Pulmonary arterial distension does not cause pulmonary vasoconstriction

Distension of the main pulmonary artery or its major branches with an intraluminal balloon has been reported to cause pulmonary vasoconstriction by an unknown mechanism. This study was an attempt to confirm the pressor response and explore its cause. Several balloon distension methods were tried and discarded because they caused unintentional obstruction. Ultimately, I inflated a balloon placed retrogradely and confined to the left main pulmonary artery of six anesthetized open-chest dogs after ligating left lobar arterial branches. Blood flow and systemic gas composition were controlled by interposing an external pump oxygenator between the left ventricle and aorta. Pressures in the aorta, main pulmonary artery, and left atrium were recorded. Alveolar hypoxia was used as an independent test of pulmonary vasoreactivity. Although hypoxic pressor responses occurred, challenges with arterial distension did not change lung perfusion pressure. Silicone rubber casts were made of the arteries of six dogs used in pilot experiments. These revealed the limited lengths in which distenders can be placed without unintentional encroachment on flow. I could not support the conclusion that arterial distension causes vasoconstriction and am suspicious that the perfusion pressure increases reported by others may have been caused by undetected obstruction of a major arterial branch.