Table 2.

Study Characteristics of Observational Studies

Author/Year	Diagnosis / OSA Criteria	N	Sample Characteristics	Study Type	PAP treatment Dosage/Duration	Control or comparison group	Assessment measures	Main Findings	Hours adherent; % adherent
Costa et.al (2022) [39]	AD, Mild MCI, VaD, VaMC+/AHI>15 or an AHI>5 with a significant oxygen desaturation of 88%	171	(mean age=69.8 ± 10.6 years); 68.4% male	retrospective	PAP use 4 hours/night, for 7 days a week at follow-up.	<4 h of PAP use per night	MoCA, MMSE	Adherence >4h associated with improved MoCa and MMSE scores. There was inconclusive evidence of an association between PAP adherence and changes in other MoCA subdomain scores.	NA; 35.6% .
Liguori et. Al (2021) [41]	MCI or AD / and OSA	24	65–84 (mean age = 74.8 years); 67% male.	retrospective	use PAP for ≥4 hours per night for >5 nights per week	<4 h of PAP use per night, or no use at all	MMSE, CDR	In the whole study sample, a significant decrease was found in MMSE scores, and a significant increase was found in CDR scores. Non-adherent PAP users showed a significantly higher mean change of CDR scores compared to PAP adherent patients.	NA; 50%
Skiba et. Al (2020) [40]	MCI / Mild to severe OSA (AHI 5–30)	96	40–92 (mean age at MCI diagnosis=70.4 years); 66% Caucasian, 66% male.	retrospective	used PAP for average of >4 hours a night	<4 h of PAP use per night, or no use at all	CDR. Modified CERAD included the following sub-tests: orientation, clock drawing, verbal fluency, phonemic fluency, Boston naming, word list learning, recall and recognition, constructional praxis learning and recall, simple and complex visuospatial praxis (Rey–Osterrieth complex figure test), simple calculations, and Trail Making Test part A and part B.	No statistically significant differences in cognitive measures between the PAP and non-PAP group.	3.88 hours; 44%.
Trousierre et. al (2014) [46]	Mild to moderate AD diagnosis / OSA (AHI >30)	23	(73.4 mean age in PAP group) 14 men, 9 women.	single blind, observational study	PAP use for more than 4 hours a night and for more than five nights per week, on average	<4 h of PAP use per night	MMSE	PAP adherence was associated with significantly slower MMSE decline over a three-year follow-up period.	NA; 60.9%.

⁺Diagnosed according to the National Institute on Aging-Alzheimer’s Association (NIA-AA) and the National Institute of Neurological Disorders and Stroke in contribution with the Association Internationale pour la Recherche et l’Enseignement en Neurosciences (NINDS-AIREN)