Development of standard tests to examine viscoelastic properties of blood of experimental animals for pediatric mechanical support device evaluation

We investigated the applicability of measuring the viscoelasticity of bovine, ovine, and porcine whole blood for the evaluation of sublethal damage to red blood cells (RBCs). An increase in blood viscosity and elasticity without changes in hematocrit and plasma viscosity would signify a decrease in RBC deformability. Blood viscoelasticity was assessed using a Vilastic Scientific viscoelastometer. Due to the natural absence of RBC aggregation and small RBC size in normal bovine and ovine blood, viscoelastic properties are less readily detected. However, we found that adjustment of blood hematocrit to a standard level of 40-50% allows for sensitive assessment of viscoelasticity in these blood types demonstrating a marked non-Newtonian behavior mostly related to RBC deformability. Porcine blood showed a pronounced non-Newtonian behavior at all tested hematocrit values, which makes it rheologically comparable to human blood. Both viscosity and elasticity were elevated after blood exposure to a uniform mechanical stress. RBCs rigidified by heat exposure demonstrated a loss of viscoelasticity dependence on shear rate. Measurements of blood viscoelasticity can be meaningful in bovine, ovine, and, especially, porcine blood, and can be used for evaluation of sublethal blood damage during in vitro and animal trials of heart-assist devices.

Study on Mechanical Circulatory Support and Currently Available Supporting Parts in China

The research and development on extracorporeal and assisted circulation in China have been painstaking. On one hand, China has the largest population of 1.3 [corrected] billion in the world, and the demands for supporting equipment are huge. On the other hand, as a developing country, China is not wealthy. It is urgent to design and fabricate affordable circulatory support parts, machines, and artificial hearts for Chinese market. In this regard, we have made our own heart-lung machine, mechanical and tissue valves, oxygenators, and artificial hearts and their improved versions. The cost of these parts is much lower as compared with those in the Western market. Although the results of clinical application are good so far, the quality of these lifesaving parts needs to be continuously improved.

Percutaneous cardiopulmonary support as a bridge to emergency operation--two surviving cases

Two patients had percutaneous cardiopulmonary support (PCPS) used as a bridge to emergency surgery. A 66-year-old man admitted with profound cardiogenic shock underwent direct stenting under PCPS with the diagnosis of acute myocardial infarction of the left main trunk, with the intention of performing revascularization as soon as possible. Subsequently, double coronary artery bypass grafting was successfully accomplished. A 69-year-old woman, admitted with acute heart failure due to critical aortic stenosis, manifested cardiogenic shock while undergoing catheterization. PCPS was immediately instituted until the acute deterioration of her hemodynamic state could be reversed, and was continued uneventfully till aortic valve replacement was performed. These results suggest that the current PCPS system is an effective response to acute circulatory collapse and will contributed to the improved survival of patients.

Technical standards for medical devices. Assisted circulation devices

The steep rise in the clinical use of high technology biomedical devices and materials, involving multidisciplinary competencies, points out the problem of mutual standards defining, first of all, functional characteristic and tests able to characterise and qualify devices, materials and minimal safety requirements both for patients and operators. Standards defined by consent of the parties or by law are used to this aim. Fast technical development in specific sectors produces besides lack of rules, which must be quickly filled up. The aim of this paper is both the presentation of the approach to problems related to technical standards for biomedical devices and the presentation of the set up of a technical standard for mechanical heart assist devices.

Hydraulic assessment of the floating impeller phenomena in a centrifugal pump

A compact eccentric inlet port centrifugal blood pump (C1E3) has been perfected for a long-term centrifugal ventricular assist device as well as a cardiopulmonary bypass pump. The C1E3 pump incorporates a sealless design and a blood stagnation free structure. The pump's impeller is magnetically coupled to the driver magnet in a sealless manner. The latest hemolysis study reveals that hemolysis is affected by the magnetic coupling distance between the driver and impeller magnet. Furthermore, a floating phenomenon can be observed in a pivot bearing supported pump. Attention was focused on the relationship between the floating phenomenon's characteristics and the magnetic coupling design in the C1E3 pump. Studies were conducted to evaluate the hydromechanical performance in the floating phenomenon. In this study, the relationship between the magnetic coupling design and the floating phenomenon was verified with a smooth spinning condition. The optimized magnetic coupling distance for the floating mode was estimated to be 12 mm for left ventricular assist device and 9 mm for cardiopulmonary bypass pump. Obtaining an optimal spinning condition is required for regulating the magnetic coupling force. To develop a double pivot bearing pump, it is necessary to establish an optimal spinning and/or floating condition and to determine the proper magnetic coupling and magnetic force between the impeller and driver.

Skeletal muscle ventricles: frontiers in 1995

Skeletal muscle ventricles (SMVs) constructed from electrically conditioned latissimus dorsi muscle (LDM) may become an alternative for assisting the failing heart. Left and right heart circulatory assist using SMVs has been performed successfully in both acute and chronic animal models. The configurations used to connect SMVs to the circulation have included a left atrium to aorta bypass, a left ventricle apex to aorta bypass, aortic counterpulsators, a cavopulmonary bypass, and a right ventricle to pulmonary artery bypass. One SMV used as an aortic counterpulsator functioned effectively in the circulation for more than 27 months. Recent application of the pericardium to the SMV as an inner layer and design changes in the connection of the SMV to the circulation have reduced the risk of thrombus formation and SMV rupture. Although several problems have yet to be solved, the goal of the SMV as a permanent circulatory assist device without the limitation of an external power source seems within reach.

Seal-less centrifugal blood pump with magnetically suspended rotor: rot-a-flot

Limitations of current centrifugal blood pumps are related to heat generation of bearings and leakage of seals, to dead water zones, and to poor efficiency. A new concept is proposed in this paper to ameliorate these problems based on a miniaturized magnetic drive, and a prototype is introduced. The pump rotor is suspended and driven by a radial permanent magnetic field that stabilizes the impeller in 4 of the 6 spatial degrees of freedom and allows it to be top-spun on a single blood-flushed pivot bearing with minimal load and friction. A shrouded impeller with an open center and 4 logarithmically curved channels is run inside a cone-and-plate-type housing with a spiral volute chamber. In vitro testing was performed comparing this design with the BioMedicus, St. Jude, and Sarns pumps. The prototype is demonstrated to have the smallest internal volume (35 ml), surface (190 qcm), and passage time (0.5 s at 4 L/min), as well as the highest hydraulic efficiency (up to 0.4) of all devices studied.

The need for standardizing the index of hemolysis

Hemolysis is one of the most important performance parameters of blood pumps. However, comparative in vitro evaluation of the reported hemolysis effect is difficult owing to the lack of uniformity in the test methods used. Currently, three types of formulas are generally accepted and widely used for the index of hemolysis: the traditionally used index of hemolysis (defined as grams of plasma free hemoglobin released per 100 L of blood pumped); the normalized index of hemolysis (normalized by hematocrit); and the modified index of hemolysis (taking into account not only hematocrit but also hemoglobin). In addition, the tested blood conditions are often not indicated in the reports. To address this confusing situation, all three indices of hemolysis were routinely derived in our laboratory. To avoid further confusion, the tested blood conditions and test loop were defined in each study in our laboratory. If we limit the acceptable range of hemoglobin in human blood, the normalized index of hemolysis is sufficient. Furthermore, using milligrams as the unit of expression would be easier and reasonable for comparing the less hemolytic blood pumps, such as the centrifugal pumps that are currently available clinically. We would like to propose this value of a normalized index of hemolysis in milligrams as the most useful formula for the index of hemolysis in the assessment of various types of rotary blood pumps.

Mechanical circulatory support decreases neurologic complications in the treatment of traumatic injuries of the thoracic aorta

The surgical treatment of traumatic injuries of the thoracic aorta is controversial because a number of technical approaches have been recommended. Despite the technique employed, spinal cord ischemia continues to be a persistent problem. Nineteen patients with confirmed aortic injuries secondary to blunt trauma were treated at the Yale-New Haven (Conn) Medical Center from 1984 to 1991. The patients were analyzed in two groups: group 1 (n = 10) underwent repair using mechanical circulatory support and group 2 (n = 9) underwent repair without mechanical circulatory support. Sixteen patients survived. Three patients died of complications of multiple trauma. The groups were comparable with respect to aortic cross-clamp time, preoperative systolic blood pressure, and Injury Severity Score. Three patients in the nonmechanical support group developed neurologic complications (P less than .05). No patient in the mechanical support group had a neurologic complication. We believe that mechanical circulatory support reduces the incidence of neurologic complications following traumatic injuries of the thoracic aorta and should be used whenever clinically feasible.

Current perspectives on the use of circulatory assist devices

An overview of currently available circulatory assist devices (CADs) is presented with discussion of each system's optimal use and limitations. Successful application of CAD technology for bridge to transplant or pending recovery of the natural heart requires understanding issues involving team readiness, patient selection, device limitations, patient management, and complications. Currently, many of these devices are in clinical trials with the Food and Drug Administration (FDA). The FDA and the National Institutes of Health play major roles in the ongoing development of this technology. In the near future the learning curve continues as totally implantable systems are used. The ultimate goal is to maintain patients with heart failure on implantable devices with a good quality of life at a reasonable cost.

Circulation control of experimental and clinical profound left ventricular failures by automatic left ventricular assist system

It is desirable that circulation control of the patient using a left ventricular assist device (LVAD) should be achieved appropriately and safely. We have developed an automatic LVAD system, which can maintain the normal circulation irrespective of the severity of heart failure and can restore the failing heart by decreasing the bypass flow (BF) through the LVAD as the heart recovers. The main part of the control-drive unit is an automatic level control (ALC) system for left atrial pressure (LAP) and total flow (TF). Profound left ventricular failure (LVF) was made by complete interception of blood supply to the extent of 50% (5 goats) and 70% (5 goats) of the LV free wall. The air-driven diaphragm-type LVAD was implanted between LA and aorta. At the beginning of LVAD pumping, BF tended to be very high to keep LAP at the preset level (0-5 mmHg) and to maintain TF at somewhat higher level (120-140 ml/kg/min). The recovering heart was able to decrease LAP gradually. Since the LAP was set at a certain level, the ALC of LAP decreased BF to maintain LAP at the preset level. During the recovering stage from LVF, preset level of LAP was gradually raised while checking the pulmonary function. When natural heart output exceeded 100 ml/kg/min, LVAD was removed. The 50% LVF group recovered between 17 hours and 3 days, and 70% LVF group between 6th and 16th postoperative day. This LVAD system was then applied to the postoperative profound LVF in a MVR patient whose entire circulation was maintained normal during 14 day pumping. The failed heart gradually recovered and the pump was successfully removed. We consider that the decompression of LV will prevent overextension of impaired myocardium and simultaneously accelerate the solid scar formation. And gradual increase of LV work will promote the compensation ability of the residual myocardium. Continuous LVAD assistance can therefore earn time for the impaired myocardium to recover while maintaining normal circulation.

Clinical evaluation of the Percor percutaneous intraaortic balloon: cooperative study of 722 cases

Clinical experience with the Percor percutaneous intraaortic balloon (IAB) was reviewed in 722 cases performed by 59 clinicians (35 surgeons and 24 cardiologists). Compared with standard IABs, Percor was judged to provide easier insertion by 88% of clinicians, easier femoral-iliac passage by 29%, easier aortic passage by 36%, and easier final positioning by 19%; the Percor IAB was rated more difficult in these respects by 2-5% of users; the rest of the responders found no significant difference in these measures. Technical problems included an inability to negotiate sclerotic vessels in 12.6%, delayed hemostasis in 1.9%, and the need for surgical repair of the arteriotomy site in 2%. Medical complications included peripheral ischemia in 5.3%, emboli in 3.6%, arterial dissection in 1.9%, dislodged arterial plaque in 1.1%, perforation of the arterial tree in 1.0%, local femoral thrombosis in 1.0%, and poor intraoperative hemostasis in 0.3%. Local wound infection, ischemic amputation or neuropathic sequelae were not reported. Mechanical counterpulsation with Pecor was equivalent to that of standard IABs, but by subjective judgments, 80% rated Percor more desirable and 47% safer; 3% rated it less desirable and 10% less safe. With Percor, earlier clinical use of IAB pumping was seen by 73%, and new or additional indications were recommended by 19%.

[The efficacy of the intra-aortic balloon pump for patients with heart failure complicating acute myocardial infarction (author's transl)]

Assisted circulation was carried out with the help of an intra-aortic balloon pump in 22 patients with acute transmural myocardial infarction and heart failure (despite medication). Two patients died in hospital. The combination of the balloon pump and nitrates proved to be particularly effective. The follow-up examination of the survivors showed a distinct pulmonary arterial pressure during ergometry. All of the examined patients revealed extensive akinetic and diskinetic areas, significant stenosis being detectable either in the proximal area of the Ramus descendens anterior or in two or three blood vessels.