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Biomedical subjects

J W Long

Publications and source records attributed to J W Long.

50 records · Page 3Linked to original sources
PubMedDate not supplied

Oxygen metabolism in animals with total artificial hearts.

The relationship between indices of oxygen metabolism has been widely used in clinical practice to evaluate the adequacy of tissue perfusion, to predict the outcome of the critically ill patient, and to evaluate the effectiveness of therapies. This study quantitated and correlated the relationship between oxygen delivery (DO2), oxygen consumption (VO2), and oxygen extraction rate (EO2) in 14 animals with total artificial hearts (TAH) to investigate the oxygen metabolism in animals with TAH during different physiologic and pathologic conditions. These 14 animals were subdivided into healthy, critical, and exercise groups. There was a physiologic dependence of DO2 to VO2 in animals in the healthy and exercise groups, whereas a pathologic dependence of VO2 to DO2 appeared to occur in animals in the critical group. Reduced or inadequate VO2 leads to organ dysfunction, shock syndrome, multiple organ failure, and finally, mortality. Providing a higher level of DO2 by restoring circulating blood volume, increasing cardiac output, raising hematocrit levels, and improving pulmonary function to achieve a higher level of oxygen extract efficiency and oxygen consumption in animals with TAH that are in a critical condition might be helpful for the treatment of complications and result in decreasing mortality. Using the relationship between indices of oxygen metabolism as a physiologic modifier for TAH control algorithms also might improve the physiologic performance and quality of life of TAH recipients.

Animals↗
PubMedDate not supplied

Pulsatile operation of a centrifugal ventricular assist device with magnetic bearings.

A prototype bench top model of a continuous flow ventricular assist device using an impeller suspended by magnetic bearings has been developed. Generation of a pulsatile pressure was studied using both a computer model and in vitro loop tests of the prototype. The motivation for developing a computer model for a blood pump in the natural circulation is two-fold. First, it allows simulation of the pump under a large variety of operating conditions. Second, it provides insight into what parameters of the system design are important for achieving a specific result. For example, in one case, an aortic pressure of 118/87 mmHg was generated by varying the speed from 2,000 to 2,600 rpm. The computer model was verified by coupling the centrifugal pump prototype to a mock circulatory system. The results of the model were verified by generating an aortic pressure of 113/78 mmHg while varying the speed from 2,000 to 2,600 rpm. These experiments have shown that it is possible to generate pulsatile pressure similar to that of native physiology using a centrifugal left ventricular assist device. Further tests will be required to quantify the effects on hemolysis.

Biomedical Engineering↗
PubMedDate not supplied

Implantable centrifugal pump with hybrid magnetic bearings.

Test methods and results of in vitro assessment of a centrifugal pump with a magnetically suspended impeller are provided. In vitro blood tests have been completed with a resulting normalized milligram index of hemolysis (NmIH) of 12.4 +/- 4.1, indicating that hemolysis is not a problem. Hydraulic characterization of the system with water has shown that a nominal pumping condition of 6 L/min at 100 mmHg was met at 2,200 rpm. Maximum clinically usable cardiac output is predicted be 10 L/min. The magnetic bearing supported impeller did not contact the housing and was shown to be stable under a variety of pumping conditions. The driving motor efficiency is 75% at the nominal condition. Finally, a description of the clinical version of the pump under development is provided.

Heart-Assist Devices↗
PubMedDate not supplied

Myocardial mechanics, energetics, and hemodynamics during intraaortic balloon and transvalvular axial flow hemopump support with a bovine model of ischemic cardiac dysfunction.

Unlike the mechanisms of intraaortic balloon pump (IABP) support, the mechanisms by which transvalvular axial flow Hemopump (HP) support benefit dysfunctional myocardium are less clearly understood. To help elucidate these mechanisms, hemodynamic, metabolic, and mechanical indexes of left ventricular function were measured during conditions of control, ischemic dysfunction, IABP support, and HP support. A large animal (calf) model of left ventricular dysfunction was created with multiple coronary ligations. Peak intraventricular pressure increased with HP support and decreased with IABP support. Intramyocardial pressure (an indicator of intramyocardial stress), time rate of pressure change (an indicator of contractility), and left ventricular myocardial oxygen consumption decreased with IABP and HP support. Left ventricular work decreased with HP support and increased with IABP support. During HP support, indexes of wall stress, work, and contractility, all primary determinants of oxygen consumption, were reduced. During IABP support, indexes of wall stress and contractility were reduced and external work increased. These changes were attributed primarily to changes in ventricular preload, and geometry for HP support, and to a reduction in afterload for IABP support. These findings support the hypothesis that both HP and IABP support reduce intramyocardial stress development and the corresponding oxygen consumption, although via different mechanisms.

Animals↗
PubMedDate not supplied

Successful repair of a ventricular assist system percutaneous lead.

A patient with an implanted, electrically powered, ventricular assist device (Thermo Cardiosystems VE HeartMate) experienced a partial break of the percutaneous lead 5 months after implantation. The break (limited to the Silicone rubber tube) occurred at the junction of the lead with the Y-connector to the controller and vent, leaving approximately 5 cm of exposed lead from the skin exit site to the connector. Electronic and pumping functions of the pump continued, but the opening in the lead (which went more that half way around the circumference) prevented the use of pneumatic actuation as a back-up mode for pump operation, and placed the pump at risk for contamination. Repair of the lead without surgical intervention was desirable, with ease of repair and minimal risk to the patient being the top priorities. The use of multiple layers of heat-shrink tubing or external metal stents was ruled out in favor of a three stage repair procedure. The first stage involved the removal of the Dacron velour in-growth material from the lead to expose the underlying Silicone rubber tube. While the opening in the tube was held shut, a coating of medical grade Silicone rubber adhesive was applied to the tube, then wrapped with a woven Dacron mesh, followed by two layers of plastic wrapping material to protect the adhesive. This initial layer was secured by an external stent of tubing with cable ties. After several days to allow for complete curing of the adhesive, the adhesive coating with mesh was repeated. The final step involved a double layer wrap of a 1 mm thick Silicone rubber sheeting with mesh incorporation and adhesive secured in place with cable ties. After completion of the repair and verification of the ability to operate the device with pneumatic actuation, the patient was discharged with no recurrence of the problem after 8 months of weekly follow-up. This experience demonstrates the need to clinically anticipate component repair or replacement without total device replacement in future implantable blood pump systems.

Adhesives↗
PubMedDate not supplied

In vitro analysis of an atrial shunt in balancing an electrohydraulic total artificial heart.

In vitro tests were performed to evaluate the use of an interatrial shunt in balancing a dual energy converter, actively filled, volumetrically coupled, electrohydraulic total artificial heart. The in vitro atrial shunt was comprised of a 8 mm (PTFE) Teflon graft placed between the left and the right atrium. Other features under study were 1) cardiac output (CO) response to preload, 2) CO relationship to mean aortic pressure, and 3) balance of ventricular outputs. The tests were performed by varying the right filling pressure and monitoring ventricular output and inflow/outflow pressures. Effects of changes in afterload were simulated by varying the (AoP) pressure from 80 mmHg to 120 mmHg, and the (PAP) pressure from 15 mmHg to 40 mmHg. The test results indicated a rise in CO from 4 L/min to 9 L/min, with a change in mean right atrial pressure from 0 mmHg to 12 mmHg. No significant difference in CO was found as afterload pressures were varied. The interatrial shunt (IAS) was effective in establishing ventricular balance over a wide range of preload and afterload conditions, and a mean positive flow from left to right was maintained in the atrial shunt, even at conditions simulating an extreme left-right imbalance.

Blood Flow Velocity↗
PubMedDate not supplied

Right-left ventricular balance in implanted electrically powered artificial hearts.

An electrohydraulic total artificial heart (EHTAH), using an interatrial shunt (IAS) for right-left heart balance, was evaluated in acute, in vivo, open-chested calves. The EHTAH system demonstrated physiologic autoregulation with Starling-like responsiveness to preload. Output varied from 4 to 9 L/min, as right atrial pressure increased from 3 to 15 mmHg. Device output was minimally influenced by afterload. The efficacy of an IAS to balance the EHTAH was demonstrated over a wide range of preload and afterload conditions. Interatrial shunt flow rates, reflective of the degree of right-left imbalance, varied from 2% to 14% (IAS flow from left to right) of cardiac output. Left atrial pressures typically did not exceed right atrial pressures by more than 6-8 mmHg using an instrumented vascular graft such as the IAS. The simplicity and distinct anatomic, surgical, and engineering advantages of the IAS approach to right-left balance of implanted electrically powered artificial hearts justify further development toward a reliable long-term design.

Animals↗
PubMedDate not supplied

Hemodynamic influence of LVAD on right ventricular failure.

Left ventricular assist device (LVAD) pumping has hemodynamic and anatomic influences on right ventricular performance. A total artificial heart (TAH) model was employed to better understand the hemodynamic influence of an LVAD on the failing right ventricle. Biventricular failure was simulated by reducing both ventricular drive pressures of the TAH. After getting hemodynamic data, LVAD pumping in the case of right ventricular failure was simulated by increasing just the left ventricular drive pressure. In the LVAD-simulating condition, cardiac output increased and right atrial pressure decreased significantly (p less than 0.05) compared with the biventricular failure condition, whereas right ventricular function and minute work were the same in these two conditions. Even though changes were accompanied by adaptive increases in pulmonary resistance, substantially lower pulmonary artery and left atrial pressures resulted in the LVAD-simulating condition. From a hemodynamic perspective, these results indicate that an LVAD can increase right ventricular volume work by decreasing right ventricular pressure work, whereas right ventricular net pressure-volume work is unchanged and right ventricular failure is not worsened.

Animals↗
PubMedDate not supplied

Contractile and metabolic function following an ischemia-reperfusion injury in skeletal muscle: influence of oxygen free radical scavengers.

Skeletal muscle contraction and metabolism was evaluated using an in vivo, intact autoperfused canine hindlimb model during 7 hours of reperfusion following 4 hours of complete ischemia, with and without bolus administration of superoxide dismutase (SOD) and catalase (CAT) at the start of reperfusion. Contractile tension of paw dorsiflexion during reperfusion demonstrated small but statistically non-significant increases of recovery towards pre-ischemic baseline with SOD/CAT (i.e. 43% +/- 10 vs 32% +/- 9 with muscle-stimulated tetanic tension). Oxygen utilization by the hindlimb rose during reperfusion from a baseline in the control group of 2.4 +/- 0.3 ml 02/min to 5.4 +/- 1.1 during the first 10 minutes and plateaued at 3.5 +/- 1.3 by the first hour with no differences in the SOD/CAT group. Lactate clearance was prompt (increase from a pre-ischemia value of zero to 0.93 +/- .14 mM/min by 5 minutes and return to near-zero by 1 hour in controls) exhibiting no sustained anaerobic metabolism and was not affected by SOD/CAT. These finding demonstrate irreversible loss of 60-70% of skeletal muscle contraction with preservation of aerobic metabolic capacity at 225% of basal activity. Bolus administration of SOD/CAT at the start of reperfusion offered no significant improvement in metabolic or contractile function. These observations, in a model simulating the in vivo setting, necessitate evaluating alternate ischemia reperfusion conditions and modified free-radical inhibitor protocols before any clinical benefit can be assumed.

Animals↗
PubMedDate not supplied

Adaptive full-ejection point detection for automatic control of the electrohydraulic total artificial heart.

An adaptive algorithm to detect full ejection points was developed for the automatic control of the electrohydraulic total artificial heart (EHTAH). To automatically control the EHTAH, systole in each ventricle is completed when a hyper-pressurization spike is detected on the oil side of that ventricle. A problem associated with the method of determining ventricular full ejection under variable afterload pressure is that a fixed level comparison method could fail to provide a normal full ejection condition. To increase system stability, safety, and efficiency, there is a definite need to vary the full ejection trigger level with changes in afterload. In this study, the full ejection trigger level for the current beat was changed based on the estimated afterload derived from the previous beat's pressure waveform. To increase this estimate's accuracy, an adaptive averaging window was used to determine which part of the previous pressure waveform would be used for the afterload estimation. With this enhanced control scheme, mock circulation tests with the EHTAH device demonstrated that estimated afterload tracked actual afterload. This scheme was also used successfully to control the EHTAH device implanted in three chronic calves.

Animals↗
PubMedDate not supplied

In vivo long-term evaluation of the Utah electrohydraulic total artificial heart.

An electrohydraulic total artificial heart (EHTAH) has been developed and evaluated by long-term in vivo studies. The EHTAH is composed of blood pumps with an interatrial shunt (IAS), an energy converter, and electronics. The EHTAH with external electronics was implanted in four calves weighing from 81-90 kg. Two animals died on the 1st and 5th post operative days, the third animal survived for 32 days, and the fourth for 159 days. The IAS was free of thrombus at autopsy in all animals. The longest surviving animal increased in size from a pre operative weight of 81 kg to 134 kg on day 144. Cardiac output ranged from 9.3 to 10.5 L/min, whereas right and left atrial pressures increased with the calf's growth from 4-10 to 16-20 mmHg and from 8-14 to 18-22 mmHg, respectively. The animal favorably tolerated up to 3.4 km/hr of treadmill exercise, both hemodynamically and metabolically. The elevation of atrial pressures during treadmill exercise was significantly alleviated by employing an automatic control mode. It is concluded that the device has the potential to be a totally implantable system for permanent use.

Animals↗
PubMedDate not supplied

Adaptive responses of total artificial heart animals to treadmill exercise.

The hemodynamic and metabolic adaptations to exercise in five calves implanted with the Utah-100 total artificial heart (TAH) were investigated. The outputs of the left and right ventricles (LCO, RCO) were measured with a cardiac output monitoring and diagnostic unit (COMDU). Arterial and venous oxygen content (CaO2, CvO2) and blood lactate levels (Lac) were measured by blood gas analysis and enzymatic methods. Oxygen consumption (VO2), oxygen delivery (DO2), oxygen extraction rate (EO2), index of metabolic adequacy (IMA), and systemic and pulmonary vascular resistance (SVR, PVR) were calculated. The intensity of exercise was categorized into three horizontal grades: low speed (LS) 0.7-1.0 mph, medium speed (MS) 1.0-1.4 mph, and high speed (HS) 1.4-1.8 mph, each for 30 min. During LS, MS, and HS exercise, the LCO, RCO, LAP, RAP, VO2, DO2, and EO2 all increased, and the SVR and PVR decreased. During exercise, there was a positive correlation between DO2, EO2, and VO2. The blood pH, BE, SBE, and lactate levels were within normal ranges, and the IMA exceeded 1.5, denoting that tissue perfusion was adequate and anaerobic metabolism did not occur. This study implies that Utah-100 TAH animals could physiologically accommodate to exercise with an intensity of up to 1.8 mph for 30 min by increasing cardiac preload, cardiac output, oxygen delivery, and oxygen extraction rate, and by decreasing systemic and pulmonary vascular resistance without transition to anaerobic metabolism.

Animals↗
PubMedDate not supplied

Development of a prototype magnetically suspended rotor ventricular assist device.

A continuous flow centrifugal blood pump with magnetically suspended impeller has been designed, constructed, and tested. The system can be functionally divided into three subsystem designs: 1) centrifugal pump and flow paths, 2) magnetic bearings, and 3) brushless DC motor. The centrifugal pump is a Francis vane type design with a designed operating point of 6 L/min flow and 100 mmHg pressure rise at 2,300 RPM. Peak hydraulic efficiency is over 50%. The magnetic bearing system is an all active design with five axes of control. Rotor position sensors were developed as part of the system to provide feedback to a proportional-integral-derivative controller. The motor is a sensorless brushless DC motor. Back electromotive force voltage generated by the motor is used to provide commutation for the motor. No slots are employed in the motor design in order to reduce the radial force that the bearings must generate. Tests pumping blood in vitro were very encouraging; an index of hemolysis of 0.0086 +/- 0.0012 was measured. Further design refinement is needed to reduce power dissipation and size of the device. The concept of using magnetic bearings in a blood pump shows promise in a long-term implantable blood pump.

Blood Volume↗