PEI-LIN LEEGooley, JoshuaJoshuaGooleyMENG-YUEH CHIENLai, Shang-RuShang-RuLaiFeng, Hsin-ChunHsin-ChunFengLin, Ming-TzerMing-TzerLinChiu, Hung-ChihHung-ChihChiuChen, Shih-KuoShih-KuoChenLiu, Po-KangPo-KangLiuYUNG-HSUAN CHENKu, Bo-WenBo-WenKuWang, Su-MeiSu-MeiWangChang, Chin-HaoChin-HaoChangWEI-SHIUNG YANGCHONG-JEN YU2025-06-172025-06-172025-05https://scholars.lib.ntu.edu.tw/handle/123456789/730042Introduction The relationship between sleep regularity and health outcomes in obstructive sleep apnea (OSA) is gaining recognition; however, its connection to continuous positive airway pressure (CPAP) treatment remains underexplored. This study hypothesized that CPAP treatment enhances sleep regularity, which may subsequently improve cognitive function and reduce 24-hour ambulatory blood pressure (BP) variability. Methods Patients with moderate-to-severe OSA from two centers were randomized (1:1) to 12 weeks of CPAP or inactive control. The primary endpoint was 7-day sleep onset, offset, and midsleep time measured by actiwatch. Secondary endpoints included mean reaction time from the Psychomotor Vigilance Task (PVT), correct trials from the Digit Symbol Substitution Test (DSST), and 24-hour BP. Variability in outcomes was assessed using standard deviation. CPAP effects were analyzed by intention-to-treat and per-protocol methods, including participants who adhered to the protocol. Results Of 67 participants, 52 were randomized to CPAP (n=26) or control (n=26). In the CPAP group, 75.2% averaged ≥4 hours of nightly use. CPAP did not significantly affect sleep onset (median=00:06), offset (median=-00:17), midsleep time (median=-00:16), PVT mean reaction time (median=5 msec), or DSST correct trials (median=0) (all P>0.05). However, CPAP reduced variability in awake systolic (median=-1 mmHg) and mean BP (median=-1 mmHg), as well as asleep diastolic (median=-2.6 mmHg) and mean BP (median=-2.5 mmHg) (all P< 0.05). Conclusion Short-term CPAP treatment did not improve sleep regularity but significantly reduced 24-hour ambulatory blood pressure variability, with no notable effects on cognitive function. Support (if any) National Science and Technology Council, Taiwan (NSTC 113-2314-B-002 -284 -MY3; 111-2314-B-002-293); Ministry of Education (MOE) in Taiwan (NTU-107L900502, 108L900502, 109L900502);Taiwan University Hospital (NTHU 109-42, 111-S0298, 111-X0033,113-S0286); MediaTek Inc. (201802034 RIPD)enjournal articlehttps://doi.org/10.1093/sleep/zsaf090.0711