Altered mechanical properties of lung parenchyma in postobstructive pulmonary vasculopathy

Postobstructive pulmonary vasculopathy (POPV) produced by chronic unilateral ligation of one pulmonary artery, results in perfusion of the pulmonary capillaries with systemic arterial blood. As a consequence, gas exchange occurs primarily in the contralateral nonligated lung. To determine whether the mechanical properties of the lung parenchyma are changed in POPV, we compared five dogs with chronic ligation of the left main pulmonary artery with five control dogs. Separate measurements of left and right lung airway flows, tracheal pressures, and alveolar pressures were made during mechanical ventilation at frequencies between 5 and 40 breaths/min. We calculated pulmonary elastance (EL) and pulmonary (RL), airway (Raw), and tissue (Rti) resistances. At all frequencies, dogs with POPV had higher left (ligated) EL and Rti and lower right (normal) lung Rti but similar EL compared with the respective lungs from control animals. Raw was the same in both lungs. Histology showed visceral pleura thickening and encroachment of new bronchial collaterals and lymphatics on the parenchyma of the ligated lungs. The contralateral lungs were entirely normal. We conclude that in POPV 1) there is an increase, in the ligated lung, of both EL and RL, the latter likely due to histological changes of the lung parenchyma, and 2) there is a reduction of Rti in the contralateral lung.