An evaluation of the plethysmographic method of measuring cranial blood flow in the new-born infant

The development of cardiovascular and cerebral vascular control in preterm infants

Over the past three decades there has been a steady increase in the incidence of preterm birth. The worldwide rate of preterm birth is estimated to be 9.6% of all births, a total of almost 13 million births annually. Preterm birth is associated with a range of adverse cardiovascular and central nervous system outcomes, which may be attributed to altered development of these systems following preterm birth. Preterm birth has a considerable impact on cardiovascular parameters with preterm infants displaying higher heart rates and reduced blood pressure when compared to term born infants at matched ages. Furthermore, premature infants have altered autonomic control of cardiovascular parameters which manifests as abnormalities in heart rate variability and baroreflex mediated control of heart rate and blood pressure. As a result, systemic cardiovascular parameters can be unstable following preterm birth which may place stress on the neonatal brain. The brain of a preterm infant is particularly vulnerable to these fluctuations due to immature cerebral haemodynamics. Preterm infants, particularly those who are very preterm or unwell, display fluctuating pressure-passivity between systemic blood pressure and cerebral blood flow representing a considerably increased risk of cerebral haemorrhage or hypoxia. This is further compounded by immaturity of cerebral blood flow-metabolism coupling, which means increased metabolic demand cannot adequately be met by increased cerebral blood flow. It has been suggested that adverse long-term outcomes following preterm birth may occur as a result of exposure to physiological stress either in-utero or early in infancy.

Evolving understanding of hypoxic-ischemic encephalopathy in the term infant

Our aim was to document changes in the evaluation and prognosis of term-born infants with neonatal encephalopathy of hypoxic-ischemic origin, with particular reference to our own experiences and influences, and to summarize the debate on causation and the relative importance of antenatal and perinatal factors. High quality neonatal cranial ultrasound and magnetic resonance imaging and spectroscopy have enabled the accurate early visualization of different patterns of hypoxic-ischemic brain injury and prediction of their associated outcomes. Long-term follow-up shows that cognitive and memory difficulties may follow even in children without motor deficits. The very early use of electrophysiologic methods has allowed broad prognostic categorization of infants when this is not possible from clinical assessment or imaging, providing a rationale for entry into intervention trials, such as therapeutic hypothermia. This work has also shown that most of these infants have evidence of acute hypoxic-ischemic brain injury that explains their symptoms and outcomes.

Dynamic trend monitoring of cerebral blood flow velocity in newborn infants

A method for obtaining reproducible Doppler cerebral blood flow velocity (CBFV) measurements over several hours, utilizing a probe fixation technique and an on-line system for making beat-to-beat area under the curve (AUC) measurements, is described. Thirty heartbeat samples were collected at three time intervals over 3 hours in a group of 22 healthy preterm infants. The stability of the AUC measurements despite changes in behavioral state was demonstrated by randomized block ANOVA. The sampling error was +/- 6.92%, with 95% confidence intervals of +/- 13.1%. By facilitating reproducible serial measurements of CBFV, this trend monitoring technique encourages a dynamic view of cerebrovascular control, and may be used to probe central nervous system autoregulatory pathophysiology and to evaluate the effects of therapeutic interventions.

The effects of intermittent positive pressure ventilation on cerebral arterial and venous blood velocities in the newborn infant

Cerebral arterial and venous blood velocities were measured using pulsed Doppler ultrasound in 25 newborn infants requiring intermittent positive pressure ventilation (IPPV). The aim was to investigate whether these velocities altered in relation to the peak inflation pressure (PIP) used. Continuous recordings were made on the superior sagittal sinus and an intracranial artery both at the clinically prescribed PIP, and while this was altered in steps. A majority of the infants had, at some stage of their illness, variations in their venous and arterial velocities in phase with IPPV and related to the PIP used. These variations could be reduced by lowering the PIP. This was done in 5 infants whilst we were still able to maintain adequate ventilation.