NOCTURNAL BLOOD PRESSURE FLUCTUATIONS IN PATIENTS WITH OBSTRUCTIVE SLEEP APNEA

Abstract

Objective: Reverse dipping of nocturnal blood pressure (BP) is a sensitive predictor of cardiovascular morbidity and mortality. Nocturnal blood pressure fluctuations (NBPF) related to obstructive sleep apnea may be causative. Studies based on ambulatory blood pressure measurements (ABPM) can only provide mean BP values and long-term BP variability due to low frequent variability during the night. This limits the explanatory power of the method. Here, we apply non-invasive, continuously measuring methods to investigate NBPF in patients with obstructive sleep apnea syndrome (OSAS). Design and method: In a first study, we included 34 patients with suspected diagnosis of sleep apnea undergoing polysomnography. BP was estimated using pulse transit time (PTT, SOMNOscreenTM) as well as measured by Portapres®. In a second study, we included 97 patients with an apnea/hypopnea index greater than 30 (severe OSA). The systolic BP (SBP) was continuously determined using PTT (SOMNOscreenTM) during polysomnography. Results: In the first study, 11 patients with OSA were analyzed. Sleep apnea related SBP fluctuations >8mmHg measured by Portapres™ were included. Both, the PTT-based method and Portapres® detected the same apnea related SBP fluctuations during night. Bland Altman plot showed a mean difference <1mmHg between both methods, with limits of agreement of ±13.4 mmHg. Mean apnea related SBP fluctuations were between 28 and 29 mmHg for both methods. In the second study, we found, in addition to normal NBPFs, BP fluctuations arranged like steps in 48 patients. Thereby, the SBP decrease after the event did not reach the level before the apnea. This led to a continuous increase of the SBP baseline called “superposition” of BP. Further, this phenomenon resulted in extremely high SBP values in some of the patients. Conclusions: BP fluctuations induced by OSA may contribute to the non-dipping/reverse dipping phenomena in OSA patients. The continuously measuring methods used here offer detailed insight into patterns of BP fluctuations. This improves our understanding of BP control during night time and helps to identify patients with increased risk for cardiovascular events.