Indirect relation between rises in oxygen consumption and left ventricular output at birth in lambs

Smolich, J.J.; Soust, M.; Berger, P.J.; Walker, A.M.

Circulation Research 71(2): 443-450


ISSN/ISBN: 0009-7330
PMID: 1628399
DOI: 10.1161/01.res.71.2.443
Accession: 007448583

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To examine the relation between increased newborn oxygen requirements and the postnatal rise in cardiac output, we measured left ventricular (LV) output, organ blood flows, and whole-body oxygen consumption using radioactive microspheres in late-gestation sheep fetuses and in the same animals 1 and 4 hours after cesarean section delivery. LV output rose from 264 .+-. 23 ml .cntdot. min-1 .cntdot. kg body wt-1 in fetuses to 444 .+-. 33 ml .cntdot. min-1 kg body wt-1 in lambs at 1 hour after delivery (p < 0.005) and was unchanged at 4 hours after delivery. This rise in LV output was associated with a more fourfold increase in the LV flow contribution to tissues situated distal to the ductus arteriosus (fetus, 51 .+-. 9 ml .cntdot. min-1 .cntdot. kg body wt-1; lamb, 226 .+-. 22 ml .cntdot. min-1 .cntdot. body wt-1p p < 0.005), which were mainly perfused by the right ventricle in utero. However, average blood flow to body tissues was similar in fetuses (37 .+-. 4 ml .cntdot. min-1 .cntdot. 100 g tissue-1), 1-hour lambs (39 .+-. 4 ml .cntdot. min-1 .cntdot. 100 g tissue-1), and 4-hour lambs (40 .+-. 5 ml .cntdot. min-1 .cntdot. 100 g tissue-1). Oxygen consumption increased by 58%, from 7.84 .+-. 0.43 ml .cntdot. min-1 .cntdot. kg body wt-1 in fetuses to 12.38 .+-. 2.4 ml .cntdot. min-1 .cntdot. kg body wt-1 in 1-hour lambs (p < 0.01), and was unchanged in 4-hour lambs. Although systemic blood flow did not change after birth, the arteriovenous oxygen content difference increased by 54%, from 1.98 .+-. 0.16 ml/dl in fetuses to 3.05 .+-. 0.19 ml/dl in 1-hour lambs (p < 0.005), and was unaltered in 4-hour lambs. We conclude that 1) an increased LV output after birth results from the LV taking over the perfusion of tissues supplied by the right ventricle in utero, 2) the perinatal rise in LV output maintains overall systemic perfusion, 3) an increased newborn oxygen consumption is achieved through a rise in arteriovenous oxygen extraction, and 4) rises in oxygen consumption and LV output at birth are not directly related to one another.