[Event related potentials and neuropsychological studies in sleep apnea patients]

Patients with obstructive sleep apnoea syndrome (OSAS) commonly complain about daytime sleepiness and a decline of cognitive functions. Several diagnostic tools have been established to judge objectively vigilance and cognitive impairment. Forty OSAS patients aged between 34 and 74 years were examined via several neuropsychological tests (e.g. vigilance test of the Wiener Testsystem, number connection test ("Zahlenverbindungstest-ZVT") to assess working velocity and information processing, d2-test to rate concentration on exertion) before starting continuous positive airway pressure (CPAP) therapy. In addition, visual evoked event-related potentials (ERPs) were recorded; the P3-component was evaluated. All patients subjectively stated daytime sleepiness and cognitive dysfunctions to variable degrees. Each patient showed at least one pathological result in the neuropsychological tests; vigilance impairment could be revealed only in 7 patients. P3-latencies were increased in OSAS patients when compared to age-matched controls (408.1 +/- 44.4 ms versus 373.4 +/- 32.5 ms; p < 0.03). P3-latencies and concentration on exertion showed a significant correlation with respect to the relative part of the total sleep time in which the patient's oxygen saturation was below 90% (p < 0.05). Thus it could be demonstrated that cognitive deficits in OSAS patients are a result of chronic intermittent oxyhaemoglobin desaturation rather than of a decline in daytime vigilance. ERPs represent an objective neurophysiological tool in neuropsychological examination. As they are also generated in subcortical cerebral structures they may indicate cognitive dysfunctions which cannot be evaluated by neuropsychological tests. If lead of ERPs is possible in special sleep centres they should be additionally used in the assessment of cognitive functions in OSAS patients.