Rationale: Although cognitive deficits are well documented in patients with sleep apnea, the impact on memory remains unclear.
Objectives: To test the hypotheses that (1) patients with obstructive sleep apnea have memory impairment and (2) memory impairment is commensurate with disease severity.
Methods: Patients with obstructive sleep apnea and healthy volunteers (apnea-hypopnea index <5 events/h) completed a test battery specially designed to differentiate between aspects of memory (semantic, episodic, and working) versus attention. Sleepiness was measured on the basis of the Epworth Sleepiness Scale and Oxford Sleep Resistance test. Memory performance in patients versus control subjects was compared (Mann-Whitney U test; P < 0.01, Bonferroni corrected for multiple comparisons) and relationships between performance and disease severity were analyzed by linear regression.
Measurements and main results: Sixty patients and healthy control subjects matched for age (mean +/- SD: patients, 51 +/- 9 yr; control subjects, 50 +/- 9 yr) and education (patients, 14 +/- 3 yr; control subjects, 15 +/- 3 yr) participated. Patients demonstrated impaired Logical Memory Test results (immediate recall: patients, median [range], 36 [9-69]; control subjects, 43 [19-64], P = 0.0004; and delayed recall: patients, 22 [6-42]; control subjects, 27 [10-46]; P = 0.0001). There were minimal differences in attention, visual episodic, semantic, or working memory; patients performed better than control subjects on Spatial Span forward and backward. Regression analysis revealed that Logical Memory Test performance was not significantly related to disease severity after controlling for age, education, and sleepiness.
Conclusions: Obstructive sleep apnea is associated with impairment in verbal, but not visual, memory. The impairment was present across a range of disease severity and was not explained by reduced attention. Such verbal memory impairment may affect daytime functioning and performance.