J Physiol Volume 584, Number 2, 693-704, October 15, 2007 DOI: 10.1113/jphysiol.2007.142778
Intrauterine growth restriction improves cerebral O2 utilization during hypercapnic hypoxia in newborn piglets
Reinhard Bauer1,2,
Bernd Walter3 and
Ulrich Brandl2
1 Institute of Molecular Cell Biology
2 Department of Neuropaediatrics, Children's Hospital, Friedrich Schiller University, D-07740 Jena, Germany3Department of Neurosurgery, Zentralklinik Bad Berka GmbH, D-99437 Bad Berka, Germany
Data are scant regarding the capacity of cerebrovascular regulation during asphyxia for prevention of brain oxygen deficit in intrauterine growth-restricted (IUGR) newborns. We tested the hypothesis that IUGR improves the ability of neonates to withstand critical periods of severe asphyxia by optimizing brain oxygen supply. Studies were conducted to examine the effects of IUGR on cerebral blood flow (CBF) regulation and oxygen consumption (cerebral metabolic rate for oxygen, CMRO2) at different stages of asphyxia (hypercapnic hypoxaemia) in comparison to pure hypoxia (normocapnic hypoxaemia). We used 1-day-old anaesthetized and ventilated piglets. Animals were divided into normal weight (NW) piglets (n = 47; aged 11–26 h, body weight 1481 ± 121 g) and IUGR piglets (n = 48; aged 13–28 h, body weight 806 ± 42 g) according to their birth weight. Different stages of hypoxaemia were induced for 1 h by appropriate lowering of the inspired fraction of oxygen (moderate hypoxia: 
= 31–34 mmHg; severe hypoxia: 
= 20–22 mmHg). Fourteen NW and 16 IUGR piglets received additionally 9% CO2 in the breathing gas, so that a 
of 74–80 mmHg resulted (hypoxia/hypercapnia groups). Eight NW and nine IUGR animals served as untreated controls. Furthermore, affinity of haemoglobin for oxygen was measured under hypoxic and asphyxic conditions. During asphyxia cerebral oxygen extraction was markedly increased in IUGR animals (P < 0.05). This resulted in a significantly diminished CMRO2-related increase of CBF at gradually reduced arterial oxygen content (P < 0.05). Therefore, an enhanced effectivity in oxygen availability appeared in newborn IUGR piglets under graded asphyxia by improved cerebral oxygen utilization (P < 0.05). This was not supported by related O2 affinity of haemoglobin. Thus, IUGR newborns are more capable to ensure brain O2 demand during asphyxia (hypercapnic hypoxia) than NW neonates.
(Received 13 August 2007;
accepted after revision 20 August 2007;
first published online 23 August 2007)
Corresponding author R. Bauer: Institute of Molecular Cell Biology, Center for Molecular Biomedicine (CMB) and Department of Neuropaediatrics, Children's Hospital, Friedrich Schiller University, D-07740 Jena, Germany. Email: reinhard.bauer{at}mti.uni-jena.de
Copyright © 2007 The Physiological Society.
