Is there link between hypoxemia severity and impaired functional connectivity? electrophysiological evidence from patients with obstructive sleep apnea syndrome

Abstract

AbstractBackgroundApneas occur more than 30 times per hour in severe obstructive sleep apnea syndrome (OSAS) patients. Each apnea results in decrease of oxygen saturation that leads to recurring intermittent hypoxemia (IH). IH was suggested as a possible factor to contribute cognitive impairment in OSAS. In the present study, we aimed to investigate the functional connectivity in low and high hypoxemia OSAS sub‐groups.MethodThe study included 56 severe OSAS patients and age‐, gender‐ and education matched 33 healthy controls (HC). The OSAS group was divided into two subgroups according to their minimum SO2 level: low‐hypoxemia OSAS (SO2 dropped never below 80%, LHO, n = 29) and high‐hypoxemia OSAS (SO2 dropped below 80%, HHO, n = 27). All participants underwent detailed neuropsychological testing and an EEG recording, using auditory classical oddball paradigm. Imaginary coherency (ICOH) was calculated for intra‐hemispheric, inter‐hemispheric and midline electrode pairs in delta, theta, alpha, beta, and gamma frequency bands.ResultLHO patients did not differ from HC in any frequency band. HHO patients showed reduced intra hemispheric ICOH values at delta, theta and beta frequency bands compared to LHO patients. HHO patients also showed decreased intra hemispheric ICOH values at theta, alpha and beta frequency bands compered to HC. Inter hemispheric group differences were found at beta band indicating decreased ICOH values in HHO patients compared to LHO patients. Midline gamma ICOH values decreased in HHO patients compared to both HC and LHO patients. HHO patients showed decreased memory scores compared to both HC and LHO groups and decreased attention scores compared only to HC.ConclusionAs far as we know, this is the first study to investigate event‐related ICOH changes in OSAS. Above results indicates that decreased connectivity in OSAS may be due to increased IH. Patients with low levels of hypoxemia did not differ from healthy controls, yet patients with high hypoxemia showed diffuse functional connectivity changes. Coherency measures revealed a parallel pattern with the neuropsychological tests underpinning the adverse effect of IH on cognitive functions. Considering OSAS as a modifiable risk factor for developing Alzheimer’s disease, treatment methods to prevent intermittent hypoxemia (i.e., positive airway pressure treatment) gains additional importance.