Response of the Cerebral Circulation to Hypocarbia in Postasphyxia Newborn Lambs

Rosenberg, Adam A.

doi:10.1203/00006450-199211000-00008

Cited by 24 publications

(13 citation statements)

References 16 publications

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“…The slowing of EEG and increased CFOE observed at lower levels of PaCO 2 is likely to be the result of decreased cerebral oxygen delivery induced by hypocarbia. Hypocarbia reduces cerebral oxygen delivery (a) by cerebral vasoconstriction resulting in decreased cerebral blood flow (5)(6)(7)20,21) and (b) by decreasing oxy-haemoglobin dissociation resulting in decreased oxygen availability (22). The EEG changes observed at lower levels of PaCO 2 were similar to those described in relation to hypoxaemia by Roberton (1969) (23).…”

supporting

confidence: 67%

Effect of carbon dioxide on background cerebral electrical activity and fractional oxygen extraction in very low birth weight infants just after birth

et al. 2005

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Decreased arterial carbon dioxide tension (PaCO 2 ) results in decreased cerebral blood flow, which is associated with diminished cerebral electrical activity. In such a situation, cerebral fractional oxygen extraction (CFOE) would be expected to increase to preserve cerebral oxygen delivery. This study aimed to determine whether changes in blood gases in infants less than 30 wk' gestation were associated with changes in background electroencephalograms (EEG) and CFOE. Thirty-two very low birth weight infants were studied daily for the first three days after birth. Digital EEG recordings were performed for 75 min each day. CFOE, mean blood pressure and arterial blood gases were measured midway through each recording. EEG was analysed by (a) spectral analysis and (b) manual calculation of interburst interval. Blood pressure, pH and PaCO 2 did not have any effect on the EEG. On day one, only PaCO 2 showed a relationship with the relative power of the delta frequency band (0.5-3.5 Hz) and the interburst interval. The relative power of the delta band remained within normal limits when PaCO 2 was between 24 and 55 mm Hg on day one. There was a negative association between PaCO 2 and CFOE. The associations between PaCO 2 and EEG measurements were strongest on day one, weaker on day two, and absent on day three. The slowing of EEG and increased CFOE at lower levels of PaCO 2 are likely to be due to decreased cerebral oxygen delivery induced by hypocarbia. When PaCO 2 was higher, there was suppression of the EEG. Periventricular leukomalacia is an important cause of neurologic morbidity in very low birth weight infants (1) and has been associated with severe hypocarbia during the first 24 h after birth. This effect of arterial carbon dioxide tension (PaCO 2 ) on the brain is likely to be mediated through its effect on cerebral blood flow, which is decreased by hypocarbia. In such a situation, cerebral fractional oxygen extraction (CFOE) would be expected to increase, as cerebral oxygen delivery is reduced (8). Decreased cerebral oxygen delivery would also be expected to be associated with reduced cerebral electrical activity. A positive relationship between cerebral blood flow and integrated amplitude of the EEG has been demonstrated on a group of infants between 27 and 33 wk' gestation (9). However, no studies have described the relationship between background cerebral electrical activity and PaCO 2 in very low birth weight infants.Electroencephalography provides a noninvasive technique for monitoring cerebral electrical activity. The normal EEG pattern of infants less than 30 wk' gestation is markedly discontinuous and consists of long isoelectric periods called interburst intervals, interspersed with bursts of high voltage and mixed frequency activity (10). Two separate studies have linked adverse neurologic outcome of such infants with an abnormal background EEG activity characterised by prolonged Received February 18, 2004; accepted November 16, 2004

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confidence: 67%

Effect of carbon dioxide on background cerebral electrical activity and fractional oxygen extraction in very low birth weight infants just after birth

et al. 2005

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“…Overall, these adjustments in cerebrovascular reactivity between the neonate and the adult appear to involve a generalized decrease in sensitivity to many contractile agonists [3,6,7,10,16]. Conversely, cerebrovascular reactivity to a broad variety of vasodilator stimuli appears to increase with age [2,[29][30][31]. Although changes in receptor density and affinity [16,32] can explain some of the observed age-related changes in cerebrovascular reactivity, other, as yet unknown, mechanisms are clearly also involved.…”

Section: Discussionmentioning

confidence: 91%

Developmental Changes in the Calcium Sensitivity of Rabbit Cranial Arteries

Akopov

Zhang

Pearce³

1998

Neonatology

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The present experiments examine developmental changes in cerebrovascular Ca²⁺ sensitivity. Common carotid (COM), basilar (BAS) and femoral (FA) arteries from adult (n = 16), 8- to 9-day-old (n = 15) and 24- to 25-day-old rabbits (n = 12) were denuded of the endothelium and permeabilized with β-escin. Bath calcium concentrations were controlled via EGTA-Ca²⁺ buffer solutions. Adult pCa-force relations were right-shifted relative to those of 8- to 9-day-old rabbits but were similar to those of 24- to 25-day-olds. Adult pD₂ (–log ED₅₀) values for Ca²⁺ averaged 6.36 ± 0.03 (COM), 6.77 ± 0.04 (BAS) and 6.40 ± 0.04 (FA). Corresponding 8- to 9-day-old values were 6.85 ± 0.03, 7.08 ± 0.08 and 6.76 ± 0.05. In all arteries studied, the addition of 5-hydroxytryptamine (5-HT) subsequent to contraction by a constant submaximal (EC₃₀) concentration of Ca²⁺ produced a dose-dependent and GDPβS-sensitive increase in tension attributable to an increase in Ca²⁺ sensitivity. The magnitudes of 5-HT-induced increases in Ca²⁺ sensitivity were significantly greatest in 8- to 9-day-old rabbits, intermediate in 24- to 25-day-old rabbits, and least in adults. GTPγS mimicked the effects of 5-HT and prevented further increases in Ca²⁺ sensitivity induced by 5-HT in all arteries from all age groups. GDPβS completely reversed all effects of 5-HT on Ca²⁺ sensitivity. From these data we conclude that baseline Ca²⁺ sensitivity is elevated in newborn relative to adult rabbits, at least in femoral, common carotid and basilar arteries. In these arteries, 5-HT can increase Ca²⁺ sensitivity via a G-protein-dependent mechanism which is more effective in neonatal than adult arteries. These effects of maturation on vascular Ca²⁺ sensitivity may play an important role in developmental changes in vascular reactivity.

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“…Hyperventilation causes hypocapnia, which again results in cerebral vasoconstriction and may decrease cerebral perfusion 217 . Hypocapnia is associated with poor outcome after HIE 218 , while permissive hypercapnia may be beneficial up to a certain level 219 .…”

Section: Resuscitation and Supportive Carementioning

confidence: 99%

Post-hypoxic hypothermia is protective in human NT2-N neurons regardless of oxygen concentration during reoxygenation

et al. 2009

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Response of the Cerebral Circulation to Hypocarbia in Postasphyxia Newborn Lambs

Cited by 24 publications

References 16 publications

Effect of carbon dioxide on background cerebral electrical activity and fractional oxygen extraction in very low birth weight infants just after birth

Effect of carbon dioxide on background cerebral electrical activity and fractional oxygen extraction in very low birth weight infants just after birth

Developmental Changes in the Calcium Sensitivity of Rabbit Cranial Arteries

Post-hypoxic hypothermia is protective in human NT2-N neurons regardless of oxygen concentration during reoxygenation

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