0029 Reading the Clock Through the Heart: Circadian Modulation of Heart Rate in Sleep Disorders

Abstract Introduction Introduction: The circadian rhythm exerts direct control over autonomic tone and, consequently, over heart rate (HR), producing an expected pattern of nocturnal HR reduction (dipping) and morning elevation. Alterations in this profile—whether due to sleep disorders, sleep fragmentation, or circadian misalignment—suggest a decoupling between the biological clock and the cardiovascular system. Objective:To evaluate the association between the circadian rhythm, heart rate (HR), and oxygen saturation (SpO2) in patients with Obstructive Sleep Apnea (OSA). Methods Methods: This was a cross-sectional study nested within a cohort, evaluating 36 individuals, 58.1% of whom were women, with a mean age of 53.95 + 11.86 years. Patients diagnosed with OSA were included, and the following measures were collected: HR, SO 2 , and data from the Morningness-Eveningness Questionnaire for Sleep Apnea (MEQ-SA). Results Results: The mean score for the MEQ-SA was 22.4 + 4.8. We divided the sample into two blocks: the first composed of individuals scoring above 22 and the second of individuals scoring below 22 on this questionnaire. The results for the two blocks (Above 22 vs. Below 22) were: Minimum HR (56.67 + 6.40 vs 49.31 + 5.76), Mean HR (72.44 + 8.95 vs 68.46 + 10.15), Maximum HR (109.22 + 9.80 vs 110.69 + 13.22), ΔHR (36.78 + 8.06 vs 41.77 + 13.22), Minimum SO 2 (83.89 + 5.01 vs 81.08 + 15.09), and Mean SO 2 (93.56 + 2.50 vs 93.54 + 7.30). Conclusion Conclusion: The systematic incorporation of heart rate rhythm into sleep disorder assessment transforms HR from a static vital sign into a biomarker of circadian organization. Patterns such as the absence of nocturnal HR dipping, persistent tachycardia during sleep, or a phase shift in HR can signal autonomic vulnerability and a mismatch between the biological clock and the cardiovascular system, with potential prognostic impact. Support (if any)