Biomedical subjects

M Gámez

Publications and source records attributed to M Gámez.

At least 19 recordsLinked to original sources

PubMed2006

Monitoring in a Lotka-Volterra model.

The problem of monitoring arises when in an ecosystem, in particular in a system of several populations, observing some components, we want to recover the state of the whole system as a function of time. Due to the difficulty to construct exactly this state process, we look for an auxiliary system called an observer. This system reproduces this process with a certain approximation. This means that the solution of the observer tends to that of the original system. An important concept for this work is observability. This means that from the observation it is possible to recover uniquely the state process, however, without determining a constructive method to obtain it. If observability holds for the original system, it guarantees the existence of an auxiliary matrix that makes it possible to construct an observer of the system. The considered system of populations is described by the classical Lotka-Volterra model with one predator and two preys and the construction of its observer is illustrated with a numerical example. Finally, it is shown how the observer can be used for the estimation of the level of an abiotic effect on the population system.

Animals↗

PubMed2005

Equilibrium, observability and controllability in selection-mutation models.

In this paper we shortly discuss the problem of the equilibrium in the well-known Fisher type selection-mutation model, also providing a formula for particular three-allele models. The considered continuous-time dynamics is a known extension of the classical model of natural selection given by Fisher. We also extend the existing investigation of the observability of Fisher's model to the case when another evolutionary factor, mutation is also present. Moreover, we prove a result of technical character, which makes it possible to apply the methodology of nonlinear systems with invariant manifold, to models of artificial selection. For an illustration, a class of three-allele systems is presented in which the controllability into equilibrium is guaranteed without any condition on the biological parameters.

Algorithms↗

PubMed2005

Comparative study between living and cadaveric donors in pediatric liver transplantation.

UNLABELLED: We examined whether the results in living-related hepatic transplantation (LRLT) are better than those from a cadaveric donor (CDLT). MATERIAL AND METHODS: The last 27 consecutive LRLT, performed from 1998 to 2005, were compared with 27 CDLT matched for age, weight, date, and diagnosis. Grafts in LRLT group were left lateral segment (n = 22), left lobe (n = 3), and right lobe (n = 2). In the CDLT group, the grafts were split in situ (n = 10), hepatic reduction (n = 9) and whole liver (n = 8). We analyzed the actuarial survivals (grafts and children), retransplantation, primary nonfunction, initial graft malfunction (liver enzymes >2000 U/L), surgical complications, rejection, and resource consumption. RESULTS: Patient survivals at 6 months, 1 year, and 5 years were 100%, 96%, and 96% in LRLT and 100%, 100%, and 100% in CDLT (P = NS). Graft survivals were 93%, 89%, and 89% versus 96%, 96%, and 96%, respectively (P = NS). Complications were biliary complications (LRLT, 25% vs CDLT, 3%; P = .021); portal vein thrombosis (LRLT, 7% vs CDLT, 3%; NS), and hepatic artery thrombosis (LRLT, 0% vs CDLT, 3%; NS). The overall incidence of acute rejection was slightly higher (NS) in LRLT (LRLT, 18% vs CDLT, 11%; NS). Liver enzyme levels were higher in the CDLT group, but initial malfunction rate was not statistically different. Regarding resource consumption: blood product needs were higher in LRLT (P < .05) and hospital stay and ICU stay were longer, although not significantly, among LRLT. CONCLUSIONS: The results in LRLT among children are similar to those obtained in CDLT. We found a trend towards less initial graft malfunction in LRLT. Blood product needs were higher in LRLT. Hospital and ICU stay were longer, but not significantly different in LRLT. The benefits of LRLT are saving a scarce resource: a cadaveric donor liver graft.

Body Weight↗

PubMed2005

Intestinal transplantation in children: differences between isolated intestinal and composite grafts.

The results of the isolated intestinal grafts were compared with those of composite grafts (intestinal graft + liver) in a series of 18 transplantations performed in 17 children; 5 isolated intestinal grafts, 12 hepatointestinal grafts, and 1 multivisceral graft. Causes of intestinal failure were short bowel syndrome (n = 13), motility disorders (n = 2) and congenital epithelial disorders (n = 2). Transplantation was indicated due to end-stage liver disease (n = 14), loss of venous access (n = 2), untreatable diarrhea (n = 1) and high morbidity associated with a poor quality of life (n = 1). Six children, all with a composite graft, died after transplantation due to lymphoma (n = 2), sepsis (n = 1); intraabdominal bleeding (n = 1); pneumonia (n = 1); and overwhelming adenoviral infection (n = 1). Digestive autonomy was achieved in 16 of 18 grafts, the 11 surviving children are free of parenteral nutrition with a reasonably good quality of life. In conclusion, intestinal transplantation is a viable therapeutic alternative for children with permanent intestinal failure. The results of transplantation with an isolated intestine are clearly better that those with a composite graft.

Adolescent↗

PubMed2004

Observability in dynamic evolutionary models.

In the paper observability problems are considered in basic dynamic evolutionary models for sexual and asexual populations. Observability means that from the (partial) knowledge of certain phenotypic characteristics the whole evolutionary process can be uniquely recovered. Sufficient conditions are given to guarantee observability for both sexual and asexual populations near an evolutionarily stable state.

Animals↗

PubMed2004

[The multifocal hepatic hemangioendothelioma. Is always a benign tumor?].

UNLABELLED: The hepatic multicentric haemangioma is defined by its extension, affecting all the mass of the liver. The high mortality associated with it is mostly related with the complications produced by its enormous size (haemodynamic, platelet trapping, spontaneous rupture and bleeding). There is a general belief that is a benign tumor with possibility of spontaneous regression and cure. AIM: Retrospective analysis of our recent cases of MHH with the purpose of: 1 degrees) To show the evolution and results. 2 degrees) To realize if the "benign character" of the tumor is real or if some cases may be considered as malignant tumors. MATERIAL AND METHODS: 10 cases of MHH treated in the last 10 years. In 9 the age of presentation was less than 6 months and one patient was diagnosed at 3 and half years. The diagnosis was confirmed by image techniques in 7 cases and by biopsy in 3. In 7 patients extrahepatic vascular lesions were associated prior to the treatment. Methylprednisolone was given to all the cases and alpha-2-interferon was administered to the patients that not responded to the steroids. Vincristine was added to 2 patients. In two cases the hepatic artery embolization was tried and one patient had a liver transplant. RESULTS: Four children had at least one episode of congestive cardiac insufficiency, two patients suffered a consumption coagulopathy (Kasabach Merrit syndrome), and one presented acute hepatic failure. In six children it has been complete regression of the tumor, one more is still under treatment and three died. The dead were produced by the malignant behavior of the tumor in one case (tumoral rupture of a MHH recurrence in the transplanted liver), and possibly in other (intracranial haemorrhage and hepatic failure in a liver transplantation candidate without demonstrated extrahepatic extension in the previous studies, but with multiorgan dissemination at autopsy. In both cases it was impossible to discover signs of histologic or biologic malignancy neither in the primitive lesion nor in the metastasis. CONCLUSIONS: 1a) The regression of the MHH, spontaneous or induced by the treatment is frequent. 2a) Some cases of MHH are aggressive and develop local recurrences and distant metastasis. 3a) The discrimination between MHH of "benign" or "malignant" behaviour is not possible. 4a) Despite of the unpredictable biological conduct of the tumor, the liver transplantation must be considered as an option in the symptomatic cases that not respond to the conventional treatment.

Child, Preschool↗

PubMed2004

[Results of an intestinal transplantation program in Spain. Five years later].

BACKGROUND: More than two thirds of all intestinal transplantations (ITx) performed around the world correspondent to recipients younger than 18. OBJECTIVE: To analyze our 5-year experience in pediatric ITx. PATIENTS: We assessed the outcome of the 19 children included in list out of 41 patients considered for ITx from 1997. The main cause of intestinal failure was short bowel syndrome (14) followed by intestinal motility disorders (3) and congenit disorders of intestinal epithelium (CDIE) (2). The median of age, at the moment of including in the list, was 0.9 years (range 0.4-17) and median of weight was 6.4kg (range 0.4-29.3). Ten children were included for liver and small bowel transplantation (LSBTx), 7 to isolated small bowel (SBTx), and 2 for multivisceral transplantation (MVTx). Indications for SBx were hepatic fibrosis/cirrhosis (10), hepatic fibrosis in evolution (5) (to avoid later LSBTx), intractable diarrhoea (1), recurrent line infections (1), lost of central vein access (1), and bad quality of life in one. RESULTS: Five children died in the waiting list, after a median time of 325 days (range 19-581). Seven remain in the waiting list (median 139 days, range 30-778). In 3 of these the indication changed from SBTx to LSBTx because of progression to end stage liver disease. Six children recieved seven grafts (1 MVTx, 4 LSBTx, 2 SBx) after a median time in the waiting list of 352 days (range 66-732). Six out of seven grafts achieved normal function and all survivals reached full digestive autonomy after Tx. We had to rejection episodes, one with good response to medical treatment and one that required removal of intestinal allograft and later LSBTx. Two children died 1 because of problem not related to the procedure (hemorrage following liver biopsy) and one girl died 29 months after transplant due to post-transplantation lymphoproliferative disease. CONCLUSIONS: ITx is a realistic alternative in our country for children with intestinal failure. The main problems are immunologic (rejection, lynphoproliferative and disease) Shortage of small weight donors is a dramatic limitation that prompts the discussion of surgical alternatives.

Adolescent↗

PubMed2003

Pediatric living donor liver transplantation.

AIM: The aim of this study was to analyze the results of living donor in a pediatric liver transplantation program. PATIENTS: Twenty-six living donor liver transplantations were performed in children from 0.5 to 14.8 years of age. The main indication was biliary atresia (72%) followed by tumors (2 hepatoblastomas and 1 hepatocarcinoma). Left lateral segments were used in 23 (1 transformed into a monosegment), 1 left lobe was used in 1, and right lobes were used in 2. Arterial reconstruction employed saphenous venous grafts in the first 3 cases and end-to-end anastomoses with a microsurgical technique in the following 22 cases. RESULTS: There has been no major morbidity in the donors, with a median hospitalization of 6 days. Four grafts have been lost; 2 in the first 3 cases. In only 1 case, the graft loss was related to the procedure saphenous venous graft thrombosis). Early biliary complications were frequent (23%). Six month, 1 year, and 5 year graft and patient survival rates were 91%, 85%, and 85% and 100%, 96%, and 96%, respectively. CONCLUSIONS: Living donor liver transplantation is an excellent option for transplantation in children.

Adolescent↗

PubMed2003

Beneficial effects of HLA class II incompatibility in living donor liver transplantation.

OBJECTIVE: To analyze the impact of HLA matching in both patient and graft evolution after LDLT. MATERIAL AND METHODS: Twenty recipients underwent LDLT with follow-up of 3 to 30 months. HLA typing was performed on all donor-recipient pairs; class I antigens were typed using serological methods and class II loci (DRB1 and DQB1) using low-resolution molecular typing. Recipient sera were cross-matched with donor lymphocytes. Antigen mismatches were analyzed for each locus individually, for each class as a whole and for HLA class I immunogenic triplets according to HLA Matchmaker software. RESULTS: Eighteen of 20 donor-recipient pairs were HLA haploidentical. All but one of the recipients had a negative cross-match before transplantation. While there was not a statistically significant correlation between HLA class I mismatches and the incidence of acute rejection episodes, HLA class II matching in DRB1 and DQB1 loci appeared to be associated with a higher incidence of acute rejection episodes after LDLT. Both host-versus-graft (HvG) and graft-versus-host (GvH) HLA class II compatibilities correlated with rejection episodes, especially for the GvH direction. CONCLUSIONS: HLA class II matching for DRB1 and DQB1 loci appears to be associated with a higher incidence of acute rejection episodes after LDLT. In this study, mismatches in class I HLA antigens are not related to an higher incidence of acute rejection episodes nor other complications after LDLT. Further studies are needed to unveil the role of HLA matching in LDLT.

Adolescent↗

PubMed2003

Pediatric intestinal transplantation.

AIM: Analyze the results of a paediatric intestinal transplantation (IT) program in Spain. PATIENTS: During an 5-year period, 18 children were included as candidates for IT. The causes for intestinal failure (IF) were short bowel syndrome (n=13), motility disorders (n=3), and congenital epithelial disorders (n=2). Nine children were admitted for a combined liver-small bowel transplant (LSBT), seven for an isolated intestinal transplantation (IIT) and two for a multivisceral transplantation (MVT). In three of the candidates for IIT the indication had to be changed to LSBT because of progression of the liver damage. RESULTS: Eight candidates are on the waiting list: four for LSBT, two for IIT, and two for MVT. Four children died before transplantation. All were children under 1 year and candidates for LSBT. One child died during an attempted MVT. Five children underwent transplantation. Grafts were IIT in two and LSBT in three. Of these children, two are on a normal diet (respective follow-up times: 40 and 18 months), two died, both with functioning liver and intestinal grafts (hemorrage after liver biopsy and lymphoproliferative disease), and one developed an untreatable rejection that lead to loss of the intestinal graft; currently, she is on the waiting list for LSBT. CONCLUSIONS: The morbidity and mortality of IT are high, but it is the only possible treatment for children in IF who cannot be adequately managed with parenteral nutrition. A severe problem is the the scarcity of suitable donors for the very low weight children who are candidates for LSBT.

Adolescent↗

PubMed2003

Observability in strategic models of viability selection.

Strategic models of frequency-dependent viability selection, in terms of mathematical systems theory, are considered as a dynamic observation system. Using a general sufficient condition for observability of nonlinear systems with invariant manifold, it is studied whether, observing certain phenotypic characteristics of the population, the development of its genetic state can be recovered, at least near equilibrium.

Biological Evolution↗

PubMed2003

[Activity of a pediatric intestinal transplantation program in Spain].

AIM: To analyze the outcome of children with intestinal failure (IF) included as candidates for intestinal transplantation (IT). Patients, Eight out of 23 children with IF assessed since July 1997 met criteria for IT and were included on the waiting list. The causes of IT were Short Bowel Syndrome (SBS) in 6 and Microvillus Inclusion Disease (MID) in 2. The indication of IT were end stage liver disease (ESLD) in 5 (related to total parenteral nutrition administration, TPN), progressive hepatic fibrosis in 2 and loss of venous access in 1. The patients with ESLD were included for combined liver-small bowel transplantation (LSBT) and the remaining for isolated intestinal transplantation (IIT). RESULTS: Two children died waiting for LSBT, 4 patients are on the waiting list, 2 for LSBT and 2 for IIT (length of stay: 4-11 months). Two children were transplanted, one with IIT in a 2.5 years old boy with MID, and one with LSBT in a 22 months girl with SBS and ESLD. Both patients recovered intestinal function after transplantation and are a live (follow-up of 19 and 10 months respectively). The LSBT's patient is under treatment for postransplant lymphoproliferative disease (PTLD). CONCLUSIONS: The lack of suitable donors for the small children candidate to IT explains the long period of stay on the waiting list and the high pretransplant mortality. Two strategies are possible; early referral of children with IF to a transplant center and surgical techniques like ex vivi-hepatic reductions of the LSB graft.

Child↗

PubMed2003

[Prognostic factors in pediatric liver transplantation. Multivariate analysis].

AIM: To analyze independent risk factors associated with poor graft and patient survival in a series of 292 pediatric liver transplants (PLT) performed in 234 children during a 15 years period. MATERIAL AND METHODS. 1. Univariate graft and patient survival analysis in 45 variables related to pretransplant patient status, surgical technique and donor conditions. 2. Variables found with univariate analysis to be associated with outcome were entered into a stepwise backward proportional hazard model (Cox), to determine independent prediction of outcome. RESULTS: 11 variables influence the graft survival: recipient age, z-score recipient height, UNOS status, recipient and donor weight, transplant for immune hepatitis, platelet transfusion during the transplant, blood index > 4 during the surgery, type of arterial reconstruction, retransplantation and era of the transplant (first er: 1986-1990; 2nd. era: 1991-1995; 3rd. era: 1996-2000). Four of those variables are independent in the multivariate analysis: UNOS 1 status (Odds Ratio, OR = 2.82, 95% confidence interval = 1.36-5.85), recipient < 3 years (OR = 3.76, 95% CI = 2.13-6.63), transplants for autoimmune hepatitis and era (OR of first and second versus third era respectively 3.93 and 2.81). The independent variables influencing the patient survival were: children receiving more than one graft children less than 3 years old and transplant era. CONCLUSIONS: Liver transplant in small children is associated with an increased risk of graft loss and patient dead. The experience of the hospital in pediatric liver transplantation improves the results, particularly in small children.

Adolescent↗

PubMed2002