Hippocampus volume and subjective sleepiness in older people with sleep-disordered breathing: a preliminary report

Sleep-disordered breathing (SDB) is associated with excessive daytime sleepiness (EDS) and explained by sleep fragmentation and hypoxaemia, both contributing to brain morphology abnormalities. Recent data on middle-aged SDB patients suggest a link between hippocampus volume (HV) and EDS. We tested this hypothesis in a group of SDB older subjects. A total of 232 healthy participants aged 75 +/- 0.9 years were examined. Subjective EDS was assessed by the Epworth Sleep Questionnaire (ESS), with a mean score of 5.6 +/- 3.5. Volumetric segmentation of the right (RHV) and left HV (LHV) were measured using FreeSurfer software. All subjects underwent extensive cognitive testing to exclude neurological disease, as well as ambulatory polygraphy to assess SDB status. Sleepy subjects showed a lower HV. In a correlation analysis, RHV (r = -0.162, P = 0.01) and LHV (r = -170, P = 0.05) were correlated negatively with ESS and not associated with respiratory data. Multiple regression analysis did not reveal any effect of age, gender, SDB severity and hypoxia. ESS was the only factor possibly explaining the lower RHV (P = -0.03) and LHV (P = -0.04). In older people with SDB, the subjective EDS was associated with lower HV. This morphological finding should be considered on the pathogenesis of sleepiness in SDB patients.