Regional lung volume trajectories during expiratory flow in dogs
.
Wilson, Theodore A., Mark J. Hill, and Rolf D. Hubmayr.
Department of Aerospace Engineering and Mechanics, University of
Minnesota, Minneapolis, MN 55455; and Thoracic Research Unit, Mayo
Clinic and Foundation, Rochester, MN 55905
APStracts 2:0520A, 1995.
Parenchymal markers were placed in the left caudal lobes of
anesthetized dogs, and the three-dimensional positions of the markers
were tracked by biplane videofluoroscopy during expiration from total
lung capacity (TLC) to 30% TLC at steady expiratory flows of 0.3 to
7% TLC/s. Regional volumes of samples of parenchyma with volumes at
TLC of 1?- 5?cm3 were obtained by computing the volumes of tetrahedra
defined by taking the markers, four-at-a-time, as apices of the
tetrahedra. Regional volume vr, as a fraction of volume at TLC, was
plotted against average volume vL, as a fraction of volume at TLC,
and vr was fit by a quadratic function of vL. The initial slopes of
the plots, dvr/dvL at vL?=?1, varied by +/- 26% from the mean slope
of 1. The curvatures were highly correlated with the slopes, and the
vr vs. vL plots formed a nest of "onion skins." The initial
slopes were weakly correlated with vertical position of the centroid
of the tetrahedron with slope increasing by 20%/cm, on average, in
the dorsal direction in the supine dog. The vertical gradient in
regional volume accounted for 30% of the total variability; small
scale heterogeneity contributed the remaining 70%. These results
confirm earlier quasi-static measurements of nonuniform regional
volume and provide the first data on curvature of regional volume
trajectories. The mechanisms that cause the nongravitational
component of regional volume variability and the curvatures of the
trajectories are unknown.
Received 14 August 1995; accepted in final form 2 November 1995.
APS Manuscript Number A894-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95