During the next year of this project, I will conduct an electron microscopic analysis of the morphology of pulmonary capillaries of dog lungs exposed to hemodynamic pulmonary edema. I will use a freeze substitution technique together with a rapid freezing procedure to stabilize and fix lung structure under carefully controlled physiological conditions. Dog lungs will be ventilated and perfused in situ and edema will be induced by increasing pulmonary venous pressure. Lungs will then be frozen under the following conditions: (1) alveolar pressure exceeds pulmonary artery pressure and this exceeds pulmonary venous pressure; (2) pulmonary artery pressure greater than alveolar pressure and this greater than pulmonary venous pressure; and (3) pulmonary artery pressure greater than pulmonary venous pressure and this greater than alveolar pressure. Under each of the three conditions lungs will be frozen at transpulmonary pressures of 5, 15, and 25 cm H20. This will allow me to investigate the effect of lung volume on pulmonary capillary morphology of edematous lungs. Using the electron microscope, I will examine the widths of the pulmonary capillaries, the widths of the alveolar septum and the thickness of the alveolar-capillary membrane.