Journal of Applied Physiology, Vol 49, Issue 3 462-470, Copyright © 1980 by American Physiological Society
Coronary blood flow in conscious miniature swine during +GZ acceleration stress
M. H. Laughlin, W. M. Witt, R. N. Whittaker and E. F. Jones
One of the factors determining tolerance to +GZ acceleration may be the
ability to maintain adequate coronary blood flow. Consequently, the purpose
of these studies was to determine the effect of acute exposure (60 s) to
several levels of positive acceleration (+GZ) on total and regional
coronary blood flow in conscious adult miniature swine. Blood flow was
measured with the radiolabeled microsphere technique in chronically
instrumented miniature swine during 60-s exposures to accelerations of +3
GZ, +5 GZ, or +7 GZ with anti-G suit support. All levels of acceleration
stress caused two- to threefold increases in coronary blood flow. The
regional distribution of coronary blood flow during +GZ was similar to that
under resting control conditions as long as aortic diastolic pressure was
maintained. All left ventricular endocardial/epicardial flow ratios were
significantly greater than one, except in two animals, during exposure to
+7 GZ. These were the only animals to have aortic diastolic pressures less
than 100 Torr during +GZ stress. These studies indicate that, if an animal
is able to compensate and maintain a cardiovascular steady State, coronary
blood flow will remain adequate for myocardial needs. However, if
decompensation occurs and aortic diastolic pressure falls below a critical
value, subendocardial blood flow may become inadequate.
