Biomedical subjects

Daniel Campos

Publications and source records attributed to Daniel Campos.

12 recordsLinked to original sources

PubMed2005

Variational principles and the shift in the front speed due to a cutoff.

We apply variational principles to reaction-diffusion equations in order to predict, for a general reaction term, the sign of the shift in the front speed due to a cutoff. We develop an improved variational principle to obtain the shift in the front speed for a wide range of reaction terms, and the theoretical results so obtained are in excellent agreement with numerical solutions. This work proves that variational principles are an optimal framework to deal with fronts propagating into unstable and metastable states under cutoff.

Journal Article↗

PubMed2005

Transport on fractal river networks: application to migration fronts.

A quantitative model of the US colonization in the 19th century is presented. We explore the idea that landscape heterogeneities should have strongly affected this process, as the need for water made the colonizers follow the routes of main rivers and set up their towns near them. So, we study transport processes on fractal networks modeling river basins, a case which may have a great ecological relevance for the study of hydrochory, and in general for species which spread along corridors. The analytical reaction-diffusion model presented here allows to predict the propagation rate of fronts spreading through Peano-like basins, and comparison with the Optimal Channels Network model is also reported. Finally, the propagation rates observed are compared with the results from our model, concluding that migration through fractal media, in spite of being a mathematical idealization of the problem, mimics the dynamics of real systems reasonably well.

Emigration and Immigration↗

PubMed2005

Erlotinib in previously treated non-small-cell lung cancer.

BACKGROUND: We conducted a randomized, placebo-controlled, double-blind trial to determine whether the epidermal growth factor receptor inhibitor erlotinib prolongs survival in non-small-cell lung cancer after the failure of first-line or second-line chemotherapy. METHODS: Patients with stage IIIB or IV non-small-cell lung cancer, with performance status from 0 to 3, were eligible if they had received one or two prior chemotherapy regimens. The patients were stratified according to center, performance status, response to prior chemotherapy, number of prior regimens, and prior platinum-based therapy and were randomly assigned in a 2:1 ratio to receive oral erlotinib, at a dose of 150 mg daily, or placebo. RESULTS: The median age of the 731 patients who underwent randomization was 61.4 years; 49 percent had received two prior chemotherapy regimens, and 93 percent had received platinum-based chemotherapy. The response rate was 8.9 percent in the erlotinib group and less than 1 percent in the placebo group (P<0.001); the median duration of the response was 7.9 months and 3.7 months, respectively. Progression-free survival was 2.2 months and 1.8 months, respectively (hazard ratio, 0.61, adjusted for stratification categories; P<0.001). Overall survival was 6.7 months and 4.7 months, respectively (hazard ratio, 0.70; P<0.001), in favor of erlotinib. Five percent of patients discontinued erlotinib because of toxic effects. CONCLUSIONS: Erlotinib can prolong survival in patients with non-small-cell lung cancer after first-line or second-line chemotherapy.

Adult↗

PubMed2005

Reaction-diffusion wave fronts on comblike structures.

From the Hamilton-Jacobi formalism, an explicit expression for the speed of wave front propagation along the backbone of comblike structures is obtained. This expression, through the waiting-time distribution function, takes into account the number of sites and their distribution in the secondary branches. Our theoretical results are supported by numerical simulations of the reaction random-walk process on the structure. Finally, a more complex situation such as the Peano basin structure is also considered, both theoretically and numerically, exhibiting a good agreement too.

Journal Article↗

PubMed2005

Gallbladder pathology in morbid obesity.

BACKGROUND: Obese patients are at increased risk for biliary disease. The prevalence and type of gallbladder pathology in morbidly obese patients was evaluated, and compared with a non-obese control group. METHODS: A consecutive series of obese patients (n=478) who had undergone bariatric surgery with concurrent routine cholecystectomy and a consecutive group of organ donors (n=481) were compared. Gallbladder pathology was defined as: cholelithiasis, cholecystitis, cholesterolosis, or normal pathology. RESULTS: Mean age of obese patients and of donors was 42 +/- 9 and 43 +/- 17 years respectively and mean BMI was 52 +/- 10 and 27 +/- 7 kg/m2 respectively, P<0.05. There were more females in the obesity group (88% vs 47%, P<0.0001). 31% of obese patients and 7% of controls had a previous cholecystectomy (P<0.0001). 21% of the obese and 72% of the controls had normal gallbladder pathology (P<0.0001). Overall, obese patients had a higher incidence of cholelithiasis (25% vs 5%, P<0.0001), cholecystitis (50% vs 17%, P<0.0001), and cholesterolosis (38% vs 6%, P<0.0001) compared with controls. Obese patients with BMI <50 were more likely than those with BMI > or =50 to have normal gallbladder pathology (27% vs 14%, P<0.001). Female patients were more likely to have undergone previous cholecystectomy than males in both the obese group (34% vs 11%, P<0.001) and the control group (12% vs 2%, P<0.0001). Normal pathology was more common in male patients (80% vs 63%, P<0.0001) and patients <50 years (76% vs 66%, P<0.05) in the control group. CONCLUSIONS: Obese patients have an increased incidence of benign gallbladder disease than a group of controls, and the relative risk appears to be positively correlated with the level of increase in the BMI. Obesity appears to change the effect of age and gender on gallbladder pathology.

Adolescent↗

PubMed2004

Analysis of fronts in reaction-dispersal processes.

The existence of traveling wave front solutions with a minimum speed selected for reaction-dispersal processes is studied. We obtain a general existence condition in terms of the waiting time and dispersal distance probability distribution functions and we detail this result for situations of ecological interest. In particular, when particles disperse according to jumps of short length and any waiting time probability distribution function, we show that the minimum speed selection for traveling wave fronts is not always possible, so the waiting time and the dispersal distance distributions cannot be arbitrarily chosen.

Journal Article↗

PubMed2004

Front propagation in reaction-dispersal models with finite jump speed.

The continuous-time random walk and the Hamilton-Jacobi method are used to reach analytical expressions for the speed of traveling fronts in reaction-dispersal models. In this work the waiting time and jump length are assumed to be coupled random variables. The jump length for any jump is selected according to the waiting time at the end of the previous jump, and in consequence jumps of finite speed are performed. We study the effect of finite jump speed of the particles on the speed of the traveling fronts and find that in the parabolic and hyperbolic limits it can exceed the jump speed of the particles. We report analytical expressions for different probability distribution functions. Finally, we introduce the possibility that several particle speeds are allowed, so different dispersal mechanisms can be considered simultaneously.

Journal Article↗

PubMed2004

Description of diffusive and propagative behavior on fractals.

The known properties of diffusion on fractals are reviewed in order to give a general outlook of these dynamic processes. After that, we propose a description developed in the context of the intrinsic metric of fractals, which leads us to a differential equation able to describe diffusion in real fractals in the asymptotic regime. We show that our approach has a stronger physical justification than previous works on this field. The most important result we present is the introduction of a dependence on time and space for the conductivity in fractals, which is deduced by scaling arguments and supported by computer simulations. Finally, the diffusion equation is used to introduce the possibility of reaction-diffusion processes on fractals and analyze their properties. Specifically, an analytic expression for the speed of the corresponding travelling fronts, which can be of great interest for application purposes, is derived.

Journal Article↗

PubMed2004

Approximate solution to the speed of spreading viruses.

Recently, it has been shown that the speed of virus infections can be explained by time-delayed reaction-diffusion [J. Fort and V. Méndez, Phys. Rev. Lett. 89, 178101 (2002)], but no analytical solutions were found. Here we derive formulas for the front speed, valid in appropriate limits. We also integrate numerically the evolution equations of the system. There is good agreement with both numerical and experimental speeds.

Bacteria↗

PubMed2004

Dynamical features of reaction-diffusion fronts in fractals.

The speed of front propagation in fractals is studied by using (i) the reduction of the reaction-transport equation into a Hamilton-Jacobi equation and (ii) the local-equilibrium approach. Different equations proposed for describing transport in fractal media, together with logistic reaction kinetics, are considered. Finally, we analyze the main features of wave fronts resulting from this dynamic process, i.e., why they are accelerated and what is the exact form of this acceleration.

Journal Article↗

PubMed2003

Docetaxel and doxorubicin compared with doxorubicin and cyclophosphamide as first-line chemotherapy for metastatic breast cancer: results of a randomized, multicenter, phase III trial.

PURPOSE: This randomized, multicenter, phase III study compared doxorubicin and docetaxel (AT) with doxorubicin and cyclophosphamide (AC) as first-line chemotherapy (CT) in metastatic breast cancer (MBC). PATIENTS AND METHODS: Patients (n = 429) were randomly assigned to receive doxorubicin 50 mg/m(2) plus docetaxel 75 mg/m(2) (n = 214) or doxorubicin 60 mg/m(2) plus cyclophosphamide 600 mg/m(2) (n = 215) on day 1, every 3 weeks for up to eight cycles. RESULTS: Time to progression (TTP; primary end point) and time to treatment failure (TTF) were significantly longer with AT than AC (median TTP, 37.3 v 31.9 weeks; log-rank P =.014; median TTF, 25.6 v 23.7 weeks; log-rank P =.048). The overall response rate (ORR) was significantly greater for patients taking AT (59%, with 10% complete response [CR], 49% partial response [PR]) than for those taking AC (47%, with 7% CR, 39% PR) (P =.009). The ORR was also higher with AT in patients with visceral involvement (58% v 41%; liver, 62% v 42%; lung, 58% v 35%), three or more organs involved (59% v 40%), or prior adjuvant CT (53% v 41%). Overall survival (OS) was comparable in both arms. Grade 3/4 neutropenia was frequent in both groups, although febrile neutropenia and infections were more frequent for patients taking AT (respectively, 33% v 10%, P <.001; 8% v 2%, P =.01). Severe nonhematologic toxicity was infrequent in both groups, including grade 3/4 cardiac events (AT, 3%; AC, 4%). CONCLUSION: AT significantly improves TTP and ORR compared with AC in patients with MBC, but there is no difference in OS. AT represents a valid option for the treatment of MBC.

Adult↗

PubMed2002

Reaction-diffusion wave fronts: multigeneration biological species under climate change.

A generalization of reaction-diffusion models to multigeneration biological species is presented. It is based on more complex random walks than those in previous approaches. The new model is developed analytically up to infinite order. Our predictions for the speed agree to experimental data for several butterfly species better than existing models. The predicted dependence for the speed on the number of generations per year allows us to explain the change in speed observed for a specific invasion.

Journal Article↗