AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 2 396-R401, Copyright © 1993 by American Physiological Society
Hemodynamic changes induced by low blood oxygen affinity in dogs
J. F. Liard and M. P. Kunert
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226.
Increased tissue oxygen delivery may play a role in the increased vascular
resistance that develops in volume-expanded hypertension. This hypothesis
was tested by decreasing the affinity of hemoglobin for oxygen in dogs to
increase unloading of oxygen to the tissues. Six chronically instrumented
dogs were studied before and for 7 days after partial exchange transfusion
with red blood cells modified by incorporation of inositol hexaphosphate,
which, 1 h after exchange, increased the PO2 value at which hemoglobin is
half-saturated with oxygen (P50) to 38.8 +/- 2.1 mmHg from a control value
of 31 +/- 1.5 mmHg. Cardiac output (electromagnetic flowmeter) fell to 92.5
+/- 7.4 ml.kg-1.min-1 after 2-4 h from control values between 120.2 +/- 5.7
and 125.8 +/- 4.6 ml.kg-1.min-1. One day later, cardiac output was still
significantly decreased to 104.0 +/- 5.9 ml.kg-1.min-1. As P50 returned to
control over the next few days, so did cardiac output. Two to four hours
after exchange, total peripheral resistance was increased to 1,144 +/- 73
mmHg.l-1.kg.min from control values between 762 +/- 26 and 790 +/- 32
mmHg.l-1.kg.min. It was still increased to 993 +/- 51 mmHg.l-1.kg.min after
1 day. Oxygen consumption did not change significantly. Cardiac output and
peripheral resistance changes were significantly different from those
measured in a control group of six dogs receiving exchange transfusion with
sham-shifted red blood cells without significant P50 changes. These results
suggest that an increase in tissue oxygen delivery can raise total
peripheral resistance in dogs in the absence of primary changes in fluid
volumes, blood flow, or blood pressure.
