Scanning Electron Microscopy of Alveolar Surface Topography in Induced Acute Respiratory Insufficiency

Scanning electron microscopy has been used to assess alveolar surface topography in a canine model of induced acute respiratory insufficiency (ARI). Mongrel dogs were infused with saline solution intermittently, continuously, or continuously with intermittent furosemide treatment. Ultrastructural and pathophysiological correlates of ARI were seen only in dogs that had fluid loading continuously at 100 ml. per kilogram of body weight per hour for 4 to 6 hours and that were not treated with furosemide. In acute pulmonary edema produced by continuous fluid overloading, the alveolar cell-air interface was altered. Irregular surface elevations, extravasated erythrocytes, and an apparent reduction in the diameter of the pores of Kohn were observed only in alveoli from dogs that died terminally after 4 to 6 hours of continuous fluid overloading. The morphological changes at the alveolar gas-exchange surface correlated with data indicating that respiratory function was being compromised by pulmonary edema. These observations and their relation to the genesis of ARI induced in the dog by continuous fluid overloading may provide a model for better understanding iatrogenic clinical respiratory failure.