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Biomedical subjects

B Vargas

Publications and source records attributed to B Vargas.

13 recordsLinked to original sources
PubMed2006

Correlation between the radiologic and histologic size of hepatocellular carcinoma in patients eligible for liver transplantation.

Hepatocellular carcinoma is the most prevalent primary hepatic tumor. Early diagnosis and staging is of paramount importance to obtain favorable survivals. So far, there is no general agreement on the most appropriate imaging technique to detect the tumor for correlation between pretransplant radiologic and pathologic size of the tumor, which remains inadequate. With greater clinical experience and increasing accuracy of imaging methods, magnetic resonance (MR) appears to be the most accurate method, yielding a correlation in 67% of cases.

Carcinoma, Hepatocellular↗
PubMed2005

Effect of neosporosis on productive and reproductive performance of dairy cattle in Costa Rica.

A cross-sectional study was conducted to assess the effect of neosporosis on productive and reproductive parameters in dairy cows. Cows (n=2743) from 94 farms located in the most important dairy areas in Costa Rica were used in the study. The size of the herds ranged from 32 to 379 females (mean=110, median=125). An indirect ELISA was used to determine the serostatus of the cows towards Neospora caninum. The effect of neosporosis on milk production was analysed by a mixed linear model. In addition, the effects on calving interval (days) and calving to conception interval (days) were analysed by survival analysis. The risk of abortion in relation to N. caninum serostatus was assessed by logistic regression, with herd as a random effect. Overall, 1185 of 2743 cows (43.3%) were seropositive for Neospora. Eighty-nine of 94 (94.7%) farms were classified as Neospora-seropositive. It was estimated that cows seronegative to Neospora produced an additional 84.7L of milk (P=0.6). Serostatus did not have a significant effect on the length of the calving interval in the Cox proportional hazard survival analysis (Hazard ratio=1.2, 95% CI: 0.9, 1.4). The logistic regression model had a weak positive association between serostatus and abortion (OR 1.7, 95% CI: 0.8, 3.9), but did not show a strong association between serostatus and the number of services per conception (OR=0.95, 95% CI: 0.7, 1.3). In conclusion, there were no significant effects of Neospora serostatus on production and reproductive performance in this study.

Animals↗
PubMed2004

Genetic comparison of breeding schemes based on semen importation and local breeding schemes: framework and application to Costa Rica.

Local breeding schemes for Holstein cattle of Costa Rica were compared with the current practice based on continuous semen importation (SI) by deterministic simulation. Comparison was made on the basis of genetic response and correlation between breeding goals. A local breeding goal was defined on the basis of prevailing production circumstances and compared against a typical breeding goal for an exporting country. Differences in genetic response were <3%, and the correlation between breeding goals was 0.99. Therefore, difference between breeding objectives proved negligible. For the evaluation of genetic response, the current scheme based on SI was evaluated against a progeny testing (PT) scheme and a closed nucleus (CN) breeding scheme, both local. Selection intensities and accuracy of selection were defined according to current population size and reproduction efficiency parameters. When genotype x environment interaction (G x E) was ignored, SI was the strategy with the highest genetic response: 5.0% above the CN breeding scheme and 33.2% above PT. A correlation between breeding values in both countries lower than one was assumed to assess the effect of G x E. This resulted in permanent effects on the relative efficiencies of breeding strategies because of the reduction in the rate of genetic response when SI was used. When the genetic correlation was assumed equal to 0.75, the genetic response achieved with SI was reduced at the same level as local PT. When an initial difference in average genetic merit of the populations was assumed, this only had a temporal effect on the relative ranking of strategies, which is reverted after some years of selection because the rate of change in genetic responses remains unchanged. Given that the actual levels of genetic correlation between countries may be around 0.60, it was concluded that a local breeding scheme based on a nucleus herd could provide better results than the current strategy based on SI.

Animals↗
PubMed2000

Modeling extended lactations of dairy cows.

Nine mathematical models were compared for their ability to predict daily milk yields (n = 294,986) in standard 305-d and extended lactations of dairy cows of Costa Rica. Lactations were classified by parity (first and later), lactation length (9 to 10, 11 to 12, 13 to 14, 15 to 16, and 16 to 17 mo), and calving to conception interval (1 to 2, 3 to 4, 5 to 6, 7 to 8, and 9 to 10 mo). Of the nine models, the diphasic model and lactation persistency model resulted in the best goodness of fit as measured by adjusted coefficient of determination, residual standard deviation, and Durbin-Watson coefficient. All other models showed less accuracy and positively correlated residuals. In extended lactations, models were also fitted using only test-day records before 305 d, which resulted in a different ranking. The diphasic model showed the best prediction of milk yield in standard and extended lactations. We concluded that the diphasic model provided accurate estimates of milk yield for standard and extended lactations. Interpretation of parameters deserves further attention because of the large variation observed. As expected, the calving to conception interval was found to have a negative effect on milk yield for cows with a standard lactation length. In extended lactations, these negative effects of pregnancy on milk yield were not observed.

Animals↗
PubMed1998

Analysis of test day yield data of Costa Rican dairy cattle.

Estimates of variance components for test day records in an animal model that considered multiple traits over multiple lactations were calculated using REML methodology. Test day records were classified into 11 periods within first and later lactations. Missing ancestors in the relationship matrix were classified in genetic groups. Data were collected from Costa Rican dairy farms. Estimates of components for total and additive genetic variance were clearly heterogeneous during the lactation. Heritabilities for traits in later parities were slightly higher than those for traits in first parity. Heritabilities were highest for records of midlactation. Phenotypic and genetic correlations for adjacent test days were close to 1. Phenotypic correlations were lower than genetic correlations. Heterogeneity of variances during the lactation suggests the adequacy of the multiple-trait test day model to describe milk yield during the lactation. When missing ancestors were allocated to a single base population instead of genetic groups, the estimates of residual variance were lower, and the estimates of genetic variance and genetic correlations were higher. When standardized records were used instead of actual test day records, the estimates of residual and total variance were lower, and the estimates of genetic variance were higher. Consequently, estimates of heritability and genetic correlations were also higher. Use of standardized data obtained by interpolation procedures is not advised for estimation of genetic variance components in a test day model.

Animals↗
PubMed1998

Event-time analysis of reproductive traits of dairy heifers.

Data on the reproductive traits of dairy heifers were analyzed using event-time techniques. Traits analyzed were age at first calving (n = 4631), days to first breeding, and days open (n = 1992) during the first lactation. A proportional hazard model was used that included fixed effects of herd-year, year-season, breed type, herd weight, and heifer weight. Body weights were recorded at 390 d of age, on average. The model for days open and days to first breeding included two additional fixed effects of herd and heifer milk yield at 100 d. A significant effect of heifer weight category on age at first calving was found. The chance of calving was consistently higher for herds and heifers with higher body weight at 390 d and decreased linearly from the top to the lowest quartiles. The effects of herd weight category on days to first breeding and days open were significant. Heifers in herds with a higher average body weight were less likely to be bred, and heifers in herds with lower average body weight were less likely to get pregnant. The effect of heifer weight category on days to first breeding or days open was not significant. The effect of herd milk yield on days to first breeding was significant. Heifers in herds with lower yield were more likely to be bred. The effect of heifer milk yield category on days to first breeding and days open was significant, but no linear trend was found for the estimates of the hazard ratios. The chance of a heifer being bred and becoming pregnant was similar among the first three quartiles and was lower for heifers in the lowest quartile. The probability of a heifer reaching a first calving can be improved by increasing the body weight at 390 d. Body weight at 390 d did not appear to have a large effect on reproductive performance after first calving. High milk yield appears not to have a large negative effect on days open, at least for the milk yield levels analyzed in this study.

Aging↗
PubMed1997

[Malformations of Wolffian duct derived male genital organs (epididymis, vas deferens, seminal vesicules, ejaculatory ducts)].

OBJECTIVES: To analyse embryological phenomena, in order to define a practical approach to management. METHODS: The authors reviewed the files of eight boys with an abnormality of Wolffian duct derived genital organs, consisting of three cases of vas deferens agenesis, two of which were accompanied by homolateral renal agenesis, one case of ectopic vas deferens with contralateral renal agenesis, three cases of duplicated vas deferens and one congenital seminal vesicle cyst with renal agenesis. DISCUSSION: Congenital malformations of the epididymis consist of cysts and agenesis or partial atresia. Cysts essentially raise a problem of differential diagnosis. Treatment is only required in the case of severe discomfort. Vas deferens agenesis is the commonest lesion, an incidental finding in children. An experimental treatment is proposed in adults. Duplications, interdeferential communications and deferentomegaly are much rarer lesions. Seminal vesicle cysts are well visualized by transrectal ultrasonography and should be treated surgically. Lastly, ejaculatory ducts may present urethroseminal reflux or may be ectopic. CONCLUSION: The possibility of absent or ectopic vas deferens should be considered in the case of unilateral renal agenesis. Vas deferens agenesis justifies examination of the contralateral side and investigation to exclude renal agenesis. Congenital cysts of the epididymis only require surgery when they are symptomatic. The presence of ipsilateral renal agenesis should be investigated in the case of cystic dilatation of the seminal vesicle.

Adolescent↗
PubMed1987

Stones in the urinary bladder in children and young adults.

Bladder stones were diagnosed in 22 children and young adults at The Children's Hospital, Boston, from 1969 to 1985. One half of the patients were less than 12 years old (mean, 11.9 years). One or more lithogenic factors were implicated in all but two. The most common causes were the presence of an intravesical foreign body, infection with Proteus (a urea-splitting organism), exstrophy of the bladder, and the presence of intestinal mucosa in the urinary tract. The radiologic features of the stones were not specific, and no special techniques were needed to identify them. Heightened awareness of patients at risk will lead to prompt diagnosis and treatment.

Adult↗
PubMed1986

The coexistence of congenital megacalyces and primary megaureter.

Congenital megacalyces is a rare developmental condition of the kidney consisting of hypoplasia of the medullary pyramids and dilatation of the calyces. There is no obstruction. Primary megaureter is a form of obstructive uropathy in which there is an obstructing juxtavesical segment of ureter that is normal in caliber but that is aperistaltic. These conditions were found to occur simultaneously in the same patient six times during the past 10 years. Recognition of this rare coexistence is important so that unnecessary surgery can be avoided.

Abnormalities, Multiple↗