不同型式流体切应力对血管内皮细胞生理生化的影响

血管内皮细胞经常处于血液流动力的作用下 ,它能感知血流力的变化 ,在调节血管的功能和结构中起着重要作用。血液流动力的变化与某些血管性疾病的发生发展有着密切的关系 ,因此血液流动力对内皮细胞的影响受到广泛关注。本文就流体切应力对内皮细胞生理、生化影响的研究进展作一简要综述。     

管径比对全阻塞动脉旁路移植流场影响的数值研究

目的 研究管径比对全阻塞动脉旁路移植流场的影响,为指导动脉旁路移植手术,减少术后再狭窄提供理论依据。方法 采用数值方法研究5种不同移植管与主血管的管径比对全阻塞情况下动脉旁路移植流场的影响,分析速度、二次流、壁面切应力和壁面切应力梯度等血流动力学参数的分布及其随管径比增大的改变。同时,为表明本文所采用模型的合理性,针对目前常使用的两类模型,比较在管径比1.0情况下全阻塞完整模型（Model A）、全阻塞局部模型（Model B）和75％狭窄完整模型（Model C）之间的血流动力学差异。结果 Model A和Model C的血流动力学特性是完全不同的;移植管顶部截面内的速度分布对下游吻合处的主血管底部壁面切应力的影响是显著的,最大相差达79％。大管径比时,主血管底部的壁面低切应力区较大,但壁面切应力分布均匀,壁面切应力梯度较小。而小管径比时,主血管底部的壁面低切应力区较小,但壁面切应力梯度较大。结论 采用整体模型单独研究全阻塞情况下的管径比对流场的影响是有必要的。管径比对全阻塞动脉旁路移植的流场具有显著影响,采用大管径比进行动脉旁路移植将有助于缓解吻合口处由于再狭窄而产生的阻塞。     

维医沙疗对股动脉分支的血流动力学影响

目的研究维医沙疗对人体股动脉分叉血管血流动力学及受力的影响,进而揭示维医沙疗对人体股动脉血栓成因的作用机制。方法在室内维医沙疗系统中对受试者进行维医沙疗,用飞利浦便携式彩色多普勒超声诊断仪分别测试受试者维医沙疗前后的股动脉血流速度峰值、内径和阻力指数(resistant index,RI),并进行统计学分析;重构股动脉分支的三维流-固耦合有限元模型,采用ANSYS workbench模拟计算维医沙疗前后流场的血流速度、压力、壁面切应力和股动脉壁的应力、应变、总位移。结果维医沙疗后股动脉血流速度峰值的平均值和内径分别增大了32.43%和2.63%,RI降低了4.88%,股动脉血流速度峰值和RI维医沙疗前后差异均具有统计学意义(P0.05),股动脉内径维医沙疗前后差异没有统计学意义(P0.05)。维医沙疗后股动脉血流速度、压力和壁面切应力最大值分别增大29.91%、68.52%和46.55%;维医沙疗后股动脉壁的总位移、应力和应变最大值分别增大65.85%、45.45%和44%。结论维医沙疗对加快血流速度、降低RI有显著影响,能增大股动脉血管内径,从而改善股动脉内血液的循环;并且维医沙疗后股动脉壁面切应力、血流速度、压力以及股动脉壁所受应力、应变和总位移有所增大,分叉处的高压力区域有所减少,维医沙疗对降低股动脉粥样硬化及血栓形成有一定的积极作用。     

股动脉双路搭桥的血流动力学仿真

在传统股动脉搭桥术中，由于下游缝合区采用“端对侧”的“单路搭桥”缝合方式，移植管中血流会对缝合区底面产生很大冲击，引起局部血流动力学急剧变化，并可能因此而导致血管再狭窄和手术失败。由于缝合区几何结构的不对称必然导致流场的不均匀，本研究提出了“对称双路搭桥”的构想以图改善血流动力学。本研究对“单路”和“对称双路”两种连接模型中的血液流动进行了数值模拟。两种模型利用相同的几何参数进行建模，并采用了相同的边界条件。数值模拟结果包括流场、壁面切应力及其梯度等血流动力学参数。研究表明，“对称双路”模型比“单路”模型具有较大的纵向速度、较小的二次流、较均匀的壁面切应力等。因此，“对称双路”搭桥模型具有更好的血流动力学，可以减少股动脉搭桥术后内膜增生和再狭窄的可能性。     

Patient-Specific Multiscale Modeling of Blood Flow for Coronary Artery Bypass Graft Surgery

We present a computational framework for multiscale modeling and simulation of blood flow in coronary artery bypass graft (CABG) patients. Using this framework, only CT and non-invasive clinical measurements are required without the need to assume pressure and/or flow waveforms in the coronaries and we can capture global circulatory dynamics. We demonstrate this methodology in a case study of a patient with multiple CABGs. A patient-specific model of the blood vessels is constructed from CT image data to include the aorta, aortic branch vessels (brachiocephalic artery and carotids), the coronary arteries and multiple bypass grafts. The rest of the circulatory system is modeled using a lumped parameter network (LPN) 0 dimensional (0D) system comprised of resistances, capacitors (compliance), inductors (inertance), elastance and diodes (valves) that are tuned to match patient-specific clinical data. A finite element solver is used to compute blood flow and pressure in the 3D (3 dimensional) model, and this solver is implicitly coupled to the 0D LPN code at all inlets and outlets. By systematically parameterizing the graft geometry, we evaluate the influence of graft shape on the local hemodynamics, and global circulatory dynamics. Virtual manipulation of graft geometry is automated using Bezier splines and control points along the pathlines. Using this framework, we quantify wall shear stress, wall shear stress gradients and oscillatory shear index for different surgical geometries. We also compare pressures, flow rates and ventricular pressure-volume loops pre- and post-bypass graft surgery. We observe that PV loops do not change significantly after CABG but that both coronary perfusion and local hemodynamic parameters near the anastomosis region change substantially. Implications for future patient-specific optimization of CABG are discussed.     

单路和双路CABG中血流动力学的比较

为了改善冠状动脉搭桥术后的血流动力学，提出了对称双路搭桥的改进措施。利用有限元分析方法，对冠状动脉搭桥术中单路移植管和对称双路移植管内的生理流动进行了数值模拟，并对两种情况下的血流动力学计算结果进行了比较。计算结果分析了缝合区附近的流场、壁面剪应力等血流动力学因素在心动周期内的时空分布情况。研究结果表明，对称双路搭桥比单路搭桥具有更合理的血流动力学，可以避免动脉粥样硬化的危险性血流动力学因素，从而减少手术再狭窄的发生。     

优化原理与小动脉血流量─管径关系

作者假设血液为符合幂定律的非牛顿流体，对小动脉血管系统进行了详细的优化分析。导出了血流量与管径立方成正比的结论以及壁面切变率与管径无关的推论。此结果既包含了前人对于牛顿血流的研究成果，又能克服后者的不足，而与近期的生理测定一致。     

抗疲劳复方中药提取物对小鼠骨骼肌微血管管径及血流速度的影响

目的 :研究抗疲劳复方中药提取物 (EAFF)对小鼠骨骼肌微循环的影响。方法 :采用我室建立的小鼠骨骼肌微循环观察方法 ,以肾上腺素作为引起微循环障碍的激动剂模拟骨骼肌疲劳。局部应用EAFF ,观察其对微血管管径及血流速度的影响。结果 :应用EAFF后 ,骨骼肌微动脉管径、微静脉血流速度以及毛细血管管径及血流速度与对照组比较均有明显改善 ,差异具有显著性意义 (P均 <0 .0 5 )。结论 :EAFF具有改善骨骼肌微循环障碍的作用     

小口径微孔聚氨酯人工血管的动物体内植入研究

将内径4mm的聚氨酯微孔人工血管植入Beagle狗体内，置换一段腹主动脉，研究血管内腔的内皮细胞化过程。该小口径血管具有以下特点：内腔偶联水蛭素以增加抗血栓性；顺应性接近天然血管；血管内表面孔径为40μm，并且管壁的孔径由内到外呈梯度增大。植入初始，人工血管内腔先吸附血浆纤维蛋白。14d见有少量梭形内皮样细胞生成。41d后形成完整内膜，由表面的内皮细胞单层和其下的平滑肌细胞组成。90d后生成稳定的内膜，平均厚度223μm。偶联水蛭素组和无偶联水蛭素组的通畅率分别为88．9％和75．0％。结果表明，改善抗血栓性、顺应性和微观结构可提高小口径人工血管的性能，有效促进内腔自然内皮细胞化，显著提高长期通畅率。     

小径微孔聚氨酯人工血管的顺应性

由激光测微器、压力传感器、A／D卡、微电脑和循环回路等组成的装置测定了小径人工血管的径向顺应性，由微注射器、压力传感器等组成的装置测定了体积顺应性，轴向顺应性由体积顺应性和径向顺应性计算出。体积顺应性，径向顺应性和轴向顺应性都随血管材料弹性的增大、盐／胶比的增加（孔隙率）和浸渍层数（血管壁厚度）的减小而增大。PU血管的外周模量与径向模量分别由径向顺应性。轴向顺应性计算，外周模量与径向模量之比值接近1，即两模量大小与变形方向无关。外周模量与径向模量随血管材料弹性和盐／胶比增加而变小。但管壁厚度对其的影响不大。通过合理选择更具弹性的PU材料（Chro佳，PCU1500次之），最佳盐／胶比例（6：1）以及控制浸渍层数（4～6层），可以制备出顺应性接近天然血管的小径人工血管。     

脐动脉在搏动流作用下脱细胞制备小口径组织工程血管支架的研究

探索利用搏动流对小口径血管进行脱细胞的方法。首先将脐动脉连接到搏动流管道中进行灌注,结合0.25%胰蛋白酶和0.01%乙二胺四乙酸混合溶液的共同作用,以1%十二烷基硫酸钠为脱细胞试剂对脐动脉洗脱3h。洗脱3h后的病理切片显示脐动脉细胞被全部脱去;拉伸实验测定脐动脉脱细胞前极限应力为(3.55±0.42)N,脱细胞后其极限应力为(3.50±0.43)N(P0.05);在300mmHg压强作用下,脐动脉脱细胞前后两组(各30根血管)均有2根破裂,28根保持完好(P0.05)。此结果预示,脐动脉在脱细胞前后的力学特性无显著差异。成纤维细胞静态培养显示,成纤维细胞能在脱细胞脐动脉支架表面良好生长。研究结果表明利用搏动流将小口径血管脱细胞是一种简便、快速、有效的方法。     

Resting Arterial Diameter and Blood Flow Changes With Resistance Training and Detraining in Healthy Young Individuals

Context:

Disruptions to habitual training routines are commonly due to injury or illness and can often lead to detraining adaptations. The implications of such adaptations to the human vasculature in a trained, asymptomatic population are not fully understood.

Objective:

To determine the extent of local and systemic changes in arterial diameter and blood flow to resistance training and subsequent detraining in young adults.

Design:

Randomized controlled clinical trial.

Setting:

University physiology laboratory and fitness suite.

Patients or Other Participants:

Twenty-one healthy volunteers (aged 20.0 ± 2.8 years, 11 men and 10 women).

Intervention(s):

Eight-week lower limb resistance training period and subsequent 4-week detraining period.

Main Outcome Measure(s):

Quadriceps and hamstrings concentric torque (strength), resting heart rate, arterial diameter, and blood flow velocity in the superficial femoral and carotid arteries were measured at 0, 8, 10, and 12 weeks.

Results:

Resistance training increased quadriceps and hamstring strength (32% and 35%, respectively, P < .001), whereas strength decreased during detraining (24% and 27%, respectively, P < .05). Resting heart rate decreased after resistance training (16%, P < .01) and increased during detraining (19%, P < .001). Additionally, resistance training significantly increased superficial femoral and carotid resting arterial diameters (27% and 13%, respectively, P < .001) and mean blood flow (53% and 55%, respectively, P < .001). Detraining resulted in a significant decrease in superficial femoral and carotid resting diameter (46% and 10%, respectively, P < .001) and mean blood flow (61% and 38%, respectively, P < .05).

Conclusions:

Resistance training initiated both local and systemic changes to arterial diameter and blood flow; these changes appeared to reverse after detraining. The local changes in response to detraining showed a worsening (beyond pretraining values) of the vascular dimensional and blood flow characteristics.Key Words: conduit artery, resistance training, systemic circulation

Key Points

• With the appropriate duration and intensity of loading, the benefits of resistance training are comparable with the vascular adaptations to endurance exercise.
• When a contraindication to the often high-impact work associated with endurance exercise exists, resistance training may provide a suitable alternative.

Active individuals reportedly have improved vascular structure and function when compared with their sedentary counterparts.^1,2 Endurance performance is known to be limited by (among other factors) oxygen delivery and muscle perfusion, 2 aspects that can in part be modulated by an individual''s vasculature.³Changes in physical activity lead to acute alterations in vascular properties. An increase in physical activity, such as with endurance training, leads to increases in lumen diameter^1,2 and arterial cross-sectional area (CSA).⁴ Conversely, reductions in physical activity, such as from cessation of training and bed rest, result in decreased lumen diameter and arterial CSA.^5,6 Training and detraining adaptations occur over similar timeframes⁷; however, no intermediate data over a short-duration training and detraining period are available to confirm the rate at which these changes in vascular dimensions occur. Changes in resting and exercising arterial dimensions are known to affect oxygen delivery and ultimately oxygen consumption (Vo₂);^1,4 therefore, improvements in such dimensions could potentially enhance endurance performance. Conversely, disruptions to habitual training routines due to injury, illness, or regeneration phases could negatively affect vascular dimensions and subsequently reduce endurance performance. Resistance training offers an alternative mode of training for endurance performers experiencing such disruptions to training, and this training may in fact limit the negative effect upon vascular dimensions of a detraining period.Although local vascular adaptations to both exercise training and physical inactivity occur, the extent of systemic vascular adaptations to training and inactivity, if any, has yet to be elucidated. Some evidence of both functional and structural systemic adaptations to exercise training has been reported, including adaptations in the upper limbs after training emphasizing the lower body, which was attributed to elevated nitric oxide synthesis and shear stress on arterial walls.^8–11 Furthermore, evidence of systemic adaptations to inactivity is, perhaps as expected, from studies of whole-body inactivity such as bed rest,⁵ whereas studies using local models of physical inactivity such as unilateral lower limb suspension (ULLS)⁷ and casting⁶ demonstrated solely local vascular adaptations. It is in fact suggested that the increased dependence on the nonimmobilized limbs during ULLS or lower limb casting models could prevent any expected systemic vascular adaptations, thereby producing misleading results.¹² Adopting a detraining model of deconditioning would allow for a more accurate investigation of systemic adaptations. However, to date, the only study using a detraining protocol to assess systemic adaptations involved spinal cord injury (SCI) patients.¹³ Spinal cord injury patients experience progressive decreased vascularization after injury; the specific relative contribution of detraining or SCI to systemic vascular remodeling in this population remains unclear.Despite the evident wealth of research on vascular adaptations to both exercise training and physical inactivity, the extent of local and systemic adaptations after a resistance-training protocol and subsequent detraining period in an uninjured, healthy population remains unreported. Consequently, we had 3 goals: (1) to investigate the extent of adaptations to resting arterial diameter and blood flow after a lower limb resistance-training protocol; (2) to determine the time course of any adaptations to detraining in the recently resistance-trained healthy population; and (3) to determine whether differential pattern of local versus systemic adaptations exist in both the training and subsequent detraining phases of the protocol.During the off season, athletes experience detraining, which can lead to reduced performance and, specifically, a reduction in oxygen uptake.⁴ This has been attributed to a reduction in arterial diameter, possibly due to decreased muscle blood flow.⁴ Therefore, the findings from our study could provide evidence for prescribing resistance exercise during the off season to possibly assist in a more rapid return to full athletic performance on return to sport. We hypothesized that resistance training would initiate an increase in resting conduit artery diameter and blood flow, whereas detraining would reverse these increases. Additionally, we proposed that both local and systemic vasculature would be affected, with the greatest changes apparent locally.     

Influences of graft diameter on the blood flow in 2-way bypassing surgery

The graft diameter plays a critically important role in the long-term patency rates of bypass surgery. To clarify the influence of graft diameter on the blood flows in the femoral 2-way bypass surgery, the physiologically pulsatile flows in two femoral bypass models were simulated with numerical methods. For the sake of comparison, the models were constructed with identical geometry parameters except the different diameters of grafts. Two models with small and large grafts were studied. The boundary conditions for the simulation of blood flow were constant for both models. The maximum Reynolds number was 832.8, and the Womersley number was 6.14. The emphases of results were on the analysis of flow fields in the vicinity of the distal anastomosis. The temporal-spatial distributions of velocity vectors, pressure drop between the proximal and distal toe, wall shear stresses, wall shear stress gradients and oscillating shear index were compared. The present study indicated that femoral artery bypassed with a large graft demonstrated disturbed axial flow and secondary flow at the distal anastomosis while the axial flow at its downstream of toe was featured with larger and more uniform longitudinal velocities. Meanwhile, the large model exhibits less refluences, relatively uniform wall shear stresses, lower pressure and smaller wall shear stress gradients, whereas it does not have any advantages in the distributions of secondary flow and the oscillating shear index. In general, the large model exhibits better and more uniform hemodynamic phenomena near the vessel wall and may be effective in preventing the initiation and development of postoperative intimal hyperplasia and restenosis.