Biomedical subjects

Alfonso Martinez

Publications and source records attributed to Alfonso Martinez.

5 recordsLinked to original sources

PubMed2003

Microwave photonic filters with negative coefficients based on phase inversion in an electro-optic modulator.

We report on a novel technical approach to the implementation of photonic rf filters that is based on the pi phase inversion that a rf modulating signal suffers in an electro-optic Mach-Zehnder modulator, which depends on whether the positive or the negative linear slope of the signal's modulation transfer function is employed. Experimental evidence is provided of the implementation of filters with negative coefficients that shows excellent agreement with results predicted by the theory.

Journal Article↗

PubMed2003

Arrayed waveguide Sagnac interferometer.

We present a novel device, an arrayed waveguide Sagnac interferometer, that combines the flexibility of arrayed waveguides and the wide application range of fiber or integrated optics Sagnac loops. We form the device by closing an array of wavelength-selective light paths provided by two arrayed waveguides with a single 2 x 2 coupler in a Sagnac configuration. The equations that describe the device's operation in general conditions are derived. A preliminary experimental demonstration is provided of a fiber prototype in passive operation that shows good agreement with the expected theoretical performance. Potential applications of the device in nonlinear operation are outlined and discussed.

Journal Article↗

PubMed2002

MHC susceptibility genes to IgA deficiency are located in different regions on different HLA haplotypes.

Familial predisposition to IgA deficiency (IgAD) suggests that genetic factors influence susceptibility. Most studies support a polygenic inheritance with a susceptibility locus (designated IGAD1) in the MHC, but its exact location is still controversial. This study aimed to map the predisposing IGAD1 locus (or loci) within the MHC by investigating the pattern of association of the disease with several markers in the region. DNA-based techniques were used to type individual alleles of four polymorphic HLA genes (HLA-DR, -DQA1, -DQB1, and HLA-B), six microsatellites (all located between HLA-DR and HLA-B), and three single nucleotide polymorphisms on the TNF gene. The frequencies of these alleles were compared among ethnically matched populations comprising 182 patients and 343 controls. Additionally, we investigated parents and siblings of 100 of these patients. All four parental haplotypes were established in each family (n = 400), and transmission disequilibrium tests were performed. Surprisingly, our results did not support the hypothesis of a unique susceptibility gene being shared by all MHC susceptibility haplotypes. On HLA-DR1 and -DR7-positive haplotypes IGAD1 mapped to the class II region, whereas on haplotypes carrying HLA-DR3 the susceptibility locus mapped to the telomeric end of the class III region, as reported previously. Our results show how, in complex diseases, individuals may be affected for different genetic reasons and a single linkage signal to a region of a chromosome may actually be the result of disease-predisposing alleles in different linked genes in different pedigrees.

Alleles↗

PubMed2002

Infliximab retreatment in adults and children with Crohn's disease: risk factors for the development of delayed severe systemic reaction.

OBJECTIVES: Although effective in the treatment of refractory Crohn's disease, episodic retreatment with the antitumor necrosis factor a chimeric monoclonal antibody infliximab (Remicade, Centocor, Malvern, PA) can be associated with severe acute and delayed systemic reactions. METHODS: We analyzed episodic infliximab retreatment over 30 months in 86 adult and pediatric patients receiving 304 infusions to determine factors associated with the development of severe systemic reaction. RESULTS: Overall, 14% of patients experienced severe systemic reactions with episodic infliximab retreatment. There was a significant difference in the rates of severe systemic reaction observed in adults (11/52 [21%]) and pediatric patients (1/34 [3%]) (p < 0.02). Delayed systemic reactions, characterized by arthralgia, fever, and myalgia requiring corticosteroid treatment, were found exclusively in adults (age > 17 yr) and occurred in eight patients treated for luminal Crohn's disease. Acute systemic reactions, characterized by hypotension, mucosal irritability, and laryngospasm requiring epinephrine, diphenhydramine, and/or methylprednisolone treatment, occurred sporadically in three adults and one child, treated for both luminal and fistulizing disease. Second infliximab infusions were associated with two thirds of severe systemic reactions, and a distant second infusion (> or = 20 wk from first infusion) was poorly tolerated relative to earlier retreatment (p < 0.001). Concomitant medications were similar in adults and children. CONCLUSIONS: Episodic infliximab retreatment--specifically, a distant second infusion--is associated with high rates of severe systemic reaction in adults, but not children. We recommend multiple early infusions of infliximab if retreatment is anticipated in adult patients to avoid the development of delayed severe systemic reactions.

Adolescent↗

PubMedDate not supplied

Spontaneous improvement of the renal function in a patient with HIV-associated focal glomerulosclerosis.

Collapsing glomerulopathy is a pattern of renal injury that is seen in association with human immunodeficiency virus (HIV) infection. Patients with this HIV-associated nephropathy (HIVAN) present nephrotic syndrome and rapid deterioration of the renal function. There is no proven effective therapy for HIVAN, and the majority of the patients become dialysis dependent. We report a case of biopsy-proven HIVAN that showed spontaneous improvement of the renal function.

AIDS-Associated Nephropathy↗