title: Topography-specific spindle frequency changes in obstructive sleep apnea.
abstract: BACKGROUND
  Sleep spindles, as detected on scalp electroencephalography (EEG), are considered to be markers of thalamo-cortical network integrity. Since obstructive sleep apnea (OSA) is a known cause of brain dysfunction, the aim of this study was to investigate sleep spindle frequency distribution in OSA. Seven non-OSA subjects and 21 patients with OSA (11 mild and 10 moderate) were studied. A matching pursuit procedure was used for automatic detection of fast (≥13 Hz) and slow (<13 Hz) spindles obtained from 30 min samples of NREM sleep stage 2 taken from initial, middle and final night thirds (sections I, II and III) of frontal, central and parietal scalp regions.
  
  
  RESULTS
  Compared to non-OSA subjects, Moderate OSA patients had higher central and parietal slow spindle percentage (SSP) in all night sections studied, and higher frontal SSP in sections II and III. As the night progressed, there was a reduction in central and parietal SSP, while frontal SSP remained high. Frontal slow spindle percentage in night section III predicted OSA with good accuracy, with OSA likelihood increased by 12.1%for every SSP unit increase (OR 1.121, 95% CI 1.013-1.239, p=0.027).
  
  
  CONCLUSIONS
  These results are consistent with diffuse, predominantly frontal thalamo-cortical dysfunction during sleep in OSA, as more posterior brain regions appear to maintain some physiological spindle frequency modulation across the night. Displaying changes in an opposite direction to what is expected from the aging process itself, spindle frequency appears to be informative in OSA even with small sample sizes, and to represent a sensitive electrophysiological marker of brain dysfunction in OSA.
authors.affiliation: Sleep Laboratory, Division of Pulmonary Medicine, Hospital de Clínicas de Porto Alegre, Rua Ramiro Barcelos 2350/sala 2050, Porto Alegre, RS, 90035-003, Brazil.
authors.forename: Suzana V
authors.initials: SV
authors.lastname: Schönwald
authors.forename: Diego Z
authors.initials: DZ
authors.lastname: Carvalho
authors.forename: Emerson L
authors.initials: EL
authors.lastname: de Santa-Helena
authors.forename: Ney
authors.initials: N
authors.lastname: Lemke
authors.forename: Günther J L
authors.initials: GJ
authors.lastname: Gerhardt
mesh_terms: D000328:Adult; D001931:Brain Mapping; D058256:Brain Waves / Q000502:physiology*; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012372:ROC Curve; D012189:Retrospective Studies; D012815:Signal Processing, Computer-Assisted; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D012894:Sleep Stages / Q000502:physiology; D018709:Statistics, Nonparametric