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Biomedical subjects

W A Smith

Publications and source records attributed to W A Smith.

At least 109 records · Page 6Linked to original sources
PubMedDate not supplied

Collected nondimensional performance of rotary dynamic blood pumps.

"Nonpulsatile" or "continuous flow" blood pumps are a relatively new application of the rotary dynamic blood pumping principle. They fall outside the normal envelop of pumps, considering their small size, viscosity of the fluid pumped, need for particularly good internal flow patterns, and desire for high efficiency. This article establishes the state of the art in the field of blood pump performance. Trends in efficiency, shut off pressure coefficient, and nondimensional power behavior as a function of nondimensional flow are identified. Blood pumps show agreement with the published effects of low Reynolds numbers in conventional pumps.

Biomedical Engineering↗
PubMedDate not supplied

Sequence polymorphisms and antibody binding to the group 2 dust mite allergens.

BACKGROUND: The group 2 allergens Der p 2, Der f 2 and Eur m 2 are 14-kD proteins with > 80% sequence identity. Isoforms within each genus have been identified which differ by 3-4 amino acids. The aim of this study was to investigate the importance of these substitutions to antibody binding. METHODS: Recombinant allergens were expressed and purified from Escherichia coli. ELISA and skin testing were used to evaluate antibody binding. Molecular modeling of the tertiary structure was preformed to examine the location of substitutions. RESULTS: The three Der f 2 isoforms and two of three of the Der p 2 isoforms reacted with all monoclonal antibodies (mAb). Der p 2.0101, the isoform with aspartate at position 114, bound all mAb except 1D8. Substitution of asparagine for aspartate restored binding of rDer p 2.0101 to mAb 1D8 and increased the correlation coefficient for IgE binding from 0.72 to 0.77. The three Der p 2 isoforms showed comparable skin test reactivity to nDer p 2 and commercial extract. rEur m 2.0101 bound to all mAb except 7A1 and when compared with rDer p 2 for IgE binding, r(2) = of 0.58 (n = 72). Lep d 2 did not react with mAb or with Dermatophagoides spp. allergic sera. Modeling revealed that Eur m 2, Lep d 2 and Tyr p 2 retain the tertiary fold of Der p 2 and the substitutions are on the surface. CONCLUSIONS: mAb could distinguish isoform substitutions. IgE binding showed a good correlation among all isoforms, thus the recombinant allergens are useful for diagnosis.

Allergens↗
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Rapid high level production and purification of recombinant murine and human interferons alpha from Escherichia coli.

The availability of large quantities of pure interferon alpha (IFN-alpha) subtypes for in vivo studies has often proved difficult. This paper presents details on the use of the commercially available pGEX expression system for the production and purification of milligram (mg) quantities of recombinant Murine (Mu) and Human (Hu) IFNs-alpha-1 in Escherichia coli. Initially a fusion product is made which can be rapidly purified on a glutathione-sepharose 4B affinity matrix. Biologically active IFN-alpha can then be released from the matrix by cleavage with the restriction protease activated factor X (FXa+7,++). Routine yields of the final products were in the range of 0.5 to 2.0 mg/l of original culture.

Animals↗
PubMedDate not supplied

Buspirone effect on tobacco withdrawal symptoms: a randomized placebo-controlled trial.

BACKGROUND: Withdrawal symptoms hinder smoking cessation in nicotine-dependent smokers. This prospective, double-blind, placebo-controlled clinical trial was conducted to evaluate buspirone for nicotine withdrawal symptoms. METHODS: Fifty-four heavy smokers (mean 33.1 cigarettes per day for 24 years) were randomly prescribed 30 mg/d of buspirone or placebo beginning 3 weeks before abrupt smoking cessation. Validated nicotine withdrawal and anxiety scales were administered at baseline and serially for 2 weeks after cessation. RESULTS: Baseline demographic and nicotine-dependence measures were similar for each group. Three smokers (1 on buspirone, 2 on placebo) dropped out of the protocol prior to the quit date. Both groups had significant withdrawal effects over time (analysis of variance [ANOVA] P = 0.0001). There was a significant buspirone effect on any nicotine withdrawal symptoms (ANOVA, alpha = 0.05). Smokers who relapsed, regardless of group, reported significantly worse craving, irritability, anxiety, and difficulty concentrating than abstainers (P less than 0.05). Relapse rates at follow-up visits were not significantly different between groups. Two-week abstinence rates were 52 percent for placebo and 62 percent for buspirone (chi-square, P = 0.760). CONCLUSIONS: In these heavy smokers, buspirone offered no relief from nicotine withdrawal symptoms. Regardless of treatment, relapsing smokers experienced more intense nicotine withdrawal.

Adolescent↗
PubMedDate not supplied

Buspirone effect on tobacco withdrawal symptoms: a pilot study.

Tobacco withdrawal symptoms hamper smoking cessation. This was a pilot study of buspirone, a new azapirone anxiolytic, for tobacco withdrawal. Thirteen smokers entered an open clinical trial. Smokers were titrated to 30 mg/day of oral buspirone for 2 weeks prior to cessation. Tobacco withdrawal and Spielberger state-anxiety scales were used at baseline, on the quit date, and then at 24 hours, 48 hours, 1 week, and 2 weeks after abrupt cessation. At the final visit, smokers compared their withdrawal experience with previous cessation attempts. Two patients (15 percent) could not tolerate the medication and did not attempt smoking cessation. Of the remaining 11 smokers, 3 (27 percent) rated withdrawal relief "very definite," 6 (55 percent) "moderate," and 2 (18 percent) "slight." More than two-thirds of the smokers believed that their difficulty concentrating, craving, restlessness, and anxiety were improved compared with earlier tobacco withdrawal attempts. Five patients (46 percent) reported decreased smoking urges during the 2-week medication titration period. Tobacco withdrawal symptoms and state-anxiety scores changed significantly during the study (P less than 0.05). These results are encouraging, but they should be interpreted with caution because of the small sample size and lack of placebo control. Buspirone effect on tobacco withdrawal symptoms should be studied in a randomized, controlled clinical trial.

Adult↗
PubMedDate not supplied

Development of a completely implantable total artificial heart.

In conjunction with engineering and physiologic requirements, anatomic fit is a fundamental problem that must be carefully addressed in the design of a truly feasible implantable total circulatory support system. To facilitate the conceptualization, a three-dimensional anatomic model of an average adult thorax was developed from a data bank of 14 human cadavers, 100 radiographs, 18 computerized tomographs, 4 nuclear magnetic resonance (NMR) studies, and 31 cineangiograms. The location and orientation of the valves, the atrial chambers, venae cavae, and pulmonary hili were found to be the most critical information. As a result, configuration of a one piece, completely implantable total artificial heart (E4T system) with the hydraulic actuator placed between the two ventricles was defined and sized to provide an output of 8 L/min at 120 beats/min. The device was designed to be positioned through a midsternotomy similar to the natural ventricles (in the pericardial sac toward the left chest cavity), and the ports were carefully designed to eliminate the risk of compression of critical cardiovascular structures. Validation of the design was conducted with an E4T model implanted in three human adult cadavers, two of which were submitted to NMR imaging after the device was implanted and the incision closed. Excellent fit was observed in all cadavers, and analysis of the several sagittal, transverse, and coronal NMR images showed no compression of the natural internal structures.

Heart, Artificial↗
PubMedDate not supplied

Effect of respiration on the arterial pressure wave in calves with nonpulsatile biventricular bypass.

The possibility of idioperipheral pulsation in calves with chronic nonpulsatile biventricular bypass has been previously reported. To test the hypothesis that both spontaneous respiration and mechanical ventilation are the cause of pulsation in the arterial pressure recording in calves with nonpulsatile biventricular bypass, two protocols were used to generate data. Both right and left ventricles were bypassed using two centrifugal pumps followed by electrical fibrillation in seven calves. In protocol 1, the spontaneous respiratory rate was increased in awake calves by carbon dioxide gas inhalation. In protocol 2, the animals were anesthetized and intubated to control ventilation, and data were collected as the ventilation rate or tidal volume was changed in a stepwise fashion, as well as when the ventilation was stopped for several seconds. The results of protocol 1 showed good correlation between the arterial pulse rate and spontaneous respiratory rate (Y = 1.03 X, r = 0.822, p < 0.001). The results of protocol 2 showed that the relationship between the ventilation rate and the arterial pulse cycle was identical (Y = X, r = 1.000, p < 0.001), and no pulsation was seen when the ventilator was stopped. The authors conclude that the arterial pulsation observed in calves with nonpulsatile biventricular bypass is caused by respiration.

Animals↗
PubMedDate not supplied

The analysis, design, and testing of a blood lubricated hydrodynamic journal bearing.

The Cleveland Clinic Foundation's Innovative Ventricular Assist System (IVAS) uses a hydrodynamic journal bearing to support the rotating assembly of the blood pump. Bearing dimensions are chosen so that a stable film of lubricant develops and separates stationary and rotating pump surfaces during operation. This bearing type provides several advantages for a permanently implanted device, including essentially no wear for very long life and very high reliability, as well as a self pumping action that generates circumferential wash flow and thus lowers the risk of bearing associated deposition. However, these advantages are accompanied by design issues not encountered with typical journal bearing, such as low shear stress, bearing ends that are not at atmospheric pressure, and low radial bearing loads. To address these issues, several concepts for a hydrodynamic blood bearing were designed and analyzed using a special computer code to perform parametric studies. This design analysis code was developed to define optimum bearing performance under selected load and speed ranges and within practical tolerances. Results showed the range of dimensions and conditions over which an effective, reliable, blood lubricated journal bearing can be designed. Subsequent bench testing has validated the theoretical conclusions and shown this bearing type to be very robust in a blood pump application.

Biomechanical Phenomena↗
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Analysis of a new PM motor design for a rotary dynamic blood Pump.

The permanent magnet (PM) motor for a rotary dynamic blood pump requires high power density to coordinate the motor size with the limited pump space and high efficiency to reduce the size and weight of the associated batteries. The motor also serves as a passive axial magnetic thrust bearing, a reacting hydraulic force, and provides a stabilizing force for the radial journal bearing. This article presents analysis of a new PM motor for the blood pump application. High power density is achieved by using the Halbach magnetic array, and high efficiency is accomplished by optimizing the rotor magnet assembly and the stator slots/windings. While both radial and axial forces are greatly enhanced, pulsating components of the torque and force are also significantly reduced.

Biomechanical Phenomena↗
PubMedDate not supplied

Selection and evaluation of blood- and tribologically compatible journal bearing materials.

A critical issue in the Cleveland Clinic Foundation (CCF) Innovative Ventricular Assist System (IVAS) blood pump is the selection of materials for the blood-lubricated journal bearing. Under normal operating conditions, the journal bearing geometry creates a thick blood film that separates the rotating and stationary surfaces. However, since start-up and certain transients could cause temporary contact, the material pair selected for these surfaces must be both tribologically and blood compatible. Combinations of two biocompatible alloys were tested: a titanium-zirconium-niobium alloy (Ti-13Zr-13Nb) and a zirconium-niobium alloy (Zr-2.5Nb). A standard pin-on-disk tester was used, with the contact surfaces lubricated by glycerol/saline mixtures simulating the viscosity range of blood. One test series evaluated start-up conditions; the other modeled a high-speed rub that might occur if the fluid film broke down. Results showed that the preoxidized Zr-2.5Nb pin/Ti-13Zr-13Nb disk combination was superior at all sliding velocities; a self-mated Zr-2.5Nb pair also showed promise. The oxide film on a self-mated Ti-13Zr-13Nb pair, and a Ti-13Zr-13Nb pin and Zr-2.5Nb disk combination did not show adequate wear life. More work remains to explain distinct performance differences of certain combinations, with more data needed on mechanical properties of thin, hard coatings on softer metal substrates.

Alloys↗
PubMedDate not supplied

Design of a DSP controller for an innovative ventricular assist system.

The design and development of the digital signal processor controller for an innovative ventricular assist system is presented. A DSP56005 is used as the central processor, with other peripheral components. System hardware and software were developed through the advanced development system, and stand alone operation of the system was also accomplished. Two different control modes--current control mode and speed control mode--were developed and investigated. Performance of efficiency and dynamic response were examined through experimental testing.

Biomedical Engineering↗
PubMedDate not supplied

Development of a 6 x 18 inch rheology tunnel for experimental fluid dynamics investigation.

The Ohio State University (OSU) and the Cleveland Clinic Foundation (CCF) developed a 6 x 18 inch low velocity Rheologic Research Tunnel to do flow visualization and other experimental fluid studies, particularly on scaled-up models of cardiovascular devices, such as the CCF's Innovative Ventricular Assist System. The large test section (TS) permits detailed data to be obtained that would be inaccessible with a smaller test prototype. A particular feature of the OSU-CCF program is the use of a non-Newtonian blood analog (NNBA), so the effect of the shear-thinning behavior of blood on the local development of separation, stagnation, and flow patterns can be studied. The TS can simulate a pressure driven slit flow of 6 x 18 in., or the external flow around a vane or blade having an aspect ratio of 1. Maximum pressure is 8.5 psig, while the maximum velocity is 21.7 in/sec. The fluid supply tank has a capacity of 500 gal of NNBA and, with its associated filtration and circulation systems, can be adapted to studies of large transparent models better studied outside the TS. Using 2 pumps, flow rates of 98-610 gal/min can be provided. Instrumentation includes thermistors, a 48 port pressure scanner with pressure transducers, a data acquisition system, and a digital video camera. Dye and hydrogen bubble systems have been developed. Development of such a facility presents problems not encountered in more typical water tables or wind tunnels. These include fundamental issues such as providing a uniform flowfield; practical issues with respect to priming, operating, and obtaining data from the system; and safety considerations. For the very large volume of NNBA, a xanthan gum solution is used, whose shear-thinning behavior depends not only on concentration, but also on age and prior shear history. The lessons learned are presented, permitting others to efficiently develop systems suitable to their testing needs.

Biomedical Engineering↗
PubMedDate not supplied

Blood flow analysis for the secondary impeller of an IVAS heart pump.

The rotodynamic heart pump (IVAS), designed by the Cleveland Clinic Foundation, includes a secondary flow path along the journal bearing, through a secondary impeller, and over the rotor outer surface. The flow behaviors of the blood through the journal bearing and the secondary impeller are investigated by a computational fluid dynamics method that solves the 3-dimensional Navier-Stokes equations using a new solution algorithm. Results of the analyses include: 1) the blood flow patterns within the journal bearing, 2) the effect of the non-uniform bearing clearance on the flow patterns of the impeller cavity, 3) the flow patterns around a secondary impeller blade that include effects of tip clearance and the gap between the blade and the inner or outer side wall, 4) effects of the blade angles on the secondary impeller performance, and 5) the shear stress distribution.

Biomedical Engineering↗