AJP - Heart and Circulatory Physiology, Vol 241, Issue 6 864-H871, Copyright © 1981 by American Physiological Society
Sequential hemodynamic and oxygen transport responses in hypovolemia, anemia, and hypoxia
S. Schwartz, R. A. Frantz and W. C. Shoemaker
Sequential cardiorespiratory measurements were made in 30 mongrel dogs
during controlled hypovolemia, normovolemic anemia, and hypoxia. The
responses to each of these three types of O2 deprivation were studied both
as a function of time and of the rate of O2 delivery (normalized cardiac
output x arterial O2 content). With progressively decreasing O2 delivery,
compensations appeared, reached a maximum, and fell before the final
circulatory deterioration. O2 extraction increased in each experiment, but
there was differences in the hemodynamic responses to the three types of O2
deprivation; e.g., cardiac output increased in the anemic dogs, and there
were greater increases in systemic and pulmonary resistances after
hemorrhage. The striking finding was that O2 consumption (VO2) remained
relatively constant until the preterminal stage. At this time O2 delivery
had fallen from about 27 to less than 10 ml . min-1 . kg-1, blood volume
was less than 50%, hematocrit was less than 8%, and arterial O2 tension was
less than 30 Torr at an average fractional inspired O2 concentration of 8%,
for the hypovolemic, anemic, and hypoxic groups, respectively. Then VO2
dropped precipitously and death rapidly occurred. These results suggest
that VO2 represents a physiological marker of impending death in the face
of progressively diminishing O2 delivery.
