Analysis of ambulatory blood pressure data in antihypertensive drug trials

In recent years a number of different methods have been evolved to analyse ambulatory blood pressure monitoring data, particularly for evaluating the relationship between blood pressure and target-organ disease and for assessing the effects of antihypertensive drug therapy. The most commonly used methods include calculation of mean or median values during wakefulness and sleep, assessment of blood pressure variability and distribution, calculating blood pressure load, and, more recently, integrating the area under the blood pressure curve over time. Although all of these methods of data analysis have merit, none has been used exclusively in assessing the effects of antihypertensive therapy. The rationale for using a particular method of analysis should be based on the physiological or pharmacological modality under investigation, the reproducibility of the method, the ease of statistical manipulation and, most important, the relationship between the blood pressure determinant and indices of the hypertensive disease process (e.g. left ventricular enlargement, vascular compliance). Ambulatory blood pressure recordings are superior to clinic recordings in assessing the duration of activity of an antihypertensive drug, while Fourier transformation of individual blood pressure curves (in contrast to a group of curves) may aid the evaluation of peak and trough activity. As the blood pressure load and the area under the blood pressure curve are closely related to target-organ disease in hypertension, the use of these methods is advocated in assessing the efficacy of antihypertensive drugs.