Ariway Pressures During Positive Pressure Ventilation with Superimposed Oscillations before and after Lung Injury in the Cat

Abstract

This study was made to determine how oscillations superimposed on intermittent positive pressure ventilation (IPPV) influence the arterial blood gases, pH and the airway pressures during adequate alveolar ventilation i.e. at inhibition of inspiratory activity, before and after experimentally induced lung injury in the anaesthetized cat. Two IPPV frequencies were studied. The lung was injured by instillation of xanthine oxidase into the upper airways during IPPV. The peak, mean and end-expiratory intrapleural and airway (intratracheal) pressures at two levels were measured and the arterial blood gases and pH were determined at inhibition of inspiratory activity with and without superimposition of oscillations on the ventilatory pattern. Before lung injury, superimposed oscillations lowered the airway pressures only at an IPPV rate of 15 breaths per minute (b.p.m.). After lung injury, such oscillations increased the airway pressures only at 15 b.p.m. The airway pressures were always lower at 60 than at 15 b.p.m.