Akhtar Mohammad W, Kleis Stanley J, Metcalfe Ralph W, Naghavi Morteza
Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA.
J Biomech Eng. 2010 May;132(5):051005. doi: 10.1115/1.4001137.
Both structural and functional evaluations of the endothelium exist in order to diagnose cardiovascular disease (CVD) in its asymptomatic stages. Vascular reactivity, a functional evaluation of the endothelium in response to factors such as occlusion, cold, and stress, in addition to plasma markers, is the most widely accepted test and has been found to be a better predictor of the health of the endothelium than structural assessment tools such as coronary calcium scores or carotid intima-media thickness. Among the vascular reactivity assessment techniques available, digital thermal monitoring (DTM) is a noninvasive technique that measures the recovery of fingertip temperature after 2-5 min of brachial occlusion. On release of occlusion, the finger temperature responds to the amount of blood flow rate overshoot referred to as reactive hyperemia (RH), which has been shown to correlate with vascular health. Recent clinical trials have confirmed the potential importance of DTM as an early stage predictor of CVD. Numerical simulations of a finger were carried out to establish the relationship between DTM and RH. The model finger consisted of essential components including bone, tissue, major blood vessels (macrovasculature), skin, and microvasculature. The macrovasculature was represented by a pair of arteries and veins, while the microvasculature was represented by a porous medium. The time-dependent Navier-Stokes and energy equations were numerically solved to describe the temperature distribution in and around the finger. The blood flow waveform postocclusion, an input to the numerical model, was modeled as an instantaneous overshoot in flow rate (RH) followed by an exponential decay back to baseline flow rate. Simulation results were similar to clinically measured fingertip temperature profiles in terms of basic shape, temperature variations, and time delays at time scales associated with both heat conduction and blood perfusion. The DTM parameters currently in clinical use were evaluated and their sensitivity to RH was established. Among the parameters presented, temperature rebound (TR) was shown to have the best correlation with the level of RH with good sensitivity for the range of flow rates studied. It was shown that both TR and the equilibrium start temperature (representing the baseline flow rate) are necessary to identify the amount of RH and, thus, to establish criteria for predicting the state of specific patient's cardiovascular health.
为了在无症状阶段诊断心血管疾病（CVD），已经存在对内皮的结构和功能评估。血管反应性是对内皮对诸如闭塞、寒冷和压力等因素的功能评估，除了血浆标志物外，它是最广泛接受的测试，并且已被发现比诸如冠状动脉钙化评分或颈动脉内膜中层厚度等结构评估工具更能预测内皮的健康状况。在现有的血管反应性评估技术中，数字热监测（DTM）是一种非侵入性技术，它测量肱动脉闭塞2 - 5分钟后指尖温度的恢复情况。在解除闭塞时，手指温度会对称为反应性充血（RH）的血流速度过冲量做出反应，这已被证明与血管健康相关。最近的临床试验证实了DTM作为CVD早期预测指标的潜在重要性。对手指进行了数值模拟，以建立DTM与RH之间的关系。模型手指由包括骨骼、组织、主要血管（大血管系统）、皮肤和微血管系统等基本组件组成。大血管系统由一对动脉和静脉表示，而微血管系统由多孔介质表示。对随时间变化的纳维 - 斯托克斯方程和能量方程进行数值求解，以描述手指内部和周围的温度分布。闭塞后血流波形作为数值模型的输入，被建模为流速的瞬时过冲（RH），随后呈指数衰减回到基线流速。在与热传导和血液灌注相关的时间尺度上，模拟结果在基本形状、温度变化和时间延迟方面与临床测量的指尖温度曲线相似。对目前临床使用的DTM参数进行了评估，并确定了它们对RH的敏感性。在所呈现的参数中，温度反弹（TR）与RH水平的相关性最佳，对所研究的流速范围具有良好的敏感性。结果表明，TR和平衡起始温度（代表基线流速）对于确定RH量都是必要的，从而为预测特定患者的心血管健康状态建立标准。
