Pulmonary blood flow distribution in standing horses is not
dominated by gravity.
Hlastala, Michael P., Susan L. Bernard, Howard H. Erickson, M. Roger
Fedde, Earl M. Gaughan, Rose McMurphy, Michael J. Emery, Nayak
Polissar, Robb W. Glenny.
Department of Physiology and Biophysics and Department of Medicine,
University of Washington, Seattle, Washington and Department of
Anatomy and Physiology and Department of Clinical Sciences, Kansas
State University, Manhattan, Kansas
APStracts 3:0259A, 1996.
Recent studies using microspheres in dogs, pigs and goats have
demonstrated considerable het erogeneity of pulmonary perfusion
within isogravitational planes. These studies demonstrate a minimal
role of gravity in determining pulmonary perfusion (_) distribution.
To test whether a gravitational gradient would be more apparent in an
animal with large vertical lung height, we measured perfusion
heterogeneity in horses (vertical lung ht=55 cm). Four unanesthetized
Thoroughbred geldings (422-500?kg) were studied awake in the standing
position, with fluores cent microspheres injected into a central
vein. Between 1621 and 2503 pieces (1.3 cm3 in volume) were obtained
from the lungs of each horse with spatial coordinates and _
determined for each piece. The coefficient of variation of _
throughout the lungs ranged between 22?% and 57?% among the horses.
Considerable heterogeneity was seen in each isogravitational plane.
The relationship between _ and vertical height up the lung was
characterized by the slope and correlation coefficient of a least
squares regression analysis. The slopes within each horse ranged from
-.052 to +.021 relative flow units per cm height up the lung and
correlation coefficients varied from 0.12 to 0.75. A positive slope,
indicating that flow increased with vertical distance up the lung
(opposite to gravity), was observed in three of the four horses. In
addition, blood flow was uniformly low in three of the four horses in
the most cranial portions of the lungs. We conclude that in lungs of
resting unanesthetized horses, animals with a large lung height,
there is no consistent vertical gradient to pulmonary blood flow and
there is a considerable degree of perfusion heterogeneity, indicating
that gravity alone does not play the major role in determining
pulmonary perfusion distribution.
Received 30 November 1995; accepted in final form 30 April 1996.
APS Manuscript Number A238-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 June 96