Noninvasive Detection of Changes in Cerebral Blood Flow by Near-Infrared Spectroscopy in a Piglet Model of Hydrocephalus

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Abstract
Formulation of rational interventions in infantile hydrocephalus is limited by the inability to monitor cerebral hemodynamics quantitatively, continuously, and noninvasively. Near-infrared spectroscopy (NIRS) measures changes in cerebral concentration of oxygenated and deoxygenated hemoglobin (HbO2 and Hb); HbD is the derived difference between HbO2 and Hb. Our previous work showed that HbD reflected cerebral blood flow (CBF) measured by radioactive microspheres in a piglet model of systemic hypotension. This study was designed to determine whether NIRS detected important changes in cerebral perfusion and oxygenation in a piglet model of hydrocephalus and whether changes in HbD accurately reflected changes in CBF. Acute hydrocephalus was produced in neonatal piglets by intraventricular infusion of “mock cerebrospinal fluid.” Intracranial pressure (ICP) was maintained for several minutes at approximately 10, 20, and 30 mm Hg above the baseline ICP. CBF was measured in cerebral cortex, white matter, and basal ganglia at each ICP by radioactive microspheres. Changes in HbO2 and Hb were measured continuously by NIRS. Cerebral perfusion pressure declined with increasing ICP, and this decline was accompanied by significant decreases in HbD measured by NIRS and CBF measured by radioactive microspheres. There was a strong correlation between changes in HbD and individual changes in CBF in cerebral cortex, white matter, and basal ganglia (all p < 0.0001). This study demonstrates that changes in HbD reflect changes in CBF over a wide range of ICP in a model of acute hydrocephalus. This reproducible and easily obtained measurement by NIRS could facilitate considerably decisions concerning therapeutic interventions.