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.
Differential ventilation in unilateral pulmonary artery occlusion
