Induced Changes in the Pattern of Pulmonary Blood Flow in the Rabbit

1. In the normal, unanesthetized rabbit, resting quietly in its normal position, catheterization of the right ventricle (and central veins) altered the distribution of blood throughout the lung in a characteristic manner. 2. Regional pulmonary vasoconstriction, rather than passive changes in vascular caliber or in the flow properties of blood, seemed to be involved. 3. The mechanism for the regional pulmonary vasoconstriction is considered in terms of a neurohumoral pathway, involving afferent pathways from the right heart, connecting channels in the upper cervical segments of the spinal cord, and release of a histamine-like substance at the neuro-vascular junctions.