Aortic root size is associated with nocturnal blood pressure in a population of hypertensive patients under treatment for obstructive sleep apnea Abstract Background Obstructive sleep apnea (OSA) is associated with an increased aortic root size. This association has never been studied in patients with hypertension undergoing continuous positive airway pressure (CPAP) treatment for OSA. Methods The 24-h blood pressure (BP) monitoring of 142 hypertensive patients undergoing CPAP treatment for OSA was prospectively documented. Aortic root diameter was assessed by echocardiography. Results The population included 33.8% women, with an overall mean age of 60.7 ± 10.5 years. The median body mass index was 32.7 [29. 5–36.3] kg/m2. The median treatment score was 3 [2–4] anti-hypertensive drugs per day. The median 24-h systolic and diastolic BP were 130 [120–144] and 74.5 [69–82] mmHg, respectively. The night-time systolic and diastolic BP were 119.5 [108–136] and 67 [61–74] mmHg, respectively. The mean diameter of the aorta at the level of the Valsalva sinuses was 34.9 ± 4.4 mm and 20.4 ± 2.3 mm/m when adjusted for height. Patients underwent ventilation for a median duration of 3.8 [1. 7–7.5] years, with a median night-time duration of 6.6 [5. 5–7.5] h per night. The median residual apnea-hypopnea index under ventilation was 2 [1–4] events per hour. A multivariate analysis showed that aortic root size was associated with male gender (p < 0.01) and nocturnal diastolic BP (p < 0.01). When normalized for height, aortic root diameter was positively associated with age (p < 0.01) and nocturnal diastolic BP (p < 0.01). Conclusion In OSA patients, the relationship between aortic root diameter and nocturnal BP persists on CPAP therapy. Further studies that evaluate the potential protective effect of OSA treatment on aortic root dilatation should monitor nocturnal diastolic BP.