DECREASE IN PARIETAL CEREBRAL HEMOGLOBIN OXYGENATION DURING PERFORMANCE OF A VERBAL FLUENCY TASK IN PATIENTS WITH ALZHEIMERS-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 chan ges in cerebral hemoglobin oxygenation in the frontal and parietal cor tex during performance of a verbal fluency task in patients with Alzhe imer's disease (AD). Whereas healthy elderly subjects n = 19, age 67 /- 10 years) showed increases in concentrations of oxygenated hemoglob in [HbO(2)] (mean (arbitrary units) +/- S.E.M., 1.44 +/- 0.59) and tot al hemoglobin [HbT] (0.92 +/- 0.81) over the left superior parietal co rtex, patients with AD (n = 19, age 71 +/- 10 years) showed significan t 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 p refrontal cortex simultaneous increases in [HbO(2)] as well as [HbT] i n 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)] an d [HbT] in the frontal cortex. Simultaneous NIRS-[HbT] and PET-rCBF me asurements showed a significant correlation both when calculated in a 'banana' shaped volume approximated by using cortical thresholds as we ll as when calculated in a semisphere volume of brain tissue beneath t he 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 t o 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 degenera ting brain areas, such as the parietal cortex. (C) Elsevier Science B. V.