Experimental Cardiology, Tropical Medicine Institute, Central University, Caracas, Venezuela.
J Hypertens. 2010 Mar;28(3):459-64. doi: 10.1097/HJH.0b013e328334f220.
Conventional calculation of mean 24-h ambulatory blood pressure (BP), SBP and DBP based on the average of all BP readings disregards the fact that a larger number of measurements is usually scheduled during the daytime than at night, an imbalance possibly leading to an overestimation of 24-h average BP. The aim of our study was to quantify this possible bias and to explore its determinants.
Four hundred and fifty untreated individuals were subdivided into three groups (150 individuals each) with three different ambulatory blood pressure measurement schedules for day/night: group I, four (day)/two (night) readings/h; group II, four (day)/three (night) readings/h; and group III, with BP readings every 30 min throughout 24 h. Hourly and 24-h averages were computed. The conventional 24-h averages of all SBP and DBP values were compared with the averages of hourly SBP and DBP mean values (time-weighted quantification). The difference between 24-h conventional and 24-h time-weighted BP was computed in each group and related to the degree of nocturnal BP dip and to the ratio between the number of readings of day and night.
In the three groups, 24-h conventional and 24-h time-weighted BP values were highly correlated (r > 0.99), 24-h conventional SBP and DBP being significantly higher (P < 0.01) than the corresponding 24-h time-weighted values in groups I and II but not in group III (Bland-Altman analysis). The bias magnitude was related to the day/night ratio in number of readings and to nocturnal BP dip in groups I and II (P < 0.01) but not in group III.
The higher number of readings/h during daytime leads to an overestimation of conventional 24-h average BP, particularly in individuals with preserved nocturnal BP dipping. This can be avoided either by scheduling the same number of readings/h throughout 24 h or by performing a time-weighted quantification of 24-h BP. The clinical implications of these different approaches deserve further investigation.
常规的 24 小时动态血压（BP）、收缩压（SBP）和舒张压（DBP）平均值的计算基于所有 BP 读数的平均值，忽略了一个事实，即通常在白天安排的测量次数多于夜间，这种不平衡可能导致 24 小时平均 BP 的高估。我们研究的目的是量化这种可能的偏差，并探讨其决定因素。
将 450 名未经治疗的个体分为三组（每组 150 人），采用三种不同的日间/夜间动态血压测量方案：组 I，每小时测量 4 次（白天）/2 次（夜间）；组 II，每小时测量 4 次（白天）/3 次（夜间）；组 III，每 30 分钟测量一次 24 小时的血压。计算每小时和 24 小时的平均值。比较所有 SBP 和 DBP 值的常规 24 小时平均值与每小时 SBP 和 DBP 平均值（时间加权量化）的平均值。计算每组中 24 小时常规 BP 与 24 小时时间加权 BP 之间的差值，并将其与夜间 BP 下降程度和白天与夜间读数数量的比值相关联。
在三组中，24 小时常规和 24 小时时间加权 BP 值高度相关（r>0.99），组 I 和 II 中 24 小时常规 SBP 和 DBP 值显著高于相应的 24 小时时间加权值（P<0.01），但在组 III 中则不然（Bland-Altman 分析）。偏差幅度与白天/夜间读数数量比和夜间 BP 下降有关，在组 I 和 II 中（P<0.01），但在组 III 中则不然。
白天测量次数的增加会导致常规 24 小时平均 BP 的高估，特别是在夜间 BP 下降保存的个体中。这可以通过在 24 小时内安排相同数量的测量/h 或通过对 24 小时 BP 进行时间加权量化来避免。这些不同方法的临床意义值得进一步研究。
