Effect of neural and humoral factors on pulmonary hemodynamics and microcirculation in pulmonary embolism

Pulmonary and systemic hemodynamics and microcirculatory changes were studied following pulmonary embolism with fresh blood clot. Sudden death was related to massive obstruction. Because denervation of the lung by reimplantation did not alter the acute or progressive hemodynamic changes, neural reflexes were ruled out as an important factor. Serotonin infusions produced the same changes as clot emboli. Both could be ameliorated by reserpine pretreatment, which reduced platelet serotonin content, and by massive doses of heparin, which acts as an antiserotonin and also prevents further platelet aggregation and rupture. Clot infusion into the proximally occluded right pulmonary artery (PA) produced severe changes in the left pulmonary vascular bed and clearly demonstrated that humoral effects occur over and above any mechanical effects of emboli.