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CO2 reactivity and autoregulation in fetal brain
N Yamashita1, K Kamiya, H Nagai
1Department of Neurosurgery, Nagoya City University, Japan.
Insights
Cerebral blood flow (CBF) in preterm rabbit fetuses is low and less responsive to CO2 changes. This immaturity may contribute to intraventricular hemorrhage (IVH) in premature infants.
Area of Science:
- Neonatal physiology
- Cerebrovascular regulation
- Fetal development
Background:
- Intraventricular hemorrhage (IVH) is a major cause of morbidity and mortality in preterm infants.
- Altered cerebral blood flow (CBF) is implicated in the pathophysiology of IVH.
- The fetal cerebrovascular system's response to physiological changes is not fully understood.
Purpose of the Study:
- To measure cerebral blood flow (CBF) in near-term rabbit fetuses.
- To assess the cerebrovascular response to changes in partial pressure of carbon dioxide (PaCO2) in fetal rabbits.
- To investigate the potential link between fetal CBF regulation and the risk of intraventricular hemorrhage (IVH).
Main Methods:
- Utilized the hydrogen clearance technique to measure local CBF in near-term rabbit fetuses.
- Compared fetal CBF with maternal CBF.
- Observed the response of fetal CBF to controlled alterations in maternal PaCO2.
Main Results:
- Fetal rabbit CBF was significantly lower than maternal rabbit CBF.
- The CO2 reactivity index was lower in fetal rabbits compared to maternal rabbits.
- Fetal CBF remained stable despite maternal blood pressure variations.
Conclusions:
- The immature fetal brain exhibits reduced CBF and blunted CO2 reactivity.
- These findings suggest that even minor increases in CBF during hypercapnia could elevate the risk of intraventricular hemorrhage (IVH) in preterm infants.
- The subependymal germinal matrix's fragile vasculature may be particularly vulnerable to such CBF fluctuations.
Abstract:
Intraventricular hemorrhage (IVH) in preterm infants is well known to be associated with the high morbidity and mortality of this group. Previous studies have suggested altered cerebral blood flow (CBF) as an important pathologic factor. We measured the CBF in near-term rabbit fetuses using the hydrogen clearance technique. The local CBF of the rabbit fetuses was significantly low compared with that of the maternal rabbits. The response of CBF to changes in PaCO2 was observed in rabbit fetuses. The CO2 reactivity index of the fetal rabbit was lower than that of the maternal rabbit. This low CO2 reactivity might reflect the immaturity of the fetal brain and its low CBF. We were unable to monitor the fetal blood pressure, but the fetal CBF remained stable when the maternal blood pressure was altered. It is well known that IVH in preterm infants originates from the subependymal germinal matrix and that this has many fragile vessels. Our observation suggests that even a small increase of CBF during hypercapnia might have a large effect towards producing hemorrhage.