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Biomedical subjects

J G Martinez

Publications and source records attributed to J G Martinez.

5 recordsLinked to original sources
PubMed2002

Single-lead VDD-pacing system incorporating high impedance stimulation: a multicentre study.

AIM: The purpose of this study was to evaluate the performance of a new VDD pacing system incorporating a high impedance, single-pass VDD lead. The new lead is a bipolar, steroid-eluting, high impedance lead with a full-ring atrial dipole. METHODS AND RESULTS: The system was implanted in 46 patients with high degree atrioventricular (AV) block. Patients were followed at pre-discharge, 6 weeks, and 3 months. The mean measured P-wave amplitude was stable, with values between 1.18 and 1.43 mV. Atrial sensing was reliable during short-term evaluation at rest and in the sitting position, with AV-synchronous stimulation between 98.79 +/- 6.90% and 99.73 +/- 1.47%. Holter recordings after 6 weeks demonstrated AV-synchronous stimulation in 99.57 1.03% of all P-waves. Lead impedance was stable during follow-up, with mean values between 1000 and 1167 Q. Mean ventricular pacing thresholds (at 0.5 ms) were 0.47 V at implant, 0.49 V at pre-discharge, 0.74 V at 6 weeks, and 0.72 V at 3 months. R-wave amplitude remained stable between 14.9 and 16.7 mV during follow-up. CONCLUSION: This new single-pass VDD lead system provided reliable atrial sensing and stable high impedance stimulation during a 3-month follow-up period.

Aged↗
PubMed1998

The fate of the oxidizing tyrosyl radical in the presence of glutathione and ascorbate. Implications for the radical sink hypothesis.

Cellular systems contain as much as millimolar concentrations of both ascorbate and GSH, although the GSH concentration is often 10-fold that of ascorbate. It has been proposed that GSH and superoxide dismutase (SOD) act in a concerted effort to eliminate biologically generated radicals. The tyrosyl radical (Tyr.) generated by horseradish peroxidase in the presence of hydrogen peroxide can react with GSH to form the glutathione thiyl radical (GS.). GS. can react with the glutathione anion (GS-) to form the disulfide radical anion (GSSG-). This highly reactive disulfide radical anion will reduce molecular oxygen, forming superoxide and glutathione disulfide (GSSG). In a concerted effort, SOD will catalyze the dismutation of superoxide, resulting in the elimination of the radical. The physiological relevance of this GSH/SOD concerted effort is questionable. In a tyrosyl radical-generating system containing ascorbate (100 microM) and GSH (8 mM), the ascorbate nearly eliminated oxygen consumption and diminished GS. formation. In the presence of ascorbate, the tyrosyl radical will oxidize ascorbate to form the ascorbate radical. When measuring the ascorbate radical directly using fast-flow electron spin resonance, only minor changes in the ascorbate radical electron spin resonance signal intensity occurred in the presence of GSH. These results indicate that in the presence of physiological concentrations of ascorbate and GSH, GSH is not involved in the detoxification pathway of oxidizing free radicals formed by peroxidases.

Animals↗
PubMed1992

Re-examining repeated testing and teacher effects in a remedial mathematics course.

This study examined the impact of repeated testing and teachers' effects on student achievement in a remedial mathematics course. A 2 x 2 completely randomised factorial design was used, with final examination performance the dependent variable and testing attempts and the teacher factor the independent variables. The study found no main effects for teacher but a main effect for testing attempts and a teacher-factor/testing-attempt interaction. Post hoc findings qualified a direct interpretation of the main effect. The implications for further research and application are discussed, giving special attention to teacher effects, the needs of remedial mathematics instruction, and the claims of mastery-learning pedagogies.

Achievement↗
PubMed1986

The effect of isoxicam on neutrophil and monocyte function.

1 Isoxicam was found to inhibit monocyte and neutrophil cell chemotaxis at therapeutic concentrations. 2 The effect was observed after in vitro incubation of normal cells and in vivo in patients with rheumatoid arthritis. 3 Compared to other NSAIDs studied in our laboratory, isoxicam was shown to have a broader spectrum of inhibitory action on the cells involved in the chronic inflammation associated with rheumatoid arthritis.

Anti-Inflammatory Agents, Non-Steroidal↗