Biomedical subjects

M Abundo

Publications and source records attributed to M Abundo.

5 recordsLinked to original sources

PubMed1998

A serial study of new MS lesions and the white matter from which they arise.

OBJECTIVE: To compare MS normal-appearing white matter (NAWM) where new gadolinium-enhancing (Gd+) lesions do and do not arise. METHODS: A total of 22 relapsing-remitting MS patients and 11 healthy control subjects completed as many as 12 monthly brain MRI sessions. Quantitative measures of gadolinium enhancement (GDR), water proton density (PDN), water proton T2 relaxation time constants (T2), magnetization transfer ratio (MTR), and T1-weighted signal intensity (T1N) were followed serially in healthy control and MS NAWM. RESULTS: A total of 129 new Gd+ lesions were identified in 11 patients. PDN, T2, MTR, and T1N were diffusely abnormal in MS NAWM. NAWM regions in which new Gd+ lesions arose have increased GDR, PDN, and T2, and reduced MTR and T1N compared with contralateral homologous NAWM regions in which no new Gd+ lesions arose. Differences between these NAWM regions preceded lesion appearance for at least several months. After lesions became visible, GDR returned to baseline within 2 months, and PDN and MTR had larger residual abnormalities than T2 or T1N. CONCLUSIONS: Quantitative MRI measures are diffusely abnormal in MS NAWM. These measures are, on average, more abnormal in NAWM regions in which new Gd+ lesions arise. After the appearance of Gd+ lesions, measures of PDN and MTR may provide more appealing markers of relatively irreversible tissue damage than measures of T2 and T1N.

Adult↗

PubMed1996

A stochastic model for the sigmoidal behaviour of cooperative biological systems.

A stochastic model for cooperative transitions in biological systems based on a Markov chain is proposed. This model requires only two parameters, the mean probability, p, and the coupling capacity, Deltap, which measure the probability of forming a new weak bond depending on the number of similar bonds already formed and it is also responsible for the transition. In this paper we show how the model works for a large number of identical molecules and how it can be useful for studying the noise around the centre of the transition where, increasing the degree of cooperativity, i.e. the number n in the well-known Hill equation, the width of the noise increases along with its fractal dimension. A simple relationship between the degree of cooperativity and the parameter Deltap is proposed, suggesting that the cooperativity of real biological transitions is related to the coupling capacity Deltap of the present model.

Journal Article↗

PubMed1991

A stochastic model for predator-prey systems: basic properties, stability and computer simulation.

A simple stochastic description of a model of a predator-prey system is given. The evolution of the system is described by means of Itô's stochastic differential equations (SDEs), which are the natural stochastic generalization of the Lotka-Volterra deterministic differential equations. Since these SDEs do not satisfy the usual conditions for the existence and uniqueness of the solution, we state a theorem of existence; moreover we study the stability of the equilibrium point and perform a computer simulation to study the behaviour of the trajectories of solutions with given initial data and to estimate first and second moments.

Animals↗

PubMed1989

Numerical simulation of a stochastic model for cancerous cells submitted to chemotherapy.

A stochastic model is proposed to study the problem of inherent resistance by cell populations when chemotherapeutic agents are used to control tumor growth. Stochastic differential equations are introduced and numerically integrated to simulate expected response to the chemotherapeutic strategies as a function of different parameters. Satisfactory demonstration runs of the model indicate that it could represent a useful tool in verifying the results of experimental and clinical chemotherapy courses and planning treatment strategies. Some types of behaviour are illustrated graphically.

Drug Resistance↗

PubMed1989

A stochastic model of the acquisition of drug resistance during antineoplastic chemotherapy.

A stochastic model is proposed to simulate the phenomenon of acquisition of genetic resistance by a tumor cell population treated with antineoplastic cytotoxic agents. In the model, stochastic differential equations are numerically integrated to simulate the expected response after treatment with two different agents. The model takes into account the initial number of cells, the sequence of the agents, the time intervals between administrations, the birth and death rates of the untreated cells, the probabilities of mutations to resistance, and the induced cell-killing kinetics. Satisfactory demonstration runs of the model indicate that it could represent a useful tool in verifying the results of experimental and clinical chemotherapy courses and planning treatment strategies.

Antineoplastic Agents↗