Movement of microspheres through the pulmonary circuit

¹ Physiology Department, University of Miami School of Medicine, Coral Gables, Florida

Microspheres of styrene divinyl benzene varying in size from about 1 µ to 16 µ have been injected into the pulmonary artery of dogs. The proportion of the spheres of various sizes which reach the systemic circuit has been determined. The spheres in the groups less than 5 µ in diameter which pass through the pulmonary circuit are diminished when norepinephrine or serotonin is infused but are not affected by the infusion of acetylcholine or inhalation of carbon dioxide in oxygen. Spheres of sizes larger than 5 µ pass through the pulmonary circuit in larger proportions when CO₂ is inhaled or acetylcholine is infused but are unaffected by norepinephrine and reduced by infusion of serotonin. The central volume is usually increased in dogs given serotonin but is unchanged during inhalation of CO₂.