Obstructive sleep apnea (OSA), which causes abnormal pauses in breathing during sleep, is common in patients with vascular cognitive impairment (VCI) and Alzheimer's disease (AD), and exacerbates the cognitive deficits seen in these conditions. OSA is typically treated with continuous positive airway pressure (CPAP), which has been shown to improve cognition in VCI and slow cognitive decline in AD. Despite the need to identify OSA in patients with VCI/AD, these patients often do not undergo testing for OSA. One major barrier is that in-laboratory polysomnography (iPSG), the current standard for diagnosing OSA, is inconvenient for patients with VCI/AD who may be reliant on others for care or require familiar sleep environments. A convenient and cheaper alternative to iPSG is home sleep apnea testing (HSAT), which has been validated against iPSG to diagnose OSA and has proven feasible for use in VCI/AD. Our primary objective is to determine whether the use of HSAT is superior to iPSG in terms of the proportion of patients who complete sleep testing by 6 months post-randomization. We will also investigate cost-effectiveness, patient satisfaction, proportion of patients treated with CPAP, changes in cognition, mood, sleep-related and functional outcomes between HSAT and iPSG at 6 months.

Inclusion Criteria:

• Evidence of cognitive impairment by any one of: (i) Montreal Cognitive Assessment (MoCA) score of 13-28, or (ii) Mini Mental State Examination (MMSE) score of 18-30, or (iii) Toronto Cognitive Assessment (TorCA) score ≤281.
• A diagnosis of: (i) Single-domain amnestic or multiple cognitive domain (with one feature being amnestic) Mild Cognitive Impairment due to Alzheimer's disease (AD); or (ii) Probable AD dementia; or (iii) Possible AD dementia due to limited concomitant cerebrovascular disease; or (iv) Probable Vascular dementia or Vascular Mild Cognitive Impairment, as per the 2011 American Heart Association Scientific Statement; or (v) Patients with a suspected neurodegenerative condition known to be associated with non-OSA sleep disorders (e.g. Parkinson's disease-related dementia and dementia with Lewy Bodies); and/or (vi) Mixed disease
• Have the competency to provide informed consent, or the availability of a substitute decision maker/caregiver who can provide consent (if needed).
• The availability of a caregiver to assist in the completion of HSAT or iPSG, if needed.

Exclusion Criteria:

• Prior diagnosis of OSA within the last 2 years
• Patients already using CPAP or a dental appliance for previously diagnosed OSA.
• A known contraindication for the use of the HSAT that will be used in this study: (a) Moderate to severe pulmonary disease or congestive heart failure that could compromise the validity of the HSAT results (in users of the ApneaLink); (b) Permanent pacemaker or history of sustained non-sinus cardiac arrhythmia (in users of the WatchPAT).
• Any medical device that would interfere with the placement of the HSAT
• Significant physical impairment or language barrier that would restrict the ability to use the HSAT or complete the study assessments.