Vagotomy-induced pulmonary edema in the guinea pig

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Abstract
A method is described for measuring alterations in total thoracic mechanics during the development of vagotomy-induced lung edema in the unanesthetized guinea pig. Influences of restraint, tracheotomy, and positive-pressure ventilation on lung edema were determined prior to analysis of respiratory function. Volume-pressure relationship was obtained at inflation volumes from 2–8 ml delivered at a variety of frequencies and flow rates at intervals before and after bilateral vagotomy. Development of edema was characterized by a progressive upward shift in pressure with negligible change in compliance (ΔV/ΔP) above the tidal volume range. This shift was due mostly to an increase in the elastic component and scarcely at all to an increase in the resistive component of the volume-pressure function. Measurements revealed that the edema fulminates terminally. Good correlation was found between extent of pressure shift and increase of lung-to-body weight ratio, thereby substantiating the validity of the measurement for in vivo evaluation of degree of pulmonary edema. Attempt to use lung specific gravity as a postmortem criterion of lung edema failed because of inconstant trapping of air.