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Obstructive sleep apnoea affects morning spatial navigational memory processing in asymptomatic older individuals

Presented by
Dr Andrew Varga, Icahn School of Medicine at Mount Sinai, USA
ATS 2019
A new study led by Dr Andrew Varga (Icahn School of Medicine at Mount Sinai, USA) showed that mild obstructive sleep apnoea (OSA) in cognitively normal older adults is associated with significantly atypical morning spatial navigation performance—an early symptom of Alzheimer disease [1].

Sleep is thought to be critical for processing spatial memories, and spatial disorientation is one of the earliest hallmarks of cognitive dysfunction in Alzheimer disease. The investigators in this study wondered whether sleep disruption from OSA would negatively impact the processing of spatial navigational information in older asymptomatic individuals.

To this end, Dr Varga and colleagues recruited 42 cognitively normal older individuals (aged 66.5 ± 8 years) and had them explore a 3D computer generated spatial maze for 5 minutes, in addition to 3 timed trials (capped at 10 minutes each) to reach a target in the maze before and after polysomnographically recorded sleep. Subjects also completed a 20-minute psychomotor vigilance test (PVT) in the morning. Maze and PVT performance among 30 individuals without OSA (apnoea-hypopnoea index [AHI] 4% <5/hour) were compared with 12 individuals with OSA (AHI 4% ≥5/hour).

Median AHI 4% was 0.5/hour in subjects without OSA and 10.7/hour in subjects with OSA. N1 sleep was significantly increased in subjects with OSA (25.4% ± 4% in OSA vs 16.1% ± 1.5% in non-OSA, P=0.004) and N2 sleep was significantly decreased in subjects with OSA (41.5% ± 3% in OSA vs 48.4% ± 2% in non-OSA, P=0.034). No significant differences in N3 or REM sleep were observed. There were no significant differences in pre-sleep maze completion time, whereas post-sleep maze performance was significantly different between groups. Subjects without OSA continued to improve maze completion time on average across the 3 morning trials whereas subjects with OSA performed best on the first morning trial and performed worse on average with each subsequent trial (significant interaction between OSA group and morning trial number, P=0.016). There were no significant differences in mean reaction time (263 ms [IQR 233 ms-275 ms] in OSA vs 277 ms [IQR 251 ms-338 ms] in non-OSA, P=0.14) or number of lapses (2.5 lapses [IQR 0-4.5 lapses] in OSA vs 3 lapses [IQR 1-9.5 lapses] in non-OSA, P=0.3) on morning PVT.

The take-home message of the study was that cognitively normal older adults with mild OSA on average showed no deficits in morning vigilance, but nonetheless demonstrated significantly aberrant morning spatial navigation performance compared with individuals without OSA after equivalent spatial navigation encoding in the evening.

Dr Varga: “[The patient population] was a group of older people, average age was around 68 years old. One of the really interesting things is that these were people that were recruited from the community and did not intrinsically have any sleep complaints. So, they were not necessarily complaining that they had snoring or any other breathing issues with sleep apnoea. They were not complaining of any cognitive complaints, were not complaining of any sleepiness. We showed that, when we recruited this population, sleep apnoea is enormously prevalent, and when we kind of pushed the system and really tested them on this ability to remember space and spatial navigation, there was a deficit—even though they did not have any other issues.”

    1.  Varga AW, et al. A7263, ATS 2019, 17-22 May, Dallas, USA.

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