Changes in regional lung mechanics and ventilation distribution after unilateral pulmonary artery occlusion

Abstract

Simon, Brett A., Koichi Tsuzaki, and Jose G. Venegas.Changes in regional lung mechanics and ventilation distribution after unilateral pulmonary artery occlusion. J. Appl. Physiol. 82(3): 882–891, 1997.—Regional pneumoconstriction induced by alveolar hypocapnia is an important homeostatic mechanism for optimization of ventilation-perfusion matching. We used positron imaging of13NN-equilibrated lungs to measure the distribution of regional tidal volume (Vt), lung volume (Vl), and lung impedance ( Z) before and after left (L) pulmonary artery occlusion (PAO) in eight anesthetized, open-chest dogs. Measurements were made during eucapnic sinusoidal ventilation at 0.2 Hz with 4-cmH2O positive end expiratory pressure. Right (R) and L lung impedances ( Z rand Z l) were determined from carinal pressure and positron imaging of dynamic regional Vl. LPAO caused an increase in ‖ Z l‖ relative to ‖ Z r‖, resulting in a shift in Vt away from the PAO side, with a L/R ‖ Z‖ ratio changing from 1.20 ± 0.07 (mean ± SE) to 2.79 ± 0.85 after LPAO ( P < 0.05). Although mean L lung Vl decreased slightly, theVl normalized parameters specific admittance and specific compliance both significantly decreased with PAO. Lung recoil pressure at 50% total lung capacity also increased after PAO. We conclude that PAO results in an increase in regional lung Z that shifts ventilation away from the affected area at normal breathing frequencies and that this effect is not due to a change in Vl but reflects mechanical constriction at the tissue level.