高原低氧环境下影响肺动脉压力的相关因素分析

肺动脉压力变化是反映机体在高原低氧环境中适应习服或病理损伤的重要生理指标，不同海拔、不同时间的低氧刺激对肺动脉压力的影响也不尽相同，其中许多因素影响肺动脉压力的变化，如血管平滑肌的收缩、血流动力学改变、血管活性调节异常以及心肺功能的异常改变等，深入探讨低氧环境下肺动脉压力的调节因素对明确低氧适应和习服的相关机制及急慢性高原病预防、诊断、治疗、预后具有重要的意义。近年来关于高海拔低氧环境下影响肺动脉压力的相关因素研究有了较大的进展，本文从循环系统血流动力学、血管活性状态及心肺功能变化等方面对低氧环境下肺动脉压力的调节因素和干预措施进行综述。     

一种带有旋动流引导器的新型小口径人造血管流场的数值模拟

大尺寸人造血管的临床应用已取得很大成功,但用于冠状动脉等旁路搭桥的小口径人造血管的急性血栓堵塞问题,至今仍未解决．因此,本文设计了一种可装于小口径人造血管前的旋流导引器,以期使进入人造血管内的血流产生旋动．对带有旋流导引器的人造血管内的血流流场进行了计算机数值模拟分析,并与常规人造血管内的血流流场进行了比较．数值模拟分析揭示,这种旋流导引器的确能使人造血管内的血流产生旋动,从而改变人造血管内的血流流场和流速分布,使近壁面血液的流速和壁面剪切应力得到极大提高．本研究认为,血液在人造血管壁面的流速和壁面剪切应力的提高,可抑制小口径人造血管内急性血栓的形成,从而达到提高小口径人造血管的通畅率的目的．     

血液流变学与心血管活动

一、引言在研究血液的流动规律时,过去较多注意血管口径与驱动压力等血液动力学方面的问题,而相对地忽视血液本身的复杂流体性质对血液流动的影响。近年来的研究表明,血液及其成分的流变学特性(如血液粘度、红细胞聚集性、红细胞刚性、血小板聚集性与动态血栓形成等)对循环系统的生理与病理,特别是对微循环的机能有重要影响。某些心血管疾患,其血液流变学各因素的异常变化以及与微血管相互作用所引起的血管口径逆转效应是妨碍微循环血液灌注的关键因素。局部组织血流障碍所造成的代谢变化与热蓄     

失重/模拟失重对内皮细胞的影响实验研究进展

血管内皮作为血管壁的衬里,参与调节组织器官的局部血流和机体其它生理进程,在维持血管完整性和内环境稳定中发挥关键作用。内皮细胞对包括重力在内的机械应力刺激极为敏感,重力变化可对其形态和功能构成不同程度的影响。研究发现,失重/模拟失重通过诱导内皮细胞细胞骨架重塑、质膜caveolae重布,使其合成分泌血管活性物质、炎性介质的能力以及细胞表面粘附分子表达发生改变,这些分子变化又对内皮细胞的生长、增殖、凋亡、迁移和血管生成等具有精细调控作用。本文综合评述了失重/模拟失重对内皮细胞功能的影响,同时围绕文献报道中一些尚存争议的观点进行了适当讨论。     

犬不同血管搭桥方法及搭桥血管内流场的计算机数值模拟

目的血管搭桥术后的内膜增生往往导致手术失败,而内膜增生与搭桥血管内的流场密切相关,为改善搭桥血管中的流场结构,作者设计了偏心搭桥手术方法,利用计算机数值模拟技术,探索偏心搭桥和传统搭桥血管中流场的变化,为血管搭桥方法提供优化设计方案。方法16只犬随机分为偏心搭桥组和传统搭桥组进行血管搭桥,测定搭桥前后血管几何数据,搭桥后近心端及远心端吻合口血流量和血压。按测定的血管几何数据,FLUENT 6.2模拟搭桥血管内的流场。结果偏心搭桥近心端和远心端吻合口不在同一平面。传统搭桥中,主体动脉远心端吻合口对应面处存在一个较低壁面剪切应力（WSS）区域及流体停滞点,离脚跟较近的一部分流体会形成涡漩,血流进入主体动脉后,还会表现出迪恩涡二次流;偏心搭桥中,主体动脉吻合口对应面上的低WSS区域和流体停滞点消失,血流接触到吻合口底面后,以切向旋转的方式改变其流动方向,不会形成涡漩,且当血流进入主体动脉后,立即发生螺旋流态且能持续很长一段。结论偏心搭桥能够产生血液旋动流,显著增加远心端血流量、提高WSS。     

麻醉狗颈动脉窦及左室压变化有不同的反应

本实验检验了局限于一个反射发生区的不同压力对另一个反射发生区的压力变化反应的影响。将狗用氯醛糖(100mg/kg)麻醉,并进行人工呼吸。人工控制左室的收缩压和颈动脉窦压,即将一个套管固定在升主动脉内,并连接到一个控制左心室收缩压的压力容器。左心房压是通过把血液转移到左心房和主动脉容器之间的任何方向来控制的。将一侧后肢血管分离,用恒定血流独立地灌注隔离的后肢血管。在7条狗身上,将颈动脉窦压控制在65±2.7或243±4.7mmHg时,左心室收缩压从95±7.2mmHg升至     

机械敏感性离子通道蛋白Piezo1响应力学刺激的研究进展

2010年,Coste等首次在小鼠神经母细胞瘤中筛选鉴定出Piezo1,其为一种受力学信号刺激影响的新型机械敏感性离子通道蛋白。这类蛋白质嵌于细胞膜上,可将机械信号通过变形传递到其孔核结构,在毫秒内将机械刺激转化为电信号或生化信号,是细胞对力学产生感知和响应的分子基础。Piezo1蛋白自发现以来一直备受关注。本文详细介绍了Pieoz1蛋白的发现过程、结构特点及其介导的门控通道,总结了机械敏感性离子通道蛋白Piezo1介导不同力学形式(重力、牵张力、压力和流体剪切力)刺激对机体各部分的作用。发现重力研究主要集中于骨骼,牵张力研究集中于软骨细胞、髓核细胞和膀胱尿路上皮细胞,压力研究集中于骨骼、软骨、牙齿、血管,而流体剪切力研究主要作用于骨骼和血管。深入研究后有望为许多临床疾病提供新思路和治疗方案。     

用铷~(86)稀释法在大鼠测定儿茶酚胺的一些血流动力效应

利用靜脉注射Rb~(86)Cl后,从其血液稀釋曲綫計算心输出量,并从各器官的分布百分率計算其血流量。本文改进用心电图紙代替分段收集器收集血液,特別适用于小动物实驗。 (一)正常鼠連續两次测定,間隔10分钟,其心脏血流动力作用无改变。說明Rb~(86)及实驗过程(如放血等)对大鼠的心血管功能干扰不大。 (二)靜脉注射腎上腺素(2微克)后,血压升高,心輸出量及作功量增加非常显著,同时增加心肌、肝、肺及腎血流量,除脾血管阻力增大外,对其他部位血管阻力影响不大。去甲腎上腺素(2微克)明显增加总外周血管阻力,对心輸出量增加較少,也增加心肌、肺、肝血流量,但对腎及脾血流量影响較少。     

基于计算机模拟的介入器械放置及设计研究

心血管介入器械的使用越来越广泛，综合考虑血流、器械和血管的作用情况，研究器械的放置和设计问题，有助于减少器械诱发的并发症，提高其使用的效果。采用计算机建模，有限体积法生成网格，通过计算流场来分析器械使用前后流场改变的方法，说明了介入器械的结构和使用方式对血管有不同方面及程度的影响。对于研究其他的一些和血管接触的器械也有一定的参考价值。     

血管内皮细胞和心脏组织块的立体培养

本文旨在对比研究二维平面与三维立体培养模式下,内皮细胞和心脏组织形态学的差异。采用胶内、胶上、三明治模式、玻片培养小室模型等多种I型胶原立体培养模型,通过免疫荧光技术及显微形态学观察组织和细胞的生长情况。在二维平面培养中,原代心脏血管内皮细胞呈铺路石样排列;而在三维胶原培养模式中,内皮细胞呈长梭状形态,并迁入胶原培养介质中,和体内血管新生及血管生成过程中的内皮细胞活化表型相似。加入血管内皮生长因子(vascular endo- thelial growth factor VEGF)能增强内皮细胞管状结构的形成。在三维胶原中,心脏组织块生长良好,迁出的细胞将相邻组织块连接起来,组织块有自发的搏动。本工作表明,改进的薄层胶原培养、玻片培养小室模型和动脉条模型是较好的研究血管生成和血管新生的工具。在三维培养的情况下,内皮细胞通过空间增殖、迁移和锚定,可形成管状结构,比二维平面培养更适合用于血管新生的研究。不同的立体培养模型可用于不同目的的研究。     

Effect of load position on muscle forces, internal loads and stability of the human spine in upright postures

A novel kinematics-based approach coupled with a non-linear finite element model was used to investigate the effect of changes in the load position and posture on muscle activity, internal loads and stability margin of the human spine in upright standing postures. In addition to 397 N gravity, external loads of 195 and 380 N were considered at different lever arms and heights. Muscle forces, internal loads and stability margin substantially increased as loads displaced anteriorly away from the body. Under same load magnitude and location, adopting a kyphotic posture as compared with a lordotic one increased muscle forces, internal loads and stability margin. An increase in the height of a load held at a fixed lever arm substantially diminished system stability thus requiring additional muscle activations to maintain the same margin of stability. Results suggest the importance of the load position and lumbar posture in spinal biomechanics during various manual material handling operations.     

Neurovascular responses to mental stress in the supine and upright postures.

The purpose of this study was to determine neurovascular responses to mental stress (MS) in the supine and upright postures. MS was elicited in 23 subjects (26 +/- 1 yr) by 5 min of mental arithmetic. In study 1 (n = 9), Doppler ultrasound was used to measure mean blood flow velocity in the renal (RBFV) and superior mesenteric arteries (SMBFV), and venous occlusion plethysmography was used to measure forearm blood flow (FBF). In study 2 (n = 14), leg blood flow (LBF; n = 9) was measured by Doppler ultrasound, and muscle sympathetic nerve activity (MSNA; n = 5) was measured by microneurography. At rest, upright posture increased heart rate and MSNA and decreased LBF, FBF, RBFV, and SMBFV and their respective conductances. MS elicited similar increases in mean arterial blood pressure ( approximately 12 mmHg) and heart rate ( approximately 17 beats/min), regardless of posture. MS in both postures elicited a decrease in RBFV, SMBFV, and their conductances and an increase in LBF, FBF, and their conductances. Changes in blood flow were blunted in the upright posture in all vascular beds examined, but the pattern of the vascular response was the same as the supine posture. MS did not change MSNA in either posture (change: approximately 1 +/- 3 and approximately 3 +/- 3 bursts/min, respectively). In conclusion, the augmented sympathetic activity of the upright posture does not alter heart rate, mean arterial blood pressure, or MSNA responses to MS. MS elicits divergent vascular responses in the visceral and peripheral vasculature. These results indicate that, although the upright posture attenuates vascular responses to MS, the pattern of neurovascular responses does not differ between postures.     

Activity of respiratory muscles in upright and recumbent humans

It is established that during tidal breathing the rib cage expands more than the abdomen in the upright posture, whereas the reverse is usually true in the supine posture. To explore the reasons for this, we studied nine normal subjects in the supine, standing, and sitting postures, measuring thoracoabdominal movement with magnetometers and respiratory muscle activity via integrated electromyograms. In eight of the subjects, gastric and esophageal pressures and diaphragmatic electromyograms via esophageal electrodes were also measured. In the upright postures, there was generally more phasic and tonic activity in the scalene, sternocleidomastoid, and parasternal intercostal muscles. The diaphragm showed more phasic (but not more tonic) activity in the upright postures, and the abdominal oblique muscle showed more tonic (but not phasic) activity in the standing posture. Relative to the esophageal pressure change with inspiration, the inspiratory gastric pressure change was greater in the upright than in the supine posture. We conclude that the increased rib cage motion characteristic of the upright posture owes to a combination of increased activation of rib cage inspiratory muscles plus greater activation of the diaphragm that, together with a stiffened abdomen, acts to move the rib cage more effectively.     

Effect of load position on muscle forces,internal loads and stability of the human spine in upright postures

A novel kinematics-based approach coupled with a non-linear finite element model was used to investigate the effect of changes in the load position and posture on muscle activity, internal loads and stability margin of the human spine in upright standing postures. In addition to 397 N gravity, external loads of 195 and 380 N were considered at different lever arms and heights. Muscle forces, internal loads and stability margin substantially increased as loads displaced anteriorly away from the body. Under same load magnitude and location, adopting a kyphotic posture as compared with a lordotic one increased muscle forces, internal loads and stability margin. An increase in the height of a load held at a fixed lever arm substantially diminished system stability thus requiring additional muscle activations to maintain the same margin of stability. Results suggest the importance of the load position and lumbar posture in spinal biomechanics during various manual material handling operations.     

Effects of posture on peripheral vascular responses to lower body positive pressure

We tested the hypothesis that peripheral vascular responses (in the lower and upper limbs) to application of lower body positive pressure (LBPP) are dependent on the posture of the subjects. We measured heart rate, stroke volume, mean arterial pressure, leg and forearm blood flow (using the Doppler ultrasound technique), and leg (LVC) and forearm (FVC) vascular conductance in 11 subjects (9 men, 2 women) without and with LBPP (25 and 50 mmHg) in supine and upright postures. Mean arterial pressure increased in proportion to increases in LBPP and was greater in supine than in upright subjects. Heart rate was unchanged when LBPP was applied to supine subjects but was reduced in upright ones. Leg blood flow and LVC were both reduced by LBPP in supine subjects [LVC: 4.8 (SD 4.0), 3.6 (SD 3.5), and 1.4 (SD 1.8) ml.min(-1).mmHg(-1) before LBPP and during 25 and 50 mmHg LBPP, respectively; P < 0.05] but were increased in upright ones [LVC: 2.0 (SD 1.2), 3.4 (SD 3.4), and 3.0 (SD 2.0) ml.min(-1).mmHg(-1), respectively; P < 0.05]. Forearm blood flow and FVC both declined when LBPP was applied to supine subjects [FVC: 1.3 (SD 0.6), 1.0 (SD 0.4), and 0.9 (SD 0.6) ml. min(-1).mmHg(-1), respectively; P < 0.05] but remained unchanged in upright ones [FVC: 0.7 (SD 0.4), 0.7 (SD 0.4), and 0.6 (SD 0.5) ml.min(-1).mmHg(-1), respectively]. Together, these findings indicate that the leg vascular response to application of LBPP is posture dependent and that the response differs in the lower and upper limbs when subjects assume an upright posture.     

Human esophageal pressures and chest wall configuration in upright and head-down posture

Pressures were measured at two levels in the esophagus in 14 young healthy subjects performing slow inspiratory and expiratory vital capacity (VC) maneuvers in upright and head-down posture (180 degrees body tilt). In both postures, a gravitational pressure gradient was found, which increased very slightly with decreasing lung volumes (0.006 cmH2O X % VC-1 X cm descent-1) except for upright expiratory curves above 60% VC. The expiratory pressure gradient tended to be larger in head-down than in upright posture; however, during inspiration the opposite was true. In both postures the pressure change between 100 and 20% VC was smaller in the uppermost zone, which is consistent with the smaller changes in alveolar expansion in this zone. Also, in seven of the subjects, changes in cross-sectional area of the middle and lower part of the rib cage (HRC and LRC) and of the abdomen (ABD) were measured by respiratory inductive plethysmography in upright and head-down posture. The ratio of HRC motion to LRC motion was constant throughout the VC and did not change with posture, yet the ratio of ABD motion to mean RC motion changed with overall volume and was also larger in head-down than in upright posture. In conclusion, the changes in esophageal pressure gradient during slow VC maneuvers in head-down vs. upright posture were not related to (and thus not caused by) changes in chest wall configuration.     

Effects of pericardial constraint and ventricular interaction on left ventricular hemodynamics in the unloaded heart

Pericardial constraint and ventricular interaction influence left ventricular (LV) performance when preload is high. However, it is unclear if these constraining forces modulate LV filling when the heart is unloaded, such as during upright posture, in humans. Fifty healthy individuals underwent right heart catheterization to measure pulmonary capillary wedge (PCWP) and right atrial pressure (RAP). To evaluate the effects of pericardial constraint on hemodynamics, transmural filling pressure (LVTMP) was defined as PCWP-RAP. Beat-to-beat blood pressure (BP) waveforms were recorded, and stroke volume (SV) was derived from the Modelflow method. After measurements at -30 mmHg lower body negative pressure (LBNP), which approximates the upright position, LBNP was released, and beat-to-beat measurements were performed for 15 heartbeats. At -30 mmHg LBNP, RAP and PCWP were significantly decreased. During the first six beats of LBNP release, heart rate (HR) was unchanged, while BP increased from the fourth beat. RAP increased faster than PCWP resulting in an acute decrease in LVTMP from the fourth beat. A corresponding drop in SV by 3% was observed with no change in pulse pressure. From the 7th to 15th beats, LVTMP and SV increased steadily, followed by a decreased HR due to the baroreflex. A decreased TMP, but not PCWP, caused a transient drop in SV with no changes in HR or pulse pressure during LBNP release. These results suggest that the pericardium constrains LV filling during LBNP release, enough to cause a small but significant drop of SV, even at low cardiac filling pressure in healthy humans.     

The effect of clinorotation on vestibular compensation in upside-down swimming catfish.

Upside-down swimming catfish Synodontis nigriventris can keep upside-down swimming posture stably under pseudo-microgravity generated by clinostat. When the vestibular organ is unilaterally ablated, the operated S. nigriventris shows disturbed swimming postures under the clinorotation condition. However, about 1 month after the operation, unilateral vestibular organ-ablated S. nigriventris shows stable upside-down swimming posture under the condition (vestibular compensation). In contrast, a closely related upside-up swimming catfish Synodontis multipunctatus belonging to same Synodontis family can not keep stable swimming postures under the clinorotation conditions. In this study, we examined the effect of continuous clinorotation on vestibular compensation in intact and unilateral vestibular organ-ablated Synodontis nigriventris and Synodontis multipunctatus. After the exposure to continuous clinorotation, the postures of the catfish were observed under microgravity provided by parabolic flights of an aircraft. Unilateral vestibular organ-ablated S. nigriventris which had been exposed to continuous clinorotation showed stable swimming postures and did not show dorsal light reaction (DLR) under microgravity. This postural control pattern of the operated catfish was similar to that of intact catfish. Intact and unilateral vestibular organ-ablated S. multipunctatus showed DLR during microgravity. Our results confirmed that S. nigriventris has a novel balance sensation which is not affected by microgravity. DLR seems not to play an important role in postural control. It remains unclear that the continuous clinorotation effects on vestibular compensation because we could not keep used unilateral vestibular organ-ablated fish alive under continuous clinorotation for uninterrupted 25 days. This study suggests that space flight experiments are required to explore whether gravity information is essential for vestibular compensation.     

Effects of 20 days horizontal bed rest on maintaining upright standing posture in young persons

The effects of 20 days horizontal bed rest (BR) on postural reflex were studied by measuring fluctuation of center of gravity in the body during two legs or one leg upright standing in 10 young volunteers. The fluctuation was decided as total moving distance of the center recorded during 60sec standing on a force plate. The stability was measured by the moved area. After BR, the moving distance increased during two legs standing with open eyes (p<0.05), but statistically unchanged with closed eyes. The moving area decreased during right one-leg standing with closed eyes (p<0.05), but unchanged during left one-leg standing. Despite with open eyes the increased distance suggested that postural reflexes to maintain upright position were probably decreased by increased unsuitable feedback informations from the visual receptor deconditioning during BR. The decreased area during right one-leg standing with closed eyes also suggested that the declined standing posture reflex was probably related to more rapidly lowered functions for maintaining standing position in the dominating leg than in the other.     

Effect of posture on vital capacity

The influence of some extreme body postures on vital capacity (VC) was examined in young adult humans. Two postures required full support of body weight by the arms: arms up, hanging from a bar, and arms down with hands gripping parallel bars. Three involved muscles that flex and extend the trunk: a partial sit-up position while supine and nearly maximal spinal extension and flexion while standing. Changes at the inspiratory and expiratory volume extremes were recognized by having the subjects do two VC efforts: the first standing and the second in the posture in question while continuing to breathe on the spirometer. Control observations in which the second of a VC pair was performed in an unstressed posture allowed correction for the influence of rebreathing. The changes in corrected VC were small, the greatest being an average reduction of approximately 8% in the partial sit-up position. During full support of body weight by the arms, the VC was slightly increased due to a significant increase in the inspiratory extreme and no change in the expiratory extreme. Spinal extension produced small increases in lung volume at both extremes with no significant change in VC, whereas spinal flexion did not influence the upper extreme but did increase lung volume at the lower extreme. The changes are discussed in terms of trunk muscle action.