Fetal cerebral blood flow, electrocorticographic activity, and oxygenation: responses to acute hypoxia.

Arterial blood gases are critical in regulation of cerebral blood flow (CBF) and cerebral metabolic rate for O(2) (CMRO(2)). However, the relation of these variables to cortical tissue (t ), and electrocorticographic (ECoG) activity (high voltage low frequency, HVLF, versus low voltage high frequency, LVHF), are not well defined. In the fetus, we tested the hypothesis that ECoG pattern is associated closely with cerebral oxygenation.

Maternal caffeine administration and cerebral oxygenation in near-term fetal sheep.

The authors test the null hypothesis that maternal caffeine administration will not significantly alter fetal cerebral oxygenation. The authors measured fetal arterial blood gases, cortical tissue O(2) tension (tPO(2)), sagittal sinus blood gases, and laser Doppler cerebral blood flow in response to a 30-minute caffeine infusion (400 mg intravenously) into 7 near-term pregnant ewes, and they calculated fractional O(2) extraction and relative cerebral metabolic rate for O(2) (CMRO(2)). Following maternal caffeine infusion, both fetal cortical tPO(2) and sagittal sinus (HbO(2)) decreased significantly, from 10.

Fetal hypercapnia in high-altitude acclimatized sheep: cerebral blood flow and cerebral oxygenation.

The authors tested the hypothesis that in the high-altitude acclimatized fetus, hypercapnia has a significantly less effect on cerebral blood flow (CBF) and cerebral oxygenation than that in normoxic sea level controls. In the high-altitude acclimatized fetus (3801 m; maintained from day 30 of gestation to near term; n = 6), by use of a laser Doppler flowmeter with a fluorescent O (2) probe, the authors measured relative CBF (laser Doppler CBF [LD-CBF]), cortical tissue PO(2) (tPO(2)), and sagittal sinus oxyhemoglobin saturation (HbO(2)) in response to 20-minute hypercapnia. They also calculated cerebral O(2)delivery and cerebral fractional O(2) extraction.

Fetal cerebral oxygenation: the role of maternal hyperoxia with supplemental CO2 in sheep.

Objective: We tested the hypothesis that supplemental CO2 can enhance the effect of maternal oxygen administration on fetal cerebral oxygenation.

Study Design: In near-term fetal sheep (n = 6), we instrumented the cerebral cortex with tissue PO2-laser Doppler flow probes, and placed arterial catheters. Following a 30-minute control period, the ewe breathed 50% O2 for 15 minutes, followed by added 6% CO2 for 15 minutes.

Cerebral blood flow and oxygenation in ovine fetus: responses to superimposed hypoxia at both low and high altitude.

For the fetus, although the roles of arterial blood gases are recognized to be critical in the regulation of cerebral blood flow (CBF) and cerebral oxygenation, the relation of CBF, cortical tissue P(O2) (tP(O2)), sagittal sinus P(O2), and related indices of cerebral oxygenation to arterial blood gases are not well defined. This is particularly true for that fetus subjected to long-term hypoxia (LTH). In an effort to elucidate these interrelations, we tested the hypothesis that in the fetus acclimatized to high altitude, cerebral oxygenation is not compromised relative to that at low altitude.

Fetal hypercapnia and cerebral tissue oxygenation: studies in near-term sheep.

The precise role of CO2 in cerebral oxygenation is not as well defined as O2, especially in the immature brain. In the ovine fetus, we tested the hypotheses that arterial Pco2 (Paco2) plays a critical role not only in the regulation of cerebral blood flow but also in the regulation of cerebral tissue oxygenation. By use of a fluorescent O2 probe with a laser Doppler flowmeter and the placement of sagittal sinus catheter in six near-term fetal sheep, we measured values of cortical tissue O2 tension (tPo2), sagittal sinus oxyhemoglobin saturation ([HbO2]), and laser Doppler cerebral blood flow (LD-CBF) in response to 20 min hypercapnia induced by having the ewe breathe CO2.

Maternal oxygen administration and fetal cerebral oxygenation: studies on near-term fetal lambs at both low and high altitude.

Objective: We tested the hypothesis that O2 administration to the mother would increase arterial O2 tension (PaO2) and cortical tissue O2 tension (tPO2) in both the normoxic control fetus and that acclimatized to high altitude, and that this effect might be greater in the high altitude fetus than that at sea level.

Study Design: Pregnant ewes were divided into either low-altitude group or high-altitude group (3820 m; maintained from day 30 of gestation to near-term, term = 145 days; n = 6 each). In near-term fetuses we instrumented the cerebral cortex with tissue PO2-laser Doppler flow probes, and placed arterial catheters.