Search PubMed⌕ Search

Biomedical subjects

W S Pierce

Publications and source records attributed to W S Pierce.

At least 145 records · Page 8Linked to original sources
PubMed1976

A pressure-measuring system for long-term in vivo pressure measurements.

A new balloon-tipped catheter has been developed for the purpose of making long-term vivo intravascular pressure measurements. Among its advantages are its ability to electrically isolate the subject from the pressure transducer and be rebalanced and calibrated while in situ. Experimental results in calves indicate that the system provides a very reliable means of calibrating implanted catheter tip pressure transducers in situ and can be used as the primary long-term pressure measuring device when high frequency response is not required.

Animals↗
PubMed1976

Design and evaluation of a percutaneous transthoracic cannula.

This investigation was designed to develop a satisfactory PTC for conveying large bore cannulae as required for current use with the artificial heart and left heart assist device. A total of 50 PTCs of varying designs and 6 controls were implanted in the dorsum of canines and goats. Observations with 6 initial designs indicated that necessary requirements in the design of a PTC, include adequate fixation and the use of dacron or nylon velour as the skin interfacing material. Best results were obtained utilizing a PTC having a polycarbonate extra-cutaneous flange, a nylon velour covered polycarbonate subcutaneous skirt, and an extended threaded central conduit to also allow fixation intrathoracicly behind the 2 ribs traversed by the device. Eight such PTCs have been implanted and without complications, have exhibited good tissue ingrowth and have had negative bacterial cultures for periods averaging 6 mos. The use of a PTC of this design should be considered in conjunction with mechanical hearts or left heart assist devices where large bore conduits must cross the chest wall and function on a chronic basis without allowing the ingress of virulent organisms.

Animals↗
PubMed1976

Automatic control of the artificial heart.

An automatic control system has been developed to balance and control the output of an artificial heart. The system consisted of 2 linked negative feedback loops. The left ventricle was controlled by a Servo-Stroke Optimizer, which insured complete filling and full stroke operation of the left pump with each beat and changed the beat rate in accord with changes in aortic pressure. The right ventricle was controlled by a Servo-Variable Systolic Duration unit, which changed the stroke of the right ventricle to maintain the left atrial pressure within a preset band. In the initial animal studies, control pressures (aortic and left atrial pressure) were obtained from implanted transducers. More recently, a method has been devised whereby the control pressures were obtained from specific points on the left air line pressure wave, obviating the need for implanted transducers. The control system has been evaluated in a mock circulatory loop and in 9 calves with implanted artificial hearts. The system has provided balance of the 2 implanted ventricles and changes in flow rate in response to changes in peripheral resistance. The need for an operator to make manual adjustment to the power units has been considerably reduced. Further studies are indicated to evaluate the function of the control system in animals performing moderate-to-maximal exercise. Furthermore, the ultimate benefits of full stroke operation vs fill limited mode operation remain to be delineated.

Animals↗
PubMed1976

A comparison of three ventricles used for left ventricular bypass in the calf.

Long-term synchronized left ventricular bypass has been performed in calves using pneumatically powered pumps having a smooth lining fabricated of segmented polyurethane. Three different pump designs have been employed: a) sac pump, b) longitudinal tethered sac pump, and c) transverse tethered sac pump. Sizeable thrombi occurred in the apex of the sac and longitudinal tethered sac pumps. In the transverse tethered sac pumps, a considerably smaller thrombus was seen only at the flexion point on the inlet side of the pump. Thrombi occurred in areas of low flow velocity and were not prevented by anticoagulation or surface coating techniques. This study indicates the importance of ventricle design in the development of thrombus free pumps and suggests modifications to the present pumps to reduce or eliminate thrombus formation.

Animals↗
PubMed1975

Surface and bulk characteristics of a polyether urethane for artificial hearts.

A segmented polyether urethane was used as the blood contacting surface in a series of 10 heart assist devices implanted in calves for periods up to 35 weeks. At termination, each was examined to correlate blood compatibility and device performance with surface properties, chemical purity, physical stability and affinity for lipid absorption.

Animals↗
PubMed1975

Coarctation of the abdominal aorta with multiple aneurysms. Operative correction.

An 11-year-old asymptomatic girl with hypertension was found to have coarctation of the abdominal aorta with four aneurysms in or adjacent to the hypoplastic segment of aorta. Operative treatment included insertion of a thoracoabdominal aortic bypass graft and resection of the aneurysms. The association of abdominal coarctation and aneurysm formation is reviewed and the rationale for therapy discussed.

Aorta, Abdominal↗
PubMed1974

Complete left ventricular bypass with a paracorporeal pump: design and evaluation.

A multidiscipline group was established at The Pennsylvania State University to design and evaluate mechanical circulatory assist devices and the artificial heart. The group has designed a left ventricular to aortic assist system which consists of a sac-type pump, a synchronization unit, a pneumatic power unit, and appropriate monitoring apparatus. The assist system has been evaluated for long-term circulatory assistance in a series of ten calves. The assist pump was placed in the paracorporeal position. The longest period of continuous pumping was over eight months. The last four calves have had synchronized assist pumping which has permitted prolonged ventricular decompression and assist pump flow rates as high as 10 L/min. Three of these four calves had no evidence of thromboemboli. Additional animal studies will be required before clinical use of such an assist pump system can be safely undertaken.

Animals↗