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J F Antaki

Publications and source records attributed to J F Antaki.

At least 19 recordsLinked to original sources
PubMed2001

HeartMate II left ventricular assist system: from concept to first clinical use.

The HeartMate II left ventricular assist device (LVAD) (ThermoCardiosystems, Inc, Woburn, MA) has evolved from 1991 when a partnership was struck between the McGowan Center of the University of Pittsburgh and Nimbus Company. Early iterations were conceptually based on axial-flow mini-pumps (Hemopump) and began with purge bearings. As the project developed, so did the understanding of new bearings, computational fluid design and flow visualization, and speed control algorithms. The acquisition of Nimbus by ThermoCardiosystems, Inc (TCI) sped developments of cannulas, controller, and power/monitor units. The system has been successfully tested in more than 40 calves since 1997 and the first human implant occurred in July 2000. Multicenter safety and feasibility trials are planned for Europe and soon thereafter a trial will be started in the United States to test 6-month survival in end-stage heart failure.

Equipment Design↗
PubMed2000

Continuously maintaining positive flow avoids endocardial suction of a rotary blood pump with left ventricular bypass.

This study showed the usefulness of maintaining positive pump flow to avoid endocardial suction and as an assist bypass. Three calves were implanted with centrifugal pumps. Hemodynamics and pump parameters were measured at varying pump speeds (from 1,100 to 2,300 rpm). In each test pump, speed was adjusted to create 3 hemodynamic states: both positive and negative flow (PNF), positive and zero flow (PZF), and continuously positive flow (CPF). The pump flow volume was determined during systole (Vs) and diastole (Vd). Vs in PNF was 29.6 ml and was not significantly different from Vs in PZF (p > 0.15). Vd in PNF was significantly different from Vd in PZF (p < 0.05). All bypass rates of PNF were over 30% of pulmonary flow. All PZF bypass rates were between the PNF rate and the CPF rate. These data showed that PZF satisfied the minimum requirement of assist flow and was under 100% bypass. Thus, PZF may avoid endocardial suction.

Analysis of Variance↗
PubMed1999

Rotary blood pump flow spontaneously increases during exercise under constant pump speed: results of a chronic study.

Many types of rotary blood pumps and pump control methods have recently been developed with the goal of clinical use. From experiments, we know that pump flow spontaneously increases during exercise without changing pump control parameters. The purpose of this study was to determine the hemodynamics associated with the long-term observation of calves implanted with centrifugal blood pumps (EVAHEART, Sun Medical Technology Research Corporation, Nagano, Japan). Two healthy female Jersey calves were implanted with devices in the left thoracic cavity. A total of 22 treadmill exercise tests were performed after the 50th postoperative day. During exercise, the following parameters were compared with conditions at rest: heart rate, blood pressure, central venous oxygen saturation (SvO2), pump speed, and pump flow. The pump flow in a cardiac cycle was analyzed by separating the systole and diastole. Compared to the base data, statistically significant differences were found in the following interrelated parameters: the heart rate (66.8 +/- 5.2 vs. 106 +/- 9.7 bpm), mean pump flow (4.8 +/- 0.2 vs. 7.0 +/- 0.3 L/min), and volume of pump flow in diastole (26.0 +/- 1.8 vs. 13.5 +/- 2.5 ml). During exercise, the volume of pump flow in systole was 3 times larger than that measured in diastole. Blood pressure, SvO2, and pump speed did not change significantly from rest to exercise. These results suggested that the mean pump flow depends on the systolic pump flow. Therefore, the increase in the mean pump flow during exercise under constant pump speed was caused by an increase in the heart rate.

Animals↗
PubMed1998

Fine trabecularized carbon: ideal material and texture for percutaneous device system of permanent left ventricular assist device.

The development of a percutaneous artificial internal organ system requires a reliable biocompatible connection between the external environment and the inside of the human body. Such is necessary for the success of a permanent left ventricular assist device. However, the search for a satisfactory interface at the epidermal level has proven to be difficult. Carbon has been proposed for this application, but its texture does not typically promote ingrowth from surrounding tissue. We have therefore employed a new processing method to produce a fine trabecularized carbon implant. The method for preparing the implant involves infiltrating low temperature pyrolytic carbon into the surface of a carbon core which is wrapped with carbon fabric. This results in a tightly woven porous structure of carbon (carbon fiber diameter: 35-50 microm, maximal pore size >200 microm) with gradually increasing porosity from 15-75%. We implanted test samples percutaneously in a calf for in vivo histological evaluation. Thirty days after implantation epidermal downgrowth was minimal. Microscopic analysis revealed that a thin fibrous capsule surrounded the implant, and mature connective tissue with accompanying blood vessels filled the pores of the fine trabecularized carbon layer. From these results we suggest that fine trabecularized carbon is ideally suited for a percutaneous device system in a permanent left ventricular assist device.

Animals↗
PubMed1998

An implantable centrifugal blood pump with a recirculating purge system (Cool-Seal system).

A compact centrifugal blood pump has been developed as an implantable left ventricular assist system. The impeller diameter is 40 mm, and pump dimensions are 55 x 64 mm. This first prototype, fabricated from titanium alloy, resulted in a pump weight of 400 g including a brushless DC motor. The weight of a second prototype pump was reduced to 280 g. The entire blood contacting surface is coated with diamond like carbon (DLC) to improve blood compatibility. Flow rates of over 7 L/min against 100 mm Hg pressure at 2,500 rpm with 9 W total power consumption have been measured. A newly designed mechanical seal with a recirculating purge system (Cool-Seal) is used for the shaft seal. In this seal system, the seal temperature is kept under 40 degrees C to prevent heat denaturation of blood proteins. Purge fluid also cools the pump motor coil and journal bearing. Purge fluid is continuously purified and sterilized by an ultrafiltration unit which is incorporated in the paracorporeal drive console. In vitro experiments with bovine blood demonstrated an acceptably low hemolysis rate (normalized index of hemolysis = 0.005 +/- 0.002 g/100 L). In vivo experiments are currently ongoing using calves. Via left thoracotomy, left ventricular (LV) apex descending aorta bypass was performed utilizing an expanded polytetrafluoroethylene (ePTFE) vascular graft with the pump placed in the left thoracic cavity. In 2 in vivo experiments, the pump flow rate was maintained at 5-9 L/min, and pump power consumption remained stable at 9-10 W. All plasma free Hb levels were measured at less than 15 mg/dl. The seal system has demonstrated good seal capability with negligible purge fluid consumption (<0.5 ml/day). In both calves, the pumps demonstrated trouble free continuous function over 6 month (200 days and 222 days).

Alloys↗
PubMed1998

Effect of pressure-flow relationship of centrifugal pump on in vivo hemodynamics: a consideration for design.

We have been developing centrifugal pumps for an implantable left ventricular assist device. We manufactured 2 prototype centrifugal pumps (PI, PII). These two have similar designs except for the PII having a volute casing and a large output port. To determine the differences in the hydraulic characteristics between the PI and PII, we carried out in vitro and in vivo experiments. In vitro study showed that the PII had a shallower H-Q curve than that of the PI, and the PII required a pump speed faster than the PI for the same flow rate and pressure head. On the other hand, in vivo study showed that the PII demonstrated a flow pulsatility greater than that of the PI at 1,900 rpm and 8 L/min although no significant change was observed at low pump speeds (< or = 1,500 rpm). This greater pulsatility consisted of a large discharge according to the small differential pressure during the systolic phase and a small discharge according to the large differential pressure during the diastolic phase. In contrast, the PI, having the steeper H-Q curve, showed a small discharge in the systolic phase and a large discharge in the diastolic phase. These results showed that pulsatility synchronized with the native heart beating depended on the slope of the H-Q curve. As a result, the slope of the H-Q curve is important to determine the component of pulsatility synchronized with native cardiac output. Regarding the slope of the H-Q curve, a pump having a volute casing and a large outlet port demonstrates a shallow slope in the H-Q curve. In conclusion, we suggest that a centrifugal pump for use in left ventricular aortic bypass should be designed considering the effect on the native heart pulsatility.

Animals↗
PubMed1998

Acoustical and physical dynamics of the diatonic harmonica.

The harmonica is arguably the most widely played instrument in the world, yet there is a surprising paucity of published studies of its acoustics or physical dynamics. The typical diatonic harmonica and the physical forces involved in its natural function are described, and simple observations of the harp's functions are reported. The speaking of the reeds, naturally, when producing a bend, and when speaking as an overblow or overdraw is discussed and investigated by simple stopping of the reeds, by videostroboscopic analysis, and by recording vibration of the reeds with displacement gauges. The reeds of the ten hole harmonica can be made to vibrate at varying frequencies depending on the size and shape of the player's vocal tract. Three different modes of speaking from each hole and its pair of reeds are revealed and studied: first, naturally in a closing mode, either blown or drawn; second, as a bend, either blown or drawn, with pitch in the interval between the two notes in the hole; and third, as an overblow or overdraw in an opening mode with a pitch outside the interval between the two natural notes of the hole. This dynamic interaction allows the player to speak with the instrument perhaps as with no other.

Acoustic Stimulation↗
PubMed1996

Long-term animal survival with an implantable axial flow pump as a left ventricular assist device.

We are developing an axial flow blood pump with Nimbus Inc. (AxiPump). For in vivo evaluation the AxiPump has been used as a left ventricular assist device with a left ventricular and descending aorta cannulation and implantation in a small pocket on the left lateral abdominal wall just posterior to the costal margin. Electrical and flow probe leads exit the body transcutaneously. A purge line that delivers the purge fluid for lubrication of the seal between the rotor and stator bodies in the purge fluid bearing system is tunneled with the other leads. Following acute animal studies, 3 animals have been supported for over 1 month with this AxiPump system. All laboratory results were within normal limits except during a recovery period from surgical damage. Hemolysis was not a serious problem. In the first case, the purge system failed at 28 days, and in the second and third cases, the nonpurge bearing system worked well for 57 and 52 days, respectively. Bearings are still under development in this kind of pump. However, this success encourages us to improve the AxiPump as a long-term assist device.

Animals↗
PubMed1996

Pulsatile perfusion system for ex vivo investigation of biochemical pathways in intact vascular tissue.

We have constructed and performed initial validation of an innovative perfusion system that allows exposure of intact segments of vascular tissue to realistic physiological and hemodynamic environments ex vivo. Computer-controlled opening and closing of an in-line gate valve allows generation of arterial pressure waveforms. The control algorithm predicted resultant pressure waveforms with a high degree of accuracy (Pearson correlation coefficient > 0.97). To document vascular homeostasis ex vivo, vasomotor bioassays and morphological studies were performed. The bioassays consisted of injecting epinephrine (2 x 10(-3) mg/ml) into the perfusion system followed by acetylcholine (100 microM) while concurrently measuring vessel diameter with a laser micrometer, significant vasomotion was measured for canine carotid arteries (n = 4) bioassayed after 1, 24, and 48 h of perfusion (P < 0.03). Additionally, human saphenous vein segments were perfused for 24 h (n = 4) and viewed with laser confocal scanning microscopy and transmission electron microscopy; photomicrographs show typical vascular morphology. We conclude that the vascular perfusion system described herein is well suited for investigating the response of intact vascular tissue to hemodynamic variables.

Acetylcholine↗
PubMed1996

High-resolution fluorescent particle-tracking flow visualization within an intraventricular axial flow left ventricular assist device.

Flow visualization is typically applied in blood pump development to both confirm the design expectations and identify regions that may be predisposed to blood element deposition and trauma. Rotary pumps, in particular, place high demands on the technique chosen to visualize the flow given the limited visual accessibility of the flow path and the high impeller speeds. Fluorescent image-tracking velocimetry currently is used at the University of Pittsburgh Medical Center to visualize flow accurately inside of these pumps both qualitatively and quantitatively. Flow patterns under steady conditions within an intraventricular axial flow, left ventricular assist pump (prototype No. 7, SUN Medical Technology Research Corporation, Nagano, Japan) were investigated using this technique. The flow fields at the impeller-stator interface and at the pump outlet were given specific attention. This allowed the assessment of the fluid dynamics throughout the hydrodynamic design limits of the pump.

Biomechanical Phenomena↗
PubMed1996

Controller for an axial flow blood pump.

A rotary blood pump inherently provides only one noninvasive "observable" parameter (motor current) and allows for only one "controllable" parameter (pump speed.) To maintain the systemic circulation properly, the pump seed must be controlled to sustain appropriate outlet flows and perfusion pressure while preventing pulmonary damage caused by extremes in preload. Steady-state data were collected at repeated intervals during chronic trials of the Nimbus AxiPump (Nimbus, Inc., Rancho Cordova, California, U.S.A.) in sheep (n = 7) and calves (n = 12). For each data set, the pump speed was increased at increments of 500 rpm until left ventricular and left atrial emptying was observed by left atrial pressure diminishing to zero. The effect of decreasing preload was evaluated perioperatively by inferior vena cava occlusion at a constant pump speed. Fourier analysis established a relationship between changes in the pump preload and the power spectra of the pump current waveform. Based on these results, a control method was devised to avoid ventricular collapse and maintain the preload within a physiologic range. The objective of this controller is the minimization of the second and third harmonic of the periodic current waveform. This method is intended to provide a noninvasive regulation of the pump by eliminating the need for extraneous transducers.

Animals↗
PubMed1995

A mathematical model for shear-induced hemolysis.

The time-varying history of stress exposure within a rotary blood pump makes it difficult to arrive at a quantifiable design criterion for predicting cell traumatization. Constant stress experiments have revealed that there is a threshold stress level above which damage to blood cells occurs depending upon the time of exposure. The shear stress history experienced by cells within a rotary blood pump, however, is highly unsteady. In order to better predict cell trauma under these realistic conditions, a mathematical damage model based on a concept of "damage accumulation" has been developed. This model is evaluated within the context of red cell trauma. Experimental results support the hypothesis that the rate of damage accumulation increases nonlinearly with the stress level as well as the age of the cell.

Erythrocytes↗
PubMed1995

Computational flow optimization of rotary blood pump components.

In an effort to improve and automate the fluid dynamic design of rotary blood pumps, a coupled computational fluid dynamics (CFD) shape optimization methodology has been developed and implemented. This program couples a finite element flow simulation with a gradient-based optimization routine to modify automatically the shape of an initial candidate blood path, according to a variety of desired fluid dynamic criteria, including shear stress, vorticity/circulation, and viscous dissipation. Preliminary results have led to both intuitive and nonintuitive transformations of the initial blood flow paths for both internal and external flows. This application of computer design optimization offers the ability to explore a much broader design space much more efficiently than would be possible with traditional parametric methods. It is believed that this computer tool can assist developers of rotary blood pumps in designing blood-wetted components that minimize thrombosis and hemolysis while simultaneously providing maximum flow performance.

Biomechanical Phenomena↗
PubMed1995

An improved left ventricular cannula for chronic dynamic blood pump support.

Ventricular unloading with dynamic blood pumps can be markedly affected by the geometry of the cannula tip within the ventricular chamber. Due to the ability of these pumps to develop significant negative inflow pressure, existing cannula tips designed for passively filling blood pumps can be predisposed to inflow occlusion by intraventricular anatomic structures. A novel "trumpet" mouth cannula was constructed to overcome this limiting problem. This design was based on two criteria: to provide additional stenting to the ventricular apex, and to assure placement of the tip opening relative to the endocardial surface. This prototype cannula was evaluated in vivo against conventional caged, blunt, and tapered designs to assess anatomic and hemodynamic interaction within the ventricular apex. Post mortem examination revealed the inflow tract to be devoid of myocardial obstruction in all cases. These initial studies indicate that a trumpet mouth cannula can provide satisfactory hemodynamic performance required by dynamic blood pumps.

Animals↗
PubMed1990

Experience with univentricular support in mortally ill cardiac transplant candidates.

Between July 1987 and March 1989, 11 patients underwent left ventricular support with the Novacor left ventricular assist system irrespective of apparent degree of right ventricular failure. The first 2 patients died of multisystem organ failure while on support. All the remaining patients survived the support period, and actuarial survival after transplantation was 100% at 6 months and 89% at 1 year. In no patient did bacterial infection develop during support or after transplantation. Right ventricular ejection fraction before implantation of the left ventricular assist system was lower than 15% in 6 of 8 patients, yet it increased twofold during left ventricular support. The need for excessive inotropic support (2 patients) or temporary (four days) mechanical right ventricular support (2 patients) while on the left ventricular support system appeared to be related to elevated pulmonary vascular resistance during support in association with large preimplantation ventricular volumes. It appears that even patients with compromised right ventricular performance can be supported long term with a left ventricular assist device. Patients with elevated pulmonary vascular resistance may require temporary right ventricular support.

Adult↗
PubMed1989

Measurement of capsular contracture: the conventional breast implant and the Pittsburgh implant.

At present, there is no accurate, reliable method of experimentally measuring capsular contracture. This study had four goals: (1) to define the parameters of capsular contracture employing principles of biomechanics of soft tissues, (2) to develop laboratory techniques to measure the parameters, (3) to design an implant that mechanically impedes the process of encapsulation, and, (4) to test this implant against a conventional one. We have developed a breast implant (the Pittsburgh implant) with an altered surface topography. Its silicone shell is punctuated by projections 1 mm in height and 1 mm in diameter. Two techniques were devised to measure contracture. The first involved measuring the force deformation along a coronal axis. The second involved measuring hydrostatic pressures within the implant resulting from the injection of known quantities of saline. Measurements were performed in vivo on 36 animals. By both force and pressure measurements, the Pittsburgh implant showed less capsular contracture (p = 0.12 and 0.012, respectively). Histology revealed that the prototype surface alters the linear arrangement of myofibroblasts and redirects the laminar collagen into a waveform pattern. We conclude from this experimental study that an altered surface topography may serve as a means of rendering a capsule less mechanically effective. We feel that the proposed methods can be used in the laboratory to characterize the extent of capsular contracture.

Animals↗
PubMedDate not supplied

Development of an axial flow blood pump LVAS.

Nimbus, Inc., (Rancho Cordova, CA) and the University of Pittsburgh (Pittsburgh, PA) are collaborating to develop an implantable rotary blood pump that can be used as a left ventricular assist system (LVAS). The short-term goal of this project is to show that an LVAS based on this pump can operate safely and reliably during chronic implantations in animals. Work conducted to date includes in vitro testing of hydraulic performance, hemolysis, endurance demonstration, and flow visualization. Results indicate that the pump is capable of generating an output of up to 10 L/min at physiologic pressures. Associated electrical power to drive these pumps is in the range of 6-10 watts. One integrated pump was placed in a mock flow loop and operated continuously at a fixed speed (10,000 rpm), pressure (100 mmHg), and flow rate (6 L/min) for 90 days with no apparent difficulty. In vitro hemolysis test results have consistently ranged between 3-6 g of liberated hemoglobin/day, which is an acceptable range for chronic use. Two in vivo trials of 7 and 14 days were performed using calves, after which tests have been done using sheep as the animal model. Five short-term sheep experiments have been conducted with good results. Future studies will include implantations in sheep of 3 months duration.

Animals↗