Educación médica y diversidad cultural en Chile: un diálogo pendiente / Medical education and cultural diversity in Chile: a pending dialogue

Medical education in Chile has a good research productivity. National educators are skilled in complex curricular design processes and in didactic innovation. However, the question of what it means to be doctor in a society that moves towards interculturality, has not been addressed thoroughly. Using the structure of a clinical record, we outline our critical view about the relationship between medical education and diversity. To describe the medical history, we refer to some variables of the training process such as the Hegemonic Model of Medicine, the epistemological beliefs of the students, the hidden curriculum and the educational environment. Then, the empirical evidence of the clinical picture, diagnosis and internationally recommended treatment is described, to end with a local therapeutic proposal.

Intervención para el aprendizaje en clases didácticas prolongadas de asignaturas clínicas / Intervention for learning in lengthened didactic lessons of clinical subjects

Introducción: las clases didácticas o magistrales son utilizadas frecuentemente en educación médica, aunque se sabe que la atención de los estudiantes disminuye progresivamente y la retención de la información es limitada. Las clases interactivas reducen estos inconvenientes, pero su efecto sólo se ha evaluado en clases de una hora o menos de duración y predominantemente en el ciclo básico de medicina. Objetivo: evaluar la intervención implementada para el alcance de un mayor aprendizaje en clases didácticas prolongadas de asignaturas clínicas. Método: la intervención se realizó en un módulo educativo del ciclo clínico de la carrera de medicina de una universidad privada chilena. Participaron 60 estudiantes de 5to año. Las clases de la unidad intervenida se impartieron en 4 h académicas sucesivas de 45 min cada una. Al inicio de cada clase, los estudiantes respondieron un cuestionario con sentencias en formato verdadero o falso referidas a los objetivos centrales de cada temática. Las clases se estructuraron con el método clásico y el estilo docente predominante fue proveedor visual de información. La evaluación se realizó después de 3 meses mediante un test de conocimientos con 40 preguntas de opción múltiple (11 de cardiología). Se incluyó una selección de sentencias de verdadero y falso de aquellas utilizadas durante las clases y una encuesta de satisfacción en formato Likert. Además, se aplicó una escala diferencial semántica para recolectar información sobre las clases de las demás unidades con el propósito de controlar el efecto halo atribuido a preferencias de docentes participantes. Resultados: el promedio de las calificaciones en las preguntas de cardiología del test de conocimientos fue significativamente superior al promedio de las otras unidades de geriatría [t(59)=-28,3; p< 0,001]. El porcentaje promedio de aciertos del post-test fue 45,2 por ciento superior al pretest [t(59)= -24,9; p< 0,001]. La metodología fue bien evaluada: 100 por ciento de estudiantes estimó que mantuvo su atención durante las clases. La apreciación de las clases impartidas por los diferentes docentes del módulo de geriatría fue positiva, sin diferencias entre ellos. Conclusiones: el uso de cuestionarios con sentencias de verdadero y falso, referidas a los objetivos educacionales, antes de cada sesión de clases prolongadas es una estrategia que permite mantener la atención de los estudiantes y favorece el rendimiento cognitivo en asignaturas clínicas del pregrado de Medicina(AU)

Introduction: didactic or master classes are frequently used in medical education, although the students' attention is known to decrease progressively and information retention is limited. Interactive classes reduce these disadvantages, but their effect has only been evaluated in one-hour or less lessons and predominantly during the basic medical cycle. Objective: to evaluate the intervention implemented for attaining greater knowledge in extended didactic classes on clinical subjects. Method: the intervention was carried out in an educational module of the clinical cycle of the medical major of a Chilean private university. Sixty fifth-year students participated. The lessons of the intervened unit were taught in four consecutive academic hours of 45 minutes each. At the beginning of each lesson, the students answered a questionnaire with statements for the true/false format and referring the central objectives of each subject. The lessons were structured with the classical method and the predominant teaching style was visual information provider. The evaluation was carried out after 3 months through a knowledge test with 40 multiple-choice questions (11 about cardiology). It included a selection of true/false statements from those used during the lessons and a satisfaction survey in the Likert format. In addition, a differential semantic scale was applied to collect information about the lessons of the other units with aim at controlling the halo effect attributed to the preferences of participating teachers. Results: the average of the scores in the cardiology questions of the knowledge test was significantly higher than the average of the other geriatric units (t (59)= -28.3, p< 0.001). The average percentage of correct answers in the post-test was 45.2 percent, higher than the pretest (t (59)= -24.9, p< 0.001). The methodology was evaluated well: 100 percent of students considered that they kept their attention during the lessons. The appreciation of the lessons given by the different teachers of the geriatric module was positive, without differences between them. Conclusions: the use of questionnaires with true/false statements and referring the educational objectives, before each session of extended lessons, is a strategy that allows to keep the students' attention and favors the cognitive performance in undergraduate medical-clinical subjects(AU)

¿Cómo han cambiado los estudiantes que ingresan a medicina? Aprendizaje autodirigido y antecedentes académicos de las cohortes 2010 a 2014 de una universidad tradicional / Self-directed learning and academic background of 2010 to 2014 cohorts of medical students

Background: The widespread growth of higher education is increasing the heterogeneity of university students in terms of socioeconomic characteristics, academic story and cultural background. Medical schools are not an exception of this phenomenon. Aim: To compare the academic background and self-directed learning behavior of students who entered to a public medial school between 2010 and 2014. Material and Methods: A non-probabilistic sample of 527 medical students aged between 17 and 29 years (60% men), was studied. Their academic information was collected from the University data base; they answered the Self-directed learning readiness scale of Fisher. Results: Students from the 2014 cohort had higher high school grades than their counterparts. The scores in mathematics of the Scholarship Aptitude Test (SAT) were higher in the cohorts of 2010 and 2011. Those of the sciences test were superior in the 2013 cohort. The 2014 cohort had the lower general score of self-directed learning behaviors. Conclusions: The lower SAT and self-directed learning scores of the students entering medical school in 2014, indicate the progressive increase in the heterogeneity of Medical students.

Prevalencia de síntomas habitualmente asociados a la hipertensión arterial en población normotensa e hipertensa / Prevalence of headache, epistaxis, subconjunctival hemorrhages and dizziness in people with normal or high blood pressure

Background: High blood pressure should be symptomless. However, popular knowledge attributes some symptoms such as headache, epistaxis or dizziness to high blood pressure. Aim: To compare the prevalence of headache, epistaxis, subconjunctival hemorrhages and dizziness in people with normal or high blood pressure. Subjects and methods: A representative sample of an urban population in Chile was studied. Each subject with high blood pressure was paired with a non-related individual of the same sex and age. These subjects were interrogated about the presence of symptoms. Results: One thousand forty eight subjects with high blood pressure (481 male) and 1052 individuals with normal pressure (483 male), were studied. In subjects with high or normal blood pressure, the prevalence of headache was 22 and 21.8 percent respectively, epistaxis was 11.6 and 11 percent respectively, dizziness was 7.4 and 7.6 percent respectively, tinnitus was 9.1 and 9.4 percent respectively and subconjunctival hemorrhage was 2.9 and 3.1 percent respectively (p = NS). Conclusions: No differences in the prevalence of symptoms, popularly attributed to hypertension, were observed between subjects with normal or high blood pressure

Utilización del aprendizaje basado en problemas en la enseñanza de física en estudiantes de medicina: comparación con enseñanza tradicional / Problem based learning in physics: comparison with traditional teaching in medical students

Background: Problem based learning, integrating basic science with clinical problems, is one of the most recommended forms of teaching for medical schools. Aim: To compare a problem based learning program for physics with traditional teaching methods. Material and methods: In the physics course, first year medical students were separated in groups with traditional learning and problem based teaching. Both groups were subjected to the same knowledge and qualitative evaluations. Results: At the end of the course, cognitive performance in both groups was similar (60.8 and 61.3 percent among traditional teaching and problem based learning groups respectively). However, students assigned to the problem based learning group evaluated significantly better the teaching methodology and process. Conclusions: Physics education, using problem based learning, obtains the same cognitive results but a higher degree of satisfaction than traditional teaching among students

Comparación de la eficacia antihipertensiva de monoterapia en dosis crecientes versus terapia asociada en bajas dosis / Comparison of increasing doses of a single drug or combination medications in the treatment of hypertension

Background: When hypertension treatment does not achieve the expected reduction in blood pressure levels, experts recommend increasing the dose of the initially used drug or the addition of a new medication. Aim: To compare the efficacy of increasing doses of losartan or the addition of hydrochlorothiazide to achieve adequate blood pressure levels in patients with hypertension. Patients and methods: Seventy three patients aged 64.4 ñ 5.3 years, with stage 1 or 2 essential hypertension were studied. If after four weeks of treatment with losartan 50 mg od, blood pressure levels were still high, the dose was increased to 100 mg od. After four weeks with this new schedule, the treatment was switched to losartan 50 mg and hydrochlorothiazide 12.5 mg for another four weeks. Results: Thirty seven patients normalized blood pressure with losartan 50 mg od. Of the 36 patients that did not respond, 69 percent achieved a normal blood pressure with losartan 100 mg od and 81 percent did so with the combination of losartan and hydrochlorothiazide. Combination therapy resulted in a better blood pressure lowering than monotherapy (33.2 ñ 3.2 and 29.5 ñ 3.4 mm Hg for systolic blood pressure respectively, 16.4 ñ 3.2 and 13.2 ñ 3.4 mm Hg for diastolic blood pressure, p <0.05). No changes in blood glucose, total and HDL cholesterol, triglycerides, urea nitrogen and uric acid were observed with the combination therapy. Conclusions: In this group of patients, combination therapy achieved better blood pressure levels than monotherapy in high doses

Evaluación del rendimiento educacional mediante la utilización de diferentes opciones metodológicas aplicadas a estudiantes de medicina, en el área de la hipertensión arterial / Assessment of educational performance of different teaching methodologies applied to medical students

Background: Modernization of medical teaching includes the use of new teaching methodologies and among these, computer assisted tutorials. Previous experience has shown that this type of methodology is associated with better student performances. Aim: To assess the cognitive performance of fourth year medical students using different teaching methodologies. Material and methods: During the hypertension course, medical students were allowed to choose to receive a printed booklet (group A), to receive the booklet and attend lectures (group B), to receive the booklet and use a multimedial educational program (group C) and to use all three methodologies (group D). Cognitive performance was evaluated with a multiple choice test scored from 0 to 100. Results: The mean scores obtained by students were 84.5 in group A, 82.4 in group B. 88.9 in group C and 84.4 in group D. This overall score of 83.6 in hypertension was significantly better than the mean score of 72.5 obtained in the cardiology test. Conclusions: Allowing students to choose the most suitable method to learn according to their personal preferences, results in a better cognitive performance

Estudio colaborativo chileno-argentino, para evaluar nifedipina OROS en hipertensos esenciales / Collaborative Chilean-Argentinean study of nifedipine GITS in patients with essential hypertension

Ocho centros chilenos y 5 argentinos evaluaron eficacia, tolerabilidad y seguridad de Nifedipina Oros en 355 hipertensos esenciales durante 8 semanas de tratamiento, previo placebo. 67 por ciento pacientes respondieron a 30, y 33 por ciento a 60 mg/día. El descenso de presión arterial fue 23/15 ñ 0.6/0.3 (ES) mmHg (p < 0,0001). Las variaciones de presión fueron similares en decúbito y de pie,sin causar diferencias en frecuencia cardíaca en ambas posiciones. La relación trough: peak (28:6-8 h) varió entre 0,91-0,95 con dosis inicial o de mantención. Ochenta y cuatro por ciento de hipertensos leves y 93 por ciento de moderados respondieron con decrementos de 10 o más mmHg; 59 por ciento alcanzaron normotensión. No se observaron respuestas significativamente diferentes según edad y terciles de Na urinario nocturno al ingreso. No hubo modificación de parámetros de laboratorio. 29 por ciento de los pacientes presentaron efectos colaterales durante tratamiento activo; en 65 por ciento únicos, en 63 por ciento leves y bien tolerados. Los más frecuentes al final del tratamiento fueron cefaleas (4,7 por ciento) y edema (2,6 por ciento). Once pacientes fueron retirados por efectos que interferían la vida habitual y 4 abandonaron control. Concluimos que Nifedipina GITS posee alta eficacia, similar para distintos grupos etáreos e ingesta de sodio, un efecto mantenido a lo largo de las 24 horas y efectos colaterales mayoritariamente leves y bien tolerados

Evaluación de la aplicabilidad de un programa de educación médica a distancia / Assessment of the feasibility of a distance medical education program

To assess the feasibility of a distance medical education program prepared in a written format, 90 physicians aged 25 to 29 years old and with 1 to 4 years of medical practice, working mostly in rural locations, participed in the program. The sending of 10 ussues with medical topics was programmed. The topics were selected according to the results of an survey done among physicians of the region. Each issue contained an evaluation that had to be returned to the authors. Eigthy two physicians completed the program and 59 returned the evaluations. The mean obtained score in the cognitive evaluation was 80ñ6 points (range 68 to 97 points) of a scale from 0 to 100. The qualitative survey revealed a high degree of approval of the issue's format, contents and evaluation system. The favorable effect on patients' management and on the detection and control of chronic diseases was emphasized. This distance medical education program had a good receipt and compliance among physicians and contributed to continuing medical training

Eficacia clínica y aceptabilidad de ramipril en el tratamiento de la hipertensión arterial esencial etapas 1 y 2: resultados de un estudio multicéntrico / Clinical effectiveness and tolerance of ramipril in the treatment of essential arterial hypertension level 1 and 2: results of a multicentric study

One hundred eighty eight hyoertensive patients, aged 21 to 80 years old, coming from 4 Chilean hospitals were studied. Using an open non controlled design, they were treated with placebo for two weeks and with the active drug during eight weeks, in initial doses of 2.5 mg/day that were adjusted to 5 mg/day in diastolic blood pressure did not drop below 90 mm Hg or if its reduction was less than 10 mm Hg. During the active drug treatment period, systolic blood pressure decreased from 164.8ñ7.2 to 147.3ñ4.8 mm Hg. Diastolic blood pressure dropped from 102.3ñ3.1 to 87.8ñ3.0 mm Hg. Seventy percent of patients achieved a diastolic blood pressure of less than 90 mm Hg, 56.9 percent with 2.5 mg/day and 13.8 percent with 5 mg/day. Dizziness, cough and headache were the main adverse reactions, observed in 3.7, 3.2 and 2.1 percent of patients respectively. Adherence to treatment was 98 percent. There were no changes in laboratory values during the treatment period. Ramipril is effective and well tolerated in the treatment of essential hypertension

Felodipino en el tratamiento de la hipertensión arterial esencial de adultos mayores / Felodipine in the treatment of essential arterial hypertension in elders

Felodipine is a calcium channel inhibitor with high vascular selectivity. To studu the effectiveness of felodipine in the treatment of essential hypertension in subjects older than 64 years old, 50 subjects were studied. After a washout period of 4 weeks, subjects received a placebo for 2 weeks followed by the active drug given in an initial dose of 5 mg/day, adjusted to 10 and 20 mg every 21 days if normal blood pressure levels were not attained. Compared to the placebo period, Felodipine treatment reduced blood pressure from 173ñ7.5/102ñ3.3 mm Hg to 158ñ6.3/91ñ4.4 mm Hg. There was no orthostatic reduction of blood pressure and 87 percent of subjects attained systolic and diastolic pressure levels below 140 and 90 mm Hg respectively. Adverse reactions (edema, cephalea and flushing) were reported by 38 percent of subjects and in 3, the drug was discontinued. There were no changes in laboratory parameters during the treatment period. Quality life improved during treatment in the items of concentration, health status perception, mood, physical condition, depression, effects of hypertension on life evets and initiative. Felodipine is effective in the treatment of elders with essential hypertension

Evaluación de un programa de estudio independiente basado en la computación, aplicado a estudiantes de IV año de medicina / Assessment of an independent study program based in computation, applied to medicine students of IV grade

The aim of this work was to assess an independent study program on hypertension using a computer multimedia program developed by the authors. Twenty-four randomly chosen students participated in the program and 76 students that continued to attend to classical lectures were used as controls. At the end of the program, a cognitive test with 40 multiple choice questions and an opinion questionnaire were applied. The experimental group had higher grades in the test than controls (71,4 and 64,6 percent respectively p<0,001) and a highly favourable opinion of the program. It is concluded that computer teaching programs are useful and feasible alternative to lectures

Estudio controlado del efecto de anticonceptivos orales sobre la presión arterial / Controlled study of oral contraceptive effect over arterial pressure

The possible hypertensive effect of oral contraceptives is a controversial issue. We studied 371 women, admitted to the family planning program of a atate funded outpatient clinic, that were followed during 12 months. These women were divided in 4 groups. Group 1 was constituted by 98 women that used intrauterine devices. Group 2 by 98 women taking 30 µg of estrogen and 300 µg of progestogen. Group 3 by 83 women taking 35 µg of estrogen and 500 µg of progestogen and Group 4 by 92 puerperal women taking 30 µg of levonorgestrel, that after six month started to use an intrauterine device (n=35) or the contraceptives of group 2 (n=38) or group 3 (n=19). Age, initial blood pressure and weight were similar in the 4 groups. There was no significant change in blood pressure after 6 or 12 centrations up to 35 µg and progestogen concentrations between 300 and 500 µg do not induced changes in blood pressure

Resultados de una experiencia educacional basada en problemas aplicada a estudiantes de primer año de medicina / Results of a problem-based learning experience applied to first year medical students

The aim of this work was to study the feasibility of applying problem-based learning methodologies to first year medical students. During 1992, they participated in tutorial gruops composed by ten students, that undertook the study of 3 clinical problems from biological, psychological and social perspective. Cognitive tests that included multiple choice and developmental questions were used for assesment. An anonymous enquiry about the students opinion towards the educational experience was also applied. Students achieved 76 percent of the predetermined goals for each problem. Scoring was better for developmental than multiple choice questions. The experience had a great acceptance among students, that considered as positive features the learning motivation, the stimulus for active participation, the achievement of personal expectancies, the integration of knowledge areas and the encouragement of team work and information seeking

Evaluación ergométrica de pacientes hipertensos tratados con diltiazem de liberación sostenida / Effects of slow release diltiazem in hypertensives: an ergometric evaluation

Ha sido convenientemente demostrado que algunos fármacos antihipertensivos limitan la capacidad de ejercicio mientras que otros son ineficaces la respuesta presora en esa condición. En el presente estudio se evaluó la respuesta al test ergométrico de 30 hipertensos esenciales leves a moderados, mayores de 55 años de edad, físicamente activos y adecuadamente tratados con Diltiazem-90 (D). El D se utilizó en dosis entre 180 y 360 mg. al día, efectuándose pruebas de esfuerzo en cicloergómetro tanto antes como al cabo de 12 semanas de terapia activa. Los promedios de presión sistólica (PS), presión diastólica (PD), frecuencia cardíaca (FC) y doble producto (DP) disminuyeron significativamente en relación al período basal: PS: 188 vs 175 mmHg, p < 0,01; PD: 100 vs 89 mmHg, p < 0,01;: FC: 135 vs 121. p < 0,01 y DP: 27800 vs 19900, p < 0,001, durante el esfuerzo submáximo. Para el nivel de esfuerzo máximo hubo una reducción significativa de PD (106 vs 91 mmHg, p < 0,01, FC (162 vs 153, p < 0,01) y DP (34900 vs 31100, p <0,01). La carga de trabajo tolerada aumentó en 25% (de 90 a 112 Watts) y el promedio del tiempo total de ejercicio aumentó de 278 a 325 segundos. Se concluye que el uso de D en hipertensos leves y moderados permite un significativo incremento de la capacidad de ejercicio y modula favorablemente la respuesta presora al esfuerzo, reduciendo el trabajo miocárdio

La hipertensión arterial en una comunidad urbana de Chile / Prevalence of hypertension in an urban community of Chile

Se comunican los resultados de un estudio epidemiológico sobre prevalencia de hipertensión arterial obtenidos de una muestra urbana, no institucional de 10139 personas mayores de 14 años de edad. Se efectuaron dos registros de presión en la primera visita, separados por no menos de 20 minutos, y un tercer registro en una fecha ulterior en quienes resultaron con cifras elevadas durante la primera visita y que no recibían tratamiento. En ellos se evaluó el posible efecto de fármacos presores y/o de las ingesta alcohólica. Las tasas de prevalencia obtenidas fueron significativamente diferentes para cada oportunidad en que se efectuaron las determinaciones: 25,9%, 22,1% y 18,6% para primer control, segundo control y segunda visita, respectivamente. La diferencia entre las dos últimas tasas fue en gran parte determinada por los factores intercurrentes aun cuando un 20% normalizó sus cifras en ausencia de tales factores. La prevalencia aumenta con la edad en ambos sexos siendo mayor en los hombres bajo los 50 años, relación que se invierte por sobre ese límite. En los adultos es de 18,6% y en los senescentes alcanza al 58,8%. Predominan las formas leves (50,5%) y sistólica límite aislada (17,2%), seguidas de la sistólica aislada (12,3%), moderada (7,5%) y severa (4,8%). Un 34% de los hipertenson desconocía su condición, un 30% no recibía terapia pese a conocer su enfermedad, un 28% recibía terapia insuficiente y sólo el 7,5% estaba normalizado por el tratamiento

Resultados inmediatos y seguimiento a 2 años luego de valvuloplastía percutánea en estenóticos mitrales considerados malos candidatos para comisurotomía quirúrgica / Immediate and late results of mitral balloon valvuloplasty in patients who are poor candidates for surgical valvuloplasty

Los pacientes portadores de Estenosis Mitral (EM) considerados malos candidatos a comisurotomía mitral (CM) generalmente son mayores de 40 años con patología agregada, valvulopatías asociadas, cardiomegalia severa, fibrilación auricular y la válvula está muy engrosada, poco móvil, con o sin calcio y engrosamiento importante del aparato subvalvular. Con el fin de evaluar la valvuloplastía Mitral percutánea (VMP) en este tipo de pacientes analizamos los resultados inmediatos y a 22 ñ 1 meses en 27 pacientes considerados no candidatos a CM por su anatomía valvular desfavorable y patología agregada que contraindicaba la cirugía. 9, (33%) presentaben contraindicación quirúrgica: 2 caquexias severas, 3 cirrosis hepática y 4 falla ventricular derecha refractaria. Después de la VMP el área mitral aumentó de 0,92 ñ 0,17 cm* a 2.03 ñ 0,14 cm* (p < 0,0005), hubo un fracaso técnico, 2 resultados insuficientes y 1 fallecimiento debido al procedimiento. Durante el seguimiento el área ecocardiográfica varió de 1.98 ñ 0,1 cm* a 1,72 ñ 0,1 cm* (p < 0,05), hubo 2 fallecimientos de causa mitral importante. Al final del seguimiento 19 pacientes (70%) mantenían una mejoría sintomática importante, el área mitral en rango de estenosis leve y ninguno estaba en tratamiento anticoagulante. Los 3 pacientes fallecidos (11%) tenían contraindicación quirúrgica. Concluimos que la VMP es útil y razonablemente segura para el tratamiento de las EM con contraindicación quirúrgica o indicación de recambio valvular

Diltiazem de liberación sostenida (diltiazem - 90) en hipertensión arterial esencial leve y moderada / Sustained-released diltiazem (diltiazem-90) in mild to moderate essential hypertension

Por poseer acciones intermedias entre verapamilo y dihidropiridinas, el Diltiazem-90 (D) representa una alternativa como parte del enfoque terapéutico individualizado de pacientes hipertensos. Este estudio se orientó a conocer su eficacia, sus efectos secundarios y el comportamiento de algunos parámetros de laboratorio en hipertensos esenciales leves a moderados, mayores de 55 años, a través de un seguimiento de 12 semanas. Después de 4 semanas de medidas generales se indicó D, 90 mg c/12 hrs en 42 pacientes cuyas presiones diastólicas (PD) persistieron sobre 94 mm Hg, previéndose duplicar la dosis si la PD era mayor de 89 mm Hg al cabo de otras 4 semanas. Por último, se concibió la asociación de 25 mg de hidroclorotiazida (HCT) en caso de no alcanzar ese objetivo en igual período. Los promedios de PD y presión sistólica disminuyeron significativamente con D, tanto en posición sentado como de pie y no se presentó hipotensión ortostática. PD < 90 mm Hg se logró en 23 pacientes (55%) con 90 mg c/12 hrs, en 14 (33%) con 180 mg c/12 hrs y en 5 (12%) con la asociación de HCT. En 7 pacientes (16,8%) hubo efectos secundarios pasajeros y de escasa intensidad. Los exámenes de laboratorio realizados no experimentaron variaciones significativas, incluyeron: glicemia, creatininemia, uricemia, colesterolemia, HDL-colesterol, triglicéridos, orina y electrolitos plasmáticos. El presente estudio comprueba la utilidad clínica del Diltiazem de liberación sostenida en hipertensos leves y moderados mayores de 55 años