[Ambulatory blood pressure, reproducibility, variability and change, placebo effect]

Blood pressure assessment by ambulatory recordings is a recent clinical method. What is the reproducibility and variability of the results and what is the circadian variation of blood pressure? How useful is the technique for evaluating therapeutic efficacy? Several groups have reported that the reproducibility is good within a group of patients but that this is not observed in case by case and measurement by measurement analysis; however, when the periods of observation are sufficiently long (several hours) the recordings are comparable. In clinical practice for an individual patient, it would seem better to compare the average daily pressure load, at rest and during activity, which is more reproducible than the hourly average of blood pressure. The circadian variation of blood pressure and short-term (within the hour) or long-term (24 hours) variability have been analysed in depth and although the ambulatory blood pressure shows the same circadian variation as invasive arterial measurement, it does not show instantaneous variability. The placebo effect is not marked when a large group of patients is studied. On the other hand, case by case analysis shows the persistance of this phenomenon in small numbers of cases and, in practice, these results make the maintenance of a placebo period in therapeutic trials a necessity. In conclusion, ambulatory blood pressure recording in daily medical practice enables the study of therapeutic variations in blood pressure over a 24 hour period. However, it does not yet enable satisfactory analysis of the variability of blood pressure.