The major cause of death in pulmonary embolism is the mechanical obstruction of blood flow through the lungs. In certain cases, however, it appears evident that the mechanical block is too small to account for death. It is possible that certain noxious reflexes may occur, such as pulmonary vasoconstriction, coronary vasoconstriction, reflex bronchial constriction, bronchial hypersecretion, and cardiac arrhythmia. The studies on pulmonary vasoconstriction have produced conflicting results, since most investigations require manipulations and anesthesia which result in serious errors of interpretation.
A method was developed wherein the pulmonary circulation was studied by embolizing the unanesthetized animal with 5μ size graphite particles and studying their distribution in the lungs.1 In this manner it was demonstrated that pulmonary vasoconstriction was associated with minute pulmonary emboli and that it could be absolished by ether, pentobarbital (Nembutal), or atropine. Vagectomy did not change the vascular response.2 It is the purpose of