RESPIRATORY MECHANICS AND GAS-EXCHANGE IN POSTOBSTRUCTIVE PULMONARY VASCULOPATHY

Chronic unilateral pulmonary artery ligation induces formation of new bronchial collateral vessels in the affected lung. These vessels form precapillary anastomoses with the pulmonary circulation and the lung i s perfused with arterial blood. Inspired gas is diverted to the contra lateral lung to maintain the ventilation/perfusion ratio (VA/Q) and ga s exchange. This study was designed to determine McGill University the mechanism responsible for this shift of ventilation, which has not pr eviously been investigated. We studied six dogs, before and 6 months a fter ligation of the left main pulmonary artery. We measured pulmonary resistance (RL) and elastance (EL), minute ventilation (VE), O-2 cons umption (VO2) and CO2 production (VCO2) of the right and left lungs. W e also examined the effect of CO2, atropine and isoproterenol on RL an d EL. In the lung with ligated pulmonary artery: 1) VE was significant ly reduced; 2) RL and EL were increased and were unresponsive to CO2, atropine and isoproterenol; and 3) VO2 decreased more than VCO2 and, c onsequently, respiratory quotient (RQ) was greater than 1. We conclude that, with chronic pulmonary artery obstruction, ventilation shifts t o the contralateral lung because of an increase in RL and EL not relat ed to airway smooth muscle tone.