Body mass index and ambulatory blood pressure monitoring.

Body Mass Index and Ambulatory Blood Pressure Monitoring To the Editor: Kotsis et al evaluated the relationship between body mass index and various ambulatory blood pressure parameters in referred untreated subjects (Hypertension, April 2005 issue).1 They report increased incidence of white-coat hypertension and nondipping pattern among obese subjects. We believe these findings were produced by a flawed analysis of the data. Although white coat hypertension was not defined in the article, we assume it conformed to an accepted definition, namely clinic hypertension accompanied by normal awake daytime ambulatory pressure.2 Thus, Kotsis et al reportedly found a greater incidence of normal awake ambulatory blood pressure among obese clinic hypertensive subjects than among their normal-weighing counter-subjects. However, a brief inspection of the 24-hour blood pressure diagrams accompanying the text reveals a late-afternoon blood pressure decline. This dip is associated with the siesta, a known and common phenomenon among Greek (as well as other) populations.3–5 In fact, in the two 24-hour ambulatory blood pressure studies from Greece that reported the siesta, it was practiced by not more than 75% of the participants (!), and the blood pressure diagrams in the study of Kostis et al are consistent with such a rate. In view of the fact that the authors have not excluded measurements taken during afternoon naps from awake daytime averages as recommended in such populations,6 many subjects had their lower daytime sleep blood pressure averaged with their high daytime awake blood pressure, and subsequently some were misclassified as awake normotensive subjects. Because obese subjects were found to have higher ambulatory blood pressure, the effect of such misclassification is expected to be more pronounced in this subgroup. Thus we are lead to an erroneous impression that white coat hypertension is more common among the obese. A similar inclusion of daytime sleep in a falsely low daytime average artificially reduces nocturnal blood pressure decline, leading to the reportedly higher rate of nondipping pattern that Kotsis et al found among obese patients.1