Simulated Epicardial Potential Maps During Paced Activation Reflect Myocardial Fibrous Structure

Using a three-dimensional propagation model of the human ventricular myocardium, we studied the role of fibrous structure in generating epicardial potential maps. This model represents the myocardium as an anisotropic bidomain with an equal anisotropy ratio, and it incorporates a realistic representation of anatomical features, including epi-endocardial fiber rotation in the compact portion of the wall (compacta) and a distinct fiber arrangement of the trabeculated portion (trabeculata). Activation sequences were elicited at various intramural depths, and maps were calculated throughout a 60 ms sequence. The simulated maps closely resembled those measured by others in the canine heart. During the early stages of activation, a typical map featuring a central minimum flanked by two maxima emerged, with the axis joining these extrema approximately parallel to the fibers near the pacing site, and the axis joining the maxima rotated in the same direction as the fibers for different pacing depths; for endocardial and subendocardial pacing this map changed into one with an oblong positive area. During the later stages of activation, the positive areas of the maps expanded and rotated with the transmural fiber rotation. In concurrence with experiments, we saw a fragmentation and asymmetry of expanding and rotating positive areas. The latter features—apparently caused by the interface between the compacta and trabeculata, variable local thickness of the wall, or local undulations of the vetricular surface—could not be reproduced by more idealized, slab models. © 1998 Biomedical Engineering Society. PAC98: 8722-q, 8710+e     

Electroporation and Shock-Induced Transmembrane Potential in a Cardiac Fiber During Defibrillation Strength Shocks

Experimental studies have shown that the magnitude of the shock-induced transmembrane potential (V_m) saturates with increasing electric field strength. This study uses a mathematical model to investigate the effects of electroporation and membrane kinetics on V_m in a cardiac fiber. The model consists of the core conductor equation for a one-dimensional fiber, where excitability is represented by the Luo–Rudy dynamic model (1994–1995) and electroporation is described by a membrane conductance that increases exponentially with V_m squared. For shocks delivered during the plateau of an action potential, the model reproduces the experimentally observed saturation of V_m with a root mean square error of 4.27% and a correlation coefficient of 0.9992. For shocks delivered during diastole, the saturation of V_m is qualitatively reproduced even when the sodium and calcium channels are inactivated. Quantitative replication of the response to diastolic shocks is hindered by the choice of electroporation parameters (optimized for shocks delivered during the plateau) and differences in the membrane kinetics between model and experiment. The complex behavior of V_m during large shocks is due to a combination of electroporation, electrotonus, propagation, and active membrane kinetics. The modeling results imply that the experimentally observed saturation of V_m is due to electroporation of the lipid bilayer. © 1998 Biomedical Engineering Society. PAC98: 8722Fy, 8710+e, 8722Jb     

Changes in Cardiac Refractory Period During Signalled Shock Avoidance in Dogs

The effect of training during an aversive conditioning schedule on the ventricular effective refractory period (ERP) and the occurrence of repetitive extrasystoles (RE) was investigated in 11 dogs. The ERP was decreased significantly at avoidance onset during the first 5 days of the experiment. but remained unaltered during the second 5 days of testing. The changes in ERP were most pronounced on the first day. REs were observed most during avoidance in the animal with the greatest decrease in ERP but inconsistently in other animals. The potential use of aversive Training procedures to study the role of neural factors in cardiac arrhythmias is discussed.     

Effect of a perfusing bath on the rate of rise of an action potential propagating through a slab of cardiac tissue

Experiments show that the rate of rise of the action potential depends on the direction of propagation in cardiac tissue. Two interpretations of these experiments have been presented: (i) the data are evidence of discrete propagation in cardiac tissue, and (ii) the data are an effect of the perfusing bath. In this paper we present a mathematical model that supports the second interpretation. We use the bidomain model to simulate action potential propagation through a slab of cardiac tissue perfused by a bath. We assume an intracellular potential distribution and solve the bidomain equations analytically for the transmembrane and extracellular potentials. The key assumption in our model is that the intracellular potential is independent of depth within the tissue. This assumption ensures that all three boundary conditions at the surface of a bidomain are satisfied simultaneously. One advantage of this model over previous numerical calculations is that we obtain an analytical solution for the transmembrane potential. The model predicts that the bath reduces the rate of rise of the transmembrane action potential at the tissue surface, and that this reduction depends on the direction of propagation. The model is consistent with the hypothesis that the perfusing bath causes the observed dependence of the action-potential rate of rise on the direction of propagation, and that this dependence has nothing to do with discrete properties of cardiac tissue.     

Influence of the Electric Axis of Stimulation on the Induced Transmembrane Potentials in Ellipsoidal Bidomain Heart

This theoretical study was provoked by and designed to interpret, complement and extend the implications of recent experimental observations by Wikswo and Lin (PACE, 21:940, 1998) on the epicardial surface of rabbit hearts. Using a macroscopic bidomain representation of the cardiac structure and the finite element method, we model the response of the heart to uniform electric fields applied under different angles. To overcome intra- and interspecies differences in the geometric and structural characteristics of the cardiac muscle, the analysis is conducted for an idealized ellipsoidal heart. Although idealized, this heart model incorporates important structural features, i.e., fiber curvature, transmural fiber rotation, and unequal anisotropy for the intra- and extracellular domains. This study shows that regions of maximum polarization of opposite sign may develop along an axis, significantly deviating from the axis of the applied electric field. The polarization evoked inside the ventricular wall seems to be a major contributor to this phenomenon. Nonperiodic structural inhomogeneities on multicellular level (endocardial trabeculation in our model) result in local unaligned polarization dipoles weakening the magnitude of the global polarization dipole and reducing its deviation from the axis of stimulation. Our results might be helpful in improving current understanding of defibrillation mechanisms. © 2000 Biomedical Engineering Society. PAC00: 8719Nn, 8719Hh, 8750Rr     

益母草注射液对失血性休克大鼠转归时淋巴循环的干预作用

目的探讨益母草注射液（LHI）对失血性休克转归时淋巴循环的干预作用。方法采用淋巴学研究方法，对16只Wistar雄性大鼠进行研究，观察LHI对失血性休克大鼠肠淋巴循环的作用。结果失血性休克时，肠淋巴流量、淋巴细胞输出量明显降低，淋巴液中有少量单核细胞，经LHI治疗后，肠淋巴流量、淋巴细胞输出量增加，并且淋巴液中单核细胞增多，与对照组比较有显著性差异（P〈0．05）。此外，LHI可明显降低淋巴液黏度，其作用明显强于对照组（P〈0．05）。结论LHI能通过增强淋巴转运功能、降低淋巴液黏度而改善失血性休克时的淋巴循环障碍。     

电极配置对MUAP检测影响的仿真研究

本研究采用模型的方法,研究了电极配置对运动单位动作电位检测的影响.根据肌肉的形态结构和生理特征,从细胞内动作电位开始,仿真了运动单位动作电位序列.在此基础上,研究了电极的配置对运动单位动作电位的波形和统计特征的影响.结果表明:尺寸较小的电极选择性较好;差分电极的选择性优于单电极,适当调整其电极间距离和角度,可提高检测质量.     

Latency of Alpha Blocking as a Function of Photic Stimulation During the Cardiac Cycle

Changes in reaction time during the cardiac cycle have been reported by a number of investigators. The present study concerns changes in the latency of alpha blocking as a function of the time of presentation of photic stimulation during the cardiac cycle. Stimuli were presented at intervals of 0, 25, 50, 75, 100, 200, 300, 400, and 500 msec following the peak of the R-wave of the EKG. Alpha blocking latency was found to be shorter for stimulus presentation early in the cardiac cycle.     

Incidental in vivo detection of an isolated hemangioma of the aortic valve in a man with a history of renal transplantation

Hemangiomas of the cardiac valves are exceptional. To our knowledge, only ten cases of valve hemangiomas, six in the mitral and four in the tricuspid valve, have been reported in the English literature. We describe an incidentally detected aortic valve hemangioma of a 62-year-old man with chronic, degenerative aortic valve stenosis, who underwent renal transplantation 7 years before. We believe that this is the first report of a hemangioma in this localization and the first one in association with solid organ transplantation. The review of the literature of the adult cases of valve hemangioma, including this report, revealed that the average age was 47.2 years (range, 24 to 68 years). No clear sex predominance has been noted. Patients can be asymptomatic or experience sudden death. Symptomatic patients have complaints of palpitations, dyspnea, or syncopal episodes. Histologically, these valve tumors are classified as capillary, cavernous, and mixed. Mean tumor size is 1.1 cm (range, 0.6 to 2 cm). In 50% of cases the hemangioma is an incidental finding at autopsy or in a removed valve. Valve aortic hemangioma, despite its rarity, should be considered in the differential diagnosis of vascular lesions of this cardiac valve.     

Influence of a diet rich in fish oil on blood pressure,body weight and cardiac hypertrophy in spontaneously hypertensive rats

Summary The effects of a diet rich in fish oil on arterial blood pressure, body weight, left ventricular weight and heart rate have been investigated in 8 month old spontaneously hypertensive male rats (SHR) as compared to age-matched hypertensive controls. A diet containing 10% fish oil decreased blood pressure by about 40 mmHg within 20 days of starting the experiment, and this effect persisted over the observation period of 80 days. Permitting the animals free access to food, the body weight of the diet group increased by 25%. The degree of hypertrophy as evaluated by relating left ventricular weight to tibial length was significantly reduced (10%) in the diet fed group. Heart rate was increased by 53%. The study demonstrates that a diet rich in fish oil can lower arterial blood pressure over several weeks without a recognizable loss in function despite a considerable increase in body weight. It can be assumed that a more marked regression of left ventricular hypertrophy is counteracted by a reflex increase in sympathetic efferentation to the heart.     

Differential analysis in the time domain of the baroreceptor cardiac reflex sensitivity as a function of sequence length

Analysis of baroreceptor sensitivity (BRS) in the time domain through the spontaneous sequence method used a measure of BRS based on the average of all sequences detected, without making any distinction in cardiac cycle length. In this article, we study differentially the functioning of the baroreflex as a function of the length of the cardiac sequences (3, 4, 5, or 6 cardiac cycles). One hundred and four students performed three mental stress tasks: mental arithmetic, memory, and visual attention. The results show that (1) as sequence length decreases, the relationships between BRS and indexes of vagal cardiac control increase, (2) the BRS associated with the more short sequences (3 and 4 beats) is the most vulnerable to mental stress, particularly the mental arithmetic task, and (3) BRS increases progressively as sequence length decreases. These results suggest that the nature and functioning of the baroreflex differ as a function of the length of the cardiac sequences.     

Micro-Perfusion for Cardiac Tissue Engineering: Development of a Bench-Top System for the Culture of Primary Cardiac Cells

Tissue-engineered constructs have high metabolic requirements during in vitro culture necessitating the development of micro-perfusion systems to maintain high functional performance. In this study, we describe the design, fabrication, and testing of a novel micro-perfusion system to support the culture of primary cardiac cells. Our system consists of a micro-incubator with independent stages for 35-mm tissue culture plates with inflow/outflow manifolds for fluid delivery and aspiration. A peristaltic pump is utilized for fluid delivery and vacuum for fluid aspiration. Oxygen saturation, pH, and temperature are regulated for the media while temperature is regulated within the micro-incubator, fluid reservoir, and oxygenation chamber. Validation of the perfusion system was carried out using primary cardiac myocytes, isolated from 2- to 3-day-old neonatal rat hearts, plated on collagen-coated tissue culture plates. Two million cells/plate were used and the perfusion system was run for 1 h (without the need for a cell culture incubator) while controls were maintained in a standard cell culture incubator. We evaluated the cell viability, cell adhesion, total protein, total RNA, and changes in the expression of SERCA2 and phospholamban using RT-PCR, with N = 6 for each group. We found that there was no significant change in any variable during the 1-h run in the perfusion system. These studies served to demonstrate the compatibility of the perfusion system to support short-term culture of primary cardiac cells.     

Anatomical study of a left single coronary artery with special reference to the various distribution patterns of bilateral coronary arteries

A left single coronary artery of heart was observed during anatomy practice at Kumamoto University School of Medicine in a 73-year-old female cadaver who died from a thalamic hemorrhage. The left single coronary artery, having a single orifice in the left aortic sinus, bifurcated into the anterior interventricular (IVa) and circumflex (CIR) arteries. No orifice of the right coronary artery was found on the aortic wall. Giving off a branch which traversed the upper part of the infundibulum to supply the anterior upper region of the right ventricle, the IVa descended in the anterior interventricular sulcus to supply the apex of the heart. The CIR curved leftwards in the atrioventricular sulcus to reach the posterior surface, after which it continued to emerge again into the anterior surface. The atrial arteries showed no anomalous distribution pattern and histological observation revealed no pathological abnormality other than a slightly thickened tunica intima. Furthermore, we observed the distribution patterns of bilateral coronary arteries in 377 hearts dissected during anatomical practice over 13 years at Kanazawa University (1980–1986) and Kumamoto University (1993–1998). Although the reason why only the right coronary artery was absent is left unexplained, it was concluded that the left single coronary artery in this study, having the developed left conal and circumflex branches, was an extreme case of the left dominant series of coronary arteries. The formation of single coronary arteries can be explained embryologically by the change of flow in the capillary plexus established on the ventricle wall.     

A phylogenetic journey through the vague and ambiguous Xth cranial nerve: a commentary on contemporary heart rate variability research

Contemporary heart rate variability research is discussed within a historical context. Implicit in this history is the discovery that the central nervous system regulates the heart and how information regarding neural regulation of the heart is imbedded in the beat-to-beat heart rate pattern. As methodologies have become more sensitive to neural regulation and as theories have expanded to integrate behavior and psychological processes with neurobiological principles, researchers are becoming better positioned to successfully understand how neurovisceral processes mediate the expression of health and disease. The contributions to this special issue describe research representing different levels of scientific inquiry and focus on different features of the complex neural feedback system that are manifested in the robust relationships between heart rate variability and several behavioral, psychological, physiological, and health processes. This article provides a commentary to these contributions.     

Shearing Mechanics and the Influence of a Flexible Symphysis During Oral Food Processing in Sphenodon (Lepidosauria: Rhynchocephalia)

The New Zealand tuatara, Sphenodon, has a specialized feeding system in which the teeth of the lower jaw close between two upper tooth rows before sliding forward to slice food apart like a draw cut saw. This shearing action is unique amongst living amniotes but has been compared with the chewing power stroke of mammals. We investigated details of the jaw movement using multibody dynamics analysis of an anatomically accurate three‐dimensional computer model constructed from computed tomography scans. The model predicts that a flexible symphysis is necessary for changes in the intermandibular angle that permits prooral movement. Models with the greatest symphysial flexibility allow the articulation surface of the articular to follow the quadrate cotyle with the least restriction, and suggest that shearing is accompanied by a long axis rotation of the lower jaws. This promotes precise point loading between the cutting edges of particular teeth, enhancing the effectiveness of the shearing action. Given that Sphenodon is a relatively inactive reptile, we suggest that the link between oral food processing and endothermy has been overstated. Food processing improves feeding efficiency, a consideration of particular importance when food availability is unpredictable. Although this feeding mechanism is today limited to Sphenodon, a survey of fossil rhynchocephalians suggests that it was once more widespread. Anat Rec, 2012. © 2012 Wiley‐Periodicals, Inc.