Spindle frequency remains slow in sleep apnea patients throughout the night

Background: Our previous data suggested that in normal sleep the frequency of individual sleep spindles would be related to sleep depth and possibly to sleep pressure. Thus far spindle frequency patterns in patients with sleep disorders have not been studied. It would be expected that the spindle frequencies might be affected by sleep fragmentation disturbing the sleep process. Methods: Twelve apnea patients with age- and sex-matched control subjects were studied with whole-night sleep recordings. Sleep spindles were visually selected and their frequency was determined by spectral analysis. Results: Sleep spindles of the patients were in general slower than in the control subjects. As in our previous study, the frequency of the spindles in the middle-part of the non-rapid eye movement (NREM) sleep episodes increased towards the end of the night in the control group, whereas in the patient group no such increase was found. Conclusions: The slow spindle frequencies in apnea patients could indicate disturbed sleep and altered neural mechanisms in the structures regulating sleep spindle activity. (C) 2003 Elsevier Science B.V. All rights reserved.