New facts concerning the circulation in the lung, its control, and its interaction with the systemic circulation.

In spite of the massive volume of hemodynamic data which has been collected in humans many basic problems of circulatory physiology, pathology and therapy remain unsolved or controversial. Blood flows and pressures cannot usually be measured, controlled and varied adequately in man; a complete, rational picture of human circulatory physiology is therefore not in existence. Hence the need for fully controlled animal experimentation. This paper summarizes information which has been accumulated during the past two years, using an experimental preparation which permits fully controlled investigations of the pulmonary and the systemic ciiculations and of their interactions. It provides for the measurement of pulmonary arterial and venous pressures while the flow of blood through the lung is known and can be regulated (Fig. 1). The lungs of open-chest dogs are perfused in situ from a pump-reservoir circuit after the pulmonary artery is ligated, the ascending aorta clamped, and the systemic circulation of the animal carried on the heart-lung machine. There is no communication between the systemic and the pulmonary circulations, except for the collateral flow in the bronchial vessels. The lungs are innervated and nourished; blood flow through the pulmonary vessels is determined at will by setting the output of a calibrated pump. In addition, the changing blood volumes in the animal and in the pulmonary circuit can be measured by isotope or dye dilution techniques. Collateral blood flow to the lungs is measured by changes of the pulmonary reservoir level and also by isotope dilution. Factors influencing collateral pulmonary flow have already been described in a separate communication.1