AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 6 1448-R1454, Copyright © 1995 by American Physiological Society
Effects of afferent neural stimulation on critical oxygen delivery: a hemodynamic explanation
E. Kirkman, H. Zhang, H. Spapen, R. A. Little and J. L. Vincent
Department of Intensive Care, Erasme University Hospital, Free University of Brussels, Belgium.
Injury and activation of somatic afferent nerve fibers may alter critical
oxygen delivery (DO2C), the point at which oxygen consumption becomes
dependent upon delivery, and hence reduce tolerance to hypovolemia. The
present study investigated the mechanism of this. Anesthetized mongrel dogs
were divided into two groups: control (n = 6) and those subject to brachial
nerve stimulation (BNS; n = 5). Whole body oxygen delivery (DO2I) and
consumption were initially similar in both groups. DO2I was reduced by
cardiac tamponade to determine DO2C. DO2C was significantly higher in BNS
compared with control (11.5: 11.0-16.7 vs. 7.5: 6.9-9.5 ml.min-1.kg-1;
median: Q1 - Q3), whereas critical oxygen extraction ratios were lower
(54.8: 39.7-61.2 vs. 78.3: 53.5-92.4%). At approximately DO2C, normalized
femoral blood flow was lower than renal flow in control (renal-femoral
difference 17.4: 8.7-40.0%) but not in BNS (-7.8: -14.8 to +11.8%). These
results indicate that activation of somatic afferent nerve fibers elevates
DO2C. This could be due to an impairment in peripheral oxygen extraction as
a consequence of a redistribution of blood flow away from metabolically
active vital organs toward relatively inactive skeletal muscle.
