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In order to estimate the role played by gaseous diffusion in the mixing disorders of chronic obstructive lung disease (COLD), the effect of breathing a gas mixture lighter than air has been studied. Twenty four patients with severe airflow obstruction have been tested in the following way: in a random order they breathed two different mixtures with the same(More)
The trachea has been approximated by an appropriate finite-element model. The three-dimensional equilibrium problems set by the tracheal deformation under various stresses have been solved using a convenient augmented Lagrangian functional. The dimensions were obtained from human tracheae. Mechanical constants for the anatomic components were calculated(More)
The thoracic trachea and the proximal portion of the major bronchi were imaged in five normal volunteers during a forced expiration maneuver using a cine-computer-tomography system. Sixteen images of two contiguous slices were obtained in less than 1 is while expiratory flow was recorded at the mouth. The area of the thoracic trachea decreased rapidly as(More)
Flow characteristics have been studied in elastic mono- and bialveolar lung models made from tubes and balloons in series. Flow rate variation is explained on the basis of two successive limiting factors governed by the mutual interaction of tube mechanical properties and flow characteristics, i.e. wave-speed and viscous limitations induced by the tube(More)
A numerical investigation of pulmonary flow properties was carried out in a monoalveolar model composed of a balloon and a compliant tube in series, subjected to pressure ramps. The flow is shown to become quickly limited by a wave-speed mechanism, occurring at the peak flow. The critical point then travels upstream, while the main part of the exit flow(More)
To understand the mechanism of flow limitation during forced expiration, flow properties were studied using a rubber model made up of two elements in series: a balloon and a thin-walled collapsible tube. This elastic model was inserted into a rigid box and flow was provided by pressure ramps in the box. Flow rate and transmural pressures were then measured;(More)