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Biomedical subjects

N Ramasamy

Publications and source records attributed to N Ramasamy.

At least 19 recordsLinked to original sources
PubMed2002

Severe lower respiratory tract infections associated with human parainfluenza viruses 1-3 in children infected and noninfected with HIV type 1.

The aim of this study was to compare the clinical course of severe lower respiratory tract infections associated with human parainfluenza virus types 1-3 (HPIV 1-3) in hospitalised children infected with the human immunodeficiency virus type 1 (HIV-1) versus that in hospitalised children not infected with HIV-1. Children were enrolled prospectively as part of a broader study that evaluated the aetiology of lower respiratory tract infections in HIV-1-infected and -noninfected children from March 1997 through March 1999. HPIV types 1-3 were isolated from nasopharyngeal aspirate samples that were analysed using immunofluorescein monoclonal antibody assays. Thirty percent (24 of 80) of the children from whom HPIV was isolated were infected with HIV-1. Sixty-six percent (47 of 62) and 22% (14 of 62) of the HPIV isolates that were typed were subtypes 3 and 1, respectively. The clinical presentation of severe lower respiratory tract infection was similar in both HIV-1-infected and -noninfected children, except that the former were less likely to have wheezing (4.2% vs. 28.6%, P=0.01). Furthermore, the duration of hospitalisation was longer in HIV-1-infected children than in HIV-1-noninfected children (median 11.5 days [range 1-15 days] vs. median 7.5 days [range 1-22 days]; P=0.02), and mortality was higher (5 of 24 [20.8%] infected children vs. 0 of 56 noninfected children; P=0.001). Importantly, four of five (80%) of the HIV-1-infected children who died had other concurrent illnesses or predisposing factors for severe HPIV-associated disease. HPIV-associated lower respiratory tract infection causes greater morbidity and mortality in HIV-1-infected children than in HIV-1-noninfected children; however, this may be due to other concurrent illnesses in HIV-1-infected children.

Child, Preschool↗
PubMed2001

Improved outcomes with an implantable left ventricular assist system: a multicenter study.

BACKGROUND: Cumulative experience with the Novacor wearable electric left ventricular assist system (LVAS) now exceeds 850 recipients. The pump inflow conduit (IFC) has been implicated in embolic complications. METHODS: Clinical outcomes were compared for two IFC designs in a retrospective, nonrandomized, multicenter study. The original IFC (woven, unsupported, crimped polyester: control group) and an alternative IFC (knitted, gelatin-sealed, integrally supported, uncrimped polyester: test group) were utilized upon availability in North American and European centers. Differences in cerebral embolism to 180 days postimplant were analyzed. RESULTS: Four hundred ninety patients implanted between August 1996 and August 1999, were studied. Two hundred eighty-eight received the control IFC and 202 received the test IFC. The groups (control, test) were well matched for age (48, 49 years), etiology (idiopathic 53%[152 of 288], 55% [112 of 202]; ischemic 34% [97 of 288], 33% [66 of 202]) and mean observation time (97, 91 days). The incidence of embolic cerebrovascular accidents (CVA) was 21% (60 of 288) in the control and 12% (24 of 202) in the test group (p = 0.010). Independent risk factors for embolic CVA were found to be preimplant acute myocardial infarction (odds ratio 4.3), age above 50 years (odds ratio 2.1), and ischemic etiology (odds ratio 1.7). There was no difference in survival between the groups (71% [205 of 288], 68% [137 of 202]). CONCLUSIONS: The alternative (test) IFC has significantly reduced the incidence of embolic CVA. This improvement is likely due to increased resistance to deformation at implant, improved neointimal adhesion, and more favorable blood flow characteristics within the conduit.

Cardiomyopathies↗
PubMed1991

Clinical experience with the Novacor ventricular assist system. Bridge to transplantation and the transition to permanent application.

At Stanford University, a Novacor left ventricular assist system (Baxter Healthcare Corporation, Novacor Division, Oakland, Calif.) was placed as a bridge to heart transplantation in 13 patients. During the hospitalization preceding device implantation, all patients were receiving inotropic support for biventricular failure, 11 had pulmonary edema, 6 had life-threatening ventricular arrhythmias, 5 had liver dysfunction with coagulopathy, and 2 had renal failure necessitating artificial support. The mean cardiac index before implantation of the Novacor system was 1.5. All survivors with the Novacor device had a dramatic increase in cardiac output (mean cardiac index = 3.1). One patient with cardiac allograft rejection died during implantation of the left ventricular assist system. Two patients died of pulmonary sepsis and multiorgan failure after the device was implanted. All patients who had the Novacor device implanted for more than 7 days were able to walk and ride stationary bicycles while awaiting transplantation. Ten patients (77%) underwent successful heart transplantation after a mean of 18 days' support with the Novacor device. One patient died of presumed sepsis 2 days after transplantation. Nine patients (90%) are alive 4 months to 6 years after transplantation. In the overall United States experience, 68 patients (as of May 1990) have had a Novacor left ventricular assist device implanted. Five were still being supported, 39 had received a transplant (62%), and 35 patients (90%) survived the transplant hospitalization (1 died later). No instances of device failure have occurred. Overall, the Novacor assist system provided effective bridging to transplantation, with posttransplant survival similar to results after routine transplantation. Modifications and improvements based on this clinical experience have been made in the areas of patient selection, techniques of operative placement, postoperative management, and design of the assist system. Isolated left heart support with a fully implantable left ventricular assist system will be offered as an alternative to heart transplantation for selected patients by 1992.

Adolescent↗
PubMed1989

Implantable electrical left ventricular assist system: bridge to transplantation and the future.

An implantable left ventricular assist system (LVAS) utilizing an electromechanically driven dual pusher-plate blood pump has been employed in a multiinstitutional trial as a bridge to cardiac transplantation. Under development for permanent circulatory support in patients with end-stage heart disease, the LVAS, in this application, derives power and control from an external console via a percutaneous lead. The LVAS was implanted in 20 patients (16 men, 4 women) who were hemodynamically unstable or in refractory cardiogenic shock. The mean age was 44.9 years (range, 25 to 63 years). Preoperative diagnosis was evenly divided between end-stage ischemic disease, cardiomyopathy, and acute myocardial infarction. Implanted in the left upper quadrant within the anterior abdominal wall, the blood pump was connected between the left ventricular apex and ascending aorta. Total support of the systemic circulation and substantial left ventricular unloading were achieved with synchronous counterpulsation for periods up to 90 days (mean, 22.7 days). All patients were stabilized hemodynamically. The mean preoperative cardiac index of 1.5 L/min/m2 increased by a factor of 2. Pulmonary arterial pressures decreased substantially. Serious complications occurred in 16 patients, precluding cardiac transplantation in 10. Most complications (greater than 70%) were in patients who did not receive transplants; the most common complication was bleeding. Twelve of 13 patients with LVAS implants for more than seven days were mobilized, and 4 were fully ambulatory and completely rehabilitated. Orthotopic cardiac transplantation was performed in 10 patients after implants ranging from two to 90 days (mean, 30.3 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Isolated left ventricular assist as bridge to cardiac transplantation.

The electrically driven Novacor implantable left ventricular assist device has been implanted in six patients (four men and two women) since Sept. 7, 1984. In four of the six patients (67%) the device was a successful bridge to cardiac transplantation. One patient died of multiple organ failure and Candida sepsis after 16 days of support with the device. One patient died in the operating room of uncontrollable hemorrhage and biventricular failure caused by severe cardiac rejection. Three patients are alive with cardiac transplants 38, 17, and 10 months after transplantation. One patient died after cardiac transplantation of presumed sepsis. The Novacor left ventricular assist device performed in all cases without mechanical or electrical failure. Excluding the intraoperative death, assist duration ranged from 2 to 16 days. The cardiac index (synonymous with device output) ranged from 2.4 to 3.4 L/min/m2. No embolic events (cerebrovascular or systemic) occurred during assistance with the device. Minimal red cell hemolysis was documented during the period of support. The Novacor left ventricular assist device is a safe and effective bridge to cardiac transplantation in patients with refractory cardiogenic shock.

Adult↗
PubMed1983

The blood interface at artificial surfaces within a left ventricular assist system.

A left ventricular assist system presents a very complex set of interfaces to the blood. The interactions of the various components, their junctions, and fluid dynamic effects have been discussed at a macroscopic, cellular and molecular level. Failure of any part of the system can seriously compromise LVAS function or host response whether due to gross thrombosis with occlusion, proliferative PNI formation, or thromboembolic events. It has been stated that: "When artificial hearts are designed properly, nearly any surface goes." Unfortunately, the blood interface within any circulatory support system, and indeed in much simpler systems, is a much more complex function than design, which includes the surface, materials and many other factors (Table 6).

Adsorption↗
PubMed1980

Long-term function of NCGT vascular conduits in a multicenter trial: evaluation of physical chemical parameters.

Our experience with the NCGT graft has now encompassed 12 years in experimental animals and 4.5 years clinical experience with 134 grafts in man. It has previously been suggested that vessel wall structure, interface-charge, electric potential, and polarity of the blood intimal interface appear critical in the prevention of intravascular thrombosis in all vascular prosthetic bypass grafts. This concept has now been confirmed using ferritin, colloidal iron and fluorescamine intimal labelling. These provide a quantitative special characterization of the surface charges of several grafts, including the NCGT graft. Study indicates that each step in the production of the NCGT graft results in a cumulative increase in the structured negative charge of the vascular interface. The more dense the structured negative charge of the prosthesis, the more resistant is the graft to short and long-term thrombosis in experimental animals and man. The experience has been confirmed with a comparative analysis of implantation results in 105 patients up to 4.5 years with 65 to 70% patency rate over that time interval. Statistical analysis of parameters confirm again that the polarity and structure of the vascular interface is important in the effective function and patency rate of the grafts.

Animals↗
PubMed1975

Hormonal steroids: effects on the vascular system.

An increase in the incidence of thromboembolic disorders has been associated with oral contraceptive use, though the causative mechanisms remain unclear. Our studies indicate that the contraceptive steroids, irrespective of the intermediary metabolic processes involved, cause changes in the surface charge characteristics of the blood vessel wall and blood cells in the following cases: (i) in experiments using dogs, the hormonal steroids result in a greater reduction in the pore surface charge of veins than in arteries; (ii) in rats, the current induced mesenteric occlusion times are significantly lowered following administration of combined contraceptives steroids; (iii) in humans, the electrophoretic mobilities of erythrocytes and platelets from women taking Ovral and Demulen are lower than in controls, and (iv) there is no significant alteration of plasma coagulation times of women who are on injectable progestin therapy. Demulen and Ovral appear to result in a slight decrease in activated partial thromboplastin times compared to controls.

Animals↗
PubMed1975

Nonthrombogenic ac polarized copper prosthesis.

In previous studies from our laboratories, it was shown that metals and alloys which register negative potentials in blood vs the normal hydrogen electrode tend to be antithrombogenic while those with positive potentials are invariably thrombogenic. The present paper deals with a novel approach of maintaining an implanted metallic prosthesis at a negative potential. A copper vascular prosthesis in a dog was maintained at cathodic potentials by a small amplitude (+/- 10 mV) high-frequency ac (100 kHz) on the prosthesis. The prostheses were removed after 2 hours, 6 hours, 1 day, and 42 days, with subsequent visual and scanning electron microscopic examination of the prostheses completed. All tubes were free of thrombus deposits. Minimal junctional thrombi were found, probably due to differences in physicochemical characteristics of the vascular prostheses and recipient vessels. The results are compared with those in the control group (copper tubes with no current) and dc polarized copper tubes. While the control tubes occluded in 2 to 6 hours, the dc and ac polarized tubes remained patent. Of the ac and dc polarized tubes, the former tubes lasted up to 6 weeks with less thrombus deposit. The mechanism of operation of the ac polarized copper prosthesis is not fully understood.

Animals↗
PubMedDate not supplied

Chronic ovine evaluation of a totally implantable electrical left ventricular assist system.

The totally implantable Novacor left ventricular assist system (LVAS) comprises a pump/drive unit (VAD), electronic control and power subsystem (ECP), variable volume compensator (VVC), and belt skin transformer (BST). The system is now undergoing chronic in vivo evaluation. Cumulative animal testing of VAD, VVC, and BST subsystems are 12.1, 4.9, and 43 years, respectively. The longest implants were 279 days for the VAD, 767 days for the VVC, and 1,148 days for the BST. A chronic implant of the total system was electively terminated at 260 days. The LVAS was powered via the BST. Continuously monitored hemodynamic and pump parameters have demonstrated normal hemodynamics and LVAS operation. Periodic VVC determinations suggest a 0.8 ml/day diffusive gas loss. Tether-free operation has been demonstrated with an Ag-Zn battery backpack. The animal was healthy and free of infection as indicated by routine hematologic, biochemical and serum enzyme determinations. Hemolysis is minimal (plasma free hemoglobin less than 5 mg%). Pump output ranged from 7 to 8 L/min. Severe valve calcification was the reason for elective termination at 260 days. This preclinical in vivo experience, and in vitro reliability studies, demonstrate efficacy of the total system.

Animals↗
PubMedDate not supplied

Initial clinical experience with a wearable controller for the Novacor left ventricular assist system.

The Novacor left ventricular assist system (LVAS), an implanted electromechanically driven blood pump, has been used in an ongoing clinical trial as a bridge to cardiac transplantation since 1984. The initial configuration included a console based extracorporeal controller. Because patients supported by the device usually become rehabilitated and highly mobile, a wearable control system was developed for the ambulatory patient. Ergonomically designed for portability, comfort, and appearance, it offers the recipient greater mobility, improved self-image, and an enhanced quality of life. This wearable control system consists of a microprocessor based compact controller that drives the implanted pump/drive unit in synchronous counterpulsation to the native heart. Main and reserve rechargeable power packs, each incorporating a "smart" monitoring circuit with charge-level display and alarm, are capable of supporting the pump for as long as 7 hr. An LVAS monitor can be connected to the controller for device monitoring and adjustment or as a power supply in lieu of the main power pack. Clinical evaluation in patients with end-stage heart disease followed the same protocol as the console study. By April 4, 1994, 41 patients had been supported by the wearable system, including 9 patients currently being supported. Mean duration of use was 51 days (range, 1.5-143+ days), compared with 42 days for 170 console patients (range, 0-370 days). Survival to transplant was 66%, which was similar to the survival (60%) for the patients using the console. Post-transplant survival was 100%, compared with 90% for console patients (not significantly different). After recovering from implant surgery and pre-implant morbidity, device recipients had considerable freedom and mobility and were able to move freely within and outside the hospital. Recipients could readily switch between monitored and untethered operation and could manage power pack replacement and recharging.

Adult↗
PubMedDate not supplied

Clinical evaluation of the Novacor totally implantable ventricular assist system. Current status.

The totally implantable Novacor left ventricular assist system (LVAS) is currently approaching clinical evaluation. In vivo testing and production are underway with National Institutes of Health (NIH) support. Activity over the past year has focused on manufacturing engineering, preproduction quality assurance, and in vivo experiment completion. Subsequent to successful completion of the NIH-sponsored, 2-year preclinical device readiness test (DRT), a number of refinements were identified and approved by the NIH technical/data review board. Most of these were necessitated by obsolescence or unavailability of electronic components and the decision to use only high reliability military (MIL) qualified electronic components and processes. A few additional refinements were identified to increase design margins, all of which were qualified by accelerated testing. The development of production processes, automated test programs, and MIL compliant environmental stress screening procedures was completed. Production of LVAS subsystems, including core electronic components (hybrids, application-specific integrated circuits, and surface mount boards), was initiated. Animal studies are underway. The clinical trial, at Presbyterian-University Hospital of Pittsburgh and St. Louis University Medical Center, awaits completion of in vivo experiments, protocol development, and Food and Drug Administration approval.

Electric Power Supplies↗