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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.

Conjugated human hemoglobin as a physiological oxygen carrier--pyridoxalated hemoglobin polyoxyethylene conjugate (PHP).

Problems associated with specific physiological properties of Hb-based blood substitutes, such as a low P50, short plasma half-life and nephrotoxicity are still major issues to be addressed. Extensive investigations aimed at overcoming these problems have resulted in the preparation of pyridoxalated-hemoglobin-polyoxyethylene conjugate (PHP). PHP was developed from human hemoglobin by two major chemical modifications; pyridoxylation for the purpose of lowering the oxygen affinity (P50 of 19.5 ± 1.2 mmHg), and coupling with polyoxyethylene (POE) to increase its molecular weight (to approximately 90 kdaltons). The circulating half-life of PHP is about 40 hours in dogs. Toxicologicai and physiological studies including renal function assessments have demonstrated that PHP does not have untoward effects on major organ functions. Its efficacy in transporting oxygen has been shown in ET and intracoronary perfusion, and in in vitro studies with sickle cells. Studies to date suggest that PHP is a promising candidate as a physiological oxygen carrier. In this paper the properties of PHP, its safety and efficacy aspects, and its potential as a clinical oxygen carrier are reviewed based on studies conducted in the Authors laboratory.

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

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.

Mechanical properties of aortas and pulmonary arteries of calves implanted with cardiac prostheses

Abstract Left ventricular assist devices (LVAD) were implanted in calves of 3-months old between the natural left ventricular apices and middle descending aortas, while total artificial hearts (TAH) were implanted to replace the natural heart ventricles. The stiffness and strength of upper and lower descending aortas obtained from the calves implanted with the LVADs for 1–2 months were significantly lower than those of non-pumped control calves, accompanied by local detachment and damage of endothelial surfaces, while the mechanical properties of the aortas from TAH-implanted calves were very similar to those of the control calves. However, the decreased stiffness and strength of the aortas in the LVAD-implanted calves were recovered to the control levels by pumping for another 1 month or by the pump removal. These characteristic changes in aortic mechanics and structures by the LVAD pumping for an intermediary duration were ascribed to the distortion of blood flow produced around the anastomosis of the pump outflow conduit to the descending aorta.

In Vivo Evaluation of a Pyridoxalated-Hemoglobin-Polyoxyethylene Conjugate

A pyridoxylated-hemoglobin-polyoxyethylene conjugate (PHP) was developed from outdated human red cell hemoglobin through chemical modifications. The PHP has a mean molecular weight of approximately 90,000 daltons, with an acceptable P50 of 22 +/- 0.7 mmHg. This report describes exchange transfusion studies (ET) to a final hematocrit of 5 +/- 2% (n = 5) with PHP in mongrel dogs. Hespan (a plasma expander) was used as a control (n = 6). All the animals with PHP tolerated the procedure well and have survived more than 8 months to date. Five out of the six dogs receiving Hespan died within a week (p = 0.004). Reduction of hematological and coagulation parameters occurred following the ET and returned to the normal range by 4 weeks post ET. Serum electrolytes and renal function parameters (urea, creatinine) remained in the normal range. A transient slight increase in the hepatic enzyme SGOT was observed. At 2 weeks post ET open biopsies of major organs showed vacuolized cells in the liver and kidneys. Normal histology was noted at 3 months. The oxygen transporting properties examined showed effective oxygen delivery to the tissues for 6 hours post ET. PHP continued to transport oxygen for up to 48 hours studied post ET. Half-life of PHP in the circulation was 36.3 +/- 3.5 hours. Urinary loss of hemoglobin measured up to 48 hours after ET was 9.4 +/- 1.6% of the injected net hemoglobin. The PHP effectively supported life at lethal levels of anemia and is a physiologically acceptable solution. It has a relatively long intravascular residence time and transports oxygen to the tissue effectively for at least 6 hours.

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.

Operating point control system for a continuous flow artificial heart: In vitro study

We proposed and developed a practical and effective servo control system for rotary blood pumps. A rotary blood pump for assisting the failing natural heart should be operated only in physiologically acceptable conditions. The operation of a rotary blood pump is based on the rotational speed of the impeller and pressure head. If the pump flow and the pressure head are set within an acceptable range, the driving condition is deemed normal condition, and this control system maintains the preset operating point by applying proportional and detective control (PD control). If the pump flow or pressure head is outside the acceptable range, the driving condition is determined to be abnormal condition, and this system operates the pump in a recovery fashion. If the driving condition is kept under abnormal conditions of sudden decrease of the flow, the condition is termed a suction condition. The controller releases the pump from the suction condition and later returns it to the normal condition. In this study, we evaluated these servo control modes of the centrifugal pump and confirmed whether the performance of this proposed operating point control system was practical.

Ex vivo evaluation of the NASA/DeBakey axial flow ventricular assist device. Results of a 2 week screening test.

The authors investigated the antithombogenicity of the NASA/DeBakey axial flow ventricular assist device in an ex vivo calf model. The device is 3 inches in length and 1 inch in largest diameter. The pump weighs 53 g and displaces 15 ml. The unit consists of three major components: a flow straightener, a spinning inducer/impeller, and a diffuser. The impeller has rod shaped permanent magnets embedded within the six blades and is activated magnetically by a motor stator that is positioned outside the flow tube. Previous 2 day screening tests demonstrated an antithrombogenic configuration in short-term implantation. Based on the results of these 2 day screening tests, five pumps with the best configuration were implanted into a calf for 2 weeks for anti thrombogenicity confirmation. Pumps were implanted paracorporeally, and heparin was used to maintain activated clotting time to approximately 250 sec. Each pump was changed every 2 weeks as planned. During the experiment, all pumps demonstrated stable pumping. The required electric power was 7 to 8 watts and pump flow was maintained at 4 L/min. The calf was in excellent condition. Liver and renal function were maintained, plasma free hemoglobin was kept at less than 4 mg/dl (3.3 +/- 0.3 mg/dl), and lactate dehydrogenase was 1043 +/- 36 units/L. In this experimental series, all five pumps passed the 2 week implantation. Two week ex vivo test results indicated very slight thrombus in the hub areas of some pumps. For the next phase of the implantation study, minor design optimization is necessary to completely eliminate thrombus formation. According to our step by step approach, the in vivo test aiming for long-term implantation is ongoing.

Membrane plasma separation and the on-line treatment of plasma by membranes

Abstract The application of membranes for the separation of solids from liquids is quite common in industrial processes and has had a major impact on biomedical processes. Biomedical applications of blood processing range from the use of large-pore structures for filtration of blood for the removal of large particles (> 20 μm) (transfusion filters) to membranes for the dialysis of blood for the removal of low molecular weight solutes in the treatment of renal failure. Within the past decade membranes have been applied in the separation of plasma from whole blood. Compared to centrifugal plasma separation membrane plasma separation is preferred when used with on-line plasma fractionation since the plasma is free of cells. Also, membranes have been applied in the on-line treatment of the plasma for the selective removal of macromolecules in selected disease states obviating the need for plasma replacement products. The membranes for plasma separation and fractionation may be distinguished from conventional dialysis membranes and high-flux membranes used in hemofiltration by their very high or select passage of plasma proteins. Membrane techniques are simple and safe to apply and can be competitive to other separation technologies. Studies of membranes in the separation of components from the complex mixture of blood and their use in the separation of macromolecules in plasma are particularly useful in extending the applications of membranes in bioseparations.