Evaluation of the stability of blood flow over time in the dominant hemisphere: a functional transcranial Doppler study.

Functional transcranial Doppler (fTCD) has been used for the identification of cerebral hemispheric dominance in various cognitive tasks. In our study, we have used fTCD with the aim to compare blood flow patterns in the hemispheres not only during the task activation periods but also in the post-stimulus phase. Normal volunteers, 25 right and 25 left-handed, were included. Mean flow velocities (FVs) in the bilateral middle cerebral arteries were recorded during the performance of six cognitive tasks and during the intervals between tasks. The lateralization index (LI) was calculated separately for each test (LI1-6), on the basis of the percent change of blood FV from baseline. To estimate flow fluctuations, a novel index, the LI-variability, was also calculated using a formula constituted by the minimum and maximum mean values recorded at specific time intervals during the entire procedure. Laterization indices, LI-3 and LI-4, corresponding to word generation and reading aloud tasks, produced the highest degree of activation. A perfect agreement (Cohen's kappa=1.000, P<0.001) was observed among LI-3, LI-4, and LI-V. The repetition of recordings gave excellent test-retest reliability in 10 randomly selected participants. Our results suggest that the hemisphere that is characterized as dominant by fTCD maintains a more stable flow pattern during the performance of successive cognitive tasks. Although it could not be considered as a clinically useful tool as yet, this observation introduces a novel parameter such as the stability of blood flow over time, which could potentially provide insight in the study of cerebral functions.

Epidemiological data of multiple sclerosis in the province of Evros, Greece.

The frequency of multiple sclerosis (MS) in Greece is still debated. Our previous epidemiological field survey with a cross-check study of MS on March 31, 1984, in the province of Evros in north-eastern Greece showed a prevalence rate of 10.1/100,000. In 1990, Milonas et al. recorded a prevalence rate of 29.5/100,000 in northern Greece. So Greece is classified in the medium-frequency zone according to Kurtzke. This study was performed to estimate the prevalence of MS in the province of Evros and the annual incidence rates from 1974 to 1999. Patients were identified from several sources. A clinical follow-up was performed in 95% of the cases, and, if clinically indicated, new paraclinical examinations were performed and cases classified by Poser's criteria. The prevalence rate of the definite MS cases on December 31, 1999, was 38.9/100,000 and places the area in the high-risk zone. The mean annual incidence measured in 5-year intervals increased from 0.66/100,000 in 1974-1978 to 2.36/100,000 in 1994-1999 (p < 0.01). The increase in prevalence can be attributed to other causes than etiological changes, but the increase in the annual incidence rate indicates the possibility of a variation in risk factors of the disease.