Atrial septostomy benefits severe pulmonary hypertension patients by increase of left ventricular preload reserve

At present, it is unknown why patients suffering from severe pulmonary hypertension (PH) benefit from atrial septostomy (AS). Suggested mechanisms include enhanced filling of the left ventricle, reduction of right ventricular preload, increased oxygen availability in the peripheral tissue, or a combination. A multiscale computational model of the cardiovascular system was used to assess the effects of AS in PH. Our model simulates beat-to-beat dynamics of the four cardiac chambers with valves and the systemic and pulmonary circulations, including an atrial septal defect (ASD). Oxygen saturation was computed for each model compartment. The acute effect of AS on systemic flow and oxygen delivery in PH was assessed by a series of simulations with combinations of different ASD diameters, pulmonary flows, and degrees of PH. In addition, blood pressures at rest and during exercise were compared between circulations with PH before and after AS. If PH did not result in a right atrial pressure exceeding the left one, AS caused a left-to-right shunt flow that resulted in decreased oxygenation and a further increase of right ventricular pump load. Only in the case of severe PH a right-to-left shunt flow occurred during exercise, which improved left ventricular preload reserve and maintained blood pressure but did not improve oxygenation. AS only improves symptoms of right heart failure in patients with severe PH if net right-to-left shunt flow occurs during exercise. This flow enhances left ventricular filling, allows blood pressure maintenance, but does not increase oxygen availability in the peripheral tissue.     

CORRECTION OF ANOMALOUS VENOUS RETURN FROM THE RIGHT LUNG TO THE INFERIOR VENA CAVA (SCIMITAR DEFORMITY)

Anomalous pulmonary venous drainage to the inferior vena cava is a rare congenital cardiac defect. Oxygenated blood from the right lung enters the right atrium resulting in a left-to-right shunt. Because the radiographic shadow of the anomalous vein resembles a curved saber, this defect has been called the "scimitar" deformity. From 1958 through June 30, 1975, 11 patients underwent surgical correction of this anomaly at our institution with 10 survivors. Diagnosis was made by routine roentgenography of the chest in all but one patient. Eight patients had total correction which consisted of implanting the anomalous vein into the right atrium, opening the interatrial septum and applying a patch graft as a baffle to direct pulmonary venous blood into the left atrium. Five patients had associated cardiac defects which were also repaired. Three patients underwent pneumonectomy and all survived. The only operative death occurred in a 5-year-old female with an atrial septal defect and endocardial cushion defect. We believe the existence of a large left-to-right shunt justifies surgical intervention. The prognosis appears to depend upon the presence of other cardiac or pulmonary anomalies.     

A radiological study of the central circulation in the lungfish, Protopterus aethiopicus

The dipnoan heart is only in part structurally developed to support a separated circulation in pulmonary and systemic circuits. In the present investigation biplane angiocardiography has been used to describe the extent of such a double circulation and the factors which may modify it in the African lungfish, Protopterus aethiopicus. Contrast injections in the pulmonary vein revealed a clear tendency for aerated blood returing from the lungs to be selectively dispatched to the anterior branchial arteries giving rise to the major systemic circulation. Contrast injections in the vena cava delineated the sinus venosus as a large receiving chamber for systemic venous blood. Contraction of the sinus venosus discharged blood into the right, posterior part of the partially divided atrial space. Contrast injection in the pulmonary vein showed that vessel to pass obliquely from right to left such that blood was emptied distinctly into the left side of the atrium. During contraction the atrial space tended to retain a residual volume in its anterior undivided part which minized mixing. Ventricular filling occurred through separate right and left atrio-ventricular connections. Right-left separation in most of the ventricle was maintained by the partial ventricular septum, the trabeculated, spongelike myocardium and the mode of inflow from the atria. Mixing in the anterior undivided portion of the ventricle during the ejection phase was slight due to a streamlined ejection pattern. The outflow through the bulbus cordis occurred in discrete streams which in part were structurally separated by well developed spiral folds. In the anterior bulbus segment the spiral folds are fused and make completely separate dorsal and ventral outflow tracts. The ventral bulbus channel provides blood to the three anterior branchial arteries. The second and third branchial arteries are large and represent direct shunts to the dorsal aorta. The fourth and fifth branchial arteries are gill bearing and receive blood form the dorsal bulbus channel. The most posterior epibranchial vessels give rise to the pulmonary arteries.     

The role of the cardiac-pulmonary blood volume in the changes in left ventricle output during stimulation of the afferent fibers of somatic nerves

Stimulation of tibial nerve afferent fibers has revealed heterogeneous shifts of left ventricular output, as well as pulmonary artery and posterior vena cava blood flow in anesthetized cats. Uniform changes in left ventricular output and pulmonary artery blood flow were noted in the majority of cases, with venous return most often exceeding pulmonary artery blood flow. beta-adrenoreceptor blockade failed to influence changes in pulmonary artery blood flow. It is concluded that the increase in pulmonary artery blood flow depends on the rise in venous return, but not on neurogenic influence upon the right ventricle. The reduction in left ventricular output is the result of decreased right ventricular outflow due to its overload caused by pulmonary vasoconstriction.     

In vivo porcine left atrial wall stress: Computational model

Most computational models of the heart have so far concentrated on the study of the left ventricle, mainly using simplified geometries. The same approach cannot be adopted to model the left atrium, whose irregular shape does not allow morphological simplifications. In addition, the deformation of the left atrium during the cardiac cycle strongly depends on the interaction with its surrounding structures. We present a procedure to generate a comprehensive computational model of the left atrium, including physiological loads (blood pressure), boundary conditions (pericardium, pulmonary veins and mitral valve annulus movement) and mechanical properties based on planar biaxial experiments. The model was able to accurately reproduce the in vivo dynamics of the left atrium during the passive portion of the cardiac cycle. A shift in time between the peak pressure and the maximum displacement of the mitral valve annulus allows the appendage to inflate and bend towards the ventricle before the pulling effect associated with the ventricle contraction takes place. The ventricular systole creates room for further expansion of the appendage, which gets in close contact with the pericardium. The temporal evolution of the volume in the atrial cavity as predicted by the finite element simulation matches the volume changes obtained from CT scans. The stress field computed at each time point shows remarkable spatial heterogeneity. In particular, high stress concentration occurs along the appendage rim and in the region surrounding the pulmonary veins.     

右心导管法测大鼠肺动脉压力的改良

目的:目前常用的测量大鼠肺动脉压力的右心导管法存在一定的缺陷,且很难得到典型的压力曲线图。本实验对大鼠经颈外静脉插管与测压的方法进行改良,同时与已有报道的实验结果进行比较,并提供正常SD大鼠右心房、右心室及肺动脉的压力参考值及典型的压力曲线图,以协助研究人员判断导管位置,及时调整导管的深度和方向,快速测出肺动脉压力。方法:雌雄不分的清洁级SD大鼠共30只,体重180~230 g,6~7周龄。应用自制的末端呈一弧形的PE-10管,采用改良后的右心导管法,经颈外静脉插入大鼠心腔及肺动脉,检测并计算大鼠右心房、右心室和肺动脉的收缩压、舒张压及肺动脉平均压。结果:右心房压力波动较平缓,呈小波浪形;右心室压力曲线波动大,骤升骤降;肺动脉压力曲线有重搏波。正常SD大鼠右心房舒张压为(2.03±2.56)mmHg,收缩压为(2.82±1.85)mmHg;右心室舒张压为(5.72±3.99)mmHg,收缩压为(18.73±4.80)mmHg;肺动脉舒张压为(15.27±2.64)mmHg,收缩压为(18.49±2.53)mmHg,肺动脉平均压为(16.34±2.32)mmHg。右心室收缩压与肺动脉收缩压无明显差异(P0.05)。结论:改良后的方法可准确到达大鼠肺动脉,提供的压力参考值及曲线图有助于研究人员顺利完成测压实验。     

Hemodynamic adjustments to head-up posture in the partly arboreal snake, Elaphe obsoleta

Radioactively-labeled microspheres were used to quantify adjustments of regional blood flows in 15 snakes (Elaphe obsoleta) subjected to 45 degrees head-up tilt. Heart rate and peripheral vascular resistance increased during tilt to compensate for the passive drop of pressure at the head. Two snakes failed to regulate blood pressure, but in 13 others arterial pressure increased at midbody (where passive changes in pressure are unexpected due to tilt alone) and arterial pressure at the head averaged 67% of the pretilt value. Tissue blood flow was reduced significantly in visceral organs, posterior skin and posterior skeletal muscle, but was maintained at pretilt levels in brain, heart, lung and anterior tissues. Ventricular systemic output averaged 24 ml/min X kg in horizontal posture and 9.4 ml/min X kg during tilt. Comparable values for pulmonary output were 4 and 6.5 ml/min X kg. Patterns of intraventricular shunting of blood acted to maintain pulmonary flow during tilt. A large right-to-left shunt (mean 76%) was present in horizontal snakes, but the shunted fraction declined during tilt (mean 54%). Left-to-right shunt increased during tilt from 7% to 14%.     

Functional Anatomy of the Heart of Reptiles

Intravascular pressures, distributions of blood oxygen, dye-dilutioncurves, cineradiography, and electromagnetic flowmeters in majorvessels suggest a highly directional flow oE systemic and pulmonaryvenous blood through reptilian hearts. The lacertilian rightaortic arch contains blood from the pulmonary, and the leftfrom the pulmonary or sometimes both pulmonary and systemicveins. Traces made of the pressure and blood flow show thatthe lacertilian and chelonian cava venosum and pulmonale arefunctionally distinct. Atrioventricular valves probably preventregurgitation during ventricular systole and form an obstructionbetween the cava arteriosum and venosum during ventricular filling.The muscular ridge approaches the ventral ventricular wall atsystole forming a functional ventricular septum. Low pulmonaryvascular resistance favors pulmonary ejection before systemic.In Pseudemys the balance between pulmonary and systemic resistancecauses a left-to-right shunt during respiration and a right-to-leftshunt during diving; the latter probably reduces the expenditureof cardiac energy during hypoxia. Pressure traces and cineradiographyindicate separation of systemic and pulmonary venous returnsin alligators. The left ventricle perfuses both aortic archesand the right the pulmonary arch. Right ventricular pressuremay exceed pulmonary pressure during ejection suggesting animpedance in the pulmonary outflow tract. Pulmonary resistancein crocodilians may increase during diving, instituting a right-to-leftshunt.     

Functional morphology and patterns of blood flow in the heart of Python regius

Brightness‐modulated ultrasonography, continuous‐wave Doppler, and pulsed‐wave Doppler‐echocardiography were used to analyze the functional morphology of the undisturbed heart of ball pythons. In particular, the action of the muscular ridge and the atrio‐ventricular valves are key features to understand how patterns of blood flow emerge from structures directing blood into the various chambers of the heart. A step‐by‐step image analysis of echocardiographs shows that during ventricular diastole, the atrio‐ventricular valves block the interventricular canals so that blood from the right atrium first fills the cavum venosum, and blood from the left atrium fills the cavum arteriosum. During diastole, blood from the cavum venosum crosses the muscular ridge into the cavum pulmonale. During middle to late systole the muscular ridge closes, thus prohibiting further blood flow into the cavum pulmonale. At the same time, the atrio‐ventricular valves open the interventricular canal and allow blood from the cavum arteriosum to flow into the cavum venosum. In the late phase of ventricular systole, all blood from the cavum pulmonale is pressed into the pulmonary trunk; all blood from the cavum venosum is pressed into both aortas. Quantitative measures of blood flow volume showed that resting snakes bypass the pulmonary circulation and shunt about twice the blood volume into the systemic circulation as into the pulmonary circulation. When digesting, the oxygen demand of snakes increased tremendously. This is associated with shunting more blood into the pulmonary circulation. The results of this study allow the presentation of a detailed functional model of the python heart. They are also the basis for a functional hypothesis of how shunting is achieved. Further, it was shown that shunting is an active regulation process in response to changing demands of the organism (here, oxygen demand). Finally, the results of this study support earlier reports about a dual pressure circulation in Python regius. J. Morphol., 2009. © 2008 Wiley‐Liss, Inc.     

Relation of prostanoids to strength of hypoxic vasoconstriction in dogs with lobar atelectasis

In dogs with acute lobar atelectasis, meclofenamate administration decreases shunt fraction uniformly and moderately without abolishing the wide variation of strength of hypoxic vasoconstriction and resultant variability of shunt fraction (J. Appl. Physiol. 54: 284-289, 1983). To further assess the role of prostanoids, we measured prostanoid metabolites as well as shunt fraction and pressor response to alveolar hypoxia. In six intact anesthetized dogs with acute left lower lobe atelectasis, shunt fraction during normoxia was measured with SF6. Levels of 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 in arterial, mixed venous, and left lower lobe venous blood were measured with the double antibody radioimmunoassay technique. Ten percent O2 was administered to assess pressor response. Twenty-one percent O2 was restarted, meclofenamate was administered, and measurements were repeated 30 min later. Atelectasis did not elevate levels of prostanoid metabolites. 6-Keto-PGF1 alpha averaged 88 +/- 65 pg/ml prior to atelectasis and 81 +/- 73 pg/ml after atelectasis (F = 0.7, P = NS). Likewise, thromboxane B2 values were normal. No transpulmonary concentration differences were found. 6-Keto-PGF1 alpha did not correlate with shunt values, which ranged from 14 to 35% (mean 21%). Meclofenamate effectively blocked cyclooxygenase, as demonstrated by decreases in prostanoid metabolite levels. It seems likely that in dogs with acute atelectasis prostacyclin localized in the pulmonary vasculature decreases strength of hypoxic vasoconstriction modestly and uniformly without raising blood levels of prostacyclin metabolite.     

Effect of high altitude exposure on the hemodynamics of the bidirectional Glenn physiology: Modeling incremented pulmonary vascular resistance and heart rate

The considerable blood mixing in the bidirectional Glenn (BDG) physiology further limits the capacity of the single working ventricle to pump enough oxygenated blood to the circulatory system. This condition is exacerbated under severe conditions such as physical activity or high altitude. In this study, the effect of high altitude exposure on hemodynamics and ventricular function of the BDG physiology is investigated. For this purpose, a mathematical approach based on a lumped parameter model was developed to model the BDG circulation. Catheterization data from 39 BDG patients at stabilized oxygen conditions was used to determine baseline flows and pressures for the model. The effect of high altitude exposure was modeled by increasing the pulmonary vascular resistance (PVR) and heart rate (HR) in increments up to 80% and 40%, respectively. The resulting differences in vascular flows, pressures and ventricular function parameters were analyzed. By simultaneously increasing PVR and HR, significant changes (p <0.05) were observed in cardiac index (11% increase at an 80% PVR and 40% HR increase) and pulmonary flow (26% decrease at an 80% PVR and 40% HR increase). Significant increase in mean systemic pressure (9%) was observed at 80% PVR (40% HR) increase. The results show that the poor ventricular function fails to overcome the increased preload and implied low oxygenation in BDG patients at higher altitudes, especially for those with high baseline PVRs. The presented mathematical model provides a framework to estimate the hemodynamic performance of BDG patients at different PVR increments.     

Effects of ectopic pacing on repolarization of the chicken left ventricle

Effects of ectopic pacing on left ventricular repolarization were studied in six anesthetized open-chest chickens. In each animal, unipolar electrograms were acquired from as many as 98 sites with 14 plunge needles (seven transmural locations between epicardium and endocardium in each needle). Activation-recovery intervals (ARIs), corrected to the cycle length, were used for estimating repolarization. At baseline, the nonuniform ARI distribution in the left ventricle resulted in the apicobasal differences being greater than the transmural gradient. Nonuniform ARI prolongation caused by ectopic pacing resulted in decreasing the transmural repolarization gradient and increasing the differences in the apex-to-base direction. The basal, but not apical transmural differences contributed to the total left ventricular transmural gradient. The total left ventricular apicobasal gradient was contributed by the apicobasal differences in mid-myocardial and subendocardial layers more than in subepicardial ones. Thus, in in situ chicken hearts, the transmural and apicobasal ARI gradients exist within the left ventricle with the shortest ARIs in the basal subepicardium and the longest ARIs in the subendocardium of the apical and middle parts of the left ventricle. Apicobasal compared to transmural heterogeneity of local repolarization properties contributes more to the total left ventricular repolarization gradient.     

Heart inflow tract of the African lungfish Protopterus dolloi

We report a morphologic study of the heart inflow tract of the African lungfish Protopterus dolloi. Attention was paid to the atrium, the sinus venosus, the pulmonary vein, and the atrioventricular (AV) plug, and to the relationships between all these structures. The atrium is divided caudally into two lobes, has a common part above the sinus venosus, and appears attached to the dorsal wall of the ventricle and outflow tract through connective tissue covered by the visceral pericardium. The pulmonary vein enters the sinus venosus and runs longitudinally toward the AV plug. Then it fuses with the pulmonalis fold and disappears as an anatomic entity. However, the oxygenated blood is directly conveyed into the left atrium by the formation of a pulmonary channel. This channel is formed cranially by the pulmonalis fold, ventrally by the AV plug, and caudally and dorsally by the atrial wall. The pulmonalis fold appears as a wide membranous fold which arises from the left side of the AV plug and extends dorsally to form the roof of the pulmonary channel. The pulmonalis fold also forms the right side of the pulmonary channel and sequesters the upper left corner of the sinus venosus from the main circulatory return. The AV plug is a large structure, firmly attached to the ventricular septum, which contains a hyaline cartilaginous core surrounded by connective tissue. The atrium is partially divided into two chambers by the presence of numerous pectinate muscles extended between the dorsal wall of the atrium and the roof of the pulmonary channel. Thus, partial atrial division is both internal and external, precluding the more complete division seen in amphibians. The present report, our own unpublished observations on other Protopterus, and a survey of the literature indicate that not only the Protopterus, but also other lungfish share many morphologic traits.     

The use of smoothed particles approach in realistic mathematical model of intracardiac blood flow: Simulation of a self-organizing tornado-like flow

We performed computer simulation and visualization of blood flow in the left ventricle by the method of smooth particle hydrodynamics (SPH). This visualization qualitatively describes the evolution of twisted stream and graphically demonstrates the direction of velocity field at each moment of time. The geometrical features of the left ventricle are approximated by three-dimensional segmentation of experimental clinical images obtained from multispiral computer tomography (MSCT). The model adequately describes the possible configuration of swirling flow in the left ventricle and is a part of a comprehensive study of swirling flows in different compartments of heart, which comply with a family of the exact solutions of hydrodynamic Navier–Stokes equations for the class of quasipotential¹ swirling flows. Computer visualization shows how simulated by SPH method jet of a model liquid, which is placed in limited space, remains continuity and keeps its clockwise vorticity along the direction of the flow propagation during the whole cycle. Then it turns on approximately 120° by the time of ejection into the aorta. Such structure of the flow provides more effective pumping of blood as a model liquid through the ventricle as compared to a lamellar flow mode.     

Three-dimensional computational model of left heart diastolic function with fluid-structure interaction

Aided by advancements in computer speed and modeling techniques, computational modeling of cardiac function has continued to develop over the past twenty years. The goal of the current study was to develop a computational model that provides blood-tissue interaction under physiologic flow conditions, and apply it to a thin-walled model of the left heart. To accomplish this goal, the Immersed Boundary Method was used to study the interaction of the tissue and blood in response to fluid forces and changes in tissue pathophysiology. The fluid mass and momentum conservation equations were solved using Patankar's Semi-Implicit Method for Pressure Linked Equations (SIMPLE). A left heart model was developed to examine diastolic function, and consisted of the left ventricle, left atrium, and pulmonary flow. The input functions for the model included the pulmonary driving pressure and time-dependent relationship for changes in chamber tissue properties during the simulation. The results obtained from the left heart model were compared to clinically observed diastolic flow conditions for validation. The inflow velocities through the mitral valve corresponded with clinical values (E-wave = 74.4 cm/s, A-wave = 43 cm/s, and E/A = 1.73). The pressure traces for the atrium and ventricle, and the appearance of the ventricular flow fields throughout filling, agreed with those observed in the heart. In addition, the atrial flow fields could be observed in this model and showed the conduit and pump functions that current theory suggests. The ability to examine atrial function in the present model is something not described previously in computational simulations of cardiac function.     

Cardiovascular dynamics inCrocodylus porosus breathing air and during voluntary aerobic dives

Summary Pressure records from the heart and out-flow vessels of the heart ofCrocodylus porosus resolve previously conflicting results, showing that left aortic filling via the foramen of Panizza may occur during both cardiac diastole and systole. Filling of the left aorta during diastole, identified by the asynchrony and comparative shape of pressure events in the left and right aortae, is reconciled more easily with the anatomy, which suggests that the foramen would be occluded by opening of the pocket valves at the base of the right aorta during systole. Filling during systole, indicated when pressure traces in the left and right aortae could be superimposed, was associated with lower systemic pressures, which may occur at the end of a voluntary aerobic dive or can be induced by lowering water temperature or during a long forced dive. To explain this flexibility, we propose that the foramen of Panizza is of variable calibre. The presence of a right-left shunt, in which increased right ventricular pressure leads to blood being diverted from the lungs and exiting the right ventricle via the left aorta, was found to be a frequent though not obligate correlate of voluntary aerobic dives. This contrasts with the previous concept of the shunt as a correlate of diving bradycardia. The magnitude of the shunt is difficult to assess but is likely to be relatively small. This information has allowed some new insights into the functional significance of the complex anatomy of the crocodilian heart and major blood vessels.Abbreviations bpm beats per minute - LAo left aorta (aortic) - LV left ventricle (ventricular) - PA pulmonary artery - RAo right aorta (aortic) - RV right ventricle (ventricular) - SC subclavian artery Deceased     

Experimental ductus arteriosus: the relationships of atrial pressure, dilatation and flow with ANF secretion

The design of the study was to determine whether an increased blood flow as seen in shunt lesions could serve as a stimulus for the secretion of atrial natriuretic factor (ANF). Since atrial pressure, flow, and dilatation are closely related, an experimental ductus arteriosus model was utilized, in which acute changes of flow are assumed not to dilate the left atrium. In six dogs, a Dacron graft was constructed between the main pulmonary artery and the innominate artery. Constricting and releasing the tape around the graft adjusted the amount of "ductal" shunting. The total pulmonary flow and the shunt flow were measured by electromagnetic-flow transducers around the aortic root and around the graft. Plasma ANF concentration was measured from both cardiac atria. The size of the left atrium was determined from echocardiographic measurements made from a short-axis view. The total pulmonary flow varied between 1.2 and 5.8 1/min. The highest measured ANF was 396 pg/ml, and this was from the left atrium when the pressure was 18 mmHg, the highest left atrial pressure recorded. The highest right atrial pressure (5 mmHg) also correlated with the highest right-atrial level of ANF (366 pg/ml). The right atrial pressure had a significant correlation with plasma ANF concentration (R = 0.43, p less than 0.05). Pulmonary flow and plasma ANF concentration did not correlate; neither did left atrial size and ANF levels in 16 flow states where the size was measured. In the absence of atrial dilatation there was minimal stimulus for ANF secretion. A transient increase of left atrial pressure, without a concomitant significant atrial dilatation, did not serve as a significant stimulus for ANF secretion.     

Mutation of weak atrium/atrial myosin heavy chain disrupts atrial function and influences ventricular morphogenesis in zebrafish

The embryonic vertebrate heart is composed of two major chambers, a ventricle and an atrium, each of which has a characteristic size, shape and functional capacity that contributes to efficient circulation. Chamber-specific gene expression programs are likely to regulate key aspects of chamber formation. Here, we demonstrate that epigenetic factors also have a significant influence on chamber morphogenesis. Specifically, we show that an atrium-specific contractility defect has a profound impact on ventricular development. We find that the zebrafish locus weak atrium encodes an atrium-specific myosin heavy chain that is required for atrial myofibrillar organization and contraction. Despite their atrial defects, weak atrium mutants can maintain circulation through ventricular contraction. However, the weak atrium mutant ventricle becomes unusually compact, exhibiting a thickened myocardial wall, a narrow lumen and changes in myocardial gene expression. As weak atrium/atrial myosin heavy chain is expressed only in the atrium, the ventricular phenotypes in weak atrium mutants represent a secondary response to atrial dysfunction. Thus, not only is cardiac form essential for cardiac function, but there also exists a reciprocal relationship in which function can influence form. These findings are relevant to our understanding of congenital defects in cardiac chamber morphogenesis.     

Computational modeling of left heart diastolic function: examination of ventricular dysfunction

A computational model that accounts for blood-tissue interaction under physiological flow conditions was developed and applied to a thin-walled model of the left heart. This model consisted of the left ventricle, left atrium, and pulmonary vein flow. The input functions for the model included the pulmonary vein driving pressure and time-dependent relationship for changes in chamber tissue properties during the simulation. The Immersed Boundary Method was used for the interaction of the tissue and blood in response to fluid forces and changes in tissue pathophysiology, and the fluid mass and momentum conservation equations were solved using Patankar's Semi-Implicit Method for Pressure Linked Equations (SIMPLE). This model was used to examine the flow fields in the left heart under abnormal diastolic conditions of delayed ventricular relaxation, delayed ventricular relaxation with increased ventricular stiffness, and delayed ventricular relaxation with an increased atrial contraction. The results obtained from the left heart model were compared to clinically observed diastolic flow conditions, and to the results from simulations of normal diastolic function in this model [1]. Cases involving impairment of diastolic function were modeled with changes to the input functions for fiber relaxation/contraction of the chambers. The three cases of diastolic dysfunction investigated agreed with the changes in diastolic flow fields seen clinically. The effect of delayed relaxation was to decrease the early filling magnitude, and this decrease was larger when the stiffness of the ventricle was increased. Also, increasing the contraction of the atrium during atrial systole resulted in a higher late filling velocity and atrial pressure. The results show that dysfunction can be modeled by changing the relationships for fiber resting-length and/or stiffness. This provides confidence in future modeling of disease, especially changes to chamber properties to examine the effect of local dysfunction on global flow fields.     

脑室镜和腹腔镜辅助脑室腹腔分流术治疗老年脑积水的疗效

目的:探讨脑室镜和腹腔镜辅助脑室腹腔分流术治疗老年脑积水的疗效。方法:选择我院90例老年脑积水患者,按随机数字表法平均分为A、B、C 3组各30例,A组患者给予传统脑室腹腔分流术治疗,B组患者给予腹腔镜辅助下脑室腹腔分流术治疗,C组患者给予脑室镜和腹腔镜综合辅助下脑室腹腔分流术治疗,比较3组患者治疗有效率及术后并发症发生率。结果:C组患者治疗有效率为90.0%,明显高于A组63.3%及B组76.7%,比较差异具有统计学意义(均P0.05);C组患者术后感染及分流管堵塞并发症发生率明显低于A组和B组,比较差异均有统计学意义(均P0.05);B组和C组脑实质内出血发生率均低于A组,与A组比较差异具有统计学意义(P0.05)。结论:脑室镜和腹腔镜综合辅助下脑室腹腔分流术治疗老年脑积水的疗效显著,术后并发症少,值得推广。