The effects of various definitions of dipping and daytime and night-time on the characterization of 24 h profiles of blood pressure

Background. Ambulatory blood pressure monitoring allows characterization of the patient's average blood pressure load as well as various profiles of blood pressure. Results from clinical studies suggest that dippers (patients whose blood pressures decrease during night-time) have a lower risk of cardiovascular events than do nondippers with similar daytime blood pressures. However, the definitions of dipping as well as of daytime and night-time vary among clinical studies. Objective. To determine whether various definitions lead to markedly different classifications of dipper status. Design and methods. We analyzed 894 24 h ambulatory blood pressure recordings that had been performed at our institution according to three previously published definitions of daytime and night-time and five definitions of dipping. Results. There were small but statistically significant differences among the mean daytime and night-time blood pressures determined using the various definitions. Likewise, the proportions of dippers varied significantly with definitions of dipping and of daytime and night-time. Conclusions. Differences among definitions of dipping as well as of daytime and night-time lead to significant variations in the characterization of patients' 24 h blood blood pressure profiles. The results of this analysis can be used when comparing the results of clinical studies as well as in their design. (C) 2000 Lippincott Williams and Wilkins.