Outcome respiratorio a lungo termine nei soggetti affetti da cardiopatia congenita sottoposti ad intervento cardiochirurgico

Introduction: In the last years cardiac surgery for congenital heart disease (CHD) reduced dramatically mortality modifying prognosis, but, at the same time, increased morbidity in this patient population. Respiratory and cardiovascular systems are strictly anatomically and functionally connected, so that alterations of pulmonary hemodynamic conditions modify respiratory function. While very short-term alterations of respiratory mechanics after surgery were investigated by many authors, not as much works focused on long-term changes. In these subjects rest respiratory function may be limited by several factor: CHD itself (fetal pulmonary perfusion influences vascular and alveolar development), extracorporeal circulation (CEC), thoracotomy and/or sternotomy, rib and sternal contusions, pleural adhesions and pleural fibrosis, secondary to surgical injury. Moreover inflammatory cascade, triggered by CEC, can cause endothelial damage and compromise gas exchange. Aims: The project was conceived to 1) determine severity of respiratory functional impairement in different CHD undergone to surgical correction/palliation; 2) identify the most and the least CHD involved by pulmonary impairement; 3) find a correlation between a specific hemodynamic condition and functional anomaly, and 4) between rest respiratory function and cardiopulmonary exercise test. Materials and methods: We studied 113 subjects with CHD undergone to surgery, and distinguished by group in accord to pulmonary blood flow (group 0: 28 pts with normal pulmonary flow; group 1: 22 pts with increased flow; group 2: 43 pts with decreased flow; group 3: 20 pts with total cavo-pulmonary anastomosis-TCPC) followed by the Pediatric Cardiology and Cardiac Surgery Unit, and we compare them to 37 age- and sex-matched healthy subjects. In Pediatric Pulmonology Unit all pts performed respiratory function tests (static and dynamic volumes, flow/volume curve, airway resistances-raw- and conductance-gaw-, lung diffusion of CO-DLCO- and DLCO/alveolar volume), and CHD pts the same day had cardiopulmonary test. They all were examined and had allergological tests, and respiratory medical history. Results: restrictive pattern (measured on total lung capacity-TLC- and vital capacity-VC) was in all CHD groups, and up to 45% in group 2 and 3. Comparing all groups, we found a significant difference in TLC between healthy and group 2 (p=0.001) and 3 (p=0.004), and in VC between group 2 and healthy (p=0.001) and group 1(p=0.034). Inspiratory capacity (IC) was decreased in group 2 related to healthy (p<0.001) and group 1 (p=0.037). We showed a direct correlation between TLC and VC with age at surgery (p=0.01) and inverse with number of surgical interventions (p=0.03). Reduced FEV1/FVC ratio, Gaw and increased Raw were mostly present in group 3. DLCO was impaired in all groups, but up to 80% in group 3 and 50% in group 2; when corrected for alveolar volume (DLCO/VA) reduction persisted in group 3 (20%), 2 (6.2%) and 0 (7.1%). Exercise test was impaired in all groups: VO2max and VE markedly reduced in all but especially in group 3, and VE/VCO2 slope, marker of ventilatory response to exercise, is increased (<36) in 62.5% of group 3, where other pts had anyway value>32. Comparing group 3 and 2, the most involved categories, we found difference in VO2max and VE/VCO2 slope (respectively p=0.02 and p<0.0001). We evidenced correlation between rest and exercise tests, especially in group 0 (between VO2max and FVC, FEV1, VC, IC; inverse relation between VE/VCO2slope and FVC, FEV1 and VC), but also in group 1 (VO2max and IC), group 2 (VO2max and FVC and FEV1); never in group 3. Discussion: According with literature, we found a frequent impairment of rest pulmonary function in all groups, but especially in group 2 and 3. Restrictive pattern was the most frequent alteration probably due to compromised pulmonary (vascular and alveolar) development secondary to hypoperfusion in fetal and pre-surgery (and pre-TCPC)life. Parenchymal fibrosis, pleural adhesions and thoracic deformities can add further limitation, as showed by the correlation between group 3 and number of surgical intervention. Exercise tests were limited, particularly in group 3 (complex anatomy and lost of chronotropic response), and we found correlations between rest and exercise tests in all but group 3. We speculate that in this patients hemodynamic exceeds respiratory contribution, though markedly decreased.

Perioperative metabolic changes in patients undergoing cardiac surgery

Perioperative metabolic changes in cardiac surgical patients are not only induced by tissue injury and extracorporeal circulation per se: the systemic inflammatory response to surgical trauma and extracorporeal circulation, perioperative hypothermia, cardiovascular and neuroendocrine responses, and drugs and blood products used to maintain cardiovascular function and anesthesia contribute to varying degrees. The pathophysiologic changes include increased oxygen consumption and energy expenditure; increased secretion of adrenocorticotrophic hormone, cortisol, epinephrine, norepinephrine, insulin, and growth hormone; and decreased total tri-iodothyronine levels. Easily measurable metabolic consequences of these changes include hyperglycemia, hyperlactatemia, increased aspartate, glutamate and free fatty acid concentrations, hypokalemia, increased production of inflammatory cytokines, and increased consumption of complement and adhesion molecules. Nutritional risk before elective cardiac surgery-defined as preoperative unintended pathologic weight loss/low amount of food intake in the preceding week or low body mass index-is related to adverse postoperative outcome. Improvements in surgical techniques, anesthesia, and perioperative management have been designed to minimize the stressful stimulus to catabolism, thereby slowing the wasting process to the point where much less nutrition is required to meet metabolic requirements. Early nutrition in cardiac surgery is safe and well tolerated.

Giant aneurysm after aortic coarctation: repair without circulatory arrest

We describe the case of a 23-year-old patient presenting for redo aortic arch surgery because of recoarctation and poststenotic aneurysm formation after patch aortoplasty in infancy. Using the hemi-clamshell approach, the entire aortic arch was replaced and the supraaortic branches were reimplanted. The applied surgical technique using hypothermic extracorporeal circulation without cardiac arrest allowed an uninterrupted cerebral and spinal cord perfusion due to stepwise clamping of the aortic arch during reconstruction and resulted in an excellent neurologic outcome at six-month follow-up.?

The Bernese Hypothermia Algorithm: a consensus paper on in-hospital decision-making and treatment of patients in hypothermic cardiac arrest at an alpine level 1 trauma centre

INTRODUCTION: Guidelines for the treatment of patients in severe hypothermia and mainly in hypothermic cardiac arrest recommend the rewarming using the extracorporeal circulation (ECC). However,guidelines for the further in-hospital diagnostic and therapeutic approach of these patients, who often suffer from additional injuries—especially in avalanche casualties, are lacking. Lack of such algorithms may relevantly delay treatment and put patients at further risk. Together with a multidisciplinary team, the Emergency Department at the University Hospital in Bern, a level I trauma centre, created an algorithm for the in-hospital treatment of patients with hypothermic cardiac arrest. This algorithm primarily focuses on the decision-making process for the administration of ECC. THE BERNESE HYPOTHERMIA ALGORITHM: The major difference between the traditional approach, where all hypothermic patients are primarily admitted to the emergency centre, and our new algorithm is that hypothermic cardiac arrest patients without obvious signs of severe trauma are taken to the operating theatre without delay. Subsequently, the interdisciplinary team decides whether to rewarm the patient using ECC based on a standard clinical trauma assessment, serum potassium levels, core body temperature, sonographic examinations of the abdomen, pleural space, and pericardium, as well as a pelvic X-ray, if needed. During ECC, sonography is repeated and haemodynamic function as well as haemoglobin levels are regularly monitored. Standard radiological investigations according to the local multiple trauma protocol are performed only after ECC. Transfer to the intensive care unit, where mild therapeutic hypothermia is maintained for another 12 h, should not be delayed by additional X-rays for minor injuries. DISCUSSION: The presented algorithm is intended to facilitate in-hospital decision-making and shorten the door-to-reperfusion time for patients with hypothermic cardiac arrest. It was the result of intensive collaboration between different specialties and highlights the importance of high-quality teamwork for rare cases of severe accidental hypothermia. Information derived from the new International Hypothermia Registry will help to answer open questions and further optimize the algorithm.

Minimized cardiopulmonary bypass combined with a smart suction device: the future of cardiopulmonary bypass?

OBJECTIVE: The standard heart-lung machine is a major trigger of systemic inflammatory response and the morbidity attributed to conventional extracorporeal circulation (CECC) is still significant. Reduction of blood-artificial surface contact and reduction of priming volume are principal aims in minimized extracorporeal circulation (MECC) cardiopulmonary bypass systems. The aim of this paper is to give an overview of the literature and to present our experience with the MECC-smart suction system. METHODS AND RESULTS: At our institution, 1799 patients underwent isolated coronary artery bypass grafting (CABG) surgery, 1372 with a MECC-smart suction system and 427 with CECC. All in-hospital data were assessed and the results were compared between the 2 groups. Patient characteristics and the distribution of EuroSCORE risk profile in our collective were similar between both groups. Average age in the MECC collective was 67.5 +/- 11.4 years and average EuroSCORE was 5.0 +/- 1.5. Average number of distal anastomoses was similar to the average number encountered in patients undergoing CABG surgery with CECC (3.3 +/- 1.0 for MECC versus 3.2 +/- 1.1 for CECC; P = ns). Myocardial protection is superior in MECC patients with lower postoperative maximal cTnI values (11.0 +/- 10.8 micromol/L for MECC versus 24.7 +/- 25.3 micromol/L for CECC; P < .05). Postoperative recovery was faster in patients operated on with the MECC-smart suction system and discharge from the hospital was earlier than for CECC patients (7.4 +/- 1.9 days for MECC versus 8.8 +/- 3.8 days for CECC; P < .05). CONCLUSIONS: The MECC-smart suction system is a safe perfusion technique for CABG surgery. In patients operated on with this system, the clinical outcome seems to be better than in patients operated on with CECC. This promising and less damaging perfusion technology has the potential to replace CECC systems in CABG surgery.

Perioperative anaesthetic management of mediastinal mass in adults

Mediastinal mass syndrome remains an anaesthetic challenge that cannot be underestimated. Depending on the localization and the size of the mediastinal tumour, the clinical presentation is variable ranging from a complete lack of symptoms to severe cardiorespiratory problems. The administration of general anaesthesia can be associated with acute intraoperative or postoperative cardiorespiratory decompensation that may result in death due to tumour-related compression syndromes. The role of the anaesthesiologist, as a part of the interdisciplinary treatment team, is to ensure a safe perioperative period. However, there is still no structured protocol available for perioperative anaesthesiological procedure. The aim of this article is to summarize the genesis of and the diagnostic options for mediastinal mass syndrome and to provide a solid detailed methodology for its safe perioperative management based on a review of the latest literature and our own clinical experiences. Proper anaesthetic management of patients with mediastinal mass syndrome begins with an assessment of the preoperative status, directed foremost at establishing the localization of the tumour and on the basis of the clinical and radiological findings, discerning whether any vital mediastinal structures are affected. We have found it helpful to assign 'severity grade' (using a three-grade clinical classification scale: 'safe', 'uncertain', 'unsafe'), whereby each stage triggers appropriate action in terms of staffing and apparatus, such as the provision of alternatives for airway management, cardiopulmonary bypass and additional specialists. During the preoperative period, we are guided by a 12-point plan that also takes into account the special features of transportation into the operating theatre and patient monitoring. Tumour compression on the airways or the great vessels may create a critical respiratory and/or haemodynamic situation, and therefore the standard of intraoperative management includes induction of anaesthesia in the operating theatre on an adjustable surgical table, the use of short-acting anaesthetics, avoidance of muscle relaxants and maintenance of spontaneous respiration. In the case of severe clinical symptoms and large mediastinal tumours, we consider it absolutely essential to cannulate the femoral vessels preoperatively under local anaesthesia and to provide for the availability of cardiopulmonary bypass in the operating theatre, should extracorporeal circulation become necessary. The benefits of establishing vascular access under local anaesthesia clearly outweigh any associated degree of patient discomfort. In the case of patients classified as 'safe' or 'uncertain', a preoperative consensus with the surgeons should be reached as to the anaesthetic approach and the management of possible complications.

Aortic valve replacement and concomitant procedures with the Perceval valve: results of European trials.

BACKGROUND The Perceval (Sorin Group, Milan, Italy) is a self-anchoring sutureless aortic valve prosthesis. We report the short- to midterm results of combined aortic valve replacement (AVR) with concomitant procedures in elderly patients undergoing operation as part of 3 consecutive prospective multicenter European studies. METHODS From April 2007 to February 2013, 243 patients (mean age, 79.7 ± 5.1 years; female patients, 61%; median EuroSCORE, 9%) underwent AVR with concomitant procedures. The concomitant procedures were coronary artery bypass grafting (CABG) (182 cases), septal myectomy (21 cases), CABG + other procedures (18 cases), and 22 other procedures. Primary and secondary end points included implant feasibility and safety (for mortality and morbidity) and efficacy (New York Heart Association [NYHA] class improvement and hemodynamic results) of the prosthesis at the different follow-up periods. Data were expressed as mean ± standard deviation. Kaplan-Meier analysis was performed for survival analysis. RESULTS Mean aortic cross-clamp and extracorporeal circulation (ECC) times were 50.7 ± 22.8 minutes and 78.9 ± 32.3 minutes, respectively. Thirty-day mortality was 2.1%. Mean postoperative gradient and effective orifice area were 10.1 ± 4.7 mm Hg and 1.5 ± 0.4 cm(2) and 8.9 ± 5.6 mm Hg and 1.6 ± 0.4 cm(2), respectively, at 1 year. There were early explantations, 4 of which resulted from paravalvular leaks. One additional valve explantation resulted from aortic root bleeding, probably caused by excessively extensive decalcification. In the late period, there was 1 mild paravalvular leak and no intravalvular insufficiency. No migration, dislodgement, or degeneration of the valve occurred during follow-up. Median follow-up was 444 days. CONCLUSIONS These trials confirm the safety and efficacy of the Perceval sutureless aortic valve, especially in elderly patients requiring AVR + concomitant procedures. In this patient group, sutureless valves may be advantageous compared to transcatheter valve implantations as concomitant procedures other than percutaneous coronary artery angioplasty are not always possible in the latter.

Oxygen-transfer performance of a newly designed, very low-volume membrane oxygenator.

OBJECTIVES Oxygenation of blood and other physiological solutions are routinely required in fundamental research for both in vitro and in vivo experimentation. However, very few oxygenators with suitable priming volumes (<2-3 ml) are available for surgery in small animals. We have designed a new, miniaturized membrane oxygenator and investigated the oxygen-transfer performance using both buffer and blood perfusates. METHODS The mini-oxygenator was designed with a central perforated core-tube surrounded by parallel-oriented microporous polypropylene hollow fibres, placed inside a hollow shell with a lateral-luer outlet, and sealed at both extremities. With this design, perfusate is delivered via the core-tube to the centre of the mini-oxygenator, and exits via the luer port. A series of mini-oxygenators were constructed and tested in an in vitro perfusion circuit by monitoring oxygen transfer using modified Krebs-Henseleit buffer or whole porcine blood. Effects of perfusion pressure and temperature over flows of 5-60 ml × min(-1) were assessed. RESULTS Twelve mini-oxygenators with a mean priming volume of 1.5 ± 0.3 ml were evaluated. With buffer, oxygen transfer reached a maximum of 14.8 ± 1.0 ml O2 × l(-1) (pO2: 450 ± 32 mmHg) at perfusate flow rates of 5 ml × min(-1) and decreased with an increase in perfusate flow to 7.8 ± 0.7 ml ml O2 × l(-1) (pO2: 219 ± 24 mmHg) at 60 ml × min(-1). Similarly, with blood perfusate, oxygen transfer also decreased as perfusate flow increased, ranging from 33 ± 5 ml O2 × l(-1) at 5 ml × min(-1) to 11 ± 2 ml O2 × l(-1) at 60 ml × min(-1). Furthermore, oxygen transfer capacity remained stable with blood perfusion over a period of at least 2 h. CONCLUSIONS We have developed a new miniaturized membrane oxygenator with an ultra-low priming volume (<2 ml) and adequate oxygenation performance. This oxygenator may be of use in overcoming current limitations in equipment size for effective oxygenation in low-volume perfusion circuits, such as small animal extracorporeal circulation and ex vivo organ perfusion.

Oxygen-transfer performance of a newly designed, very low-volume membrane oxygenator

Gebiet: Chirurgie Biomedizintechnik Biophysik Transplantationsmedizin Kardiologie Abstract: OBJECTIVES: – Oxygenation of blood and other physiological solutions are routinely required in fundamental research for both in vitro and in vivo experimentation. However, very few oxygenators with suitable priming volumes (<2-3 ml) are available for surgery in small animals. We have designed a new, miniaturized membrane oxygenator and investigated the oxygen-transfer performance using both buffer and blood perfusates. – – METHODS: – The mini-oxygenator was designed with a central perforated core-tube surrounded by parallel-oriented microporous polypropylene hollow fibres, placed inside a hollow shell with a lateral-luer outlet, and sealed at both extremities. With this design, perfusate is delivered via the core-tube to the centre of the mini-oxygenator, and exits via the luer port. A series of mini-oxygenators were constructed and tested in an in vitro perfusion circuit by monitoring oxygen transfer using modified Krebs-Henseleit buffer or whole porcine blood. Effects of perfusion pressure and temperature over flows of 5-60 ml × min(-1) were assessed. – – RESULTS: – Twelve mini-oxygenators with a mean priming volume of 1.5 ± 0.3 ml were evaluated. With buffer, oxygen transfer reached a maximum of 14.8 ± 1.0 ml O2 × l(-1) (pO2: 450 ± 32 mmHg) at perfusate flow rates of 5 ml × min(-1) and decreased with an increase in perfusate flow to 7.8 ± 0.7 ml ml O2 × l(-1) (pO2: 219 ± 24 mmHg) at 60 ml × min(-1). Similarly, with blood perfusate, oxygen transfer also decreased as perfusate flow increased, ranging from 33 ± 5 ml O2 × l(-1) at 5 ml × min(-1) to 11 ± 2 ml O2 × l(-1) at 60 ml × min(-1). Furthermore, oxygen transfer capacity remained stable with blood perfusion over a period of at least 2 h. – – CONCLUSIONS: – We have developed a new miniaturized membrane oxygenator with an ultra-low priming volume (<2 ml) and adequate oxygenation performance. This oxygenator may be of use in overcoming current limitations in equipment size for effective oxygenation in low-volume perfusion circuits, such as small animal extracorporeal circulation and ex vivo organ perfusion. – – © The Author 2015. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.

Antifactor Xa Activity for the Management of Anticoagulation during Cardiac Surgery

Background In patients with autoimmune diseases associated with antiphospholipid antibodies, precise management of anticoagulation during extracorporeal circulation (ECC) is complicated. It was the aim of the present study to determine whether antifactor Xa (aXa) activity is useful in guiding heparin therapy during ECC. Methods In 15 patients undergoing cardiac surgery, anticoagulation with unfractionated heparin (UFH) and its reversal with protamine were guided using activated clotting time (ACT) (>400 second during ECC; ≤100 second for UFH reversal). For each ACT, the corresponding aXa activity levels were measured. Results A total of 144 blood samples were obtained. ACT and aXa activity were significantly correlated (r = 0.771, p< 0.0001, Spearman rank-order correlation). Using receiver operating characteristic curve (ROC) analyses, the cutoffvalues for aXa activity were 1.14 IU/mL (area under the ROC curve [AUC]: 0.89; inaccuracy rate: 9.4%) to predict ACT > 400 seconds and 0.55 IU/mL (AUC: 0.85; inaccuracy rate: 13.3%) for ACT ≤ 100 seconds. Conclusion AXa activity is strongly correlated with ACT, and therefore may be feasible for managing anticoagulation with UFH during ECC.

Extracorporeal membrane oxygenation support after heart explantation: a proposal on how to deal with hyperacute rejection of heart transplant

Purpose: In extreme situations, such as hyperacute rejection of heart transplant or major bleeding per-operating complications, an urgent heart explantation might be the only means of survival. The aim of this experimental study was to improve the surgical technique and the hemodynamics of an Extracorporeal Membrane Oxygenation (ECMO) support through a peripheral vascular access in an acardia model. Methods: An ECMO support was established in 7 bovine experiments (59±6.1 kg) by the transjugular insertion to the caval axis of a self-expanded cannula, with return through a carotid artery. After baseline measurements of pump flow and arterial and central venous pressure, ventricular fibrillation was induced (B), the great arteries were clamped, the heart was excised and right and left atria remnants, containing the pulmonary veins, were sutured together leaving an atrial septal defect (ASD) over the cannula in the caval axis. Measurements were taken with the pulmonary artery (PA) clamped (C) and anastomosed with the caval axis (D). Regular arterial and central venous blood gases tests were performed. The ANOVA test for repeated measures was used to test the null hypothesis and a Bonferroni t method for assessing the significance in the between groups pairwise comparison of mean pump flow. Results: Initial pump flow (A) was 4.3±0.6 L/min dropping to 2.8±0.7 L/min (P B-A= 0.003) 10 minutes after induction of ventricular fibrillation (B). After cardiectomy, with the pulmonary artery clamped (C) it augmented not significantly to 3.5±0.8 L/min (P C-B= 0.33, P C-A= 0.029). Finally, PA anastomosis to the caval axis was followed by an almost to baseline pump flow augmentation (4.1±0.7 L/min, P D-B= 0.009, P D-C= 0.006, P D-A= 0.597), permitting a full ECMO support in acardia by a peripheral vascular access. Conclusions: ECMO support in acardia is feasible, providing new opportunities in situations where heart must urgently be explanted, as in hyperacute rejection of heart transplant. Adequate drainage of pulmonary circulation is pivotal in order to avoid pulmonary congestion and loss of volume from the normal right to left shunt of bronchial vessels. Furthermore, the PA anastomosis to the caval axis not only improves pump flow but it also permits an ECMO support by a peripheral vascular access and the closure of the chest.

A naturally shaped silicone ventricle evaluated in a mock circulation loop : a preliminary study

Mock circulation loops are used to evaluate the performance of cardiac assist devices prior to animal and clinical testing. A compressible, translucent silicone ventricle chamber that mimics the exact size, shape and motion of a failing heart is desired to assist in flow visualization studies around inflow cannulae during VAD support. The aim of this study was therefore to design and construct a naturally shaped flexible left ventricle and evaluate its performance in a mock circulation loop. The ventricle shape was constructed by the use of CT images taken from a patient experiencing cardiomyopathic heart failure and used to create a 3D image and subsequent mould to produce a silicone ventricle. Different cardiac conditions were successfully simulated to validate the ventricle performance, including rest, left heart failure and VAD support.

Simulation and development of a mock circulation loop with variable compliance

Heart disease is attributed as the highest cause of death in the world. Although this could be alleviated by heart transplantation, there is a chronic shortage of donor hearts and so mechanical solutions are being considered. Currently, many Ventricular Assist Devices (VADs) are being developed worldwide in an effort to increase life expectancy and quality of life for end stage heart failure patients. Current pre-clinical testing methods for VADs involve laboratory testing using Mock Circulation Loops (MCLs), and in vivo testing in animal models. The research and development of highly accurate MCLs is vital to the continuous improvement of VAD performance. The first objective of this study was to develop and validate a mathematical model of a MCL. This model could then be used in the design and construction of a variable compliance chamber to improve the performance of an existing MCL as well as form the basis for a new miniaturised MCL. An extensive review of literature was carried out on MCLs and mathematical modelling of their function. A mathematical model of a MCL was then created in the MATLAB/SIMULINK environment. This model included variable features such as resistance, fluid inertia and volumes (resulting from the pipe lengths and diameters); compliance of Windkessel chambers, atria and ventricles; density of both fluid and compressed air applied to the system; gravitational effects on vertical columns of fluid; and accurately modelled actuators controlling the ventricle contraction. This model was then validated using the physical properties and pressure and flow traces produced from a previously developed MCL. A variable compliance chamber was designed to reproduce parameters determined by the mathematical model. The function of the variability was achieved by controlling the transmural pressure across a diaphragm to alter the compliance of the system. An initial prototype was tested in a previously developed MCL, and a variable level of arterial compliance was successfully produced; however, the complete range of compliance values required for accurate physiological representation was not able to be produced with this initial design. The mathematical model was then used to design a smaller physical mock circulation loop, with the tubing sizes adjusted to produce accurate pressure and flow traces whilst having an appropriate frequency response characteristic. The development of the mathematical model greatly assisted the general design of an in vitro cardiovascular device test rig, while the variable compliance chamber allowed simple and real-time manipulation of MCL compliance to allow accurate transition between a variety of physiological conditions. The newly developed MCL produced an accurate design of a mechanical representation of the human circulatory system for in vitro cardiovascular device testing and education purposes. The continued improvement of VAD test rigs is essential if VAD design is to improve, and hence improve quality of life and life expectancy for heart failure patients.

A compact mock circulation loop for the in vitro testing of cardiovascular devices

In vitro cardiovascular device performance evaluation in a mock circulation loop (MCL) is a necessary step prior to in vivo testing.A MCL that accurately represents the physiology of the cardiovascular system accelerates the assessment of the device’s ability to treat pathological conditions. To serve this purpose, a compact MCL measuring 600 ¥ 600 ¥ 600 mm (L ¥ W¥ H) was constructed in conjunction with a computer mathematical simulation.This approach allowed the effective selection of physical loop characteristics, such as pneumatic drive parameters, to create pressure and flow, and pipe dimensions to replicate the resistance, compliance, and fluid inertia of the native cardiovascular system. The resulting five-element MCL reproduced the physiological hemodynamics of a healthy and failing heart by altering ventricle contractility, vascular resistance/compliance, heart rate, and vascular volume. The effects of interpatient anatomical variability, such as septal defects and valvular disease, were also assessed. Cardiovascular hemodynamic pressures (arterial, venous, atrial, ventricular), flows (systemic, bronchial, pulmonary), and volumes (ventricular, stroke) were analyzed in real time. The objective of this study is to describe the developmental stages of the compact MCL and demonstrate its value as a research tool for the accelerated development of cardiovascular devices.

Modeling circulation of train-set with multiple routing

Planning on utilization of train-set is one of the key tasks of transport organization for passenger dedicated railway in China. It also has strong relationships with timetable scheduling and operation plans at a station. To execute such a task in a railway hub pooling multiple railway lines, the characteristics of multiple routing for train-set is discussed in term of semicircle of train-sets' turnover. In programming the described problem, the minimum dwell time is selected as the objectives with special derive constraints of the train-set's dispatch, the connecting conditions, the principle of uniqueness for train-sets, and the first plus for connection in the same direction based on time tolerance σ. A compact connection algorithm based on time tolerance is then designed. The feasibility of the model and the algorithm is proved by the case study. The result indicates that the circulation model and algorithm about multiple routing can deal with the connections between the train-sets of multiple directions, and reduce the train's pulling in or leaving impact on the station's throat.