Circulatory changes induced by isovolumic increase in red cell mass in fetal lambs
a The Fetal Cardiology Unit Pediatric
Cardiology Service Sainte-Justine Hospital 3175 Côte Ste Catherine University of Montreal Quebec
Canada H3T 1C5, b Department of Obstetrics
Correspondence to: Dr Jean-Claude Fouron. Email: fouron{at}sympatico.ca
Accepted 17 May 1998
AIM
To verify whether extra uterine
changes in total peripheral vascular resistance and cardiac output,
caused by raised haematocrit, occur in fetal life and if they can be
documented using conventional ultrasound techniques.
METHODSAn exchange transfusion with packed red
cells was performed on five fetal lambs at 140 days of gestation
(weight 3.44, SD 0.48 kg); three others were used as controls. The
haematocrit was raised from 44 ± 3 to 64 (SD2)%.
RESULTSBody temperature, blood gas, and pH
remained within normal limits. Blood viscosity increased from 5.3 (
0.3) to 9.6 (1.6) cps. Combined cardiac output fell to 30% of its
initial value. The pulsatility index (PI) remained unchanged in the
umbilical artery (0.66, SD 0.1) and descending aorta (1.3, SD 0.3). A
significant positive correlation was found between haematocrit and PI
only in the carotid artery (r=0.67, p<0.01).
CONCLUSIONIn the fetus, as in adults, an increase
in blood viscosity is associated with a fall in cardiac output.
However, the low resistance and the relative inertia of the placental
vascular bed blunt the velocimetric changes that could be induced in
the lower body vascular system by an increase in resistance. Such
changes were observed only in the carotid artery. These results could
be of interest in the Doppler monitoring of human fetuses at risk of an
abnormal increase in their haematocrit.
© 1998 by Archives of Disease in Childhood
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