Neuropsychological investigations and event-related potentials in obstructive sleep apnea syndrome before and during CPAP-therapy.

Patients with obstructive sleep apnea syndrome (OSAS) suffer from daytime sleepiness and a decline of cognitive functions. The study evaluated whether special cognitive disabilities predominate in OSAS. Besides the number connection test (ZVT), judging information processing and working velocity, computer-assisted (Wiener Testsystem and Zimmermann Testbatterie) neuropsychological testing was performed in 31 OSAS patients (50.1 +/- 9.4 years) before starting nasal continuous positive airway pressure (nCPAP) therapy. Identical test battery was performed in 10 male healthy volunteers (48 +/- 9.9 years). In addition visual evoked event-related potentials (ERPs) were recorded, the P3-component was evaluated. Impairment of alertness (P < 0.001), selective attention (P < 0.001) and continuous attention (P < 0.001) could be revealed, vigilance was not altered. Cognitive deficits were correlated with the degree of nocturnal hypoxemia. They were not linked to the apnea/hypopnea-index (AHI), arousal index or vigilance parameters. During 6 months of nCPAP-therapy (15 patients) alertness and continuous attention improved significantly (P < 0.01), intra-individual different pathological results persisted however. P3 latencies also remained prolonged. Chronic intermittent nocturnal hypoxemia in OSAS-patients obviously leads to cognitive deficits. ERP partially generated in subcortical cerebral structures represent a neurophysiological tool indicating brain dysfunction which cannot be evaluated by neuropsychological tests. Objective neuropsychological testing is needed in revealing therapeutic effects in OSAS-patients. Remaining deficits during sufficient nCPAP-therapy may reflect irreversible hypoxic cerebral damage.