In the isolated perfused dog lung lobe we have achieved successful micropuncture of lung surface pulmonary arterioles, venules and capillaries (vessels between 10-50 micron diameter), recorded hydrostatic pressure and determined the longitudinal distribution of vascular resistance under conditions of constant vascular driving pressures. We will use this procedure in dog and sheep lung lobes to determine the longitudinal distribution of microvascular hydrostatic pressures compared to simultaneous estimates of overall lobe isogravimetric pressure. We will determine the sites of vasoconstriction by drugs (serotonin, norepinephrine, prostaglandins and histamine), by changes in alveolar oxygen and carbon dioxide concentrations, and explore resistance changes as alveolar pressure is varied relative to pulmonary venous outflow pressure (zone III and zone II/III boundary). We will measure regional interstitial free-fluid pressure and obtain fluid samples or protein analysis in mild to moderate interstitial edema. We will develop the method further to measure microvascular pressures in open-thorax, self-perfused lungs, and ultimately, in the closed-thorax, anesthetized, spontaneously breathing animal with a thoracic window.