Blood pressure dipping pattern has clinical and prognostic consequences. However, reproducibility of night-time blood pressure fall during 24-h ambulatory blood pressure monitoring is considered limited. This limited reproducibility is possibly a result of inadequate day–night definitions. We retrospectively examined the reproducibility of blood pressure dipping in clinical practice, applying a method that accounts for sleep–awake states and does not rely on arbitrary day–night definitions. We also examined dipping repeatability in subjects with changing blood pressure.
Of 962 consecutive ambulatory measurements performed in our unit during a 3-year period, 100 patients (age 60±15) had a prior session, and were the subjects of this study. Based on patients' report we defined ‘awake blood pressure’ as the average of pressure recordings while the subject was awake, including night-time arousals, and ‘sleep blood pressure’ as the average of pressure recordings while the subject was sleeping, including afternoon naps.
We found systolic blood pressure dipping not less reproducible than 24-h, awake- and sleep systolic blood pressure, as evaluated by both Pearson correlations (r=0.52 versus 0.5, 0.5, 0.49, respectively, P≤0.0002 in all), and Bland-Altman repeatability. In a subgroup of 35 subjects (age 63±15) with at least 10 mmHg change in systolic blood pressure between the two sessions, systolic blood pressure dipping remained reproducible (r=0.45, P<0.007).
When interpreted in a way that accounts for sleep–awake pattern, sleep-induced systolic blood pressure dipping in clinical practice is a very reproducible feature of ambulatory blood pressure monitoring, in accordance with its vital prognostic implications