Inter-relation between changes in ventricular function, myocardial
blood flow and o2 consumption at birth in lambs.
Smolich, Joseph J., Philip J. Berger, and Adrian M. Walker.
Institute of Reproduction and Development, Monash University,
Clayton, Victoria, Australia
APStracts 2:0349H, 1995.
We studied the inter-relationship of changes in ventricular external
work, myocardial blood flow and O2 consumption at birth. Eleven fetal
sheep were instrumented under general anesthesia at 133-134 days
gestation with arterial, peripheral venous and left atrial catheters,
and in 5 fetuses, a coronary sinus catheter. Fetal left (LV) and
right (RV) ventricular outputs and myocardial blood flows
(radioactive microspheres), hemodynamics and LV O2 consumption were
measured 1 week later. Fetuses were then delivered by cesarean
section and measurements repeated 1 and 4 hr after birth. Comparing
ventricles, RV minute work (mm Hg x L x kg -1) was greater in fetuses
(10.8 +/- 0.5 vs. 15.6 +/- 1.0, P < 0.001), but due to increased
LV minute work (to 20.9 +/- 1.4, P < 0.005) and unchanged RV
minute work, this pattern was reversed by 1 hr after birth. RV
myocardial blood flow (ml x min -1 x 100g -1) was predominant in
fetuses (234 +/- 25 vs. 306 +/- 27, P < 001), but this also
reversed in lambs, related to an unchanged 1 hr (248 +/- 16) and
lower 4 hr LV myocardial blood flow (199 +/- 9; P < 0.05), and a
progressive fall in RV myocardial blood flow (1 hr: 245 +/- 20, P
< 0.05; 4 hr: 174 +/- 12, P < 0.005). LV O2 consumption (ml
x min -1 x 100g -1) increased between fetal (8.1 +/- 0.6) and 1 hr
lambs (18.9 +/- 1.3; P < 0.005), due to a rise in the LV
arterio-venous O2 content difference (3.6 +/- 0.4 vs. 7.5 +/- 0.6 ml
x dl -1, P < 0.005). External work performed per unit myocardial
blood flow (mm Hg x L x ml -1) in the LV increased between fetal and
1 hr lambs (1.92 +/- 0.14 to 3.33 +/- 0.15; P < 0.001) and, in
the RV, between fetal and 4 hr lambs (2.09 +/- 0.18 to 2.92 +/- 0.24;
P < 0.01). The proportion of consumed O2 converted to external
work was, however, similar in fetal (34.6 +/- 3.1%), 1 hr (31.3 +/-
2.9%) and 4 hr lambs (34.5 +/- 3.6%). These findings indicate that:
1) a switchover from a fetal RV to a newborn LV dominance is due to
increased LV pumping performance; 2) an associated switchover in LV
and RV myocardial blood flow patterns is mainly related to a fall in
RV myocardial blood flow; 3) a postnatal rise in LV O2 consumption
results from enhanced LV arterio-venous O2 extraction, and not
increased LV myocardial blood flow; 4) ventricular external work per
unit myocardial blood flow increases postnatally, particularly in the
LV; 5) LV mechanical efficiency is not altered after birth.
Received 7 July 1994; accepted in final form 2 August 1995
APS Manuscript Number H590-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.