RESUMEN
The present study measured stretch-induced changes in transepithelial permeability to uncharged tracers (1.5-5.5 A) using cultured monolayers of alveolar epithelial type-I like cells. Cultured alveolar epithelial cells were subjected to uniform cyclic (0, 0.25 and 1.0 Hz) biaxial stretch from 0% to 12, 25 or 37% change in surface area (DeltaSA) for 1 h. Significant changes in permeability of cell monolayers were observed when stretched from 0% to 37% DeltaSA at all frequencies, and from 0% to 25% DeltaSA only at high frequency (1 Hz), but not at all when stretched from 0% to 12% DeltaSA compared with unstretched controls. At stretch oscillation amplitudes of 25 and 37% DeltaSA, imposed at 1 Hz, tracer permeability increased compared with that at 0.25 Hz. Cells subjected to a single stretch cycle at 37% DeltaSA (0.25 Hz), to simulate a deep sigh, were not distinguishable from unstretched controls. Reducing stretch oscillation amplitude while maintaining a peak stretch of 37% DeltaSA (0.25 Hz) via the application of a simulated post-end-expiratory pressure did not protect barrier properties. In conclusion, peak stretch magnitude and stretch frequency were the primary determining factors for epithelial barrier dysfunction, as opposed to oscillation amplitude.
Asunto(s)
Epitelio/metabolismo , Alveolos Pulmonares/metabolismo , Alveolos Pulmonares/fisiopatología , Animales , Células Cultivadas , Células Epiteliales/citología , Fibronectinas/química , Volumen Espiratorio Forzado , Masculino , Microscopía Electrónica , Modelos Biológicos , Oscilometría , Permeabilidad , Ratas , Ratas Sprague-Dawley , Mucosa Respiratoria/metabolismoRESUMEN
Previous studies have demonstrated that high tidal volumes can cause interstitial and alveolar edema, with degradation of pulmonary epithelial barrier integrity. Separate studies have shown that F-actin disruption and decreased intracellular ATP (ATP(i)) levels in the nonpulmonary epithelium can increase tight junction (TJ) permeability. We hypothesized that large epithelial stretch perturbs ATP(i) and actin architecture, each of which adversely affects TJ structure, and thus increases TJ permeability. Primary alveolar epithelial cells were subjected to a uniform 25% or 37% change in surface area (DeltaSA), cyclic biaxial stretch (15 cycles/min) for 1 h, or treated with either glycolytic metabolic inhibitors or cytoskeletal disrupting agents. Unstretched, untreated cells served as controls. Changes in the TJ proteins occludin and ZO-1 were determined by immunocytochemical evaluation. A stretch amplitude of 25% DeltaSA did not produce any significant cytologic changes compared with controls, but an amplitude of 37% DeltaSA stretch resulted in significant decreases in the intensity of the peripheral occludin band, the degree of cell-cell attachment (CCA), and total cellular occludin content. ATP depletion significantly diminished the occludin band intensity and decreased CCA. Actin disruption did not affect TJ protein band intensities (although the occludin distribution became punctate) but altered CCA. Untreated cells stretched cyclically at 25% or 50% DeltaSA for 1 h had significantly decreased ATP(i) compared with unstretched controls. These results suggest that stretch-induced ATP(i) reduction and actin perturbation disrupt TJ structure and CCA, which may lead to the alveolar flooding associated with high tidal volumes.
Asunto(s)
Alveolos Pulmonares/fisiología , Mucosa Respiratoria/fisiología , Uniones Estrechas/metabolismo , Actinas/fisiología , Adenosina Trifosfato/metabolismo , Animales , Western Blotting , Células Cultivadas , Citoesqueleto/fisiología , Masculino , Proteínas de la Membrana/análisis , Proteínas de la Membrana/metabolismo , Ocludina , Fosfoproteínas/análisis , Fosfoproteínas/metabolismo , Alveolos Pulmonares/citología , Ratas , Ratas Sprague-Dawley , Mucosa Respiratoria/citología , Estrés Mecánico , Volumen de Ventilación Pulmonar , Proteína de la Zonula Occludens-1RESUMEN
A 67-year-old man suffering cardiopulmonary arrest had an apparently uneventful placement of an esophageal obturator airway (EOA) by a well-trained ambulance crew. Subsequent clinical evaluation showed ventilation to be marginal. Attempts to insert an endotracheal tube were unsuccessful because the larynx could not be visualized. A subsequent postmortem examination showed that the EOA tube was kinked and bent back on itself so that the distal (balloon) end lay underneath the larynx, displacing it anteriorly.