增强指数评价大动脉僵硬度的数学缺陷

The Limitation of Augmentation Index in Evaluating Arterial Stiffness

目的通过3个研究探讨增强指数(AIx)在动脉僵硬度评估方面的有效性。方法选取156名持续性非卧床腹膜透析(CAPD)患者为研究对象,根据是否患有糖尿病分为两组,测量患者的AIx;运用数学推理方法来验证AIx的有效性;运用临床数据来验证AIx公式的价值。结果糖尿病CAPD患者的AIx比非糖尿病患者低(P<0.05),这与预期结果完全相反。进一步研究显示AIx与外周脉压(PP)之间只存在弱相关性,研究也发现中心增强压力(AP)一般随着中心脉压(C-PP)的变化而变化。而在AIx的计算公式中,AP和C-PP分别作为其中的分子和分母,如果分母不确定,分子的增大并不能决定商必然增大。第2个研究通过数学推理的方法来验证AIx的有效性,数学推理显示,AIx是一个多因素决定的数值F=(ΔSBP-ΔDBP)×[心脏射血波峰(P1)-反射波波峰(P2)]+(ΔP2-ΔP1)×[SBP(收缩压)-DBP(舒张压)],提示其可能并非总是随着P2和AP的变化而变化,此结果在第3个研究中得到证实。结论AIx可能并非反映中心压力波形改变的敏感指标,而只是大动脉功能改变的一种表现,其局限性源于计算公式存在数学缺陷。

Objective To study the validity of augmentation index（AIx） in evaluating aortic stiffness. Methods One hundred and fifty six consecutive ambulatory peritoneal dialysis patients were divided into two groups according to whether they were diabetic, and the AIx in patients was determined; to test the validity of AIx through mathematical ratiocination; to test the value of the AIx formula with clinical data. Results Alx in diabetic was lower than non-diabetic patients （P〈0.05）, which was in variance with the previous studies. Further analysis showed that AIx was just weakly correlated with brachial pulse pressure （PP）-a known index of arterial stiffness. We also found the increase of augmentation pressure（AP） was usually accompanied with increased central PP（C-PP）. AP and C-PP were used as numerator and denominator in AIx formula, the increase in numerator（AP） would not necessarily result in increase of quotient（AIx） if the denominator（C-PP） was not stabled.Mathematical ratiocination showed that AIx was a multifator-determined index [F= （△SBP-△DBP）×（P1- P2）＋ （△P2-△P1）×（SBP-DBP）],suggesting the change of AIx would not be always consistent with the changes in second peak（P2） and AP. Conclusion Through our series studies and ratiocination, we proved that augmentation index （Alx or AIx@75 beats/min） might not be a sensitive surrogate index to reflect the change in central pressure waveforms-the manifestation of large artery function. The limitation of AIx as an index of arterial stiffness was derived from calculated formula, which had obvious mathematical and logical flaw.