天麻素对动脉血管顺应性以及血流动力学的影响

本文旨在研究天麻素对动脉血管顺应性和血流动力学等的作用。采用改良风箱模型来计算动脉管的顺应性和血管中血流惯性。在静脉注射天麻素前后，分别记录和计算出狗的血压，心输出量，外周阻力，血流惯性以及中央和外周动脉血管的顺应性。结果表明天麻素具有降低血压和外周务管阻力，增加动脉血管中血流惯性，以及中央和外周动脉血管的顺应性等作用。因此，天麻素是一种有效的能够改善由血管顺应性下降所致的高血压－老年性高血压的中     

阻塞性睡眠呼吸暂停低通气综合征对心血管功能影响的动态观察

目的 探讨阻塞性睡眠呼吸暂停低通气综合征(OSAHS)患者夜间睡眠低氧状态下对心血管功能的影响。方法 通过多导睡眠呼吸监测仪对鼾症患者睡眠过程的监测,得出31例患者(轻度4例,中度6例,重度21例)符合OSAHS的诊断标准,同步心血管血液动力学分析仪动态对本组31例患者在鼾症事件前、鼾症事件中,心功能的重要指标变化监测对照。结果 发现OSAHS患者外周血管阻力、心率、动脉血氧饱和度在鼾症事件前与鼾症事件中存在显著差异(P均<0.05)。轻度,外周血管阻力增加38％、SaO_2下降11％;中度,外周血管阻力增加34％、SaO_2下降18％;重度,外周血管阻力增加19％、SaO_2下降33％;平均心率减慢。结论 OSAHS患者在鼾症事件前存在不同程度的缺氧,且外周血管阻力、动脉血氧饱和度在鼾症事件前与鼾症事件中存在差异性,OSAHS的程度越重,低氧血症越重,外周血管阻力增大,进一步影响心泵功能,产生对多器官的损害。     

用强迫振荡技术评估中心及外周呼吸阻力

本文介绍一种用强迫振荡技术评估中心以及外周呼吸阻力的方法。通过测定大耳白兔的呼吸有效阻力，并进行中心阻力Ｒｃ和外周阻力Ｒｐ的分离。结果表明新斯的明注射组的外周阻力Ｒｐ比正常对照组有非常显著性增加（Ｐ＜０．００１），而中心阻力Ｒｃ无显著性差异（Ｐ＞０．０５）。中心气道狭窄组的中心阻力Ｒｃ比正常对照组有非常显著性增加（Ｐ＜０．００１），而外周阻力Ｒｐ无显著性差异（Ｐ＞０．０５），与理论预期一致。说明利用强迫振荡有效阻力的频率依赖性可以分离中心和外周呼吸阻力。     

影响体外反搏效果的因素

对体外反搏过程采用线性单弹性腔模型及其等效回路进行了讨论。利用连续方程解出了独立的人体总外周阻力R、顺应性C和不受气囊控制的部分外周阻力Ru。利用上述模型评估不同的气囊压力、充气开始时刻和充气维持时间对体外反搏的效果。     

兔肾盂积水体外模型的肾动脉扩张性对阻力指数影响的研究

目的　评价增加输尿管压力对肾动脉扩张性及阻力指数的影响。方法　对7个离体兔肾血管进行搏动性灌注,同时经输尿管给肾盂加压。测定肾血管的压力、血流速度、阻力(压力/流速)和传导率(流速/压力),与同时测量的阻力指数进行线性回归分析比较。将传导指数(收缩期传导率-舒张期传导率/收缩期传率)的变化与阻力指数也进行同样的比较。结果　输尿管压力的升高与下列因素显著相关:1阻力指数的增加,2平均肾血管阻力指数的增加,3平均传导率的降低,4传导指数的增高(各相关性均P<0.05)。阻力指数的增加与传导指数的升高显著相关。该研究表明提高输尿…     

吸氧对高原动物心和肺功能的影响

我们观察了9只高原猪吸氧后的心肺功能变化。高原猪吸入纯氧后,右室收缩压、右室dp/dt max、肺动脉压和肺血管阻力明显降低,但左室dp/dt max、心指数、主动脉压和外周阻力无明显变化。这些结果提示肺血管收缩在慢性缺氧性肺动脉高压的发生中起重要作用。吸入纯氧后右室dp/dtmax下降,这表明慢性缺氧可致右室功能增加而肺分流率下降,提示高原幼猪存在肺通气/灌流不均。     

原发性高血压患者血浆PRA和ANP水平相关性分析

原发性高血压(EH)是血压调节机制多方紊乱的结果，高血压患者中此类原因不明的EH占85％。但在高血压发病机理上，主要为三方面因素影响，即血容量，心排出量和外周阻力，三者受神经体液调节因素支配，又互相影响保持血压平稳。     

外周阻力的测量与临床研究

目的：研究外周阻力与脉搏波之间的关系及其外周阻力在临床中的应用。方法：利用脉搏波理论和弹性腔模型提出一种便捷易行的外周阻力算法。采用临床中测试高血压患者125人和健康者125人对外周阻力与血压进行相关性分析。结果：通过大量病例分析和临床测试证实了算法的有效性和可靠性，而且此算法已经应用LabVIEW7．0开发成软件并在医院进行临床应用。结论：外周阻力能帮助人们了解自己的动脉硬化情况，随时提醒人们注意身体状况，减少疾病的发生，同时也能够为医生判断病人的心血管系统疾病提供重要的参考指标。     

老年人用药应注意的问题

随着科学的进步,人类的平均寿命正在延长,高龄比例增高,老年疾病和用药也来越受到重视。笔者就老年人用药问题作以下简述。 1 心血管系统药物的反应 老年人心血管功能减退,压力感受器植物神经调节功能障碍,心容积缩小,心肌纤维增重增厚,泵血功能降低,心输出量减少,老年脂肪比例增加,易在血管壁沉积,致使血管弹性降低,外周血管阻力增加,各脏器血流灌注减少,并易患动脉粥样硬化,心传导障碍,高血压,心绞痛等心血管疾病。 1.1老年人心肌和血管中β受体数目减少,因此     

376例慢性疾患具有低排高阻时微循环变化

我们在2681例慢性疾病患者中,观察到376例病人有心输出量降低,外周阻力升高,这些病人每分心输出量(CO)平均3.71(L/min)、心指数(Cl)平均2.43(L/mln/m~2)和每搏输出量(SV)平均48.7(ml)均低于正常水平并伴有左心室有效泵力和左心室有效泵力指数下降,表明有心泵功能减弱。总外周阻力(RT)平均为     

Pressure/flow relation in the peripheral pulmonary vascular bed in dogs: a preliminary study.

In order to test a technique for the determination of the pressure/flow relationship in the peripheral pulmonary vascular bed, the perfusion pressure changes with increasing and then decreasing flow in a small part of the lung (around 1 ml) were studied in anaesthetized supine dogs, after insertion of a specially designed double distal lumen Swan-Ganz catheter. One lumen was used for the pressure measurement, one for infusion of saline by a pump with variable flow, from 0.1 to 1.0 ml s-1. A conventional thermodilution Swan-Ganz catheter was also advanced in the pulmonary artery, to measure pressures in the pulmonary circulation as well as cardiac output. During infusion in the wedged catheter, right atrial, pulmonary arterial and balloon occlusion wedge pressures did not change. The pressure/flow curve of the occluded vascular bed showed a shape similar to that of collapsible tubes, with a pressure plateau at high flow, but this could also be due to vascular recruitment. The curve exhibited hysteresis, with a lower pressure when flow decreased. The slope of the initial part of the curve increased, on average, from 54 +/- 9 during normoxia to 91 +/- 27 mmHg s ml-1 during hypoxia (FIO2 = 0.10); this difference was not significant, but the perfusion pressure at high flow was significantly higher during hypoxia (P less than 0.05). Using blood instead of saline would allow the determination of the peripheral pulmonary vascular resistance under physiological conditions, and further work is needed to estimate the sensitivity and the reproducibility of this technique.     

Influence of vascular parameters on the effectiveness of intra-aortic balloon pumping: A model study

The intra-aortic balloon pump has been widely used as a temporary heart-assist device. In this investigation, a nonlinear mathematical model of the arterial system and intra-aortic balloon pump was studied analytically. Thus, the influences of a number of vascular parameters on the effectiveness of intra-aortic balloon pumping (IABP) were determined. The effects of changes in vascular parameters of the model on a number of performance indexes were investigated. These performance indexes (aortic mean diastolic pressure, aortic end diastolic pressure, cardiac output, coronary flow and phase differences between the fundamental Fourier components of aortic root pressure and flow) were used as the criterion for an evaluation of the effectiveness of the assist pump. The following vascular parameters were perturbed by four steps (±10%, ±20%) from the values in the standard model: heart rate, peripheral resistance, left ventricular pressure, aortic elastance, aortic radius, arterial wall thickness, and aortic length. This model was evaluated for a wide range of balloon-pump phase-control settings (assisted case) and for the unassisted case (when the pump is disabled). It is concluded that changes in heart rate, peripheral resistance and left ventricular pressure cause the most significant changes in pump performance. Dr. Ohley is with the Datascope Corporation Dr. Kao is with the Technicare Corporation     

Some Physical Properties of the Pulmonary Arterial Bed Deduced from Pulsatile Arterial Flow and Pressure

This study aimed to quantify changes of vascular compliance and resistance of the proximal and the peripheral pulmonary arterial vessels when vascular smooth muscle was stimulated. These above vascular characteristics were derived from registrations of pulsatile pressure and flow in the pulmonary artery (PA). An in situ cat lung preparation was used, with the right heart by-passed by a pulsatile blood pump. Vascular input impedance was derived from PA pulsatile pressure and flow recordings, and impedance characteristics were used for calculation of the variables of a simple lumped analog representation of the arterial bed. PA smooth muscle was stimulated by infusions of collagen suspension, by general hypoxia and by nor-adrenaline injections. Collagen caused 40% reduction of vascular compliance (C), no changes in proximal arterial resistance (Rl) and 18076 increase in peripheral vascular resistance (R2). Hypoxia caused 5096 reduced C, 20% increased R1 and 70% increased R2. Noradrenaline caused 20:6 reduced C and 30 % increased R1 and R2. These results, together with results derived from simulation of the observed impedance changes in a computer model of the lung arterial bed, indicated that collagen infusion elicited contraction of small and medium-sized arteries, with increased arterial volume as result of increased distending pressure. Hypoxia and noradrenaline, seemed both to cause contraction of the total arterial bed. This effect being most pronounced during hypoxia.     

In vitro evaluation of an axial flow pump: mock-pump interaction and an approach to control

Continuous flow pump support has emerged as an alternative therapy in patients with congestive heart failure. For long-term applications, it is important to have a control system that changes the pump function according to the physiological conditions of the patient, thereby preventing risk situations. In the early stages of development, the evaluation of control algorithms for artificial blood pumps can be done in vitro using cardiovascular mock systems. A systemic cardiovascular mock loop was constructed and an axial flow pump was connected to it. The level of pump assistance was estimated using a pulsatility index (IPAo) obtained from the aortic pressure wave. An IPAo proportional-integral control system was implemented and its responses to peripheral resistance and systemic compliance changes were evaluated. IPAo is an indicator of the assistance level of a continuous flow pump operated at constant speed. The IPAo control algorithm responds by increasing the pump speed when peripheral resistance or systemic compliance is reduced. Control system operation around an IPAo fixed value provides a safety point for pump operation by maintaining aortic pressure pulsatility and avoiding ventricular suction. In vitro experimental results show that the IPAo can be taken into consideration in multiobjective control algorithm designs.     

Pressure/flow relation in the peripheral pulmonary vascular bed in dogs: a preliminary study

In order to test a technique for the determination of the pressure/flow relationship in the peripheral pulmonary vascular bed, the perfusion pressure changes with increasing and then decreasing flow in a small part of the lung (around 1 ml) were studied in anaesthetized supine dogs, after insertion of a specially designed double distal lumen Swan–Ganz catheter. One lumen was used for the pressure measurement, one for infusion of saline by a pump with variable flow, from 0.1 to 1.0 ml s^-1. A conventional thermodilution Swan–Ganz catheter was also advanced in the pulmonary artery, to measure pressures in the pulmonary circulation as well as cardiac output. During infusion in the wedged catheter, right atrial, pulmonary arterial and balloon occlusion wedge pressures did not change. The pressure/flow curve of the occluded vascular bed showed a shape similar to that of collapsible tubes, with a pressure plateau at high flow, but this could also be due to vascular recruitment. The curve exhibited hysteresis, with a lower pressure when flow decreased. The slope of the initial part of the curve increased, on average, from 54±9 during normoxia to 91±27 mmHg s ml^-1during hypoxia (FIO₂= 0.10); this difference was not significant, but the perfusion pressure at high flow was significantly higher during hypoxia (P < 0.05). Using blood instead of saline would allow the determination of the peripheral pulmonary vascular resistance under physiological conditions, and further work is needed to estimate the sensitivity and the reproducibility of this technique.     

Constant flow- vs. constant pressure-perfusion for studies of pulmonary vasoactive responses

We have compared the pulmonary vascular responses to a standardized hypoxic vasoconstrictor stimulus (F_1,0,2=0.02) obtained during 1) constant volume inflow, with pulmonary arterial pressure as the dependent variable, and 2) constant inflow pressure, with flow as the dependent variable. Isolated rat lungs were perfused at different baseline transvascular pressures. The experimental arrangement allowed changes between the two types of perfusion. Hypoxia at constant pressure perfusion gave a higher percentage rise in pulmonary vascular resistance (PVR) at all pressure levels. This advantage was however, more than offset by the finding that a) vascular closure (total or partial) often occurred, particularly below arterial pressure of 3 kPa, making detection of graded responses impossible, and b) the control situation was rarely regained. Responses obtained during constant flow were less reduced by elevations in baseline transvascular pressure, and the control situation was rapidly and completely regained. The observation that hypoxic vascular closure may occur in the pulmonary vascular bed supports the hypothesis that high altitude edema is caused by precapillary occlusion of a major part of the vascular bed, thereby subjecting still perfused regions to very high pressures and flow.     

Comparison of the reflex vasomotor responses to separate and combined stimulation of the carotid sinus and aortic arch baroreceptors by pulsatile and non-pulsatile pressures in the dog

1. In the anaesthetized dog the carotid sinuses and aortic arch were isolated from the circulation and separately perfused with blood by a method which enabled the mean pressure, pulse pressure and pulse frequency to be varied independently in each vasosensory area. The systemic circulation was perfused at constant blood flow by means of a pump and the systemic venous blood was oxygenated by an extracorporeal isolated pump-perfused donor lung preparation.2. When the vasosensory areas were perfused at non-pulsatile pressures within the normal physiological range of mean pressures, the reflex reduction in systemic vascular resistance produced by a given rise in mean carotid sinus pressure was significantly greater than that resulting from the same rise of aortic arch pressure.3. On the other hand, when the vasosensory areas were perfused at normal pulsatile pressures and within the normal physiological range of mean pressures, there was no difference in the size of the reflex vascular responses elicited by the same rise in mean pressure in the carotid sinuses and in the aortic arch.4. Whereas the vasomotor responses elicited reflexly by changes in mean carotid sinus pressure are modified by alterations in pulse pressure, those evoked by the aortic arch baroreceptors through changes of mean pressure are only weakly affected by modifications in pulse pressure. Evidence for this was obtained from single stepwise changes of mean pressure in each vasosensory area during pulsatile and non-pulsatile perfusion, and from curves relating the mean pressure in the carotid sinuses or aortic arch and systemic arterial perfusion pressure.5. The vasomotor response elicited by combined stimulation of the carotid sinus and aortic arch baroreceptors was greater than either response resulting from their separate stimulation.6. When the mean perfusion pressures in the two vasosensory areas are changed together, the curve relating mean pressure to systemic arterial pressure during pulsatile perfusion of the areas is considerably flatter than that for non-pulsatile perfusion.7. Increasing the pulse pressure in the carotid sinuses or aortic arch caused a decrease in systemic vascular resistance, the response elicited from the carotid sinuses being the larger.8. Altering the phase angle between the pulse pressure waves in the carotid sinuses and aortic arch had no effect on systemic vascular resistance.9. In both vasosensory areas, increasing the pulse frequency caused a reduction in systemic vascular resistance.     

Continuous flow total artificial heart: modeling and feedback control in a mock circulatory system

We developed a mock circulatory loop and used mathematical modeling to test the in vitro performance of a physiologic flow control system for a total artificial heart (TAH). The TAH was constructed from two continuous flow pumps. The objective of the control system was to maintain loop flow constant in response to changes in outflow resistance of either pump. Baseline outflow resistances of the right (pulmonary vascular resistance) and the left (systemic vascular resistance) pumps were set at 2 and 18 Wood units, respectively. The corresponding circuit flow was 4 L/min. The control system consisted of two digital integral controllers, each regulating the voltage, hence, the rotational speed of one of the pumps. The in vitro performance of the flow control system was validated by increasing systemic and pulmonary vascular resistances in the mock loop by 4 and 8 Wood units (simulating systemic and pulmonary hypertension conditions), respectively. For these simulated hypertensive states, the flow controllers regulated circuit flow back to 4 L/min within seconds by automatically adjusting the rotational speed of either or both pumps. We conclude that this multivariable feedback mechanism may constitute an adequate supplement to the inherent pressure sensitivity of rotary blood pumps for the automatic flow control and left-right flow balance of a dual continuous flow pump TAH system.     

Influence of carotid baroreceptors on different components of the vascular system

1. Reflex changes in wall tension of the lateral saphenous vein of one hind limb, the splenic veins and capsule, and the resistance vessels of the other hind limb caused by changes in baroreceptor activity were measured in vagotomized dogs under thiopentone-chloralose anaesthesia.2. Three different methods were used to alter pressure in one or both carotid sinuses. (1) Both carotid sinuses were vascularly isolated and filled with fully oxygenated Krebs-Ringer bicarbonate solution (pH 7.4) from a reservoir in which the pressure could be altered at will. (2) One sinus was denervated, and the contralateral sinus was perfused with arterial blood at different flow rates. (3) One sinus was denervated, and the innervated sinus was perfused with arterial blood at constant flow, the pressure being altered by changing the outflow resistance.3. The left saphenous vein was perfused at constant flow with autologous blood; changes in perfusion pressure were used as a measure of changes in veno-motor activity. The right common iliac artery was perfused at constant flow to measure changes in resistance vessel activity. Blood flow through the spleen was temporarily arrested, trapping a fixed volume of blood in the organ. Under these conditions, changes in splenic vein pressure were a measure of changes in smooth-muscle tension in the splenic capsule and veins.4. In order to assess the responses to baroreceptor stimulation in terms of alterations in sympathetic nerve traffic to different components of the peripheral vascular system, ;frequency-response curves' were constructed for spleen, saphenous vein, and limb resistance vessels by electrical stimulation of the splenic nerves and lumbar sympathetic chains.5. The saphenous vein showed no consistent response to changes in baroreceptor activity. Reduction in carotid sinus pressure from 180 to 100 mm Hg caused an increase in venous pressure in the isovolumetric spleen and in the iliac artery perfusion pressure. These results were confirmed by electrical stimulation of the carotid sinus nerve. Whereas the peak responses of the limb resistance vessels corresponded to an increase in lumbar sympathetic nerve traffic of 6-10 c/s, the maximal splenic responses were equivalent to an increase in splenic nerve traffic of 1-4 c/s. These results are consistent with selective autonomic nervous control of different components of the peripheral vascular system.     

Computational Analysis of the Effects of Exercise on Hemodynamics in the Carotid Bifurcation

The important influence of hemodynamic factors in the initiation and progression of arterial disease has led to numerous studies to computationally simulate blood flow at sites of disease and examine potential correlative factors. This study considers the differences in hemodynamics produced by varying heart rate in a fully coupled fluid-structure three-dimensional finite element model of a carotid bifurcation. Two cases with a 50% increase in heart rate are considered: one in which peripheral resistance is uniformly reduced to maintain constant mean arterial pressure, resulting in an increase in mean flow, and a second in which cerebral vascular resistance is held constant so that mean carotid artery flow is nearly unchanged. Results show that, with increased flow rate, the flow patterns are relatively unchanged, but the magnitudes of mean and instantaneous wall shear stress are increased roughly in proportion to the flow rate, except at the time of minimum flow (and maximum flow separation) when shear stress in the carotid bulb is increased in magnitude more than threefold. When cerebral peripheral resistance is held constant, the differences are much smaller, except again at end diastole. Maximum wall shear stress temporal gradient is elevated in both cases with elevated heart rate. Changes in oscillatory shear index are minimal. These findings suggest that changes in the local hemodynamics due to mild exercise may be relatively small in the carotid artery. © 2003 Biomedical Engineering Society. PAC2003: 8719Uv, 8719Rr, 8380Lz