EEG FREQUENCY CHANGES DURING SLEEP APNEAS

To study the effect of transient, apnea-induced hypoxemia on electroco rtical activity, five patients with severe obstructive sleep apnea syn drome (OSAS) were investigated during nocturnal sleep. Polysomnographi c and simultaneous digitized electro encephalographic (EEG) recordings for topographic and compressed spectral array analysis were made. The EEG recordings were timed exactly to respiratory events. During nonra pid eye movement (NREM) apneas, delta band amplitude increased, starti ng on average 13 seconds after the apnea onset. Average differences we re 268% between initial and maximal values and 202% between initial an d final values. In contrast, significant increases in delta amplitudes between the onset and end of REM apneas did not occur, although some caused deep oxygen desaturations. Changes in delta activity were nor c orrelated to NREM apnea duration or degree of desaturation. These resu lts indicate that the increased delta activity during NREM apneas may not be caused by arterial hypoxemia. It could instead be due to either an arousal mechanism, since arousals may be preceded by slow waves in EEG, or to a breakthrough of slow-wave-sleep activity. The sleep dist urbance in severe OSAS may create such a propensity for slow-wave slee p that stages pass much more rapidly than in normal persons.