RESUMEN
Experiments show that when a monolayer of cells cultured on an elastic substratum is subject to a cyclic stretch, cells tend to reorient either perpendicularly or at an oblique angle with respect to the main stretching direction. Due to stochastic effects, however, the distribution of angles achieved by the cells is broader and, experimentally, histograms over the interval [Formula: see text] are usually reported. Here we will determine the evolution and the stationary state of probability density functions describing the statistical distribution of the orientations of the cells using Fokker-Planck equations derived from microscopic rules for describing the reorientation process of the cell. As a first attempt, we shall use a stochastic differential equation related to a very general elastic energy that the cell tries to minimize and, we will show that the results of the time integration and of the stationary state of the related forward Fokker-Planck equation compare very well with experimental results obtained by different researchers. Then, in order to model more accurately the microscopic process of cell reorientation and to shed light on the mechanisms performed by cells that are subject to cyclic stretch, we consider discrete in time random processes that allow to recover Fokker-Planck equations through classical tools of kinetic theory. In particular, we shall introduce a model of reorientation as a function of the rotation angle as a result of an optimal control problem. Also in this latter case the results match very well with experiments.
Asunto(s)
Conceptos Matemáticos , Modelos BiológicosRESUMEN
This paper addresses the economic relevance of appropriately staging progression of disease for cost assessment and projection. Illustrations are drawn from two Dutch cost-of-illness studies for Diabetes Mellitus (DM) and AIDS. Our disease-staging specifies a separate late stage to capture terminal high-intensity care for end-stage complications. Data are used from a registration of national hospital resource utilization for DM and from a detailed database on AIDS hospital care and costs. In particular, differences in average length of hospital stay for several potential DM end-stage complications are compared with non-DM patients. Neglecting the separation of a specific late stage is estimated to possibly miscalculate 15-20% of the hospital bed needs for DM and AIDS in the Netherlands. In particular, confidence intervals of future projections for AIDS hospital beds--using respectively staged and non-staged models--do not overlap. AIDS hospital costs are overprojected by almost 11% in the non-staged model. Our estimation of DM hospital bed needs raises the percentage in total Dutch hospital beds from 1.7% (neglecting a specific late stage) to 2.0%. For DM and AIDS an appropriate disease-staging averts structural biases in estimations of bed needs and costs, and therefore benefits the planning of hospital care facilities. Obviously, gathering comparable information and developing similar methodology on other diseases, such as respiratory disease, cardiovascular disease and cancer, is needed and could benefit planning in these fields.
Asunto(s)
Síndrome de Inmunodeficiencia Adquirida/economía , Costo de Enfermedad , Diabetes Mellitus/economía , Progresión de la Enfermedad , Modelos Econométricos , Síndrome de Inmunodeficiencia Adquirida/patología , Síndrome de Inmunodeficiencia Adquirida/terapia , Comorbilidad , Diabetes Mellitus/patología , Diabetes Mellitus/terapia , Predicción , Política de Salud , Costos de Hospital/estadística & datos numéricos , Humanos , Países Bajos , Índice de Severidad de la Enfermedad , Estados UnidosRESUMEN
The most common presentation of cerebral palsy is spastic diplegia, which in severe cases can impede nursing care and in less severe cases can impair a child's ability to move around with facility. A procedure has been developed to decrease spasticity in which there is selective section of portions of the dorsal roots L2-S2. In a series of such operations in 19 children with spastic diplegia, we were able to decrease their spasticity significantly with resultant improvement in motor function and self care. There were no significant complications and patient and family satisfaction was high. Our experiences further confirm existing evidence that this procedure is very helpful and highly recommended for selected children with spasticity due to cerebral palsy.