Pulmonary Lymphatics and Edema Accumulation

In a past study of hyperoxia-induced lung injury, extensive lymphatic filling occurred that could have resulted from lymphatic proliferation or simple lymphatic recruitment. This study sought to determine if brief lung injury could produce similar changes, to show which lymphatic compartments fill with edema, and to compare their three-dimensional structure. Tracheostomized rats were ventilated at high tidal volume (12-16 mL) or low tidal volume (3-5 mL) or allowed to breathe spontaneously for 25 minutes. Light microscopy showed more perivascular, interlobular septal, and alveolar edema in the high-tidal volume ventilated animals (p < 0.0001). Scanning electron microscopy of lymphatic casts showed extensive filling of the perivascular lymphatics in the high tidal volume group (p < 0.01), but the nonventilated group had more filling than the low tidal volume group (p < 0.01). The three-dimensional structures of the cast interlobular lymphatics was similar to the cast perivascular lymphatics. There was little filling and no difference in pleural lymphatic casts among the three groups. Larger blood vessels accumulated more edema in their surrounding lymphatics than smaller blood vessels. Brief high tidal volume lung injury caused pulmonary edema that was similar to that seen with chronic hyperoxic lung injury except that it was largely restricted to perivascular and septal lymphatics and prelymphatic spaces. KEY (MESH) WORDS: PULMONARY EDEMA; BAROTRAUMA, VENTILATOR; LYMPHATICS; CORROSION CASTING; MICROSCOPY, SCANNING ELECTRON.