Background

Obesity is a widespread condition that is more prevalent in Western countries compared to others. Aortic atherosclerosis (AA) is a condition that frequently has been associated with obesity. An obesity paradox, where morbidly obese decedents had either no or minimal AA compared to nonobese decedents, recently has been described by some of us. The explanation for this almost counterintuitive paradox has yet to be determined, but a number of hypotheses were advanced, including hemodynamic factors producing aortic wall shear stress (WSS). The purpose of the present study was to determine if there was a relationship between AA and WSS, as determined by postmortem measurement of aortic wall diameters.

Methods

Circumferences of the aorta at the levels of the ascending, thoracic and abdominal aorta were measured in 274 consecutive autopsies over 2-year period of time. AA was assessed using a previously described grading scale as either mild or severe. Circumferences were mathematically converted to diameters and WSS was calculated using the Hagene-Poiseuille formula. Two different methods to estimate cardiac output were used, both based on literature methods, one of which was body mass index (BMI) dependent, and the other BMI independent. Univariate and multivariable analyses of the relationship between WSS, age, BMI, gender, race and severity of AA were performed.

Results

Of the 274 decedents, 140 had mild and 134 had moderate to severe AA. BMI <35 was associated with moderate to severe AA. WSS was inversely correlated with AA in all these segments of the aorta in each BMI subgroup with the exception of the ascending aorta for decedents with BMI ≤35 kg/m². Contrary to what we had hypothesized, WSS was not a determinant of the obesity paradox. However, among all the variables analyzed, a history of hypertension, diabetes mellitus and age were significant factors for developing AA (relative risk [RR] 0.35, P = .039; RR 1.51, P = .0006, RR 1.19, P = .0001, respectively).

Conclusions

Our data demonstrate that WSS was unexpectedly lower in decedents with moderate and severe AA as compared to those with mild AA. This observation, which requires further investigations, was seen in all BMI ranges and was confirmed by 2 methods to calculate WSS.

中文翻译：

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一个意外的悖论：严重肥胖的动脉粥样硬化患者的主动脉壁切应力较小，而与肥胖无关

背景

肥胖是一种普遍的疾病，与其他国家相比，在西方国家更为普遍。主动脉粥样硬化（AA）是一种经常与肥胖有关的疾病。最近，我们中的一些人描述了一种肥胖悖论，其中病态肥胖者与非肥胖者相比没有AA或只有极少的AA。对于这种几乎违反直觉的悖论的解释尚待确定，但提出了许多假设，包括产生主动脉壁切应力（WSS）的血液动力学因素。本研究的目的是确定是否通过验尸测量主动脉壁直径来确定AA和WSS之间是否存在关系。

方法

在2年的时间里，在274次连续尸检中测量了升主动脉，胸主动脉和腹主动脉水平的主动脉周长。使用先前描述的轻度或重度分级量表评估AA。将周长数学转换为直径，并使用Hagene-Poiseuille公式计算WSS。使用两种不同的方法估计心输出量（CO），两种方法均基于文献方法，其中一种是BMI依赖性的，而另一种是BMI依赖性的。对WSS，年龄，BMI，性别，种族和AA严重程度之间的关系进行单变量和多变量分析。

结果

在274名死者中，有140名患有轻度AA，而134名患有中度至重度AA。BMI <35与中度至重度AA相关。在每个BMI亚组的所有这些主动脉段中，WSS与AA均呈负相关，但对于BMI≤35 kg / m ^2的后代，升主动脉除外。与我们的假设相反，WSS并非肥胖悖论的决定因素。但是，在所有分析的变量中，高血压病史，糖尿病史和年龄是发展AA的重要因素（分别为RR 0.35，p = 0.039； RR 1.51，p = 0.0006，RR 1.19，p = 0.0001）。

结论

我们的数据表明，中度和重度AA患者的WSS意外低于轻度AA患者。在所有BMI范围内都可以观察到需要进一步研究的观察结果，并通过两种计算WSS的方法得到了证实。