A knowledge of neonatal cerebrovascular physiology is essential to the understanding of diseases that frequently affect the subsequent development of the newborn brain. Recent observations indicate that the cerebral vessels of the healthy newborn infant, even the very preterm, respond to physiological stimuli in the same manner as in the mature organism. Thus, cerebral blood flow changes with changes in arterial carbon dioxide tension (Paco,), oxygen concentration (Cao,), or glucose concentration, whereas cerebral blood flow remains constant at minor fluctuations in arterial blood pressure. In pathological states, pressure autoregulation may become impaired, and in severe cases the vessels do not react to chemical or metabolic stimuli. These infants are at high risk for developing cerebral lesions, and they may be candidates for new "brain-protecting regimens." Pryds 0. Control of cerebral circulation in the high-risk neonate. Ann Neurol 1991;30321-329
The two major causes of brain injury and subsequent neurological handicap in newborn infants are hypoxicischemic encephalopathy and intracranial hemorrhage.
Estimation of Cerebral Blood Flow in
Newborn Infants
Few techniques are practical for quantitative CBF measurements in humans. A modification of the Kety-Schmidt method depends on the rate of extraction of a diffusible, inert, and radioactive indicator from the brain. The clearance is detected by means of external scintillators placed over the skull. It is possible to administer the gamma ray-emitting gas xenon 133 ( '33Xe) in the carotid artery [l6], in the inspiratory gas I171, or intravenously 118-20). Clearance of positron-emitting, inert isotopes as detected by positron emission tomography (PET) provides assessment of regional CBF [2 11, and may also be extended to identify local metabolic processes such as glucose consumption [22J Recently, near-infrared spectrophotometry was used to estimate CBF in neonates [23]. This noninvasive and nonradioactive technique detects changes in oxygenated hemoglobin in the brain following a short pulse of increased oxygen in the inspiratory gas. Regional CBF has also been recorded by nonradioactive, xenon-enhanced, x-ray transmission computed tomogra-P ~Y 1247.