Blood pressure differences between consecutive days of ambulatory monitoring in hypertensive patients:: the <<ABPM effect>>

BACKGROUND: Ambulatory blood pressure monitoring is a method of blood pressure assessment that compensates for some of the limitations of office values. While a white-coat, pressor effect on conventional determination has been defined and frequently used for the improved evaluation of hypertensive patients, there is no evidence that the ambulatory technique could also influence blood pressure. PATIENTS AND METHOD: Aimed at testing and quantifying the extent and duration over time of a possible pressor effect due to ambulatory monitoring, we studied 387 mild-to-moderate hypertensive patients (160 men), aged 54.2 (14.3) (mean [SD]). Blood pressure and heart rate were measured at 20-min intervals during the day and at 30-min intervals at night for 48 consecutive hours, and physical activity was simultaneously evaluated at 1-min intervals by means of a wrist actigraph. One third of patients were evaluated twice or more times. RESULTS: In hypertensive patients who were evaluated for the first time, results indicate a highly significant (p < 0.001) reduction, in the second day of monitoring as compared to the first, in the diurnal mean of systolic and diastolic blood pressure, but not in heart rate or physical activity. This pressor effect remains significant for at least the first 5 hours of monitoring. The nocturnal mean of blood pressure was, however, similar in the two days of sampling. This ambulatory monitoring effect, could not be observed when patients were evaluated following the same sampling scheme at the second or further times. CONCLUSIONS Ambulatory monitoring for 48 consecutive hours reveals a statistically significant pressor response that could reflect a novelty effect in the use of the monitoring device for the first time. This effect has notable implications in both research and clinical daily practice, both for proper diagnosis of hypertension and evaluation of treatment efficacy.