In the March edition of the Sleep Journal is an article featuring a cross-sectional analysis to see if patients with untreated obstructive sleep apnea (OSA) have impairments in attention, learning, memory, and ability to follow through on tasks (referred collectively as neurocognitive function). The patients are from a large study to determine if 6 months of CPAP use improves neurocognitive functioning in OSA patients.
There are studies that show that OSA is associated with neurocognitive deficits. The results from this study, however, show that the associations between OSA severity, objectively determined sleep quality, and sleep duration, and neurocognitive function are weak and inconsistent. When there was neurocognitive impairment, it was associated with severe oxygen desaturations, regardless of OSA severity.
The study authors noted that participants were more educated than the U.S. population, with 15.5 years of education on average. Perhaps because they were more educated, the study participants started out with higher intelligence than the average U.S. population. Apparently, there is evidence that patients with higher intelligence are more resistant to adverse neurocognitive effects from untreated OSA.
The point of all this is that this study did not show that neurocognitive deficits are associated with OSA (regardless of the severity) by itself. The finding that was associated was low oxygen levels (<85%) which can occur in conditions other than OSA like COPD. These results fly in the face of my clinical experience - that patients with broken up sleep from OSA (even without low oxygen levels) have trouble concentrating and don't feel as sharp. After they start CPAP, they can function better.