Made available in DSpace on 2014-12-17T14:13:42Z (GMT). No. of bitstreams: 1 RonaldoAA_TESE_parcial.pdf: 75168 bytes, checksum: a480f84f619eb88bf968f0a55bed0676 (MD5) Previous issue date: 2011-12-09 / An important unsolved problem in medical science concerns the physical origin of the sigmoidal shape of pressure volume curves of healthy (and some unhealthy) lungs. Such difficulties are expected because the lung, which is the most important structure in the respiratory system, is extremely complex. Its rheological properties are unknown and seem to depend on phenomena occurring from the alveolar scale up to the thoracic scale. Conventional wisdom holds that linear response, i.e., Hooke s law, together with alveolar overdistention, play a dominant role in respiration, but such assumptions cannot explainthe crucial empirical sigmoidal shape of the curves. In this doctorate thesis, we propose an alternative theory to solve this problem, based on the alveolar recruitment together with the nonlinear elasticity of the alveoli. This theory suggests that recruitment may be the predominant factor shaping these curves in the entire range of pressures normally employed in experiments. The proposed model correctly predicts the observed sigmoidal pressure volume curves, allowing us to discuss adequately the importance of this result, as well as its implications for medical practice / Um importante problema n?o resolvido na ci?ncia m?dica diz respeito ? origem f?sica da forma sigmoidal das curvas press?o-volume de pulm?es saud?veis (e de alguns n?o saud?veis). Tais dificuldades s?o esperadas tendo em vista que o pulm?o, a mais importante estrutura do sistema respirat?rio, ? extremamente complexo. Suas propriedades reol?gicas s?o desconhecidas, e parecem depender dos fen?menos que ocorrem a partir da escala alveolar at? a escala tor?cica. O modelo cl?ssico diz que a resposta linear, ou seja, a lei de Hooke, juntamente com a superdistens?o alveolar desempenha um papel predominante na formata??o dessas curvas, mas tais pressupostos n?o podem explicar a crucial forma emp?rica sigmoidal das curvas P-V respirat?rias est?ticas. Nesta tese de doutorado propomos uma teoria alternativa para resolver este problema, baseada no recrutamento alveolar, juntamente com a hip?tese do comportamento el?stico n?o-linear dos alv?olos. Esta teoria sugere o recrutamento alveolar como o fator predominante que modela as curvas press?o-volume em um completo intervalo de press?o normalmente utilizado nas experi?ncias. O modelo proposto prediz corretamente a forma sigmoidal observada nas curvas press?o-volume, nos permitindo discutir adequadamente a import?ncia deste resultado, assim como as suas implica??es para a pr?tica m?dica