The effect of disease severity and chronic CPAP-therapy on cognitive functions and event related potentials in OSAS

Obstructive sleep apnea syndrome (OSAS) may cause daytime sleepiness, mood changes and dysfunction in various cognitive areas due to recurrent arousals and / or chronic intermittent hypoxia. Different possibilities have been proposed regarding the most affected cognitive areas and mechanisms of OSAS. However, it is difficult to compare findings of the different studies due to the fact that individuals with different disease severities were included in the study groups. In the current study, we aimed to determine the relationship between severity of OSAS and cognitive functions, to investigate the effect of continuous positive airway pressure (CPAP) titration treatment on cognitive functions and the relationship between these changes and electrophysiological potential.

The study included 4 groups of patients with simple snoring and mild, moderate and severe OSAS. In the pre-treatment evaluations, verbal fluency, visuospatial memory, attention, executive functions, language abilities and electrophysiological tests for event-related potential were performed. The same procedure was reapplied after 4 months of CPAP-therapy.

Long-term recall scores and total word fluency scores were found to be low in the groups with moderate and severe disease compared to the patients with simple snoring (p: 0.04, p: 0.03, respectively). The information processing time was higher in patients with severe disease compared to patients with simple snoring (p: 0.02). The P200 and N100 latencies related to event related potentials (ERP) were significantly different between the groups (p: 0.004, p: 0.008, respectively). After CPAP treatment, significant differences were found in N100 amplitude and latencies and all cognitive areas except abstraction. In addition, N100 amplitude and latency change rate as well as change in attention and memory abilities were correlated (r: 0.72, p: 0.02; r: 0.57, p: 0.03, respectively).

In the current research, disease severity was found to negatively affect long-term logical memory, sustained attention and verbal fluency. Moreover, significant improvement was detected in all cognitive areas with CPAP treatment. The findings of our study support that changes in N100 potential have the potential to be used as a biomarker that can be used to monitor cognitive function recovery after treatment.