Locomoção terrestre e demanda metabólica: uma revisão histórica

The studies of terrestrial locomotion, that is, to move using a solid substrate basis, brought out two grand energetics puzzles. One is in regard of the existence of preferential speeds in each stride (walk, trot, run), and whether these speeds are related to some economy in energy. The other is related to the very nature of the energy demand during locomotion, since it is assumed that kinetic and potential energies of the center of mass interchange into each other. Besides, in opposition to flight and to swim, there is no movement of the substrate itself. The present manuscript presents, under the bias of the author, a chronological review of 40 years of research in the area, covering topics regarding the two enigmas cited above.O estudo da locomoção em meio terrestre, ou seja, sobre um substrato sólido, trouxe dois grandes enigmas quanto à energética do deslocamento. Um destes diz respeito à existência de velocidades preferenciais de deslocamento para cada tipo de passada (andar, trotar, correr), e se tais velocidades estão relacionadas a uma economia de energia. O segundo diz respeito ao que causa a demanda energética para o deslocamento, pois, supostamente, a energia cinética vertical do centro de massa é convertida a potencial, e vice-versa, além de não haver uma movimentação do substrato como ocorre no nado e no vôo. O presente artigo apresenta, sob o viés do autor, um apanhado cronológico de 40 anos de pesquisa na área, com os resultados e interpretações dadas no que tange aos dois enigmas acima citados

A theoretical model for estimating the margination constant of leukocytes

BACKGROUND: Blood leukocytes constitute two interchangeable sub-populations, the marginated and circulating pools. These two sub-compartments are found in normal conditions and are potentially affected by non-normal situations, either pathological or physiological. The dynamics between the compartments is governed by rate constants of margination (M) and return to circulation (R). Therefore, estimates of M and R may prove of great importance to a deeper understanding of many conditions. However, there has been a lack of formalism in order to approach such estimates. The few attempts to furnish an estimation of M and R neither rely on clearly stated models that precisely say which rate constant is under estimation nor recognize which factors may influence the estimation. RESULTS: The returning of the blood pools to a steady-state value after a perturbation (e.g., epinephrine injection) was modeled by a second-order differential equation. This equation has two eigenvalues, related to a fast- and to a slow-component of the dynamics. The model makes it possible to identify that these components are partitioned into three constants: R, M and S(B); where S(B) is a time-invariant exit to tissues rate constant. Three examples of the computations are worked and a tentative estimation of R for mouse monocytes is presented. CONCLUSIONS: This study establishes a firm theoretical basis for the estimation of the rate constants of the dynamics between the blood sub-compartments of white cells. It shows, for the first time, that the estimation must also take into account the exit to tissues rate constant, S(B)

Triburguers e a entropia ... ou, a história da triste constatação feita por um pensador, inútil, amigo

Agradeço aos Drs. Daniela Tathiana Soltys e Pedro Leite Ribeiro por terem chamado minha atenção, e sugerido a maneira, quanto à necessidade de melhor apresentar o termo S transformados no balanço feito

Searching strategy models: is Lévy walk the answer?

Na natureza, muitos animais lidam com o problema de encontrar parceiros, comida e abrigo. A estratégia de busca que orienta um organismo pode revelar aspectos importantes do seu comportamento, então, modelos são propostos para tratar deste problema. O passeio de Lévy é o modelo mais discutido, possui algum suporte empírico. Nosso objetivo foi comparar deslocamentos em linha reta com o passeio de Lévy e o movimento Browniano, considerando sobrevivência e probabilidade de recompensa. Os resultados mostram o deslocamento em linha reta com desempenho superior nos ambientes que criamos. Discutimos que a estratégia linha reta deveria ser considerada a mais provável estratégia de busca considerando os argumentos que dão suporte ao passeio de Lévy, contudo, ela não é vista como estratégia.In nature, many organisms must cope with the problem of finding mates, food and shelter. The strategy of search that drives an organism can reveal important aspects of its behavior; models have been proposed to address this problem. Lévy walk is the most discussed model and it has some empirical support. Our aim was to compare straight line displacements against Lévy walk and Brownian motion in terms of survival and probability of reward. Our results show that straight line displacements have better performance in all environments we created. We discuss that straight line movements should be considered more probable as a search strategy considering the arguments that support Lévy walk, however, it is not seen like a strategy.Agradecemos s comentários e revisão de Breno Teixeira Santos, José Eduardo Soubhia Natali e Vitor Hugo Rodrigues e o auxílio concedido pela agência FAPESP

Para garimpar mais que ouro - uma análise do desempenho olímpico brasileiro

The Olympic Games are sportive events of global relevance. Here, we perform an analysis of the medal table from a general perspective and of the Brazilian performance over the last 10 competitions, and we show that there is no real improvement of such a performance at all. We then try to understand the relationships among the place in the medal table and social aspects of development. We discuss that there is a physiological basis involved in how elite athletes emerge, but without the proper social investment it wouldn’t be possible to select, in a systematic and wide way, these athletes. It is in this sense, of the type of the investment, that gold medals can have a much greater social meaning to the country.As Olimpíadas são eventos esportivos de relevância mundial. No presente artigo, fazemos uma análise da evolução do quadro geral de medalhas em termos mundiais e do desempenho do Brasil ao longo dos últimos 10 eventos, mostrando que não tem havido melhora de tal desempenho. Procuramos, então, entender e estender as relações entre a colocação no quadro geral e aspectos sociais de desenvolvimento. Discutimos que existe uma base fisiológica envolvida em como despontam atletas de elite, mas que sem o devido investimento social, não há como selecionar, de maneira sistemática e ampla, tais atletas. É neste sentido, do tipo de investimento, que a obtenção do ouro olímpico pode ter um significado muito maior, de cunho social, para o país

To mine more than gold – an analysis of the brazilian olympic \ud performance

As Olimpíadas são eventos esportivos de relevância mundial. No presente artigo, fazemos uma análise da evolução do quadro geral de medalhas em termos mundiais e do desempenho do Brasil ao longo dos últimos 10 eventos, mostrando que não tem havido melhora de tal desempenho. Procuramos, então, entender e estender as relações entre a colocação no quadro geral e aspectos sociais de desenvolvimento. Discutimos que existe uma base fisiológica envolvida em como despontam atletas de elite, mas que sem o devido investimento social, não há como selecionar, de maneira sistemática e ampla, tais atletas. É neste sentido, do tipo de investimento, que a obtenção do ouro olímpico pode ter um significado muito maior, de cunho social, para o país.The Olympic Games are sportive events of global relevance. Here, we perform an analysis of the medal table from a general perspective and of the Brazilian performance over the last 10 competitions, and we show that there is no real improvement of such a performance at all. We then try to understand the relationships among the place in the medal table and social aspects of development. We discuss that there is a physiological basis involved in how elite athletes emerge, but without the proper social investment it wouldn’t be possible to select, in a systematic and wide way, these athletes. It is in this sense, of the type of the investment, that gold medals can have a much greater social meaning to the country

Pulsatile blood flow, shear force, energy dissipation and Murray's Law

BACKGROUND: Murray's Law states that, when a parent blood vessel branches into daughter vessels, the cube of the radius of the parent vessel is equal to the sum of the cubes of the radii of daughter blood vessels. Murray derived this law by defining a cost function that is the sum of the energy cost of the blood in a vessel and the energy cost of pumping blood through the vessel. The cost is minimized when vessel radii are consistent with Murray's Law. This law has also been derived from the hypothesis that the shear force of moving blood on the inner walls of vessels is constant throughout the vascular system. However, this derivation, like Murray's earlier derivation, is based on the assumption of constant blood flow. METHODS: To determine the implications of the constant shear force hypothesis and to extend Murray's energy cost minimization to the pulsatile arterial system, a model of pulsatile flow in an elastic tube is analyzed. A new and exact solution for flow velocity, blood flow rate and shear force is derived. RESULTS: For medium and small arteries with pulsatile flow, Murray's energy minimization leads to Murray's Law. Furthermore, the hypothesis that the maximum shear force during the cycle of pulsatile flow is constant throughout the arterial system implies that Murray's Law is approximately true. The approximation is good for all but the largest vessels (aorta and its major branches) of the arterial system. CONCLUSION: A cellular mechanism that senses shear force at the inner wall of a blood vessel and triggers remodeling that increases the circumference of the wall when a shear force threshold is exceeded would result in the observed scaling of vessel radii described by Murray's Law

Indexing cardiovascular and respiratory variables: allometric scaling principles

To describe the allometric scaling principles underlying appropriate indexing of cardiovascular and respiratory measurements obtained in adult mammals, and to propose guidelines for indexing experimental cardiovascular and respiratory data.PubMed, using the terms 'allometry', 'allometric', 'indexing', 'cardiovascular' and 'respiratory'.Indexing of cardiopulmonary variables is commonly used in attempts to account for the effects of body size on measurements and to standardize them. Some cardiopulmonary variables have been indexed using various functions of body mass in a process that often ignores the underlying relationship between the variable of interest and body size, as described in the allometry literature. This can result in a failure to ideally reduce the effect of body size on measurements in a manner that highlights differences. We review how commonly measured cardiopulmonary variables are related to body mass in mammalian species according to the allometry literature, and offer suggestions on how this information can be used to appropriately index cardiopulmonary variables in a simple and informative manner