Decrease in parietal cerebral hemoglobin oxygenation during performance of a verbal fluency task in patients with Alzheimer's disease monitored by means of near-infrared spectroscopy (NIRS) - Correlation with simultaneous rCBF-PET measurements

We used near-infrared spectroscopy (NIRS) to study non-invasively changes in cerebral hemoglobin oxygenation in the frontal and parietal cortex during performance of a verbal fluency task in patients with Alzheimer's disease (AD). Whereas healthy elderly subjects n = 19, age 67 +/- 10 years) showed increases in concentrations of oxygenated hemoglobin [HbO(2)] (mean (arbitrary units) +/- S.E.M., 1.44 +/- 0.59) and total hemoglobin [HbT] (0.92 +/- 0.81) over the left superior parietal cortex, patients with AD (n = 19, age 71 +/- 10 years) showed significant decreases in [HbO(2)] (-3.26 +/- 1.30, P < 0.01) as well as [HbT] (-4.45 +/- 1.57, P < 0.01). [HbR] decreased slightly in both groups (-0.62 +/- 0.29 and -1.18 +/- 0.40, respectively). Using two pairs of MRS optodes placed on the left superior partietal cortex and on the left prefrontal cortex simultaneous increases in [HbO(2)] as well as [HbT] in both cortical regions in the healthy elderly subjects (n = 8, age 60 +/- 15) were demonstrated during performance of the task, AD patients (n = 10, age 65 +/- 13 years) showed decreases in [HbO(2)] and [HbT] in the parietal cortex and, at the same time, increases in [HbO(2)] and [HbT] in the frontal cortex. Simultaneous NIRS-[HbT] and PET-rCBF measurements showed a significant correlation both when calculated in a 'banana' shaped volume approximated by using cortical thresholds as well as when calculated in a semisphere volume of brain tissue beneath the optodes placed on the head surface (patients with AD, n = 10). The correlation was dependent on the assumed penetration depth of the near-infrared light and was best for all three NIRS variables ([HbO(2)], [HbR] and [HbT]) when calculated using a semisphere radius of 0.45 cm to 1.35 cm. In conclusion, in Alzheimer's disease a marked reduction of regional cerebral blood flow and cerebral hemoglobin oxygenation may occur during activation of brain function, probably mainly in degenerating brain areas, such as the parietal cortex. (C) Elsevier Science B.V.