Investigation of volumetric magnetic resonance imaging findings and event related oscillations with selective filter and time-frequency analysis in severe obstructive sleep apnea patients

Obstructive sleep apnea syndrome (OSAS) is a sleep disorder that causes cognitive impairment when patients remained untreated. Present study aims to investigate cognitive impairment in OSAS using neuropsychological tests (NPT), evet related oscillations (ERO) and magnetic resonance imaging (MRI) techniques. The study included 74 patients with severe OSAS and 45 healthy controls aged between 18-55 years. All participants' cognitive abilities were evaluated with a comprehensive NPT battery. Procedure was followed by EEG recordings using a classical auditory and visual oddball paradigm. Participants were referred for MRI. ERO were investigated with three analyses techniques; selective filtering, event related spectral perturbation (ERSP) and inter trial coherence (ITC). Cortical and subcortical grey matter volumes were measured for the MRI analysis. NPT results revealed that OSAS patients had decreased Öktem Verbal Processes Test immediate recall and total learning, clock drawing test and simple figure copy test scores compared to healthy controls (p<0.05). ERO analyses revealed significant differences between patients with OSAS and healthy controls in delta, theta, alpha, beta and gamma frequency bands. In the MRI analyses, OSAS patients with excessive daytime sleepiness symptoms showed decreased right caudate nucleus volume compared to healthy controls. However, the significance did not survive after Bonferroni correction (p=0.065). The main result obtained from this study indicates the early cognitive changes in OSAS which cannot yet be detected by NPT or MRI can be detected by electrophysiological methods. Moreover, brain oscillatory responses of patients with OSAS were found to have a similar pattern with Alzheimer's Disease patients by showing decrease in slow frequencies and increase in fast frequencies. OSAS was reported as a risk factor for developing Alzheimer's Disease. In conclusion, this study emphasized the importance of early diagnosis and treatment, and it was suggested that OSAS could be a modifiable risk factor for Alzheimer's disease. .