Biomedical subjects

M Burguera

Publications and source records attributed to M Burguera.

At least 37 records · Page 2Linked to original sources

PubMed1994

The influence of different electrode configurations on the inhibitory effect of subthreshold high-frequency stimuli.

Subthreshold stimuli trains may inhibit the response to a subsequent suprathreshold stimulus; the inhibitory effect decreases or even disappears when the subthreshold stimuli are delivered apart from the suprathreshold stimulus. The purpose of this study is to analyse, in atrial epicardium, the influence of different electrode configurations upon the inhibitory effect of subthreshold stimuli trains delivered at a short distance from the explored zone. In 18 anaesthetized dogs, the basal atrial effective refractory period was determined using an epicardial unipolar cathodal electrode. A second determination was performed when a subthreshold stimuli train (1 ms cathodal pulses, 800 Hz, and intensity 10% less than the diastolic threshold of the train) was delivered prior to the extrastimulus through: (a) 8 electrodes equidistant (4.5 mm) from the central test electrode (Group 1, n = 5); (b) a 1 mm wide ring electrode, 2.5 mm from the central test electrode (Group 2, n = 7); and (c) a 3.5 mm wide ring electrode, 2.5 mm from the central test electrode (Group 3, n = 6). A third determination was performed in all experiments delivering both the subthreshold stimuli train and the extrastimulus through the same central test electrode. Atrial effective refractory period did not vary significantly with respect to the basal values in Group 1 (141 +/- 22 vs 142 +/- 25 ms; ns) though it increased in Group 2 (168 +/- 27 vs 142 +/- 18 ms; P < 0.01) and in Group 3 (160 +/- 20 vs 133 +/- 25 ms; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Short-coupled variant of torsade de pointes. A new electrocardiographic entity in the spectrum of idiopathic ventricular tachyarrhythmias.

BACKGROUND: Torsade de pointes is characterized not only by its particular ECG pattern but by its context of congenital or acquired long QT syndrome and the long coupling interval of the initial premature beat. METHODS AND RESULTS: We observed 14 patients aged 34.6 +/- 10 years (mean +/- SD) with no structural heart disease who presented with syncope related to a typical ECG aspect of torsade de pointes. However, there was no evidence of long QT syndrome, and the torsade had the unusual particularity of an extremely short coupling interval of the first beat or of the isolated premature beats (245 +/- 28 milliseconds). In 10 cases they deteriorated into ventricular fibrillation. Four patients had a familial history of sudden death. Only 2 patients had a tachyarrhythmia inducible by programmed stimulation. At Holter recordings the heart rate variability was globally and significantly depressed, the vagal limb of the autonomic nervous system being predominantly affected. During a mean follow-up of 7 years there were 5 deaths (4 sudden). Nine patients are alive, 3 with implanted defibrillators and 6 treated with verapamil alone. Unlike the other types of antiarrhythmic agents including beta-blockers and amiodarone, verapamil is in our experience the only drug apparently active on the arrhythmias; however, it does not prevent sudden death. CONCLUSIONS: The short-coupled variant of torsade de pointes should be identified because of their ECG pattern and the risk of sudden death in young adults with no structural heart disease.

Adult↗

PubMed1994

[The spectral analysis of heart rate variability. The methodological aspects].

OBJECTIVES: A study is made of the influence of methodology on the analysis of cardiac cycle variability in terms of frequency and time domains. METHODS: Twenty-five individuals were divided into three groups: 1) non-smokers (n = 10); 2) smokers (n = 8); and 3) non-smokers without guided respiratory frequency (n = 7). An analysis was made of RR variability during 5 min intervals in time domain (standard deviation, variation coefficient, and difference between maximum and minimum RR), and frequency domain (spectral analysis, Fast Fourier Transform algorithm using 5 types of data windows). RESULTS: On comparing the results obtained in the 25 individuals with the 5 data windows, significant differences were observed (ANOVA; p < 0.001) in maximum and total amplitudes of the spectrum (in absolute terms) in the low frequency band (0.04-0.15 Hz). No significant differences were found between the normalized values or between the low/high (0.15-0.40 Hz) frequency ratio: W1 = 1.63 +/- 0.30; W2 = 1.62 +/- 0.29; W3 = 1.65 +/- 0.31; W4 = 1.52 +/- 0.26, and W5 = 1.55 +/- 0.27 (X +/- SE). On averaging the RR intervals each 5 cycles, significant differences were encountered for great part of the parameters studied. No significant differences were encountered for great part of the parameters studied. No significant differences were noted between the non-smokers as regards the use or non-use of a metronome (low/high frequency ratio in group 1 = 1.85 +/- 0.39 vs group 3 = 1.78 +/- 0.43; NS). The linear regressions between the variability parameters in terms of time and frequency domains (absolute values), and age (group 1) were significant, with greater regression coefficients on using the linear transformation of an exponential model. On comparing groups 1 and 2, a non statistically significant trend towards smaller maximum and total amplitudes (absolute values) was noted in group 2 for both frequency bands. CONCLUSIONS: 1) The type of data window (Fourier analysis) introduces significant modifications of some parameters expressed in absolute values, but not between normalized values; 2) signal averaging greatly modifies the information obtained; 3) the decrease in variability parameters observed with age fits better to an exponential model; 4) no differences were detected on guiding or not respiratory frequency, and 5) smoking appears to induce a tendency towards reducing cardiac cycle variability.

Adult↗

PubMed1994

Effects of acute overdose of vitamin A on the hepatic content of K, Na, Mg, Fe, Cu and Zn, in rats.

Interactions among vitamin A metabolism and several metals have been reported in both normal and pathological situations. In the present report we studied, in rats, the effect of daily injections of 100.00 U.I. of vitamin A during seven days on the content of K. Na, Mg, Fe, Cu and Zn in the whole liver. The results were compared with the findings in pair-fed non-treated animals (Control Group). The mean +/- SEM for the concentrations of these elements in the control group were 3.433 +/- 234 (K), 649 +/- 19 (Na), 239 +/- 5 (Mg), 169 +/- 7 (Fe), 5 +/- 0.1 (Cu) and 31 +/- 2 (Zn) ug/g wet tissue, respectively. The hypervitaminosis A, confirmed by a significant increase in tissue concentration of the vitamin, altered the hepatic content of the above mentioned cations. While Na and Zn increased, the other cations decreased its concentrations in the whole liver. Possible mechanisms for these findings are discussed and it is concluded that high doses of vitamin A result in marked changes in the hepatic content of the studied metals.

Acute Disease↗

PubMed1993

Effects of acute and chronic lithium treatment on amphetamine-induced dopamine increase in the nucleus accumbens and prefrontal cortex in rats as studied by microdialysis.

The effects of acute and chronic administration of lithium (Li) on the basal levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxy-indoleacetic acid (5-HIAA), and the amphetamine-induced DA increase were assessed in the Nucleus Accumbens (NAC) and Prefrontal Cortex (PFC) by brain dialysis in freely-moving rats. Acute Li (2 meq/L) was locally administered by reverse dialysis. Chronic Li (2 meq/kg) was intragastrically administered for 14 days. No effect was observed after acute Li administration. However, after chronic Li administration, the basal levels of DOPAC and the amphetamine-induced DA increase in the NAC were significantly higher in the Li-treated rats than in the saline-treated controls. In the PFC, while the amphetamine-induced DA increase was not affected by chronic Li, the basal levels of DA and DOPAC were significantly decreased after Li administration. The effects of chronic Li in the NAC could be due to increased synthesis and/or decreased release of DA, whereas in the PFC the effects could be due to a decreased synthesis of DA. The absence of effects of acute Li administration is in agreement with the therapeutic inefficacy of the acute use of the cation. The changes observed after chronic treatment in the NAC and the PFC could be related to the effects of Li on mood disorders and cognitive functions, respectively.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1993

Changes in the total content of iron, copper, and zinc in serum, heart, liver, spleen, and skeletal muscle tissues of rats infected with Trypanosoma cruzi.

The effects of the Trypanosoma cruzi infection on the total content of the essential trace elements iron (Fe), copper (Cu), and zinc (Zn) in serum, heart, liver, spleen, and skeletal muscle were determined in "Wistar" rats inoculated with reticulotropic "Y" strain trypanosomes (Tryps) in their slender blood form. The 250 rats were divided in two groups of 80 rats (L-1 and L-2) and one of 90 (C) used as controls. L-1 and L-2 were inoculated with 2 x 10(5) and 5 x 10(2) Tryps, respectively. Ten rats of the C group were killed the inoculation day (i), and ten rats of each group chosen at random were killed and blood parasitemia determined at 5, 10, 15, 20, 25, 30, 60, and 90 post-i days covering the infection acute-phase myocarditis. Previously cryohomogenized and lyophilized tissues were digested in an HNO3- H2O2 mixture with the aid of a microwave oven, and the elements Fe, Cu, and Zn were determined by Flame Atomic Absorption Spectrometry. Generally, more intense changes were observed in the L-1 group. Serum Fe and Zn levels are lower and Cu levels higher in groups L-1 and L-2 than in C. However, Fe is not significantly sequestered in the liver during the acute phase of the infection as expected, but of the tissues studied, the spleen was the main site of Fe binding. Zn tended to increase in all tissues, except in the spleen, where during the acute phase of the infection, the total content of Zn in groups L-1 and L-2 was lower than in group C. Cu increased mainly in the spleen and muscle. In general, each tissue presented its own pattern of redistribution related to its nature, functions, and number of parasites inoculated, and these patterns may have been altered by the tropism of the parasite.

Animals↗

PubMed1993

Radiofrequency versus pharmacologic modification of the atrioventricular node.

Although transcatheter radiofrequency modification of the atrioventricular (AV) node has been proposed as curative treatment in AV nodal reentry tachycardias, its role for the control of the ventricular rate in atrial tachyarrhythmias remains unclear. The aim of this study was to analyze the acute effect of radiofrequency current on AV nodal conduction and refractoriness, and to compare it with the effects of two antiarrhythmic drugs such as amiodarone (class III) and flecainide (class I). Twenty-one dogs were studied: (1) radiofrequency group (5 W for less than 45 seconds; 2 to 12 discharges; seven dogs); (2) amiodarone group (5 mg/kg intravenously; seven dogs); and (3) flecainide group (2 mg/kg intravenously; seven dogs). The following parameters were measured under basal conditions and after each procedure: AH interval, AV nodal functional refractory period, Wenckebach cycle length, minimum R-R interval during atrial fibrillation, and fitting of AV nodal function curve to a hyperbolic equation using its linear transformation. The AV nodal effective refractory period could not be calculated in any dog in the basal study because it was shorter than the atrial functional refractory period.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone↗

PubMed1993

[Torsades de pointes with short coupling interval].

The authors describe a ventricular arrhythmia observed in 14 patients between 1972 and 1991, and 9 cases in the literature. The patients were hospitalised for investigations of syncope related to torsades de pointes. They were characterised by the very short coupling interval to the initiating extrasystole (average: 245 ms), by the young age of the patients (average: 34.6 years) and by the absence of overt cardiac disease. The resting electrocardiogrammes were normal, especially ventricular repolarisation. Some recordings showed isolated ventricular extrasystoles with short coupling intervals. Quite often, a family history of sudden death was obtained. These episodes of ventricular arrhythmia may degenerate to ventricular fibrillation. Pharmacological and electrophysiological investigations did not show any consistent characteristic electrophysiological behaviour. Investigations of autonomic nervous system function showed a decrease in global sinus rhythm variability and an increased sympathetic over parasympathetic activity. The clinical outcome of these patients is unpredictable with present methods. From a therapeutic point of view, Class I antiarrhythmics, betablockers and amiodarone were ineffective. Verapamil showed an electrocardiographic improvement by increasing the coupling interval of the extrasystoles and decreasing or even suppressing some repetitive forms, but without preventing recurrences. The indications for an implantable automatic defibrillator should be considered in this group of patients. These patients have clinical and electrocardiographic abnormalities which are sufficiently coherent for them to constitute a new pathological entity which the authors suggest calling "torsades de pointes with a short coupling interval".

Defibrillators, Implantable↗

PubMed1993

[Transcatheter ablation with high-frequency currents as a method for creating useful experimental models in the study of cardiac conduction and automatism].

PURPOSE: analyze the utility of transcatheter ablation with high-frequency currents to create different experimental models of altered cardiac automatism and conduction. METHOD: the results were obtained in six anesthetized dogs subjected to electrophysiological study after selectively applying transcatheter radiofrequency ablation to different zones of the specific cardiac conduction system. Ablation was carried out using conventional bipolar 7F catheter-electrodes. High-frequency currents (0.7 MHz) were emitted through the distal electrode, with variable intensity and duration according to the aim of the experiment. Anatomic (fluoroscopic) and electrophysiological criteria were used to position the electrode within the ablation zone. RESULTS: selective radiofrequency application to the atrioventricular junction zone affords complete A-V blocks with escape rhythms located in the A-V node or His-Purkinje system, together with different degrees of infra- and intra-hisian and intranodal blocks. The modification of intranodal refractoriness and conduction without interrupting atrial pulse transmission may manifest atypical patterns with truncated nodal conduction curves. The abolition of sinus function through ablation in the zone of the sulcus terminalis makes it possible to obtain supraventricular subsidiary rhythms. The obtaining of intranodal complete blocks with supra-Hisian escape rhythms demonstrates phenomena such as the modulation of subsidiary automatism by non-transmitted atrial pulses, analyzed by constructing phase-response curves. CONCLUSION: transcatheter ablation using high-frequency currents is useful in demonstrating phenomena related to intranodal and His-Purkinje conduction, subsidiary pacemaker automatism or the modulation of automatism and conduction via non-transmitted pulses.

Animals↗

PubMed1993

Application of flow injection analysis in trace element determination of body fluids.

The principle of flow injections analysis (FIA) is briefly described, along with some of its advantages for analytical measurements. A review of the development, current status and application of FIA coupled with optical or electrochemical techniques for the determination of various elements in body fluids is presented. Further, the analytical potential of FIA for the determination of elements in biological materials is then summarized and trends in the methodology are given brief consideration.

Adult↗

PubMed1992

Inhibition by trains of subthreshold high-frequency stimuli: an experimental study in spatial limitation.

The aim of this study was to determine whether the spatial limitation of the inhibitory effect of subthreshold conditioning stimuli trains (TSc) could be overcome by their simultaneous emission through several electrodes surrounding the area where the suprathreshold extrastimuli (S2) are delivered. In seven anesthaetized open chest dogs the effective ventricular refractory period was determined before and after the introduction of unipolar cathodal TSc, using epicardial electrodes. TSc pulse frequencies tested were 100 Hz, 200 Hz, 400 Hz, 600 Hz and 800 Hz, and train intensity was 10% lower than the train diastolic threshold for every pulse frequency. S2 and TSc were delivered: (a) by the same electrode; (b) by two different electrodes 3 mm apart; and (c) TSc through six peripheral electrodes surrounding the central electrode that delivered S2 (heptapolar electrode). Trains of 400 Hz showed the highest diastolic threshold, permitting the use of the highest train intensities. When TSc and S2 were delivered through the same electrode the ventricle remained unexcitable during the entire cardiac cycle in six of the seven dogs. In turn, when TSc and S2 were delivered by two different electrodes, the effective ventricular refractory period (EVRP) could only be increased by greater than or equal to 10 ms in three of the seven dogs (18 ms, 62 ms and 10 ms). When TSc was delivered simultaneously through six peripheral electrodes the increments were higher (118 ms, 88 ms and 75 ms) in these three dogs, and there was one additional dog with 12 ms increments of of EVRP.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Observation on a human intentional poisoning case by the organophosphorus insecticide fenthion.

A case of acute poisoning by oral ingestion of fenthion is reported. Plasma cholinesterase activity and fenthion whole blood concentration were thoroughly evaluated during the therapeutic intervention that consisted in administration of atropine, toxogonine and fresh plasma. Correlation studies between clinical signs, cholinesterase activity and fenthion levels revealed that pChE activity was not as helpful as the patient's clinical status in determining when the atropine infusion could be stopped. Moreover pChE was also useless in signaling sudden relapses. It is concluded, based on this case, that supportive care combined with antidotal therapy remains the cornerstone of treatment specially in severe acute poisoning cases.

Adult↗

PubMed1992

Concentration changes of electrolytes in serum of chronic chagasic myocardiopathic patients. Sodium, potassium, chloride, calcium, inorganic phosphorus and magnesium.

Sodium, potassium, chloride, calcium, inorganic phosphorus (Pi) and magnesium contents in the serum of 75 myocardiopathic chagasic patients together with that in 29 healthy controls were determined. Blood samples were taken by catheterization from the superior cava vein (SCV), coronary sinus (CS), pulmonary artery (PA) and a peripheral artery, usually the femoral (FA). The results show that the average serum sodium, potassium, chloride, calcium and PI were invariably different in most samples, except the levels of potassium in SCV and Pi levels in FA. The serum concentration of magnesium was significantly different only in the blood of CS. In general one can observe that in the chagasic patients the serum sodium, chloride and calcium tend to diminish while serum potassium, Pi and magnesium tend to increase, especially in CS blood. The coronary gradient indicates that sodium, chloride and calcium tend to deposit in heart tissues, whereas the other elements (potassium, magnesium and Pi) tend to be released from this tissue. The systemic and peripheric gradients suggest that the chemical elements under study tend either to deposit in/or be released from different tissues depending on the course of development of the chagasic myocardiopathy.

Adult↗

PubMed1991

Mechanism of the sex-dependent effect of lithium on body weight in rats.

Two experiments are reported here. First, the effect of lithium chloride (1, 2 and 4 mEq/kg IP for 21 days) on body weight was assessed in female and male rats. Food intake was measured in the rats treated with 2 mEq/kg. All the doses tested significantly increased body weight in female rats. A linear relationship between body weight gain and lithium dose was also observed. In contrast, in male rats, the low doses of lithium (1 and 2 mEq/kg) did not affect body weight, whereas the high dose (4 mEq/kg) decreased body weight. These results confirm previous reports on a sex-dependent effect of lithium on body weight in rats. In the second experiment, body weight and food intake were assessed in female rats treated with lithium alone, or in combination with insulin or sulpiride, a D2 dopamine receptor blocker. It was found that the effect of lithium on body weight and feeding was additive to the effects of sulpiride and insulin. These findings are indirect evidence that lithium enhances body weight in rats by a different mechanism than the one described for sulpiride or insulin.

Animals↗

PubMed1991

[Hematologic changes in rats treated with high doses of vitamin K3 (menadione)].

The present study describes the effect of high doses of vitamin K3 (8-30 mg/kg) administered daily by intramuscular injection during seven days; on blood smear, red blood cells (RBC) and concentration of hemoglobin (Hb) counts, value of hematocrit (Ht), mean corpuscular hemoglobin concentration (MCHC), reticulocyte and erythroblast counts, total and differential counting of leukocytes (WBC) and total and fractionated serum bilirubin concentration of albino male rats. Results were then compared with findings in normal rats treated with the same doses of sodium bisulfite. In animals treated with vitamin K3 a statistically significant decrease in the number of erythrocytes and in the concentration of Hb, Ht and MCHC was found together with a concomitant increase of erythroblast and reticulocyte counting. In regard to the blood smear, it was observed that erythrocytes vary in their hemoglobin content, size, shape and in their staining properties (polychromatophilia) where as the leukocytes were found to be morphologically normal, but in an increased number. Lymphocytes occasionally showed azurophil granules. Platelets assumed irregular shape and in normal amounts. The leukocytes count showed leukocytosis with marked neutrophilia, eosinophilia, lymphocytosis and monocytosis. Also, the presence of clinical jaundice with an increase of the serum "indirectly-reacting" bilirubin was also observed. These findings indicate that hypervitaminosis K3 induces a marked hemolytic microcytic hypochromic anemia and changes in the white blood cells count. Further studies will be pursued in order to obtain a better understanding of the causes and/or the mechanisms that induce these alterations in the blood cells.

Analysis of Variance↗

PubMed1990

Chronic lithium administration enhances serotonin release in the lateral hypothalamus but not in the hippocampus in rats. A microdialysis study.

Chronic administration of lithium displays therapeutic and prophylactic effects in bipolar affective disorders, but its mechanism of action remains unknown. Several studies in animals and humans strongly suggest that central serotonergic neurons might be involved in lithium effects. In the experiments reported here microdialysis with removable probes and high pressure liquid chromatography and electrochemical detection were used to assess the amphetamine-induced release of serotonin (5-HT) and the 5-hydroxy-indoleacetic acid (5-HIAA) levels in the perifornical hypothalamus (PFH) and hippocampus (HP) of freely moving rats before and after chronic lithium chloride administration (2 meq/kg, as intragastric daily injections for 14 days). The serum lithium levels were 0.66 +/- 0.08 meq/l. After lithium treatment, the amphetamine-induced 5-HT release was significantly enhanced in the PFH but not so in the HP. Basal levels of 5-HIAA in the control group decreased but remained unchanged in the lithium group in the PFH. No change of basal levels of 5-HIAA was observed in the HP. The effect of lithium on the PFH could be related to the improvement of the autonomic and cyclic symptoms of patients with manic depressive disorders undergoing lithium therapy.

Amphetamine↗

PubMed1990

Transcatheter ablation of the sinus node in dogs using high-frequency current.

Sinus node ablation by high-frequency current (HFC) (0.7 MHz. 5-10 W), delivered through the distal electrode of a conventional endocavitary catheter, was induced in seven thoracotomized dogs under autonomic blockade. The HFC was delivered for variable periods of time under ECG monitoring, while sinus tachycardia was produced or after attaining sinus arrest. The procedure was repeated until a stable non-sinus rhythm was obtained. Sinus rhythm was abolished in all seven dogs after a variable number (7-20) of discharges. The escape rhythm obtained after the last discharge, characterized by means of epicardial electrodes and analysis of P-wave morphology, length of PR interval and the rate, showed an atrial activation pattern different from sinus rhythm in all cases. The P-wave was retrograde in two cases, and in one case no atrial activity was detected after the last discharge; however, atrial activity recovered after 35 min, the activation pattern being different from the controls. After 2 h, sinus rhythm had not returned in any case. In no case was there perforation of the atrial wall. Acute histological findings showed coagulation necrosis of the endocardium, extending to the muscle fibres and affecting the sinus cells.

Animals↗

PubMed1990

A comparative study of methods for determining selenium in biological materials.

A comparative study of the analytical performance of fluorimetric spectrophotometric, atomic absorption spectrometric, flow injection analysis with atomic absorption spectrometric, flow injection analysis with atomic absorption spectrometric detection, hydride generation with atomic absorption spectrometric detection and hydride generation with molecular emission cavity analysis detection methods has been carried out for the determination of selenium in biological materials. Based on results concerning detection limit, linearity and sensitivity, only the fluorimetric and hydride generation with atomic absorption spectrometric detection methods were suitable for the determination of selenium in biological materials. Whereas, the spectrophotometric, flame absorption spectrometric flow injection-atomic absorption spectrometric and hydride generation with molecular emission cavity detection, due to its worse detection limits and poorer sensitivities, were found to be unsuitable for the determination of selenium in such matrices. The accuracy of the fluorimetric and hydride generation with atomic absorption spectrometric detection methods were tested by using NBS standard reference materials.

Biological Products↗