For the explanation of the mechanisms that originate the failure of the soil when it is interacted for a farm tool and the prediction of efforts have been developed more than fifty analytic models, reaching the biggest acceptance those that are based on the theory of the passive pressures of the soil. For such a reason, the present work has as objective to determine the accuracy of four models that are based on the universal equation of the soil movement, during the farming of a Rhodic Ferralsol of the occident of Cuba. Was determined experimentally the resistance of the soil during the tillage under controlled conditions in the channel of soils CS-CEMA-25, and were programmed the sequences of calculation of the models Godwin & Spoor, McKyes & Ali,; Grisso et al., in the software Mathcad 15. The main results showed the limitations of these models to predict with accuracy the efforts that arise during the farming in highly cohesive soils, as well as for tools that differ of the geometry for those which originally were developed. It was also demonstrated that a high correlation (r=0.90 to 0.98) exists among the predicted values for these models, evidencing the likeness in the theoretical approaches that base them. On the other hand was observed that the speed of advance of the working tool has very little incidence in the accuracy of the predictions of the investigated models.

Para la explicación de los mecanismos que originan la falla del suelo cuando es interactuado por una herramienta de labranza y la predicción de esfuerzos, se han desarrollado más de cincuenta modelos analíticos, alcanzando la mayor aceptación los que se basan en la teoría de las presiones pasivas del suelo. Por tal motivo, el presente trabajo tiene como objetivo determinar la exactitud de cuatro modelos que se basan en la ecuación universal del movimiento de tierra, durante la labranza de un Rhodic Ferralsol del occidente de Cuba. Para lo cual se determinó experimentalmente la resistencia del suelo durante la labranza en las condiciones controladas del canal de suelos CS-CEMA-25, y se programaron las secuencias de cálculo de los modelos Godwin & Spoor; McKyes & Ali; Grisso et al, en el software Mathcad 15. Los principales resultados mostraron las limitaciones de estos modelos para predecir con exactitud los esfuerzos que surgen durante la labranza en suelos altamente cohesivos, así como para herramientas que difieran de la geometría para los cuales originalmente fueron desarrollados. Se demostró además que existe una alta correlación (r=0,90 a 0,98) entre los valores predichos por estos modelos, evidenciando la semejanza en los criterios teóricos que los fundamentan. Por otra parte observó que la velocidad de avance del órgano de trabajo tiene muy poca incidencia en la exactitud de las predicciones de los modelos investigados.

INTRODUCTION Acute liver failure is rare in pediatric patients and is one of the most challenging medical emergencies due to its prognostic and therapeutic implications. The best scientific evidence worldwide comes from multicenter studies in developed countries. In Cuba, there are no prior studies of this disorder in children. OBJECTIVES Describe the main clinical features of Cuban children treated at a national referral center for acute liver failure, as defined by recognized diagnostic criteria for pediatric patients. METHODS A case series study was conducted comprising patients diagnosed with acute liver failure treated from 2005 to 2011 in the hepatology and liver transplant service at Havana’s William Soler University Children’s Hospital. Variables were age group, etiology of acute liver failure, grade of hepatic encephalopathy, blood chemistry variables, and clinical outcome (whether or not spontaneous recovery of liver function occurred). Associations between variables were assessed using contingency tables, and case fatality was calculated, as well as relative risk with its 95% confidence interval. The Mann-Whitney U test was used to compare means of laboratory test results. RESULTS Median age of the 31 patients studied (14 boys and 17 girls) was 24 months (range 1–180). Time between symptom onset and diagnosis of acute liver failure was 25.1 days (SD 16.8). Infection was the most common etiology, present in 61.3% of cases (19/31); nonhepatotropic viruses, especially cytomegalovirus, predominated in infants. Spontaneous recovery occurred in 15 patients (48.4%), 3 (9.7%) received transplants, and 13 died, for a case fatality of 41.9%. Outcome was not associated with etiology (p = 0.106), but was statistically associated with degree of hepatic encephalopathy (p <0.01): 77.8% of patients (7/9) with grades III-IV encephalopathy died, for a relative risk of 4.0 (95% CI 1.15–13.8), versus 11.1% (1/9) with grade II or less encephalopathy. Cholesterol levels were significantly lower in patients who failed to recover spontaneously (p <0.01). CONCLUSIONS Patients’ clinical characteristics in this case series were similar to those described in developed countries.The fact that nonhepatotropic viruses (basically, cytomegalovirus in infants) are the main cause of acute liver failure in Cuban children calls for further epidemiologic study and identification of local underlying determinants of this phenomenon.

Colonoscopy is a useful method to study colon diseases, therefore, a descriptive and retrospective study was conducted so as to define the most frequent colonoscopic diagnoses in 267 patients under 16, 142 males and 125 females, who underwent colonoscopy at "William Soler" Pediatric Teaching Hospital between January, 1987, and December, 1996, due mainly to hematochezia (80.9 %). Colonoscopy proved to be normal in 86 children and the colonic diseases most commonly found were polyps (27.6 %), unspecific colitis (21.8 %) and benign lymphoid hyperplasia (15.7 %), which was observed in a higher number of children under 6. The polyps and the unspecific colitis appeared in a similar way in both sexes. Men were more affected by lymphoid hyperplasia than women. A sample was taken from 11 children with ulcerative idiopathic colitis and from 47 with unspecific colitis for histological examination. It was reported a high colonoscopy-histology diagnostic concordance, 72.2 and 83.0, respectively (p<0.001).

La colonoscopia resulta un valioso método para el estudio de las enfermedades del colon, por lo que se realizó un trabajo descriptivo, retrospectivo con el objetivo de definir los diagnósticos colonoscópicos más frecuentes en 267 pacientes menores de 16 años, 142 del sexo masculino y 125 del femenino, a los cuales se les realizó colonoscopia en el Hospital Pediátrico Docente «William Soler», entre los meses de enero de 1987 a diciembre de 1996, por presentar fundamentalmente hematoquecia (80,9 %). La colonoscopia resultó normal en 86 niños y las enfermedades colónicas halladas con mayor frecuencia fueron los pólipos (27,6 %), la colitis inespecífica (21,8 %) y la hiperplasia linfoide benigna (15,7 %), y se encontraron éstas en proporción mayor en los menores de 6 años; los pólipos y la colitis inespecífica se presentaron en forma similar en uno y otro sexos, y se observó la hiperplasia linfoide en un tanto por ciento mayor en varones. Se tomó muestra para examen histológico a los 11 niños con colitis ulcerativa idiopática y a 47 con colitis inespecífica, y se apreció una alta concordancia diagnóstica colonoscopia-histología, 72,2 y 83,0 % respectivamente (p < 0,001).