Jacobs G

Laryngeal pacemaker. II. Electronic pacing of reinnervated posterior cricoarytenoid muscles in the canine

A fully reliable means of rehabilitating patients with bilateral vocal cord paralysis has not yet been developed. In order to improve upon existing solutions to this problem, the authors have recently described a laryngeal pacemaker, initially tested through stimulation of a cross‐over nerve‐muscle pedicle from one sternohyoid muscle to the other in the canine. Afferent stimuli, initiated through elongation of the airway during inspiration, were detected by a linear strain gauge sutured to the tracheal rings and appropriately amplified. The current report deals with the application of this concept to pace a nerve‐muscle pedicle reinnervating the posterior cricoarytenoid muscle. Videoscopie and cinematographic documentation of electrically paced abduction of the reinnervated vocal fold, synchronous with inspiration, was clearly demonstrated. Only miniaturization of an implantable electronic amplifier remains to permit an attempt at pacing of the paralyzed larynx in humans.

Voluntary control of an ileal pouch by coordinated electrical stimulation. A pilot study in the dog.

Heal reservoirs were constructed in four dogs under general anesthesia and stimulated by means of a constant current generator that produced pulse trains at frequencies between 6 Hz and 1.67 kHz. Stimulation at 6 Hz with 50 ms pulses between amplitudes of 15 and 25 mA uniformly produced pouch contraction and reservoir emptying. Stimulation at other frequencies did not cause pouch emptying although pressure increases were sometimes observed. Such electrical stimulation may be useful for voluntary control of intestinal reservoirs when used as replacement for urinary bladder or colon. The mechanism by which the intestinal contraction is preduced appears to be different than that produced by slow wave pacing

Progress in the development of a transcutaneously powered axial flow blood pump ventricular assist system.

Development of the Jarvik 2000 intraventricular assist system for long-term support is ongoing. The system integrates the Jarvik 2000 axial flow blood pump with a microprocessor based automatic motor controller to provide response to physiologic demands. Nine devices have been evaluated in vivo (six completed, three ongoing) with durations in excess of 26 weeks. Instrumented experiments include implanted transit-time ultrasonic flow probes and dual micromanometer LV/AoP catheters. Treadmill exercise and heart pacing studies are performed to evaluate control system response to increased heart rates. Pharmacologically induced cardiac dysfunction studies are performed in awake and anesthetized calves to demonstrate control response to simulated heart failure conditions. No deleterious effects or events were encountered during any physiologic studies. No hematologic, renal, hepatic, or pulmonary complications have been encountered in any study. Plasma free hemoglobin levels of 7.0 ± 5.1 mg/dl demonstrate no device related hemolysis throughout the duration of all studies. Pathologic analysis at explant showed no evidence of thromboembolic events. All pump surfaces were free of thrombus except for a minimal ring of fibrin, (∼1 mm) on the inflow bearing. Future developments for permanent implantation will include implanted physiologic control systems, implanted batteries, and transcutaneous energy and data transmission systems.

Initial Clinical Experience with a New Temporary Left Ventricular Assist Device

A new, simple left ventricular assist system has been developed and its use in experimental animals has been evaluated. The system achieves ventricular drainage by a transaortic valve cannula and utilizes a new centrifugal pump; the blood access is unique in requiring only a simple end-to-side synthetic graft anastomosis to the ascending aorta. Adequate pulsatility is obtained by concomitant use of an intraaortic balloon pump. This case report documents our initial clinical experience with this system in a postoperative patient with profound left ventricular failure unresponsive to all usual treatment. There was temporary recovery of left ventricular function upon decannulation after five and a half days of assist pumping. Despite the eventual death of the patient, the system functioned adequately, suggesting that it has good potential for use in a small, selected group of patients.

Laryngeal Pacemaker. Part I. Electronic Pacing of Reinnervated Strap Muscles lIn the Dog

The best approach to management of bilateral vocal cord paralysis, with its resultant airway compromise, has not yet been universally agreed upon. Recently proposed methods have included direct stimulation of the laryngeal dilators by the modulation of rhythmic information from the chest wall, diaphragm, phrenic nerve, or accessory muscles of respiration. In such an approach, the information obtained is not necessarily related to inspiration only, and direct implantation of a stimulating electrode into the laryngeal musculature may not be fully efficient and tolerated over time. To obviate such difficulties, the authors propose to broaden the concept of electrical pacing by (1) developing a better source for the triggering of electrical activity during inspiration and (2) devising a reliable means of long-term physiologic stimulation of denervated striated muscle not subject to deterioration over time. Such an experimental unit was constructed in the canine. It is based on afferent information that originates from the mechanical lengthening of the trachea during inspiration and is defected through a linear strain gauge sutured to the tracheal rings. The signal obtained is modulated through an impedance detector and is amplified. An efferent limb consisting of a monopolar cuffed electrode placed around a crossover nerve-muscle pedicle from one sternohyoid muscle to the other was used successfully. Such a preliminary experiment with a strap muscle avoids the extraneous factors related to function of the paralyzed larynx. Successful nerve-muscle pedicle pacing, synchronous with respiration, was verified through electromyographic recordings and direct observation in all animals studied.

Durability Testing of Components for the Jarvik 2000 Completely Implantable Axial Flow Left Ventricular Assist Device

A cable-lead tester and real time bearing tester have been developed with provisions to test future implantable electronics, transcutaneous energy transfer system (TETS), and related interconnect cabling designs. The cable/lead tester, used in 1997 to test a previously considered implantable bellows-connector-cabling system, can test up to 10 samples at a time. X-Y-Z-theta motions are applied to the proximal end of the test specimen with its distal end fixed. The real time bearing tester is of a mock loop configuration with the bearings under test housed in a fully functional, Good Manufacturing Practices assembled axial pump. A simulated left ventricular pulsatile preload is applied to the inflow of the axial pump, while its outflow is subjected to an 80 mmHg aortic afterload by pumping into a fixed height tube with no outflow restriction. The heated blood bath saline used in this system is UV sterilized and mechanically filtered by use of a commercial salt water conditioning system attached external to the main preload fluid reservoir. The cable-lead tester and real time bearing tester design include provisions to house a complete Jarvik 2000 left ventricular assist device (Transicoil Medical, Norristown, PA) for in vitro system testing.

145 days survival of calf with total artificial heart (TAH).

A calf with a biolized TAH was maintained in reasonably good physiological condition for a major portion of a 145-day experiment as indicated by near normal growth rate and laboratory data. The mechanism for the high CVP and CBV at the beginning and end of the experiment were correlated with protein metabolism. No evidence of thromboembolism was found at autopsy and only modest congestion with minimal parenchymal damage was observed. The cardiac prosthesis itself was free of thrombus, although slight calcification was found on the valves and diaphragms. The pump performance, however, remained satisfactory. In addition, endothelialization appeared to be starting on a portion on the inside of the pump.

Dynamic rehabilitation of the paralyzed face--II. Electronic control of the reinnervated facial musculature from the contralateral side in the rabbit.

This work is the continuation of a previous pilot study in the rabbit in which motion originating on the face was picked up by miniature strain gages and channeled synchronously to strap muscles reinnervated via crossover nerve-muscle pedicles. In the current series of experiments, we modified the distal limb of the system to reinnervate the previously paralyzed opposite side of the face via an ansa hypoglossi nerve–thyrohyoid muscle pedicle in five animals. Muscular contraction was induced on the intact side by stimulating different branches of the facial nerve, and corresponding information was channeled to the reinnervated side through an upgraded electronic stimulator via monopolar electrodes placed around the nerve pedicle in the neck. In addition to demonstrating perfect synchrony between intact and reinnervated sides, this facial stimulator allowed the reinnervated side of the face to follow the intact side in a graded and sustained fashion, thus demonstrating that fine tuning of reinnervated facial musculature was possible.

Muscle powered circulatory assist device for diastolic counterpulsator.

A diastolic counterpulsator that uses either skeletal muscle or pneumatic actuation was developed. The unit is positioned between the latissimus dorsi and the chest wall, without interference with collateral blood supply, and is connected in series with the descending aorta. The system was able to generate stroke volumes between 52 and 16 ccs against pressures of 60 and 140 mmHg, respectively. Stroke work at 200 msec stimulation averaged 2.8 X 10(6) ergs. Power output at an afterload of 100 mmHg, and at a rate of 60 bpm, was 0.51 W. Back-up pneumatic actuation provided by an intraaortic balloon pump resulted in a 46% increase in the endocardial viability ratio (EVR).

Towards the development of a pediatric ventricular assist device.

The very limited options available to treat ventricular failure in children with congenital and acquired heart diseases have motivated the development of a pediatric ventricular assist device at the University of Pittsburgh (UoP) and University of Pittsburgh Medical Center (UPMC). Our effort involves a consortium consisting of UoP, Childrens Hospital of Pittsburgh (CHP), Carnegie Mellon University, World Heart Corporation, and LaunchPoint Technologies, Inc. The overall aim of our program is to develop a highly reliable, biocompatible ventricular assist device (VAD) for chronic support (6 months) of the unique and high-risk population of children between 3 and 15 kg (patients from birth to 2 years of age). The innovative pediatric ventricular assist device we are developing is based on a miniature mixed flow turbodynamic pump featuring magnetic levitation, to assure minimal blood trauma and risk of thrombosis. This review article discusses the limitations of current pediatric cardiac assist treatment options and the work to date by our consortium toward the development of a pediatric VAD.