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Biomedical subjects

W S Pierce

Publications and source records attributed to W S Pierce.

At least 181 records · Page 10Linked to original sources
PubMed1967

Segmented polyurethane: a new elastomer for biomedical applications.

A segmented polyurethane elastomer, originally developed for elastic thread, is now being used for molded prostheses. Performance of this material when used for components of a heart-assist system warrants a thorough investigation of its effectiveness in a variety of biomedical devices.

Animals↗
PubMedDate not supplied

Transmission of water through a biocompatible polyurethane: application to circulatory assist devices.

The permeability characteristics of a water-segmented polyurethane (Biomer) system under the conditions encountered in circulatory-assist devices were investigated. A diffusion cell and permeability system providing precise control of membrane boundary conditions and allowing continuous measurement of water vapor transmission was designed. Liquid water at 37 degrees C was used as the donor fluid and the system incorporated a constant-flow nitrogen carrier gas and an optical dew point sensor downstream to determine the water vapor mass flow rate as a function of time. The mass flow rate was then numerically integrated and plotted against time to allow calculation of effective diffusion coefficient (D) by the dynamic time lag method. Steady-state permeabilities were found to be insensitive to donor chamber hydrostatic pressure (50-200 mm Hg) indicating that bulk flow is not a transport mechanism in these membranes. The permeability coefficient (P) was independent of membrane thickness (H) over the four samples tested (0.0102, 0.0148, 0.0269, and 0.0366 cm), with an average value of 3.29 X 10(-4) cm2/s. Thus, diffusion was Fickian with negligible boundary layers. A plot of lag time versus H2 was linear (R = 0.98) yielding a value for D of 2.18 X 10(-7) cm2/s. A water-Biomer partition coefficient was determined for each sample with an average value of 1525, indicating a moderately hydrophilic membrane with a water sorption of 6.3% at 37 degrees C. Since water transport is by Fickian diffusion in the absence of bulk flow, liquid water cannot be expected to accumulate in circulatory-assist devices unless a condensing surface is maintained within the system.

Biocompatible Materials↗
PubMedDate not supplied

In vivo performance of a transcutaneous energy transmission system with the Penn State motor driven ventricular assist device.

A transcutaneous energy transmission system (TETS) has been used to power the Penn State motor driven ventricular assist device in nine calf experiments, for a total of 316 days of cumulative in vivo experience. This is seen as an important step toward a completely implantable ventricular assist system and total artificial heart. The TETS converts an external 12 volt DC source via inductive coupling to a regulated 14 volt output voltage for use by the motor controller. A maximum output power of 70 watts is available. In calf experiments, the TETS output power averaged between 8 and 12 watts. The motor controller was not implanted in these experiments, awaiting further development of the miniaturized electronics. The TETS output was returned percutaneously to the external motor controller, allowing the TETS output to be monitored directly. System efficiency, from DC source to DC output, and including losses in 12 feet of cable, ranged from 55% to 70%, depending upon supply voltage, motor load, and degree of coil coupling. The subcutaneous coil was well tolerated, demonstrating only temporary, mild, superficial induration.

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PubMedDate not supplied

In vivo determinants of energy consumption in electric motor driven artificial hearts.

To identify factors responsible for energy consumption, a retrospective investigation of the in-vivo performance of the 100 ml electric motor-driven left ventricular assist device (ELVAD), and the e-motor 100 ml total artificial heart, was undertaken. Multivariate regression analysis of the device parameters demonstrated that device flow, and estimated outlet pressure, were the most significant independent variables for predicting changes in motor power. Weighted least-square curvefit, using the product of these two variables, showed that changes in energy consumption can be well predicted for the ventricular assist device (r2 = 0.732). However, by applying the same model to the total artificial heart (ETAH), less favorable results were achieved (r2 = 0.422). In this model, device flow seemed to be more important in predicting energy consumption for the ETAH compared to the ELVAD. Therefore, changing the model by using flow to the third order significantly improved the fit (r2 = 0.6706) for the ETAH, and could compensate in part for the greater variability of the values and increased number of outliers in this group.

Animals↗
PubMedDate not supplied

Long-term left ventricular assist device use before transplantation.

Between September 1992 and April 1995, 19 patients at the authors' institution received pneumatic, pulsatile left ventricular assist devices (LVADs) for bridging to cardiac transplantation. The mean (+/- SD) age of the patients was 51 +/- 14 years (range, 19-64 years). Nine (47%) patients had end-stage idiopathic cardiomyopathy, five (26%) had ischemic cardiomyopathy, and five (26%) other recipients were in cardiogenic shock caused by acute myocardial infarction (AMI). Fifteen (79%) patients were supported with an intraaortic balloon pump or centrifugal LVAD at the time of LVAD insertion (duration, 5.5 +/- 4.1 days). Aprotinin was given to limit bleeding; heparin, followed by warfarin sodium, was used for anticoagulation. A vigorous exercise and nutrition protocol was followed. Cardiac index averaged 2.94 +/- 0.87 L/min/m2 immediately after the implantation procedure. No patient required placement of a right VAD. Average duration of LVAD support was 45 +/- 39 days (range, 3-153 days). Major complications included bleeding requiring reoperation (three patients); cerebrovascular accident (three patients); and severe dysrhythmias requiring direct current cardioversion (four patients). Fourteen (74%) patients underwent transplantation, with one patient still being mechanically supported. All of the patients receiving transplants were discharged from the hospital. Of the individuals who died while supported with the LVAD, 75% were patients with AMI. Timely application of LVADs as part of the interdisciplinary management of end-stage heart disease has generated excellent results for transplant candidates. Right ventricular dysfunction has not necessitated right VAD placement in the authors' experience. Patients with AMI have a higher risk of death while being supported with the device than do more chronically ill recipients.

Adult↗
PubMedDate not supplied

Recent improvements in a completely implanted total artificial heart.

The total artificial heart under development by the Pennsylvania State University and 3M Health Care has undergone a number of design improvements to improve reliability, manufacturability, implantability, and performance. These improvements are nearing completion in preparation for formal durability testing. The redesigned implanted electronics canister, consisting of a welded titanium shell with hermetic connectors, contains the control, telemetry, and energy transmission electronics, as well as a 9 cell, 800 mAhr Ni-Cd battery pack. Functional changes include a reduction in the battery recharge time from 14 hours to 4 hours, and a new inductive telemetry system. The energy transmission system operating frequency has been increased from 160 kHz to 200 kHz. Electromagnetic interference filters and a more efficient control mode have also been implemented. The energy converter has been modified to incorporate a new motor with integral Hall effect position sensors, and new cable, and compliance chamber conduit fittings. High flex life cable is now used for the motor and coil cables. Two prototype durability mock circulatory loops have been built and are being tested. Substantial progress has been made in the completion of manufacturing documentation, and in the implementation of a quality system.

Animals↗
PubMedDate not supplied

In vivo observation of cavitation on prosthetic heart valves.

In this study, a method to determine the existence of prosthetic heart valve cavitation in vivo is presented. Pennsylvania State University Left Ventricular Assist Devices (LVADs) were implanted in two separate calves for this study. Björk-Shiley Monostrut (Irvine, CA) 27 mm and 25 mm valves with Delrin occluders were used in the mitral and aortic positions, respectively. A high fidelity, piezoelectric pressure transducer was mounted approximately 1.25 cm proximal to the mitral valve and measured the high frequency pressure fluctuations caused by cavitation bubble formation and collapse after valve closure. The root mean square (RMS) value of the mitral pressure signal during a 5 ms interval after valve closure was used as a measure of cavitation intensity. The pressure signals observed in vivo were similar to ones observed in vitro with the same type of pressure transducer and were associated with the visually observed cavitation. The percentage of beats with cavitation increased from 20.3% to 67.7% when pump filling was decreased by increasing beat rate. A blood test conducted during post-operative days 1-3 showed a significant increase in plasma hemoglobin during the low filling condition. However, blood tests conducted later (post-operative days 7-44) did not show a significant change in plasma hemoglobin during low filling conditions.

Animals↗
PubMedDate not supplied

Postoperative pulmonary complications in calves after implantation of an electric total artificial heart.

In long-term studies testing the Penn State Total Artificial Heart involving 30 calves, seven calves died of pulmonary complications within 2 weeks after receiving the implant (Group 1 [G1]) and seven calves survived from 2 weeks to 3 months without infection (Group 2 [G2]). Comparative studies were performed using multiple variables: cardiopulmonary bypass (CPB) time, cardiac index, central venous pressure, leukocyte count, hematocrit, total protein, albumin, serum glutamic oxaloacetic transaminase (GOT), creatinine, water balance, and transfused blood volume. In G1, CPB time was longer than in G2 (182 +/- 19 vs 156 +/- 17 minutes, respectively, p = 0.018). Postoperative minimum total protein and albumin in G1 were lower than those in G2 (56.5% +/- 6.0% and 59.0% +/- 5.5% of preoperative values vs 68.4% +/- 8.5% and 67.8% +/- 6.1%, respectively, p = 0.011 and 0.015). Water balance in G2 was more positive than in G1 (11.7 +/- 6.8 vs 1.4 +/- 8.3 L, respectively, p = 0.020). Other variables showed no significant differences. Microscopic findings of the lung in G1 were congestion, hemorrhage, aggregation of neutrophils, and proteinaceous material within the interstitial tissues and alveoli.

Animals↗
PubMedDate not supplied

Steady state hemodynamic and energetic characterization of the Penn State/3M Health Care Total Artificial Heart.

Total Artificial Heart (TAH) development at Penn State University and 3M Health Care has progressed from design improvements and manufacturing documentation to in vitro and in vivo testing to characterize the system's hemodynamic response and energetic performance. The TAH system is completely implantable and intended for use as an alternative to transplantation. It includes a dual pusher plate pump and rollerscrew actuator, welded electronics and battery assembly, transcutaneous energy transmission system, telemetry, and a compliance chamber. In vitro testing was conducted on a Penn State mock circulatory loop with glycerol/water solution at body temperature. Tests were performed to characterize the preload and afterload response, left atrial pressure control, and power consumption. A sensitive preload response was demonstrated with left atrial pressure safely maintained at less than 15 mm Hg for flow rates up to 7.5 L/min. Variations in aortic pressure and pulmonary vascular resistance were found to have minimal effects on the preload sensitivity and left atrial pressure control. In vivo testing of the completely implanted system in its final configuration was carried out in two acute studies using implanted temperature sensors mounted on the electronics, motor, and energy transmission coil in contact with adjacent tissue. The mean temperature at the device-tissue interface was less than 4 degrees C above core temperature.

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