Bedside functional imaging of the premature infant brain during passive motor activation.

BACKGROUND: Changes in regional brain blood flow and hemoglobin oxygen saturation occur in the human cortex in response to neural activation. Traditional functional radiologic methods cannot provide continuous, portable measurements. Imaging methods, which use near-infrared light allow for non-invasive measurements by taking advantage of the fact that hemoglobin is a strong absorber at these wavelengths. AIMS: To test the feasibility of a new optical functional imaging system in premature infants, and to obtain preliminary brain imaging of passive motor activation in this population. METHODS: A new optical imaging system, the Diffuse Optical Tomography System (DOTS), was used to provide real-time, bedside assessments. Custom-made soft flexible fiberoptic probes were placed on two extremely ill, mechanically ventilated 24 week premature infants, and three healthier 32 week premature infants. Passive motor stimulation protocols were used during imaging. RESULTS: Specific movement of the arm resulted in reproducible focal, contralateral changes in cerebral absorption. The data suggest an overall increase in blood volume to the imaged area, as well as an increase in deoxyhemoglobin concentration. These findings in premature infants differ from those expected in adults. CONCLUSIONS: In the intensive care setting, continuous non-invasive optical functional imaging could be critically important and, with further study, may provide a bedside monitoring tool for prospectively identifying patients at high risk for brain injury.

Trans-abdominal monitoring of fetal arterial blood oxygenation using pulse oximetry.

Pulse oximetry (oxygen saturation monitoring) has markedly improved medical care in many fields, including anesthesiology, intensive care, and newborn intensive care. In obstetrics, fetal heart rate monitoring remains the standard for intrapartum assessment of fetal well being. Fetal oxygen saturation monitoring is a new technique currently under development. It is potentially superior to electronic fetal heart rate monitoring (cardiotocography) because it allows direct assessment of both the fetal oxygen status and fetal tissue perfusion. Here we present the analysis for determining the most optimal wavelength selection for pulse oximetry. The wavelengths we chose as the most optimal are the first in the range of 670-720 nm and the second in the range of 825-925 nm. Further, we discuss the possible systematic errors during our measurements and their contribution to the obtained saturation results. We present feasibility studies for fetal pulse oximetry, monitored noninvasively through the maternal abdomen. Our preliminary experiments show that the fetal pulse can be discriminated from the maternal pulse and thus, in principle, the fetal arterial oxygen saturation can be obtained. We present the methodology for obtaining these data, and discuss the dependence of our measurements on the fetal position with respect to the optode assembly.