Lung injury produced by moderate lung overinflation in rats

In models using both intact animals and isolated lungs of rats, rabbits, lambs, and dogs, application of high airway pressure and resultant lung overdistension has been shown to cause lung injury. Under pathological conditions, the more normal portions of the lung may be subjected to relative overdistension when supranormal airway pressures are used. A small animal model of lung overdistension is presented here to demonstrate that lung injury can be caused by moderate lung overdistension. Rats were anesthetized with Ketamine and pentobarbital. A tracheostomy was performed and arterial and central venous catheters placed. The animal was placed in a plethysmograph and an infant ventilator was used to provide mechanical ventilation. In the first experiment, animals in group A (n = 6, control) were ventilated at tidal volume (TV) of 5 mL/kg for 5 hours. Animals in group B (n = 6) were ventilated at TV 15 mL/kg for 60 minutes and then were returned TV of 5 mL/kg for the remainder of the experiment. Animals in group C (n = 5) were ventilated at TV 20 mL/kg for 60 minutes and then returned to TV 5 mL/kg. Static lung compliance and arterial blood gasses were measured. Wet and dry lung weight were obtained after sacrifice. In the second experiment, animals in group D (n = 4, control) were ventilated at TV 5 mL/kg for 240 minutes and killed. Animals in group E (n = 4) were ventilated at TV 20 mL/kg for 60 minutes, returned to TV 5 mL/kg, and killed at 240 minutes. Fluorescein-labeled albumin was administered to each animal prior to mechanical ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)