Biomedical subjects

V Medina

Publications and source records attributed to V Medina.

42 records · Page 3Linked to original sources

PubMedDate not supplied

Comparison of the heart rate variability parameters obtained from the electrocardiogram and the blood pressure wave.

Four temporal and four spectral parameters of heart rate variability were compared after they were computed with two different time series generation methods: the RR intervals and the numerical values of heart rate provided by the Finapres. Recordings were obtained from 10 healthy subjects throughout five experimental conditions: supine, standing, controlled breathing, exercise and recovery. The mean and the RMS value of successive differences showed significant differences between the two methods. The spectral parameters were statistically different only during standing and exercise. The larger high frequency component and the lower HF/LF ratio by the Finapres method, observed during exercise, can be explained by the higher breathing influence on the peak-to-peak pressure intervals, in relation to RR intervals. Therefore, the high frequency component within mechanic intervals could possibly reflect the non-neural respiratory influence. In conclusion, values of heart rate provided by the Finapres are not completely interchangeable with those obtained from the ECG during the studied conditions.

Adult↗

PubMedDate not supplied

The effect of reactive oxygen species on equine sperm motility, viability, acrosomal integrity, mitochondrial membrane potential, and membrane lipid peroxidation.

The objective of this study was to examine the influence of reactive oxygen species (ROS), generated through the use of the xanthine (X)-xanthine oxidase (XO) system, on equine sperm motility, viability, acrosomal integrity, mitochondrial membrane potential, and membrane lipid peroxidation. Equine spermatozoa were separated from seminal plasma on a discontinuous Percoll gradient, and spermatozoa were incubated with 0.6 mM X and 0.05 U/mL XO for 30 minutes. Catalase (150 U/mL), superoxide dismutase (SOD, 150 U/mL), or glutathione (GSH, 1.5 mM) were evaluated for their ability to preserve sperm function in the presence of the induced oxidative stress. At the end of the 30-minute incubation, sperm motility was determined by computer-assisted semen analysis. Viability and acrosomal integrity were determined by Hoechst-Pisum sativum staining, and mitochondrial membrane potential was determined by staining with JC-1. Incubation with the X-XO system led to a significant (P < .01) increase in hydrogen peroxide production and an associated decrease (P < .01) in motility parameters. Total motility was significantly (P < .01) lower in the presence of X-XO compared with the case of the control (29%+/-9% vs 73%+/-1%, respectively). Catalase, but not SOD, prevented a decline in motility secondary to oxidative stress (71%+/-4% vs 30%+/-3%, respectively). The addition of glutathione had an intermediate effect in preserving sperm motility at the end of the 30-minute incubation (53%+/-3%). No influence of X-XO could be determined on viability, acrosomal integrity, or mitochondrial membrane potential. In order to promote lipid peroxidation, samples were incubated with ferrous sulfate (0.64 mM) and sodium ascorbate (20 mM) for 2 hours after the X-XO incubation. No increase in membrane lipid peroxidation was detected. This study indicates that hydrogen peroxide is the major ROS responsible for damage to equine spermatozoa. The decrease in sperm motility associated with ROS occurs in the absence of any detectable decrease in viability, acrosomal integrity, or mitochondrial membrane potential or of any detectable increase in lipid peroxidation.

Acrosome↗

PubMedDate not supplied

Newly-developed diamond points for conservative operative procedures.

The rapid decrease in the size of dental restorations has increased the demand for the smallest rotary cutting instrument possible. The width of cavities prepared with two experimental diamond points and the smallest commercial diamond point were compared and significant differences found. SEM observation of the head surfaces of the three diamond points revealed that the experimental points had comparable cutting characteristics with the commercial diamond point.

Analysis of Variance↗

PubMedDate not supplied

Effect of bonding variables on the shear bond strength and interfacial morphology of a one-bottle adhesive.

This study's objectives were: 1) to determine the combination of bonding procedures (with or without acid etching, moist or dry substrate, one or two applications of primer/adhesive) that would produce the highest shear bond strength of Prime & Bond and Dyract AP and 2) to characterize the resin-dentin/enamel interface produced by these bonding procedures. Ninety-six bovine incisors were randomly assigned to eight groups for shear bond testing to enamel (n = 6) and dentin (n = 6). Prime & Bond and Dyract AP were applied and cured following manufacturers' instructions. Shear bond testing was conducted in a Universal Testing Machine. Thirty-two bovine incisors were sectioned to produce blocks with enamel and dentin, then bonded in pairs for evaluation of interfacial morphology. They were polished and argon ion-etched using a high-speed argon ion-etching machine and examined by SEM. The groups where enamel was etched, kept moist or dry and received a single application of Prime & Bond produced the highest shear bond strength. Dentin bond strengths were high in the groups where dentin was etched and kept moist. The number of Prime & Bond applications had no effect on dentin bond strength. Acid etching results in better adaptation of Prime & Bond to enamel and dentin regardless of whether moisture is present.

Acid Etching, Dental↗

PubMedDate not supplied

[Electrophysiological evaluation of the treatment of patients with recurrent ventricular tachycardia].

In order to asses the predictive value of serial electrophysiologic studies in the selection of an effective long-term effective antiarrhythmic regimen, we studied 16 patients with recurrent sustained ventricular tachycardia (VT), resistant to conventional medical treatment. (group 1) Eleven patients in this group had chronic chagas myocarditis, and several hospitalizations and cardioversions had been required for therapy of VT. In addition, 35 patients (group 2: control) underwent electrophysiological studies to evaluate rhythm disturbances differences to TV. Ventricular Tachycardia was successfully initiated and terminate with programmed electrical stimulation of the right ventricle only in the group 1. After control studies, the effects of several drugs (ajmalin, amiodarone, carbamazepine, disopyramide, diphenilhydantoin, mexiletine, procainamide, propranolol, quinidine and verapamil on the ability to initiate VT were assessed. A drug was considered effective only if it prevented the initiation of VT and allowed long-term suppression o clinical VT. All the patients of group 1 were placed on chronic oral therapy with the effective agent and were followed for an average period of 16 months (range 5 to 47 months). In all 16 patients we could document complete long-term prophylaxis against VT. This method offers advantage in terms of morbidity, mortality, duration of therapy, and promptness of choosing an effective drug add expense to the patient over traditional empirical methods of drug selection.

Adolescent↗

PubMedDate not supplied

[The implant of a pacemaker cardioverter-defibrillator with a system of endocardial electrodes without thoracotomy].

This article describes the first case in Mexico of an implantable pacer-cardioverter-defibrillator in a 44-year-old man with coronary artery disease and recurrent ventricular tachycardia without the need for a thoracotomy and epicardial electrodes. The patient underwent electrophysiological evaluation that revealed drug-refractory ventricular tachycardia. Endocardial catheter ablation with radiofrequency was considered and rejected due to an unstable hemodynamic state during the tachycardia. A triple electrode system using two transvenous catheter electrodes and a subcutaneous chest patch were employed. Two monophasic unsynchronized shocks were delivered with a 18 J sequential pulse technique over two distinct current pathways. The automatic pacer-cardioverter-defibrillator was implanted in the abdominal wall and demonstrated reproducible termination of ventricular fibrillation.

Adult↗