Changes in regional lung mechanics and ventilation distribution
after unilateral pulmonary artery occlusion.
Simon, Brett A., Koichi Tsuzaki, and Jose G. Venegas.
Departments of Anesthesia and Biomedical Engineering, Massachusetts
General Hospital, Harvard Medical School, Boston, MA, Department of
Anesthesia and Critical Care Medicine, Johns Hopkins Medical
Institutions, Baltimore, MD
APStracts 3:0535A, 1996.
Regional pneumoconstriction induced by alveolar hypocapnea is an
important homeostatic mechanism for optimization of ventilation
-perfusion matching. We used positron imaging of 13NN equilibrated
lungs to measure the distribution of regional tidal volume (Vt), lung
volume (Vl), and lung impedance (Z) before and after left pulmonary
artery occlusion (PAO) in eight anesthetized, open-chested dogs.
Measurements were made during eucapnic sinusoidal ventilation at 0.2
Hz with 4 cm H2O PEEP. Right (R) and left (L) lung impedances (ZR and
ZL) were determined from carinal pressure and positron imaging of
dynamic re gional lung volume. LPAO caused an increase in |ZL|
relative to |ZR| resulting in a shift in tidal volume away from the
PA occluded side, with a L/R |Z| ratio changing from 1.20+/-0.07
(mn+/-se) to 2.79+/-0.85 after LPAO (p<0.05). Although mean L lung
Vl decreased slightly, the Vl normalized parameters specific
admittance and specific compliance both significantly decreased with
PAO. Lung recoil pressure at 50% TLC also increased after PAO. We
conclude that PAO results in an increase in regional lung impedance
which 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 .
Received 18 July 1995; accepted in final form 12 November 1996.
APS Manuscript Number A784-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996