressure when PSV was applied. Oxygen transport and oxygen consumption were unchanged. CONCLUSIONS: PSV could be a possible alternative to A/C ventilation in patients with respiratory failure. PSV caused an increase in VD/VT in association with a significantly lower pressure in the airway and I:E ratio. Randomized studies are needed to define the long-term benefits of both respiratory modes and the conditions in which PSV may be a valuable alternative to A/C ventilation.

Adult↗
PubMed1997

Monoclonal antiphosphatidylserine antibodies react directly with feline and murine central nervous system.

OBJECTIVE: Antiphospholipid antibodies (aPL), especially against phosphatidylserine and cardiolipin, are associated with a variety of neurological disorders. While it is believed aPL react with endothelial cells to cause cerebral thrombosis, it is not known to what degree aPL react with neural tissue nor which particular aPL specificities may be more relevant. We investigated direct aPL reactivity with the central nervous system (CNS) using 3 monoclonal IgM aPL that differentiate between cardiolipin and phosphatidylserine dependent antigens. METHODS: Brain and spinal cord from normal cat Felis domesticus and brain from CD-1 mice were reacted with aPL using indirect immunoperoxidase techniques. Monoclonal aPL were reacted with whole brain myelin by dot immunoblots. RESULTS: Monoclonal D11A4, reactive with cardiolipin and not phosphatidylserine (CL+/PS-), did not react with any portion of the tissue. Both monoclonal 3SB9b (CL-/PS+) and BA3B5C4 (CL+/PS+) reacted in feline and murine CNS. Both labeled myelinated fibers in grey and white matter of brain and spinal cord in an identical pattern with positive control antibody against myelin basic protein and reacted with whole human brain myelin by dot immunoblot. 3SB9b (CL-+PS+) additionally reacted with ependyma and epithelium of the choroid plexus. CONCLUSION: aPL, especially those reactive with phosphatidylserine dependent antigens, react directly with epitopes associated with myelin, brain ependyma, or choroid epithelium. Direct reactivity of aPL with nervous tissue may be relevant to neurological disorders.

Animals↗
PubMed1997

[Prenatal molecular diagnosis of cystic fibrosis. Report of 3 cases].

Cystic Fibrosis (CF) is a severe and relatively common autosomic recessive disease caused by a variety of mutations in the CFTR gene. The most frequent mutation worldwide, consists of the deletion of the phenylalanine codon at position 508 (delta F508). Here we report the first cases of prenatal diagnosis of CF by DNA analysis in couples at risk in Venezuela. The study focused on the detection of delta F508 alleles analyzing DNA recovered directly from amniocytes or from their cultures, using the polymerase chain reaction (PCR) and polyacrylamide gel electrophoresis. Two of three fetuses resulted homozygotic for the delta F508 allele and the third one turned out to be a delta F508 carrier. This information sustained the genetic counseling of the couples and allowed them to take objective reproductive decisions, a direct consequence of the availability of gene analysis at the DNA level.

Adult↗