Controlled Hypercapnia and Neonatal Cerebral Artery Doppler Ultrasound Waveforms

Archer, L. N. J.; Evans, David H.; Paton, J Y; Levene, Malcolm I.

doi:10.1203/00006450-198603000-00004

Cited by 62 publications

(15 citation statements)

References 20 publications

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“…In this study, we have shown that term infants with apnea or ALTE demonstrate cerebral vasodilation and increased cerebrovascular flow in response to elevated CO 2 . This is consistent with previous studies indicating that well-term newborns exhibit an increased CBF in response to elevated CO 2 [21,22]. Thus, the presence of apnea -which can be associated with impaired respiratory drive and immature autonomic innervationis not associated with impaired cerebral vascular responses to CO 2 in full-term infants.…”

Section: Resultssupporting

confidence: 81%

Cerebral Vascular Responses to Changes in Carbon Dioxide Tension in Term and Preterm Infants with Apnea

Koons

Hegyi²,

Mehta³

et al. 2003

Neonatology

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Carbon dioxide (CO₂) plays important roles in regulating both respiratory drive and cerebral blood flow. These effects are mediated, in part, by activity of the sympathetic nervous system. We hypothesized that the presence of acute life-threatening events or apnea in term or preterm infants, respectively, would serve as a marker for immaturity of cerebral autonomic innervation and that such infants would display a reduced cerebral vascular response to elevated pCO₂. Therefore, we evaluated the cerebral vascular response during CO₂ challenge tests in groups of term and preterm infants with primary apnea. In term infants (39 ± 2 weeks gestation) with acute life-threatening events, elevated pCO₂ was accompanied by decreasing pulsatility index and increasing mean anterior cerebral blood flow velocity. However, in preterm infants (29 ± 2 weeks’ gestation) with apnea, pulsatility index and anterior cerebral artery flow velocity did not significantly change in response to CO₂ supplementation. We conclude that preterm, but not term, infants with apnea exhibit impaired vascular responses to hypercarbia.

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Section: Resultssupporting

confidence: 81%

Cerebral Vascular Responses to Changes in Carbon Dioxide Tension in Term and Preterm Infants with Apnea

Koons

Hegyi²,

Mehta³

et al. 2003

Neonatology

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“…nonpulsatile) component of flow than there is in the systolic (i.e. pulsatile) component of blood flow (19). Inasmuch as changes induced in cerebral blood flow by other mechanisms such as blood pressure changes, may have different effects on the relative changes in pulsatile and nonpulsatile components of blood flow, our results may not be reproduced if changes in cerebral blood flow were induced by other stimuli.…”

Section: Discussioncontrasting

confidence: 52%

Comparison of Electrical Impedance and 133Xenon Clearance for the Assessment of Cerebral Blood Flow in the Newborn Infant

1988

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ABSTRACT. The peak amplitude of pulsatile cerebral electrical impedance (A&) was compared with simultaneous '33xenon clearance estimations of cerebral blood flow (CBF,) on 28 occasions in nine infants receiving assisted ventilation who had changes in Pacoz and thereby presumably in cerebral blood flow. Percentage changes from one measurement to the next in each infant were compared.Using linear regression the relationship was A& = 0.5 CBF, -1.5 with r = 0.67. The 95% confidence interval for the regression coefficient was 0.2-0.8 and the mean residual was 28%. Changes in cerebral blood flow in these clinical conditions were similarly detected by the two methods but A& underestimated the magnitude of the change in comparison with CBF, and its accuracy was insufficient to allow conclusions about the magnitude of small changes in cerebral blood flow in individual infants. (Pediatr Res 24: 461-464,1988) Abbreviations A&, peak amplitude of pulsatile cerebral electrical impedance CBF,, cerebral blood flow estimated from '33xenon clearance curve extrapolated to infinity TcPco2, partial pressure of skin carbon dioxide TcPoz, partial pressure of skin oxygen Cerebral blood flow is assumed to be a vital determinant of neurologic outcome in the sick newborn infant. Information on brain blood flow has been hampered by lack of suitable measurement techniques. '33Xenon clearance is a standard for accurate, quantitative measurement of cerebral blood flow but is limited by the time-averaged nature of the result (because it is necessary to calculate this from the clearance curve that must be collected over some time), the inability to make rapid serial measurements and the total number of studies being determined by the safe limits of ionising radiation exposure. The cerebral electrical impedance technique provides continuous information noninvasively, but the biophysical basis of the technique remains incompletely understood. It relies on the fact that the brain and blood offer a very different resistance to the passage of electric 46current. As blood volume increases in the head after cardiac systole, impedance falls. The cardiac-synchronous component of cerebral impedance is determined predominantly by the instantaneous intracranial blood volume (1). Attempts to correlate cerebral electrical impedance with cerebral blood flow have been made in dogs (1) and in adults (2, 3) with variable results. Modeling the thorax or limb as a cylinder allows reasonably accurate estimates of flow to be made (4-6), but extrapolation of the cylindrical model to the brain is inappropriate because of the complexity of cerebral blood flow. In the human newborn the technique of cerebral electrical impedance has been used to show a reduction in the impedance during tension pneumothorax when cerebral blood flow would be expected to have fallen and an increase in impedance after feeding when cerebral blood flow would be expected to have risen (7). It has also been compared with strain gauge plethysmographic assessment of cerebral blood flow and in...

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“…Thus, when downstream properties (representing vascular impedance) are incorporated into mathematical or physical models, blood flow can become dependent on resistance. 4,5 Although this has been corroborated during postischemic hyperemia in the brachial artery 6 and hypercapnea in neonatal cerebral arteries, 7 the dependence of RI on vascular resistance varies considerably among vascular beds. In rabbit kidneys perfused ex vivo with increasing concentrations of phenylephrine, 8 there was only a slight increase in RI despite a broad range of resistance not observed in vivo ( Figure 1) and the inability of vasoconstrictors or vasodilators to appropriately alter RI has also been observed in the uterine, 9 carotid, 10 and retinal 11 circulations.…”

mentioning

confidence: 99%

Renal Resistive Index

O’Neill

2014

Hypertension

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Controlled Hypercapnia and Neonatal Cerebral Artery Doppler Ultrasound Waveforms

Cited by 62 publications

References 20 publications

Cerebral Vascular Responses to Changes in Carbon Dioxide Tension in Term and Preterm Infants with Apnea

Cerebral Vascular Responses to Changes in Carbon Dioxide Tension in Term and Preterm Infants with Apnea

Comparison of Electrical Impedance and 133Xenon Clearance for the Assessment of Cerebral Blood Flow in the Newborn Infant

Renal Resistive Index

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