Jean Krieger

EEG spectral power and sleepiness during 24 h of sustained wakefulness in patients with obstructive sleep apnea syndrome

OBJECTIVE This study investigated if obstructive sleep apnea syndrome (OSAS) may be associated with higher activity in different frequency bands of the EEG during a sustained wakefulness paradigm. METHODS Twelve OSA patients and 8 healthy controls were studied with the Karolinska Drowsiness Test (KDT) and subjective ratings of sleepiness (VAS and KSS) conducted every hour during 24 h of sustained wakefulness. RESULTS The waking EEG activity, mainly in the low (0.5-7.8 Hz) and fast (12.7-29.2 Hz) frequency band, increased as time awake progressed in both groups but more obviously in OSA patients. A similar pattern was observed for rated sleepiness in both groups. Moreover, VAS ratings of alertness were closely related to the awake theta, fast alpha and beta bands in controls but not in OSA patients. CONCLUSIONS OSAS was associated with a wake-dependent increase in low (0.5-7.8 Hz) and fast (12.7-29.2 Hz) frequency range activity. Variations in behavioural sleepiness measured by VAS ratings closely reflect most of the waking EEG parameters in controls but not in OSA patients. SIGNIFICANCE In a sustained wakefulness paradigm, higher activity in delta, theta and beta bands associated with OSAS indicates that OSA patients show marked signs of higher sleepiness and stronger efforts than controls to stay awake, even though they tend to underestimate their sleepiness.

Short-Term Memory Performances during Sustained Wakefulness in Patients with Obstructive Sleep Apnea-Hypopnea Syndrome.

Both working and immediate memories were assessed every 4h by specific short-term memory tasks over sustained wakefulness in 12 patients with obstructive sleep apnea and hypopnea syndrome (OSAHS) and 10 healthy controls. Results indicated that OSAHS patients exhibited lower working memory performances than controls on both backward digit span and complex Sternberg tasks. Speed and accuracy on Sternberg tasks were affected by memory load in both groups. However, immediate memory was not impaired in OSAHS patients. Diurnal and nocturnal SaO(2) were correlated with speed and accuracy high-speed memory scanning performance on Sternberg tasks in patients. These results suggest specific working memory deficits associated with OSAHS over sustained wakefulness with a possible deficiency in the central executive responsible for the higher information processing, in addition to a potentially insufficient storage capacity. Among OSAHS patients, working memory ability involved in high-speed memory scanning may be impaired by chronic hypoxemia.

Effect of continuous positive airway pressure treatment on the subsequent EEG spectral power and sleepiness over sustained wakefulness in patients with obstructive sleep apnea–hypopnea syndrome

OBJECTIVE To determine whether sleepiness and its evolution over sustained wakefulness could be reversed by nasal continuous positive airway pressure (CPAP) therapy in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS). METHODS Twelve OSAHS patients underwent three 32-h sessions of study: one before CPAP therapy (T0), the second (T3) and the third (T6), respectively, after 3 and 6 months of therapy. Each session included one night of sleep followed by 24 h of sustained wakefulness, during which EEG recordings and subjective ratings were performed every hour. RESULTS The waking EEG in treated OSAHS patients was partially improved after 3 months of CPAP and their subjective complaint of sleepiness was normalized after 6 months. Theta power (3.9-7.8 Hz) was decreased as well as its time course during the diurnal period but beta power (12.7-29.2 Hz) remained higher. CONCLUSIONS CPAP partially reverses waking EEG abnormalities in OSAHS patients with reduced theta activity after 3 months and removes the subjective complaint of sleepiness after 6 months. Nevertheless, the persistence of increased beta activity in treated patients suggests that efforts to stay awake remain strong after CPAP treatment. SIGNIFICANCE CPAP influences the EEGs time course over sustained wakefulness in a frequency-specific manner in OSAHS patients.

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Effect of continuous positive airway pressure treatment on short-term memory performance over 24 h of sustained wakefulness in patients with obstructive sleep apnea–hypopnea syndrome

BACKGROUND Few studies have examined the impact of continuous positive airway pressure (CPAP) therapy on short-term memory (STM) over sustained wakefulness in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS). We have investigated if impaired STM can be reversed by CPAP treatment in a 24-h sustained wakefulness paradigm. METHODS Our follow-up study was conducted with repeated-memory tasks within 12 OSAHS patients and 10 healthy controls who underwent three 32-h sessions, one before CPAP (T0) and the second (T3) and the third (T6), after 3 and 6 months of treatment, respectively, for OSAHS patients. Each session included one night of sleep followed by 24h of sustained wakefulness, during which both groups performed STM tasks including both digit span (DS) and Sternberg tasks. RESULTS Untreated OSAHS patients had no deficit in the forward DS task measuring immediate memory but were impaired in STM, especially working memory assessed by the complex Sternberg task and the backward DS. However, only performance in the latter was improved after 6 months of CPAP treatment. CONCLUSIONS Because the high level of memory scanning required high speed in information processing, persistent impairment on the complex Sternberg task may be attributable to working memory slowing, possibly enhanced by sustained wakefulness.