Browsing by Subject "Hysteresis"

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    Lung histeresis: a morphological view
    (Murcia : F. Hernández, 2004) Escolar Castellón, J.de D.; Escolar castellón, A.
    The lung is an imperfect elastic body and for this reason dissipates energy. The energy applied to the lung in inspiration is not recovered in expiration. The property of dissipating energy receives the name of hysteresis. Lung hysteresis can be quantified because it applies to the area between the ascending and descending portions of the pressure-volume curve. Lung hysteresis comprises parenchymal hysteresis and bronchial hysteresis. Each point on the pressure-volume applies to a different morphology of the lung parenchyma. The changes that take place in the lung architecture during expiration are related to alveolar recruitment: in inspiration the lung volume increases by the opening of distal air units. In expiration the lung volume decreases due to derecruitment. The energy is dissipated mainly in the alveolar recruitment process, in which forces of molecular adhesion, such as surface tension, are at work. Bronchial hysteresis involves the dead space and the bronchial wall being greater in expiration.
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    Morphological hysteresis of the small airways
    (Murcia : F. Hernández, 2003) Escolar Castellón, J.de D.; Escolar, M.A.; Guzmán, J.; Roqués, M.
    The resistance to airflow that develops in most obstructive processes takes place in the small airways. The aim of the present paper is to describe bronchial hysteresis morphometrically in a respiratory cycle model. As a working hypothesis, it is proposed that the changes that take place in the respiratory tract during the respiratory cycle are related to the bronchial size. Specimen rat lungs were organized into five groups: In the first group, the lungs were filled with a liquid fixative to 25 cm of H2O transpulmonary pressure. The following four groups were inflated with air and fixed through the pulmonary artery. Groups 2 and 3 were fixed at 10 and 20 cm transpulmonary pressure in inflation. The last two groups were fixed in deflation and, for this purpose, the transpulmonary pressure was increased to 27 cm and decreased to 20 and 10 cm, respectively. The lungs were processed for morphometrical study and the following variables were quantified: pulmonary volume, internal area, internal perimeter, wall area, internal area radius and bronchial wall radius. The diameter of the airways studied varied between 84.06 µm and 526.4 µm. The results were classified into three subgroups consisting of small, medium-sized and large bronchi. With a single exception - the internal area in the medium-sized bronchi inflated to 20 cm - all the results obtained in deflation were higher than those obtained in inflation. The internal area increased or decreased significantly upon raising or lowering the transpulmonary pressure respectively, in the small and medium-sized bronchi. The wall area in the large bronchi showed significant differences between inflation and deflation at 10 and 20 cm transpulmonary pressure. The wall area was modified significantly in the lungs fixed at 20 cm in the small bronchi and at 10 cm in medium-sized bronchi. The bronchial wall radius was significantly greater in the large bronchi and smaller in the small bronchi. The lumen of the medium-sized and small bronchi increases in inspiration and decreases in expiration. The wall thickness displayed differences between inflation and deflation. The most marked hysteresis was presented by the bronchial wall in the large bronchi. Our results suggest that the behavior of the bronchi varies according to their size