Abstract

Hypoxic-ischemia of the brain (tissue oxygen deficiency due to obstructed circulation) during birth can result in neurological impairment and consequently patients that may require specialised care for the remainder of their life. An accurate method for measuring fetal brain oxygenation is therefore required. Traditional clinical techniques do not directly measure cerebral oxygenation and are unpleasant for both the mother and fetus. Near infrared (NIR) spectroscopy is a technique that allows changes in tissue chromophore concentrations to be measured non-invasively. Most NIR spectrometers use algorithms which assume that the optical pathlength of the light in the tissue does not change during the measurement. In the area of fetal NIR spectroscopy, it is of interest to determine whether contraction induced optical pathlength changes produce significant errors in the estimated concentration changes. An intensity modulated optical spectrometer (MOS) can provide optical pathlength information in addition to the pure intensity data provided by traditional NIR spectrometers. An MOS is used here to investigate the influence of contractions on the change in the oxy- and deoxy-hemoglobin status in the fetal brain. It was found that in most cases the changes in optical pathlength did not contribute significantly to any error. It appears that the pathlength changes are primarily due to contraction induced absorption changes. It also appears that artefactual pathlength and absorption changes, which occur due to maternal movement, while to0 complicated to physically characterise are readily recognisable in the raw data.

© 1996 Optical Society of America