REPRODUCIBILITY AND DETERMINANTS OF DAYTIME AND NIGHTTIME BLOOD PRESSURE VARIABILITIES

Abstract

Objective: Night-time blood pressure variability (BPV) has shown to have a greater predictive capacity than daytime BPV for adverse outcome. This has been attributed to a better reproducibility of BPV during sleep than during waking hours but studies comparing the two subperiods are lacking. Design and method: To compare the reproducibility of daytime and night-time short term BPV (Standard Deviation) and to identify the determinants of BPV we recorded 24-hour blood pressure (BP) twice 3 months apart in 1051 hypertensive subjects participating in the HARVEST study. BP was measured every 10 minutes during daytime and 30 minutes during night-time. Correlations were performed with Pearson test. Consistency was obtained by calculating the difference between baseline and repeat recording, disregarding the sign of the difference. Repeatability was defined as twice the standard deviation of the changes between the two repeated recordings. Results: Systolic BPV (mean of the 2 recordings) was higher during daytime (12.9 ± 3.2 mmHg) than during night-time (10.9 ± 3.2 mmHg). Independent predictors of daytime systolic BPV were smoking, mean daytime BP, pulse pressure, BP reaction to standing, nocturnal BP fall, white-coat effect, and physical activity habits (negative). Independent predictors of night-time systolic BPV were young age, smoking, mean night-time BP, pulse pressure, BP reaction to standing, nocturnal BP fall, and male gender. Small mean changes in systolic BPV were observed at repeat recording for both daytime and night-time BPV (−0.11 ± 3.8 mmHg and 0.3 ± 4.4 mmHg, respectively). A higher correlation was found between baseline and repeat measurement for daytime BPV than night-time BPV (0.47 vs 0.36, p = 0.002). Consistency was also better for daytime than night-time BPV (2.6 ± 2.8 vs 2.9 ± 3.3 mmHg, p = 0.007) as was repeatability (7.6 vs 8.8 mmHg, respectively). Similar results were obtained for diastolic BPV. Conclusions: Contrary to what is currently thought BPV, measured twice over a 3-month period, is more reproducible during waking hours than during sleep. Smoking, mean BP level, pulse pressure, BP reaction to standing, and nocturnal BP fall, are main determinants of both daytime and night-time BPVs. In addition, BP reactivity to stress is another strong contributor to daytime BPV.