Pulmonary vascular obstruction in graded tachypneagenic diffuse embolism

¹ Department of Physiology, Medical College of South Carolina, Charleston, South Carolina

One group of experiments revealed minimal doses of 75 µ pulmonary emboli required for eliciting increased frequency and decreased amplitude of breathing in anesthetized dogs. Others measured in vivo lung lobe autoperfusion flow rates at several constant perfusion pressures to determine the fractions of the pulmonary vascular bed obstructed by these and other quantities and to determine concurrent changes in flow-pressure relationships. The fraction of the vascular bed obstructed by threshold tachypneagenic quantities averaged 10% but in some instances was as little as 3%—values so small that the expected hemodynamic consequences in intact animals would be within physiological ranges and therefore seemingly not important as a tachypneagenic mechanism. Following embolization, resistance to blood flow increased in the nonoccluded intralobar vascular bed, particularly at lower perfusion pressures, and associated alterations in flow-pressure and resistance-pressure relationships pointed toward moderate increase in vascular tone as the cause. Quantities of emboli apparently required for completely obstructing the pulmonary vascular bed were considered in relation to established anatomical dimensions.