Search PubMed⌕ Search

Biomedical subjects

F Valenzuela

Publications and source records attributed to F Valenzuela.

At least 37 records · Page 2Linked to original sources
PubMed1983

Interaction between overdrive excitation and overdrive suppression in canine Purkinje fibres.

The interaction between overdrive excitation and overdrive suppression was studied in canine Purkinje fibres perfused in vitro with a solution containing noradrenaline (10(-6) mol . litre-1) and/or high calcium (8.1 mmol . litre-1). The following results were obtained: 1) in the presence of either high calcium or noradrenaline, a fast drive induced at times an acceleration of the spontaneous rhythm; 2) the simultaneous administration of high calcium and noradrenaline quite often allowed the onset of overdrive excitation that showed different patterns; 3) short (5 to 10 s) and fast (60 to 180 min) drives elicited a rhythm that was fastest immediately after overdrive, gradually slowed toward control and could be followed by suppression; 4) in other instances, overdrive caused little acceleration but failed to induce suppression; 5) drives longer than 15 s usually induced only suppression, although there could be a few beats before suppression; 6) intermittent drive led to an initial excitation and then to suppression; 7) driving at a rate slower than the spontaneous rate caused a temporary suppression of the spontaneous discharge which resumed even if the slow drive continued; 8) excitation was not induced by overdriving in low calcium, even in the presence of noradrenaline. It is concluded that many of the in vivo features of overdrive excitation can be reproduced in vitro in small strands of Purkinje fibres. The relationship between overdrive excitation and overdrive suppression involves the opposing actions of drive on the oscillatory potential and on diastolic depolarisation.

Animals↗
PubMed1977

Transient osteoporosis of the hip.

Osteoporosis in a painful hip is usually a sign of inflammation or tumor. There exists, however, a self-limited clinical entity that presents with pain in the hip and where the only roentgenological manifestation is osteoporosis. Eight patients with this disease are described: five men and three women, ranging in age from 29 to 50 years. In four patients, the onset of disease was related to sprain, pregnancy, or delivery. Laboratory analyses and the clinical course of the disease excluded inflammation or a neoplasm as the cause. All patients fully recovered with 12 month, with no sequelae. The etiology of the disease remains unknown.

Adult↗
PubMed1975

Familial chondrocalcinosis in the Chiloe Islands, Chile.

Studies about chondrocalcinosis in the Chiloe Islands (Chile) showed the high frequency of the disease there and how most of it is aggregated in a few highly involved families. Pedigrees and the high degree of consanguinity among parents of index cases pointed to a recessive inheritance. The presence of common Caucasian anthropological features of genetic value in the patients and the lack of Indian mixture in three of the involved families, documented back to 1600, suggest a Caucasian origin of the mutation. Biochemical studies of the patients' synovial fluid showed a significant rise in pyrophosphate concentration. Calcium, phosphorus, and alkaline phosphatase concentrations were not different from a control group.

Adult↗
PubMedDate not supplied

Estrogenic effects of the synthetic aminoestrogen 17 beta-(5-hydroxy-1-pentylamino)-1,3,5(10)-estratrien-3-ol (pentolame).

In this study, we investigated the effects of pentolame, a 17 beta-aminoestrogen derivative, upon coagulation, serum LH, pituitary progestin receptors, uterine weight, and endometrium morphological changes in the castrated female rat. Groups of animals were subcutaneously (s.c.) injected with either estradiol (E2) (0.1 up to 1000 micrograms/animal), pentolame (1 up to 1000 micrograms/animal), or the vehicle alone daily for 5 consecutive days starting 2 weeks following ovariectomy. Administration of pentolame (10 to 1000 micrograms/animal) increased significantly (p < 0.05) the blood clotting time when compared with that obtained in the group of control animals (EC50 582 micrograms). Pentolame (500 and 1000 micrograms/rat for 5 days) caused a significant inhibition (p < 0.01) of serum LH levels (IC50 860 micrograms), which remained suppressed until Day 5 post last injection. In addition, treatment with pentolame was able to restore in the castrated female rat the presence of specific estrogen-dependent progestin binding sites at the anterior pituitary level. The affinity constants and the number of binding sites of pentolame-induced progestin receptors were similar to those obtained with estradiol at equipotent doses (860 micrograms vs. 1 microgram/animal, respectively). Administration of the 17 beta-aminoestrogen derivative resulted in a significant increase in uterine weight (EC50 420 micrograms) and endometrial characteristics were indistinguishable from those observed in the group of rats treated with E2.

Amino Alcohols↗
PubMedDate not supplied

[Histamine as modulator of potassium currents in ventricular cells isolated from heart of guinea pig. A possible regulator effect of ventricular electric activity].

Histamine is present in cardiac tissues in considerable amount, but its physiological role is not well understood. There are two kinds of histamine receptors on the cardiac cells (H1 and H2). Whereas the H2 actions are very well studied little is known about H1 effects. It has been reported that stimulation of H1 receptors induce a shortening of the action potential as a decrease in excitability, but the ionic mechanisms responsible for these are not known. The aim of the present paper is to explore the possible ionic mechanisms related to these effects on isolated ventricular myocytes by means of voltage clamp technique. Histamine induced a shift in the current-voltage relationship of the potassium background current to the right. This shift implies an increase in outward current at the plateau level, responsible for the shortening, as well as for the decrease in excitability. This is, as far as we know, the first report in potassium background channel modulation by an endogenous substance and firmly support the hypothesis that histamine is playing a role in cardiac modulation.

Action Potentials↗
PubMedDate not supplied

[Changes in auriculoventricular conduction due to the effect of ethanol].

Transcoronary ablation of atrioventricular conduction by dehydrated alcohol was attempted in one patient with refractory ectopic atrial tachycardia. Ethanol (1.5 ml) was delivered after selective catheterization of the atrioventricular nodal artery in a patient in whom the artery could be identified by cineangiography. The mean creatine kinase (MB fraction) at four hour to six hour after ablation was 40 U. No electrocardiographic QRS changes was seen. The procedure was successful. The patient is asymptomatic 3 months after procedure. Transcoronary alcohol ablation of atrioventricular conduction should be considered in patients in whom electrical techniques have been unsuccessful.

Adult↗
PubMedDate not supplied

[The thickness/radius ratio (t/r) in patients with dilated and hypertrophic cardiomyopathy].

We studied 17 patients with cardiomyopathy (10 hypertrophic and 7 dilated). With two-dimensional echocardiography, we obtained a short axis view at the level of papillary muscle. We calculated the ratio between thickness (h), of ventricular wall and cavity's radius (r) in diastole and systole (h/r ratio). Hypertrophic cardiomyopathy has a high h/r ratio in diastole (inappropriate hypertrophy), hypercontractility and low and systolic wall stress. Dilated cardiomyopathy has a low diastolic h/r ratio (inadequate hypertrophy) with low contractility and elevated end-systolic, wall stress. We discuss the mechanisms and consequences of different patterns of hypertrophy on the ventricular performance.

Adult↗
PubMedDate not supplied

[The effects of histamine on the electrical and mechanical properties of the heart].

The effects of histamine on the electrical and mechanical properties of the right and left atria and papillary muscle of the guinea-pig's heart were studied. The experiments were performed using conventional techniques of intracellular recording of the electrical activity and isometric tension. It was found that the distribution of the histaminergic receptors is different in the several tissues studied. The H2 receptors predominate in the right atrium, whereas the H1 in the left one. There are both kinds of receptors in the ventricular tissues. The main effects found were: a) In the right atrium: a positive chronotropic effect, a shortening of the action potential and an increase in excitability. b) In the left atrium only a shortening of the action potential was seen. The other electrical and mechanical parameters were not affected by histamine. c) In ventricular muscle a biophasic response in the action potential duration was observed, low concentrations of histamine induced a shortening of the action potential, whereas larger concentrations provoked a lengthening. Also low doses of histamine induced a negative inotropic effect, secondary to the activation of H1 receptors, while concentrations larger than 10(-8) M provoked a positive inotropic effect due to the H2 receptor activation. Also a decrease in excitability was seen mainly due to the activation of the H1 receptors stimulation. In every tissue studied the effects of histamine were seen with concentrations as low as 1 X 10(-10) M, being the H1 receptors who shown a greater affinity, since the activation of the H2 receptors were obtained only with doses larger than 1 X 10(-8) M.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMedDate not supplied

[Effects of cyproheptadine on the electrophysiological characteristics of the sinus node, ventricular myocytes and papillary muscles of the guinea pig heart].

Cyproheptadine is an antagonist of S1 serotoninergic and H1 histaminergic receptors, with a well known cardiovascular activity, mainly vasodilation and a negative chronotropic effect. It has been suggested that cyproheptadine as other antiserotoninergic drugs act by blocking the calcium channel. In order to explore this possibility the actions of this drug were studied in several cardiac preparations: sinus node, isolated ventricular myocytes and papillary muscle from guinea-pig's heart. The experiments were performed using the conventional recording techniques of intracellular electrical activity and isometric tension. Doses from 0.25 microM to 1.0 microM were studied. The main findings were: in sinus node: a) inhibition of automatic activity, b) a decrease in the upstroke, c) a decrease in the plateau level, and d) a shortening of the action potential. In isolated ventricular myocytes: a) a decrease in the rate of depolarization, b) a decrease in the plateau level and c) a shortening of the action potential. In the papillary muscle: a) a decrease in tension and b) a shortening of the action potential. All the effects observed were dose dependent an agree with a blockade of the calcium channel.

Action Potentials↗
PubMedDate not supplied

[Effects of caffeine on post-extrasystolic potentiation and mechanical restitution in mammalian papillary muscle].

The excitation-contraction coupling theory postulates that the main source of activator calcium is the sarcoplasmic reticulum that releases calcium in response to an electrical stimulus. This happens to be true in skeletal muscle, but recently several discrepancies have been raised about the validity of this hypothesis in cardiac muscle. These discrepancies are related to morphological as well as physiological data. The new information postulates that sarcoplasmic reticulum in cardiac muscle does not supply calcium as a main source in physiological conditions. The aim of the present paper was to evaluate the sarcoplasmic reticulum role in the supply of activator calcium in excitation-contraction coupling. A series of experiments were performed using the mechanical restitution and the post-extrasystolic potentiation models in the presence of caffeine, which is known to provoke functional elimination of the sarcoplasmic reticulum. It was observed that caffeine diminished the post-extrasystolic potentiation when 1 mM was used. At higher dose (4mM) the post-extrasystolic potentiation was completely abolished. On the other hand the late part of mechanical restitution is also abolished by caffeine. The amount of calcium that recirculates seems to increase in the presence of caffeine. The results obtained seem to support the idea that the sarcoplasmic reticulum has only a minor role in the supply of activator calcium, when physiological stimulation rates are used.

Animals↗
PubMedDate not supplied

[Policy guidelines and practical considerations for the development of technology at the Instituto Nacional de Cardiología de México].

In order to face the current economical problems of the country, our Institute has intensified its efforts to replace the imports of medical goods by developing its own medical technology. This article summarizes what we have achieved in this field and describes the rules to be followed in the future. We describe the program on the designing and development of heart valve prosthesis together with an hydraulic-electrical system to test them. In the field of computed instruments, we have developed a system of "synchronos color pictures" to be applied in nuclear medicine. In the field of electrocardiography; an EKG paste, a computed program for automatic EKG interpretation and a "filter" of the 60 cycle interference. The Institute is engaged in the designing of a sophisticated EKG machine at low cost, and EKG tracing simulator for teaching purposes. These programs have been shared with others institutions of the country.

Academies and Institutes↗
PubMedDate not supplied

[Automatism: an intrinsic property of cardiac tissues].

Automaticity is an intrinsic property of some types of cardiac tissues, like the nodes and the conducting fibers. Automatic cells are characterized by the appearance, during diastole, of a slow depolarization which is capable of reaching threshold and generate an action potential. This depolarization is the so-called slow diastolic depolarization, or pacemaker potential. Tissues with automaticity do not have the same intrinsic firing frequency, which determines the existence of a true pacemaker; normally this role is assumed by the sinus node and several latent, or subsidiary pacemakers. The latter do not give any manifestation, because, since they have a slower firing frequency than that of the true pacemaker, the impulses generated by the latter will activate them before they can reach threshold. The ionic mechanisms that originate the pacemaker potential are just some of the processes that constitute the electrophysiological properties of the cardiac cell membranes. The mechanism includes the slow inactivation of an outward current combined with a constant inward current. Recently published evidence suggests that the pacemaker potential could be the resultant of an inward current that is slowly activated during the final part of the repolarization, but these data are still controversial and difficult to interpret. The factors that regulate heart rate modify the electrophysiological characteristics of the membrane by means of three major mechanisms: the slope of the pacemaker potential, the voltage of the threshold potential and, the maximum diastolic potential. Some of the most important factors that modulate heart rate include the neurotransmitters of the automatic nervous system, the plasmatic levels of some ions, like potassium and calcium, and changes in the intrinsic properties of the membrane, like the influence of heart rate on the activity of the sodium pump.

Animals↗
PubMedDate not supplied

[Effect of streptolysin O on the Purkinje fibers of the heart in dogs].

Streptolysin "O", an exotoxin of the beta-hemolytic streptococcus, has been shown to have very marked cardiotoxic effects. The data found in the literature suggest that ventricular conducting tissues are severely damaged by this toxin. The purpose of this paper is to study the effects that several concentration of the toxin have on the transmembrane potentials, input resistance and ultrastructure of canine isolate Purkinje fibers. When the preparations were exposed to the toxin, they showed important changes in most of the parameters of the transmembrane potentials. The most important were: a depolarization, a reduction of the amplitude of the action potentials and their upstroke velocities, and a marked shortening of their duration. Input resistance was also markedly decreased. These actions were progressive, until unexcitability was reached. All of the changes observed were irreversible. The ultrastructure of the cells also showed important alterations, mainly at the sarcolemma and mitochondriae. From the results described in this paper, both in terms of the electrophysiological and the morphological effects of streptolysin "O", we can conclude that the cardiotoxic effects of the toxin are due to an effect on the ventricular conducting tissues.

Animals↗
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↗