Scielo RSS <![CDATA[Revista médica de Chile]]> http://www.scielo.cl/rss.php?pid=0034-988720030006&lang=es vol. 131 num. 6 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.cl/img/en/fbpelogp.gif http://www.scielo.cl <![CDATA[Progresión de metaplasia intestinal a adenocarcinoma en esófago de Barrett: utilidad de la vigilancia endoscópica]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600001&lng=es&nrm=iso&tlng=es Background: The potential progression from intestinal metaplasia to low grade dysplasia, to high grade dysplasia and to adenocarcinoma represents a well recognized sequence in patients with Barrett's esophagus (BE). The time required for this transformation is not well known. Aim: To report the results of a 10 years follow up of patients with BE. Material and methods: Between 1989 and 2000 we followed 402 patients with BE. Results: Sixty six subjects (16.2%) presented low grade dysplasia at the time of diagnosis and 10 patients (2 women/8 men) developed adenocarcinoma during the follow-up period. Four out of these 10 patients were operated because of gastro-esophageal reflux disease, but after 3-5 years, reflux symptoms recurred. The other 6 patients rejected surgery and were on Omeprazole with good symptomatic results. Two patients had a short BE (<3 cm), seven cases had a classic BE (3-10 cm) and one patient had an extensive >10 cm BE. The mean time elapsed from intestinal metaplasia to low grade dysplasia was 9 months, to high grade dysplasia 56 months and to adenocarcinoma 82 months. From low grade dysplasia to early cancer it was 18 months, from high grade dysplasia to early cancer 14 months and from high grade dysplasia to advanced transmural cancer 14 months. All patients were subjected to esophagectomy. Five patients detected at State I are alive without any evidence of recurrence after 36 to 130 months after surgery. Five patients with advanced transmural carcinoma subjected to radical esophagectomy died because of progression of the malignancy between 3 and 24 months after surgery. Conclusions: Progression to adenocarcinoma may occur even in absence of reflux symptoms while on acid suppression therapy. Detection at early stage intestinal metaplasia in the esophagus offers a high chance of cure after surgical resection (Rev Méd Chile 2003; 131: 587-96) <![CDATA[Efecto de la administración oral de inulina sobre el perfil de lípidos y la sensibilidad a la insulina en individuos con obesidad y dislipidemia]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600002&lng=es&nrm=iso&tlng=es Background: Inulin is a non absorbable polysaccharide with prebiotic effects, whose influence on blood lipids or insulin sensitivity is not well known. Aim: To assess the effect of oral administration of inulin on lipid profile and insulin sensitivity in dyslipidemic obese subjects. Material and Methods: A clinical trial, double blind, randomized with placebo was carried out in 12 obese, hypertrygliceridemic and hypercholesterolemic subjects between 19 and 32 years old. The subjects were randomized to receive 7 g/day of inulin or placebo in the morning, during 4 weeks. Biochemical and metabolic profiles and euglycemic-hyperinsulinemic clamp technique for assessing insulin sensitivity, before and after pharmacological intervention were performed. Results: After inulin administration, there was a significant reduction of total cholesterol (248.7±30.5 and 194.3±39.8 mg/dL; p=0.028), low density lipoprotein (LDL), cholesterol (136.0±27.8 and 113.0±36.2 mg/dL; p= 0.028), very low density lipoproteins (VLDL) (45.9±18.5 and 31.6±7.2 mg/dL; p=0.046) and trygliceride concentrations (235.5±85.9 and 171.1±37.9 mg/dL; p=0.046). No effect of inulin on insulin sensitivity was observed. Conclusions: The oral inulin administration reduced total cholesterol, LDL cholesterol, VLDL and trygliceride levels in dyslipidemic and obese subjects, without modifications in the insulin sensitivity. (Rev Méd Chile 2003; 131: 597-604) <![CDATA[Efecto del bromuro de ipratropio sobre la hiperinflación pulmonar dinámica en pacientes con enfermedad pulmonar obstructiva crónica]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600003&lng=es&nrm=iso&tlng=es Background: The six minute walk test (6MW) elicits dynamic hyperinflation (DH) in severe COPD patients, which can be evaluated by reductions in inspiratory capacity (IC). Although IC is currently used to determine the effects of bronchodilators on DH during exercise tests on a cycle ergometer, its usefulness during a walking test has not been evaluated. Aim: To study the acute effects of ipratropium bromide (IB) on forced expiratory volume at l second (FEV1) and IC at rest and on DH during exercise assessed by the 6MW. Subjects and methods: Fifteen stable COPD patients were randomly allocated in a double-blind, placebo-controlled, crossover fashion to 2 treatment periods using a single dose of nebulized IB 500 mg or placebo. Spirometry, including IC, and 6MW were measured at baseline and after IB and placebo. IC was also measured 15 min after exercise. Dyspnea, oxygen saturation (SpO2) and heart rate were assessed at the end of exercise. Results: After IB, 8/15 patients exhibited a clinically significant increase in IC (<FONT FACE=Symbol>³1</FONT>0% predicted). A similar increase in FEV1 was observed in only one patient. No changes were observed with placebo. A significant increase in 6MW from baseline (p=0.007) was found after IB (45±14 m) compared to placebo (0.5±9 m), whereas dyspnea was significantly lower. Inspiratory capacity fell after 6MW with both treatments, but it reached their baseline values at 15 min after exercise only with IB. Conclusions: Our results demonstrate that IC provides additional information to conventional spirometry on the acute effects of bronchodilators and confirm its value to assess DH during a walking test (Rev Méd Chile 2003; 131: 605-612) <![CDATA[Determinación de células peroxidasa positivas en líquido seminal: ¿es un parámetro confiable para el diagnóstico de infección genital asintomática?]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600004&lng=es&nrm=iso&tlng=es Background: The presence of leukocytes, detected by peroxidase test in semen, can be a good indicator of infections in the male genital tract. Peroxidase positive cells have been positively correlated with elevated values of elastase, one of the major proteases liberated by granulocytes at the inflammation place. However, seminal granulocytes may not be adequately detected by the peroxidase test in comparison with immunological methods. Aim: To correlate the determination of peroxidase positive cells with the elastase level in the seminal plasma. Material and methods: Seminal plasma from 64 patients with a high number of round cells (>106/ml) in semen, was studied. Correlation analysis was done using the Pearson correlation coefficient. Results: No correlation between the level of granulocyte elastase and the number of peroxidase positive cells (r=0.2237, p >0.05), or even the number of round cells (r=0.03934, p >0.05) was observed. Conclusions: Our results suggest that the determination of peroxidase positive cells is not a reliable indicator of leukocytes in the seminal plasma and their absence do not discard a silent genital tract infection (Rev Méd Chile 2003; 131: 613-616) <![CDATA[Tratamiento endovascular del aneurisma de aorta torácica descendente]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600005&lng=es&nrm=iso&tlng=es Background: The natural history of aneurysms ends in rupture and death. In 1990 the first endovascular exclusion of an aneurysm, using an endoluminal graft implanted through the femoral arteries was performed. More recently, the same procedure has been used for aneurysms of the thoracic aorta. Aim: To report our experience with endovascular treatment of thoracic aorta aneurysms. Material and methods: Analysis of 14 patients (nine male), aged 30 to 79 years, treated between May 2001 and August 2002. Results: The mean diameter of the aneurysms was 6.9 cm. The etiology was atherosclerotic in nine patients. The Excluder device (Gore<FONT FACE=Symbol>â</FONT>) was preferentially used. There was no operative mortality or paraplegia. One patient had a transient leg monoparesis that reverted completely. No patient had type I endoleaks. Two patients had type II endoleaks on discharge, that sealed spontaneously. In a follow up, ranging from 2 to 17 months, one patient died of a bronchopneumonia and no aneurysm rupture has been detected. Conclusions: The short term results of endoluminal treatment of thoracic aorta aneurysms are excellent. This treatment is less invasive and has less complications than conventional surgery (Rev Méd Chile 2003; 131: 617-22) <![CDATA[Comparación farmacocinética de Sinemet<SUP><FONT FACE=Symbol>â</SUP></FONT>y Grifoparkin<SUP><FONT FACE=Symbol>â</SUP></FONT> (levodopa/carbidopa 250/25 mg) en pacientes con enfermedad de Parkinson avanzada: un estudio con dosis única]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600006&lng=es&nrm=iso&tlng=es Background: There are doubts wether generic medications have the same bioavailability and efficacy compared with the original drugs developed by pharmaceutical companies with research capabilities. Aim: To compare the pharmacokinetics and clinical (motor) responses of Sinemet<FONT FACE=Symbol>â</FONT> and Grifoparkin<FONT FACE=Symbol>â</FONT>(generic carbidopa/levodopa 250/25 mg) in patients with advanced Parkinson's disease. Patients and methods: Patients were randomly assigned to Sinemet<FONT FACE=Symbol>â</FONT> (15 patients 62±12 years old; mean disease duration 11±7 years) or Grifoparkin<FONT FACE=Symbol>â</FONT> (15 patients, 64±11 years old; mean disease duration 12±4 years) groups. Medication and food were withheld 12 h before the study. Fifteen blood samples were collected (starting 9 AM) immediately before (sample 1, t=0 min) and after (samples 2-15, t=20-360 min) oral administration of a single dose of Sinemet<FONT FACE=Symbol>â</FONT> or Grifoparkin<FONT FACE=Symbol>â</FONT>, and plasmatic L-DOPA was quantified using HPLC with electrochemical detection. Additionally, each patient was clinically evaluated every 20 minutes, using the tapping test and the unified Parkinson's disease scale Hoehn & Yarh. Results: Tmax (time at which the maximal L-DOPA concentration was reached) were 69±12 min and 64±11 min for Sinemet<FONT FACE=Symbol>â</FONT> and Grifoparkin<FONT FACE=Symbol>â</FONT> respectively (NS). Cmax (maximal L-DOPA concentration reached) was 3161±345 ng/ml for Sinemet<FONT FACE=Symbol>â</FONT> and 3274±520 ng/ml for Grifoparkin<FONT FACE=Symbol>â</FONT> (NS). The t1/2 (half life time), CL (clearance) and volume of distribution (Vd) values calculated were 159±32 min, 51.7±5.1 1/h and 3.6±1.2 l/kg for Sinemet<FONT FACE=Symbol>â</FONT> and 161±48 min, 58.7±8 l/h and 3.0±0.7 l/kg for Grifoparkin<FONT FACE=Symbol>â</FONT> (NS). UPDRS-III value for the best "on state" and for the worst "off state" were 23±11 and 50±19 for Sinemet<FONT FACE=Symbol>â</FONT> and 20±7 and 46±13 for Grifoparkin<FONT FACE=Symbol>â</FONT> respectively (NS). Conclusion: the results obtained showed that both drugs are bioequivalent in patients with advanced Parkinson's disease (Rev Méd Chile 2003; 131: 623-631) <![CDATA[Infección por virus de inmunodeficiencia humana en la embarazada: Importancia del conocimiento de la infección en el embarazo y factores de riesgo en la transmisión perinatal]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600007&lng=es&nrm=iso&tlng=es Background: Using adequate infection control measures, the rate of vertical transmission of human immunodeficiency virus (HIV) during pregnancy, has been reduced to 3% in Chile. Aim: To determine vertical transmission rate and risk factors associated to perinatal infection in pregnant women with known (KI) and unknown HIV infection (UI). Patients and methods: HIV infected pregnant women whose deliveries were attended at the San Borja Arriaran Hospital were included. Antiretroviral therapy (ART) has been used since 1995 (Zidovudine 13 patients, bitherapy 4 and triple therapy 14 patients). Newborns have received ART since 1995. Premature labor without evident cause, premature rupture of membranes, and rupture of membranes over 4 h before delivery were evaluated. Delivery was by elective cesarean section since 1993. Breast feeding was avoided. Pregnant women with UI (suspected disease after delivery due to child or mother pathology) did not received ART. Delivery and breast feeding were managed with common obstetrical-neonatal criteria. Results: Fifty three HIV infected pregnant women were studied (43 with KI and 10 with UI). Four children (36.4%) from the KI group and seven (63.6%) from the UI group became infected. The global rate of vertical transmission among KI group was significantly lower than UI group: 9.5% (4/42) vs 70.0% (7/10) p <0.001. Using ART, this rate was further reduced to 6.5% (2/31) and with bitherapy or triple therapy to 0% (0/18). Breast feeding, vaginal delivery, premature delivery with no clinical cause, premature rupture of membranes, rupture of membranes longer than 4 h and lack of ART, were significantly more common in the UI group, compared with KI group. Conclusions: Vertical transmission in pregnant women with KI is significantly lower compared with UI. Risk factors increasing HIV perinatal infection are: breast feeding, lack of ART, vaginal delivery, premature rupture of membranes, rupture of membranes >4 h and premature labor without a clinical cause (Rev Méd Chile 2003; 131: 633-640) <![CDATA[Análisis epidemiológico de la mortalidad por tumores sólidos en la Región Metropolitana, Chile, 1999]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600008&lng=es&nrm=iso&tlng=es Background: Chronic diseases are the leading cause of mortality in Chile and, among these, tumors are the second most frequent cause of death. The langest number of deaths occur in the Metropolitan Region. Aim: To describe the rates of mortality caused by solid tumors in the Metropolitan Region. Material and methods: Analysis of deaths that occurred in 1999 in the Metropolitan Region. Data from death certificates, gathered by the Ministry of Health, were used. Crude mortality rates and Potential Years of Life Lost (PYLL) caused by solid tumors were calculated. Results: Among men, gastric cancer accounts for the higher rate of mortality, followed by lung cancer. Among women, gallbladder cancer is the most frequent cause of death, followed by breast cancer. Gastric cancer also accounts for the higher amount of PYLL among men, but among women, breast cancer outweighs gallbladder cancer in this parameter. Conclusions: Gastric cancer continues to be an important cause of mortality in Chile and there is a worrysome increase in the mortality caused by gallbladder cancer (Rev Méd Chile 2003; 131: 641-9) <![CDATA[Prevalencia al nacimiento de aberraciones cromosómicas en el Hospital Clínico de la Universidad de Chile: Período 1990-2001]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600009&lng=es&nrm=iso&tlng=es Background: A cytogenetical study should be performed to every newborn with malformations. If a chromosomal aberration is found, parents must be studied to give an adequate genetic advise. Aim: To study the frequency of chromosomal aberrations in newborns with malformations. Patients and methods: In the Clinical Hospital of the University of Chile all malformations in newborns are registered, as part of the Collaborative Latin American Study of Congenital Malformations (ECLAMC). The frequency of chromosomal aberrations, determined by cytogenetical studies, was determined in newborns with malformations. Results: In the study period, there were 32,214 births. Of these, 2,268 live newborns and 43 stillbirths had malformations. Ninety nine children with malformations had chromosomal aberrations (4.3%). Trisomy 21 was the most common aberration with a rate of 23/10,000 births, followed by trisomy 18 with a rate of 4/10,000 and trisomy 18 with a rate of 1.2/10,000. Ninety four percent of these children were born alive and 16.1% died before discharge from the hospital. The masculinity indexes for Down syndrome and for trisomy 18 were 0.38 and 0.61 respectively. Conclusions: A higher frequency of female gender for trisomy 21 and male gender for trisomy 18 has not been reported previously (Rev Méd Chile 2003; 131: 651-658) <![CDATA[Hepatitis isquémica: Caso clínico]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600010&lng=es&nrm=iso&tlng=es Ischemic hepatitis or shock liver is defined as an extensive hepatocellular necrosis associated with a decrease in hepatic perfusion due to systemic hypotension. Serum aminotransferase levels (ALAT and ASAT) increase rapidly after the ischemic episode and peak within 1 to 3 days to at least 20 times the upper normal limit. After recovery, aminotransferases return to near normal levels in 7-10 days of the initial insult. Histological it is characterized by centrolobular necrosis without inflammation. We report a 47 years old woman with a rheumatic mitral valve disease, atrial fibrillation on anticoagulation and congestive heart failure. She was admitted due to a rapid auricular arrhythmia and secondary severe hypotension. She developed rapidly progressive jaundice (bilirubin up to 8.9 mg/dl) and her aminotransferases (ALAT and ASAT) increased rapidly to levels near 100 times the upper normal limit. Other causes of liver disease were excluded. With hemodynamic support and after heart rate control she improved rapidly within the following 10 days with normalization of liver function tests and complete clinical recovery (Rev Méd Chile 2003; 131: 659-64) <![CDATA[Quiste ovárico fetal: diagnóstico ecográfico prenatal. Evolución y tratamiento postnatal. Casos clínicos]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600011&lng=es&nrm=iso&tlng=es Ovarian cysts are found in 32% of necropsies performed to neonates. They can also be diagnosed during gestation by ultrasonography. The clinical evolution of these cysts is variable, but in most cases the prognosis is favorable. Some complications such as ovarian torsion, bleeding, rupture and peritonitis have been described. We report two newborn girls with ovarian cysts, diagnosed during gestation. One required an emergency operation due to vomiting and abdominal distension, interpreted as a possible torsion of the cyst. The second girl was operated at the fourth day of life, finding a left ovarian cyst with torsion of the pedicle. Both girls had a favorable postoperative evolution (Rev Méd Chile 2003; 131: 665-668) <![CDATA[Equidad de género en el acceso a la atención de salud en Chile]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600012&lng=es&nrm=iso&tlng=es Background: In the last two decades, Chile has experienced advances in economical development and global health indicators. However, gender inequities persist in particular related to access to health services and financing of health insurance. Aim: To examine gender inequities in the access to health care in Chile. Material and methods: An analysis of data obtained from a serial national survey applied to assess social policies (CASEN) carried out by the Ministry of Planning. During the survey 45,379 and 48,107 dwellings were interviewed in 1994 and in 1998, respectively. Results: Women use health services 1.5 times more often, their salaries are 30% lower in all socioeconomic strata. Besides, in the private health sector, women pay higher insurance premiums than men. Men of less than two years of age have 2.5 times more preventive consultations than girls. This difference, although of lesser magnitude, is also observed in people over 60 years. Women of high income quintiles and users of private health insurance have a better access to preventive consultations but not to specialized care. Conclusions: An improvement in equitable access of women to health care and financing is recommended. Also, monitoring systems to survey these indicators for women should improve their efficiency (Rev Méd Chile 2003; 131: 669-678) <![CDATA[La Medicina Interna: retos y oportunidades al inicio de un nuevo siglo]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600013&lng=es&nrm=iso&tlng=es Internal medicine was born at the end of the nineteenth century as the result of the great amount of medical knowledge that accrued. The word "internal" has a great meaning and symbolism that underscores a holistic view of the patient. After some years of fruitful work, internal medicine experienced the appearance of subspecialties. This meant a great technological advance but increased the costs of services and deteriorated patient-physician relationship. These tactics along with world sanitary changes, offer a unique opportunity for the resurgence of Internal Medicine. Nowadays the internist has the image of an expert able to treat patients with diseases that involve several organs or systems or to serve as a consultant for complex medical problems. The new threats of the specialty are Family Medicine and hospital physicians. The areas in which the internist should acquire expertise to cope with the new sanitary requirements are also analyzed (Rev Méd Chile 2003; 131: 679-84) <![CDATA[La Sociedad Médica de Santiago y el desarrollo histórico de la Medicina en Chile]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600014&lng=es&nrm=iso&tlng=es Internal medicine was born at the end of the nineteenth century as the result of the great amount of medical knowledge that accrued. The word "internal" has a great meaning and symbolism that underscores a holistic view of the patient. After some years of fruitful work, internal medicine experienced the appearance of subspecialties. This meant a great technological advance but increased the costs of services and deteriorated patient-physician relationship. These tactics along with world sanitary changes, offer a unique opportunity for the resurgence of Internal Medicine. Nowadays the internist has the image of an expert able to treat patients with diseases that involve several organs or systems or to serve as a consultant for complex medical problems. The new threats of the specialty are Family Medicine and hospital physicians. The areas in which the internist should acquire expertise to cope with the new sanitary requirements are also analyzed (Rev Méd Chile 2003; 131: 679-84) <![CDATA[Sobre las acciones médicas proporcionadas y el uso de métodos extraordinarios de tratamiento]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600015&lng=es&nrm=iso&tlng=es As a general rule, any medical action should be proportionated. That is, the expected benefit of the treatment provided must be commensurate to the diagnosis and prognosis, the therapeutic efforts the suffering caused to the patient, and the eventual risks. Inversely a disproportionate or excessive medical action that will result in no benefit to the patient is technically incorrect and ethically reprehensible. As opposed to ordinary methods of treatment (basic nursing, feeding, hydration, drugs and regular clinical procedures), we reserve the name of "extraordinary methods of treatment" to those medical actions using complex and invasive high-cost procedures and equipment that should be urgently indicated in any critically ill patient with a potentially reversible disease. These do not have any indication in terminally ill patients, except in the case of concomitant potentially reversible acute complications. When a DNR (do not resuscitate) order is adopted it should be reassessed periodically. The use, withholding and withdrawal of these extraordinary measures of treatment are subject to a series of medical and ethical requirements, which receive full discussion in this paper (Rev Méd Chile 2003; 131: 685-92) <![CDATA[Hipótesis explícita y su importancia en investigación clínica: Una evidencia empírica]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600016&lng=es&nrm=iso&tlng=es As a general rule, any medical action should be proportionated. That is, the expected benefit of the treatment provided must be commensurate to the diagnosis and prognosis, the therapeutic efforts the suffering caused to the patient, and the eventual risks. Inversely a disproportionate or excessive medical action that will result in no benefit to the patient is technically incorrect and ethically reprehensible. As opposed to ordinary methods of treatment (basic nursing, feeding, hydration, drugs and regular clinical procedures), we reserve the name of "extraordinary methods of treatment" to those medical actions using complex and invasive high-cost procedures and equipment that should be urgently indicated in any critically ill patient with a potentially reversible disease. These do not have any indication in terminally ill patients, except in the case of concomitant potentially reversible acute complications. When a DNR (do not resuscitate) order is adopted it should be reassessed periodically. The use, withholding and withdrawal of these extraordinary measures of treatment are subject to a series of medical and ethical requirements, which receive full discussion in this paper (Rev Méd Chile 2003; 131: 685-92) <![CDATA[Tratamiento del síndrome de piernas inquietas en pacientes urémicos en diálisis con pramipexole: resultados preliminares]]> http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600017&lng=es&nrm=iso&tlng=es As a general rule, any medical action should be proportionated. That is, the expected benefit of the treatment provided must be commensurate to the diagnosis and prognosis, the therapeutic efforts the suffering caused to the patient, and the eventual risks. Inversely a disproportionate or excessive medical action that will result in no benefit to the patient is technically incorrect and ethically reprehensible. As opposed to ordinary methods of treatment (basic nursing, feeding, hydration, drugs and regular clinical procedures), we reserve the name of "extraordinary methods of treatment" to those medical actions using complex and invasive high-cost procedures and equipment that should be urgently indicated in any critically ill patient with a potentially reversible disease. These do not have any indication in terminally ill patients, except in the case of concomitant potentially reversible acute complications. When a DNR (do not resuscitate) order is adopted it should be reassessed periodically. The use, withholding and withdrawal of these extraordinary measures of treatment are subject to a series of medical and ethical requirements, which receive full discussion in this paper (Rev Méd Chile 2003; 131: 685-92) http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0034-98872003000600018&lng=es&nrm=iso&tlng=es