The clinical relevance of adopting different definitions of night-time when assessing nocturnal blood pressure

Objective: For hypertension diagnosis, the current European guidelines recommend to combine repeated office readings with use of out-of-office blood pressure (BP) measurements, like ambulatory blood pressure monitoring (ABPM). The drop of systolic BP during night (dipping behaviour) is one of the most important information offered by 24h ABPM. Night-time is most defined as the time period between 22 and 6 h. However, ambulatory sleep studies have shown that individual sleep behaviour is heterogenous. Shifted, shortened, or prolonged time-in-bed (TIB) may lead to changes in classification of dipping behaviour. Additionally, 20% of the population suffers from insomnia, meaning that during TIB patients are partially awake. We investigated nocturnal BP and dipping classification based on actual sleep time vs. individual TIB vs. 22 - 6 h. Design and method: Thirty adults (9 women, mean age 65.1 ± 9.5 years) underwent ABPM via a validated Boso TM- 2430 device. Simultaneously, motor activity and body position were recorded (SOMNOtouch™ NIBP, SOMNOmedics) allowing determination of individual TIB and actual sleep time. Results: In nine patients (30%), individual TIB was shifted by more than two hours, usually being shifted towards later hours. Mean duration of TIB was 7:18h (2:13h to 10:08h). Mean sleep efficiency in individual TIB was 85.6% compared to 72.4% in standard 22 - 6 h. When defining TIB as 22 - 6 h, prevalence of non-dippers was 63% (n = 19). After analysing the corrected TIB, only 37% (n = 11) remained non-dippers. Individual adoption of TIB led to a change in dipping classification in 27% (n = 8) of patients (in all cases from non-dipper to dipper). Considering only BP values during actual sleep, dipping classification changed in another four patients, two patients changing from non-dipper to dipper while two patients changed from dipper to extreme dipper. Conclusions: In 12 out of 30 patients (40%), BP dipping classification changed when adjusting TIB individually and considering BP values during actual sleep. This study highlights that individually determined TIB and exclusion of wake phases during night is of critical importance for a correct assessment of dipping behaviour and may play an important role in optimizing the clinical management of arterial hypertension.