Effects of three methods of analysis on ambulatory blood pressure indices and the early morning rise in blood pressure

OBJECTIVE: To study the effects of actigraphic, diary and fixed-time methods of analysis on ambulatory blood pressure, the day (awake)-night (asleep) difference and early morning blood pressure. METHODS: We analyzed 50 ambulatory blood pressure studies of patients who also underwent actigraphic activity studies. We divided each study into awake and sleeping intervals by three methods: a patient diary of sleep hours, actigraphically determined sleep hours and a fixed schedule of estimated sleep (2200-0700 h). We then calculated the overall ambulatory blood pressure averages, the awake-asleep differences and the average blood pressure for 4 h after awakening. RESULTS: We found that actigraphic division of the data and patient-kept diaries provided similar ambulatory blood pressure averages whereas fixed-time analysis (2200-0700 h as the sleeping period) was less similar to that using the diary method. The nocturnal decline in diastolic blood pressure calculated by the diary method tended to be higher than that obtained by the fixed time method (16+/-6 versus 14+/-7%, P = 0.037). The limits of agreement for the early morning blood pressure rise for diary and fixed-time analyses were wider than those for diary and actigraphic analyses (-9.5 to +10.0/-6.6 to +7.0) versus (-4.4 to +4.7/-4.1 to +4.0 mmHg). CONCLUSION: Actigraphic division of the ambulatory blood pressure data is more similar to the diary than it is to the fixed-time method studied here. Researchers studying the early morning rise in blood pressure should consider using either actigraphy or diary rather than fixed-time methods of analysis to identify times of awakening.