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Biomedical subjects

F Valenzuela

Publications and source records attributed to F Valenzuela.

42 records · Page 3Linked to original sources
PubMedDate not supplied

[Design and evaluation of a duplication of the cardiac for the evaluation of valvular prostheses].

Recently, several different models of valvular prostheses have been developed in which biological material, like duramater and perycardium, is being used for their manufacturing. Since these valves have to be manufactured one by one, the possibility of obtaining heterogeneous results is very high, thus it is very important to have a system to evaluate the behavior of these prostheses. The objective of this project was to design and evaluate a cardiac cycle duplicator to test the function of valvular prostheses. The system consists of a double plexiglass chamber, separated by the valvular prosthesis being studied. The superior "auricular" chamber is connected to a reservoir where the height of the column of saline can be modified. The interior "ventricular" chamber is connected to a pump that generates pressure pulses at constant intervals which simulate ventricular systoles. The other end of the pump connects with an artificial Starling's resistance. The data obtained from this system allows the quantification of the following: 1) Functional diameter, form and area of maximal opening; 2) valve motility; 3) sufficiency of the prostheses; 4) velocity of valve opening and closing; 5) rigidity of the valves; 6) optimal pressure gradient for adequate valvular function. The system makes possible the evaluation and comparison of the function of these valvular prostheses.

Biocompatible Materials↗
PubMedDate not supplied

[Effects of adenosine on automaticity and post-potential oscillations in Purkinje fibers of mammals].

The aim of the present paper was to study the effects of adenosine (ADO) on automaticity and after potential oscillations on canine cardiac Purkinje fibers. ADO concentrations from 10(-8) to 10(-5) M were used. The intracellular electrical activity was recorded with conventional microelectrodes. ADO increased during the first two minutes the basic cycle length (BLC) with concentrations higher than 10(-8) M, to a value 50% above control, later there is a progression to a steady state. The dose-response curve in the steady state is sigmoidal and resembles those of receptor occupation. The slopes of pacemaker potentials have a tendency to decrease along with the increase in BLC length. After potential oscillations decrease with 10(-8) M of ADO but not with larger concentrations. There results supports the hypothesis that ADO produces an increase in the time independent potassium current similar to the one described for atrial and ventricular myocytes. This effect probably depends on specific receptor stimulation. The biphasic time course suggests the existence of subtypes of A1 receptor with different dissociation constants and affinities but with similar actions. The idea that the ADO effects depend mainly on the potassium currents and not on I(f) is supported by the absence of a dose-dependent effects in the oscillatory after potentials.

Adenosine↗
PubMedDate not supplied

[Experimental anti-arrhythmic action of perhexiline].

The antiarrhythmic action of Perhexiline phosphate, in doses of 3 and 6 mg/kg on various experimental cardiac arrhytmias and on the physiological properties of the atrial myocardium has been studied in the anesthetized dog. Its action in concentrations of 3 and 6 mcg/ml on the transmembrane action potentials in isolated Purkinje fibers has also been analyzed. The activity of perhexiline is comparatively greater in the circus movement atrial flutter and in the arrhythmias caused by ouabain and by barium chloride intoxication than in the atrial tachysystolia caused by the local application of aconitine. Perhexiline prolongs the wave length (refractory period times conduction velocity) of the atrial impulse and depresses atrial excitability. These effects may explain its action on experimental atrial flutter. In isolated Purkinje fibers, perhexiline reduces the maximum velocity of depolarization, the overshoot, the amplitude of the action potential and its duration, measured at 50% of its repolarization phase. The relation of these electrophysiological effects of perhexiline to the genesis of each type of arrhythmia may explain its different type of activity in the experimental models studied.

Animals↗
PubMedDate not supplied

[Mathematics and the heart].

Mathematical modeling in biomedical sciences is particularly difficult because of the great amount of variables that the biological phenomena imply, the difficulty in observation and experimentation, and the scarceness of mathematical methods suitable for incorporating all of these variables. Even so, many mathematical models can be found in biology which include reduccionist, structural or integrative approaches. Theoretical models in biology are designed upon clearly defined purposes and may extent from the molecular level to the intact organism. For a model to be useful, its variables, levels and links must be very explicit. Observable and measurable aspects of the heart allow a modeling approach of this organ, in normal or in pathological conditions. A few examples are mentioned. Mathematical modeling of the heart may help orient experimental research, join existing data and theories and it may also be of assistance as therapeutic guidance.

Humans↗
PubMedDate not supplied

[Pharmacological principles in pregnancy].

Drug consumption during pregnancy is a widespread practice that may produce adverse effects on the developing fetus. The magnitude of drug disposition is influenced for maternal-fetal unit physiological changes. The maternal-fetal unit represents a unique pharmacological state with multiple compartments, wherein the mother-placenta-extra-amniotic membranes-amniotic fluid and fetus are each represented as a single compartment with different functions and genetics or cellular individual characteristics. It is a problem which should be focused on several perspectives including epidemiological, pharmacological and toxicological aspects. An understanding of these aspects is essential to rational and effective health public policy on prenatal care.

Abnormalities, Drug-Induced↗