Regulation of cerebral blood flow in the ovine fetus

Jones, M. D.; Sheldon, Roger E.; Peeters, L.; Makowski, Edgar L.; Meschia, Giacomo

doi:10.1152/ajpheart.1978.235.2.h162

Cited by 40 publications

(40 citation statements)

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“…Cerebral blood flow varies inversely with arterial oxygen content, and cerebral blood flow decreases after birth as oxygen content increases (22). In previous studies, fetal oxygenation achieved by positive-pressure mechanical ventilation decreased cerebral blood flow to levels comparable to those observed in neonates (I, 3, 23).…”

Section: Control Distension Oxygenation Breathingmentioning

confidence: 58%

Effects of Lung Distension and Spontaneous Fetal Breathing on Hemodynamics in Sheep

1993

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ABSTRACT. In previous studies, we determined that pul-been shown to have independent effects on blood flow, neural monary ventilation and oxygenation were largely respon-reflexes, and hormone responses in proportion to the inflation sible for increasing pulmonary blood flow and for altering pressures achieved (5, 6), the possibility exists that some of the central blood flow patterns but could not account for the responses observed previously were a consequence of positive increase in combined ventricular output (the sum of left pressure ventilation per se, and not related to normal breathing and right ventricular outputs) that usually occurs after activity initiated at birth. birth. We had ventilated fetuses with oscillating positive Recent studies have demonstrated that spontaneous negative pressures; the possibility that high intrathoracic pressures pressure pulmonary ventilation can be initiated and maintained adversely affected cardiac output could not be ruled out. in fetal sheep when the umbilical cord is occluded while oxygen To determine the effects of negative intrathoracic pressure is introduced into the fetal trachea (7-10). We applied this ventilation, we occluded the umbilical cord of nine long-technique to determine the effects of spontaneous, rhythmic term instrumented fetal sheep at 135 f 1.2 d gestation pulmonary ventilation on blood flow patterns at birth. We while introducing humidified oxygen gas intratracheally. measured combined ventricular output, the sum of left and right This stimulated continuous fetal respiratory activity, which ventricular outputs, and peripheral blood flow distribution in a resulted in negative intrathoracic pressures and increased group of fetal sheep in utero to determine the effects of spontafetal oxygenation. Pulmonary blood flow increased from neous negative pressure ventilation on hemodynamics at birth.121 + 60 to 901 + 139 mL.min.-'.I00 g-' (mean + SD) and descending aortic blood pressure increased from 7.0 f MATERIALS AND METHODS 1.2 to 9.6 + 2.0 kPa. Central blood flow patterns were altered so that right to left shunting of blood through the Animals and Surgical Preparation. All procedures complied foramen ovale and ductus arteriosus was abolished and a with NIH guidelines and were approved by the Committee left to right shunt developed across the ductus arteriosus. on Animal Research at UCSF. We studied nine fetal sheep at However, cardiac output did not increase significantly. This 135 f 1.2 d gestational age (range 133-1 37 d; term is 145 d). may be related, in part, to the increase in afterload. It is Food, but not water, was withheld from the ewe for 24-36 h clear that pulmonary ventilation and oxygenation are the before surgery. After local anesthesia (2% lidocaine hydrochlomajor factors responsible for changing pulmonary blood ride), low spinal or epidural anesthesia was achieved with 4 mL flow and central blood flow patterns at birth. Other birth-of 1 % tetracaine hydrochloride (Pontocaine HCI, Breon Laborelated events, such as a decrease in environ...

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Section: Control Distension Oxygenation Breathingmentioning

confidence: 58%

Effects of Lung Distension and Spontaneous Fetal Breathing on Hemodynamics in Sheep

1993

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“…100 g-') = -1106 + 339 In Pcoz (torr). Pco2 changes was less than in the newborn or adult animal (1,18,19,33,34,40).…”

Section: Discussionmentioning

confidence: 83%

Regional Cerebral Blood Flow: Studies in the Fetal Lamb during Hypoxia, Hypercapnia, Addosis, and Hypotension

1984

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ABSTRACT. In order to determine the relative roles of O2 tension and content, C 0 2 tension, hydrogen ion concentration, arterial blood pressure, and cardiac output in the regulation of fetal cerebral blood flow (CBF), we used radioactively labeled microspheres to measure flow to 20 major brain regions in 24 chronically catheterized fetal lambs. We continually monitored fetal heart rate and blood pressure, and periodically measured arterial Po2, Pco2, pH, and hematocrit. In addition to CBF measurements during control periods, we measured CBF during: 1) hypoxia ( 0 2 content < 6 ml-dl-'; O2 tension c 15 torr) induced by having the ewe breathe a gas mixture with low 0 2 concentration, 2) hypercapnia (Pcoz > 50 torr) induced by increasing the maternal inspired COz, 3) acidosis and alkalosis (7.60 > pH > 6.60) induced by infusing lactic acid or bicarbonate into the fetus, and 4) hypotension (blood pressure < 35 mm Hg) and hypertension (blood pressure > 55 mm Hg) induced by rapidly phlebotomizing or transfusing the fetus. We used multiple regression analysis and analysis of covariance to examine the dependence of total cerebral blood flow on arterial O2 tension and content, COz tension, pH, blood pressure, and cardiac output. The results demonstrated that 1) fetal CBF increased linearly as oxygen tension or content decreased and a hierarchy of responsivity occurred (brainstem > subcortex and cortex), 2) fetal CBF increased as carbon dioxide tension increased with a different hierarchy of responsivity (brainstem > subcortex > cortex), and 3) autoregulation of fetal CBF over a wide range of blood pressure or cardiac output was maintained for both total CBF and the various brain regions examined. (Pediatr Res 18:1309-1316,1984 Abbreviations CBF, cerebral blood flow During the past several years, numerous investigators have used the radioactive microsphere technique to measure newborn and fetal cerebral blood flow in different species (1,19,24,25,36,40). In these studies, which have examined changes in flow as a function of changes in blood gas tensions, pH, and blood

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“…29,30 In the experimental model, with initial arterial hypoxemia, fetal vascular resistance can decrease by at least 50% to maintain CBF with a minimal decrease in oxygen delivery. [31][32][33] Critical to this state is a normal or elevated mean arterial blood pressure. However, with persistent hypoxemia, and eventual hypotension, cerebral vascular resistance cannot decrease further, resulting in a marked reduction in CBF.…”

Section: Circulatory Responsesmentioning

confidence: 99%

Pathogenesis of hypoxic-ischemic brain injury

Perlman

2007

J Perinatol

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Accumulating evidence points to an evolving process of brain injury after intrapartum hypoxia-ischemia that initiates in utero and extends into a recovery period. The processes leading to cell death include necrosis or apoptosis, and result from the combined effects of cellular energy failure, acidosis, glutamate release, intracellular Ca 2 þ accumulation, generation of free radicals that serve to disrupt essential components of the cell. Many factors including the duration or severity of the insult influence the progression of cellular injury after hypoxia-ischemia. A secondary cerebral energy failure occurs from 6 to 48 h after the primary event and involves mitochondrial dysfunction secondary to extended reactions from primary insults (e.g., calcium influx, excitatory neurotoxicity and oxygen free radicals) as well as the release of circulatory and endogenous inflammatory cells/mediators that also contribute to ongoing brain injury. Strategies aimed at neuroprotection need to be comprehensive targeting the pathways leading to eventual mitochondrial injury.

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Regulation of cerebral blood flow in the ovine fetus

Cited by 40 publications

References 0 publications

Effects of Lung Distension and Spontaneous Fetal Breathing on Hemodynamics in Sheep

Effects of Lung Distension and Spontaneous Fetal Breathing on Hemodynamics in Sheep

Regional Cerebral Blood Flow: Studies in the Fetal Lamb during Hypoxia, Hypercapnia, Addosis, and Hypotension

Pathogenesis of hypoxic-ischemic brain injury

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