Reproducibility of intra-arterial ambulatory blood pressure: effects of physical activity and posture

Objective To examine the effects of physical activity, body posture and sleep quality on the reproducibility of continuous ambulatory blood pressure monitoring. Methods Measurements were performed in 35 subjects (18 hypertensive, 11 male), mean +/- standard deviation age 49 +/- 13 years. Blood pressure (BP) was measured in the brachial artery, and beat-to-beat values of systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure and heart rate (HR) were computed. Physical activity and posture were continuously measured with five accelerometers. Subjective quality of sleep was assessed with a questionnaire. Reproducibility was expressed as an intraclass correlation coefficient and as the standard deviation of the within-subject differences. Results Posture and activity significantly influenced BP and HR. From lying to sitting, the SBP, DBP and HR increased 6 mmHg, 8 mmHg and 8 beats/min, respectively. From sifting to standing these respective increases were 4 mmHg, 2 mmHg and 13 beats/min. A further rise in activity (from standing to moving generally or walking) increased the SBP by 7 mmHg and the HR by 7 beats/min, and decreased the DBP by 8 mmHg. For daytime SBP, DBP and HR, the intraclass correlation coefficient (standard deviation of the within-subject differences) values were 0.93 (7.2 mmHg), 0.94 (3.8 mmHg) and 0.90 (4.1 beats/min). For night-time these respective values were 0.98 (4.4 mmHg), 0.97 (2.5 mmHg) and 0.96 (2.2 beats/min). Correction for physical activity level and posture hardly improved the reproducibility of daytime BP and HR. Reproducibility of night-time BP and HR was not improved by correction for physical activity, supine position or self-reported sleep quality. Conclusions Within-subject differences between ambulatory BP recordings cannot be explained by differences in physical activity and body posture. (C) 2004 Lippincott Williams Wilkins.