Motor feedback physiological control for a continuous flow ventricular assist device

The response of a continuous flow magnetic bearing supported ventricular assist device, the CFVAD3 (CF3) to human physiologic pressure and flow needs is varied by adjustment of the motor speed. This paper discusses a model of the automatic feedback controller designed to develop the required pump performance. The major human circulatory, mechanical, and electrical systems were evaluated using experimental data from the CF3 and linearized models developed. An open-loop model of the human circulatory system was constructed with a human heart and a VAD included. A feedback loop was then closed to maintain a desired reference differential pressure across the system. A proportional-integral (PI) controller was developed to adjust the motor speed and maintain the system reference differential pressure when changes occur in the natural heart. The effects of natural heart pulsatility on the control system show that the reference blood differential pressure is maintained without requiring CF3 motor pulsatility.

Biologic attachment of an allograft bone and tendon transplant to a titanium prosthesis

An Achilles tendon allograft with its bony insertion was used to bridge a Titanium implant, containing an endoprosthetic tendon anchor, and the sheep biceps muscle. Twelve sheep were operated on unilaterally and followed up clinically and histologically for 2, 4 (n = 2), 8, and 12 months (n = 4). Full function of the front limb was regained after 8 to 12 weeks. There were no signs of mechanical loosening at all times. The morphologic changes at the bone block and implant fixation site were an initial revascularization of the allograft bone, which was observed at 2 months and enhanced at 4 months but occurred without any evidence of bone remodeling. This was changed in all specimens taken at 8 and 12 months where intensive new bone development, remodeling, and bone ingrowth in the titanium implant was found. Bone mass was shifted significantly to the tendon insertion half of the bone block because of a creeping substitution of the cancellous allograft bone and bone ingrowth to the implant. Overall bone mass slightly decreased with time but resorption of allograft bone outweighed new bone development only at lesser loaded areas. Transplantation of a bone and tendon allograft to an implant resulted in a revitalized, mechanically stable, and biologically anchored compound.

High-level expression of eukaryotic polypeptides from bacterial chromosomes

Attractive economics and short development timelines have often been cited as reasons for using bacteria to express eukaryotic proteins on a commercial scale. Nevertheless, routine techniques for bacterial expression of heterologous proteins are beset by a variety of technical and legal difficulties. In particular, the use of plasmids to express foreign proteins, popular promoter systems, protein fusion partners, and histidine tags and the recovery of proteins from inclusion bodies are affected by a host of issued patents. Chromosomally encoded leaderless fusions (CELF) offer a variety of technical and legal advantages over existing bacterial expression systems. In this study, we show that CELF can be used to produce a wide assortment of eukaryotic proteins at 10-liter fermentation scale.

Performance of a continuous flow ventricular assist device: magnetic bearing design, construction, and testing

A new centrifugal continuous flow ventricular assist device, the CFVAD III, which is fully magnetic bearing suspended, has been developed. It has only one moving part (the impeller), has no contact (magnetic suspension), is compact, and has minimal heating. A centrifugal impeller of 2 inch outer diameter is driven by a permanent magnet brushless DC motor. This paper discusses the design, construction, testing, and performance of the magnetic bearings in the unit. The magnetic suspension consists of an inlet side magnetic bearing and an outlet side magnetic bearing, each divided into 8 pole segments to control axial and radial displacements as well as angular displacements. The magnetic actuators are composed of several different materials to minimize size and weight while having sufficient load capacity to support the forces on the impeller. Flux levels in the range of 0.1 T are employed in the magnetic bearings. Self sensing electronic circuits (without physical sensors) are employed to determine the impellar position and provide the feedback control signal needed for the magnetic bearing control loops. The sensors provide position sensitivity of approximately 0.025 mm. A decentralized 5 axis controller has been developed using modal control techniques. Proportional integral derivative controls are used for each axis to levitate the magnetically supported impeller.

Mechanical characteristics of four allograft tendon-to-muscle anastomotic techniques

Four methods of allograft tendon-to-muscle anastomosis were tested in single cycle distraction to failure using 10 anastomosed ovine calcaneal tendon-biceps brachii units. The tendon-muscle units were compared to intact ovine biceps brachii muscle units. Methods of tendon-to-muscle anastomosis were derived from modifications of existing muscle tendon repair and tenorrhaphy techniques. Load to failure (N), stiffness (N/cm), distraction (cm), and modes of failure were recorded. Of the four methods tested, the side-to-side technique demonstrated the highest load to failure (152.1 N), the greatest stiffness (17.6 N/cm), the least distraction (2.99 cm) before failure, and the least amount of muscle tissue trauma at failure. Results indicate that, of the methods tested, the side-to-side technique offers the greatest initial stability and should therefore allow adequate revascularization and healing of the anastomosis site.

Magnetic suspension controls for a new continuous flow ventricular assist device

A new continuous flow ventricular assist device (CFVAD III) using a full magnetic suspension has been constructed. The magnetic suspension centers the centrifugal impeller within the clearance passages in the pump, thus avoiding any contact. This noncontact operation gives very high expected mechanical reliability, large clearances, low hemolysis, low thrombosis, and relatively small size compared with current pulsatile devices. A unique configuration of a system of magnetic actuators on the inlet side and exit sides of the impeller gives full five axis control and suspension of the impeller. The bearing system is divided into segments that allow for three displacement axes and two angular control axes. For the first suspension tests, a decentralized set of proportional, derivative, and integral (PID) controllers acting along the modal coordinates are used to suspend the impeller. The controller design takes into account the blood forces acting on the magnetically suspended impeller, the unbalance forces on the impeller and gravitational loads during various body motions. In the final design, the bearing control axes will be coupled together through fluidic forces so the electronic feedback controller is a centralized multiple input, multiple output controller. The control system design must be robust against these types of externally imposed loads to keep the impeller centered and avoid blood damage. This article discusses the dynamic model, controller, and controller implementation for the magnetic suspension controller of CFVAD III.

Digital pad transposition for replacement of the metacarpal or metatarsal pad in dogs

A technique for digital pad transposition is described and illustrated. This technique has application for use in cases of metacarpal or metatarsal pad neoplasia or severe trauma. The transposed digital pad will provide a weight-bearing surface of heavy, keratinized epidermis in cases where the normal metacarpal or metatarsal footpad has been removed. The use of the technique in four clinical cases of footpad neoplasia also is reported.

Bile duct injuries during laparoscopic cholecystectomy

BACKGROUND

With the introduction of laparoscopic cholecystectomy, an increase in the incidence of bile duct injury two to three times that seen in open cholecystectomy was witnessed. Although some of these injuries were blamed on the "learning curve," many occurred long after the surgeon had passed his initial experience. We are still seeing these injuries today.

METHODS

To better understand the mechanism behind these injuries, in the hope of reducing the injury rate, 177 cases of bile duct injury during laparoscopic cholecystectomy were reviewed. All records were studied, including the initial operative reports and all subsequent treatments. Videotapes of the procedures were available for review in 45 (25%) of the cases. All X-ray studies, including interoperative cholangiograms and ERCPs, were reviewed.

RESULTS

The vast majority of the injuries seen in this review (71%) were a direct result of the surgeon misidentifying the anatomy. This misidentification led to ligation and division of the common bile duct in 116 (65%) of the cases. Cholangiograms were performed in only 18% (32 patients) of cases, and in only two patients was the bile duct injury recognized as a result of the cholangiogram. Review of the X-rays showed that in each instance of common bile duct ligation and transection in which a cholangiogram was performed the impending injury was in evidence on the X-ray films but ignored by the surgeon.

CONCLUSIONS

From this review, several conclusions can be drawn. First and foremost, the majority of bile duct injuries seen with laparoscopic cholecystectomy can either be prevented or minimized if the surgeon adheres to a simple and basic rule of biliary surgery; NO structure is ligated or divided until it is absolutely identified! Cholangiography will not prevent bile duct injury, but if performed properly, it will identify an impending injury before the level of injury is extended. And lastly, the incidence of bile duct injury is not related to the laparoscopic technique but to a failure of the surgeon to translate his knowledge and skills from his open experience to the laparoscopic technique.

Laparoscopic discectomy with anterior interbody fusion of L5-S1

BACKGROUND

A laparoscopic approach to the spine for the performance of a minimally invasive discectomy was first described in 1991. Since that time, a number of approaches to laparoscopic discectomy have appeared in the literature. Although these reports demonstrate the ability to approach the spine through a laparoscopic technique, they do not address the issues of loss of disc space, lumbar instability, and the need for interbody fusion.

METHODS

Described is a technique of laparoscopic discectomy with interbody fusion that has been performed successfully in 75 patients. Although a carbon fiber implant was utilized to aid in the fusion process, the technique can equally be performed using donor bone as the interbody support. In the 75 patients attempted, 73 procedures were successfully completed via the laparoscopic approach. One patient was converted to an open anterior approach due to extensive pelvic adhesions from prior surgery. A second patients procedure was aborted after the diagnostic laparoscopy demonstrated dense presacral scarring from a previous gynecological procedure.

RESULTS

There were no major complications in the series. Two patients with high riding bladders sustained bladder lacerations that were recognized and repaired with simple suture closure. There were no bowel injuries, and more importantly, no major vessel injury. The patients were discharged from the hospital on an average within 36 hours, with a return to work averaging between 2-4 weeks depending on the patients type of work. Using a modified pain score for evaluation, post operative pain was reduced by 75%.

CONCLUSIONS

From this study, it is concluded that laparoscopic discectomy with interbody fusion is not only feasible, but appears to give good results with follow up extending out beyond two years. Issues regarding the use of carbon fiber cages vs. bone and indications of the procedure are independent of the laparoscopic approach and are addressed extensively in the orthopedic literature. It can be concluded that when there is surgical indication for L5-S1 discectomy, that a laparoscopic approach with interbody fusion may become the procedure of choice.

A descriptive survey of management and operations at selected sports medicine centers in the United States

No uniform guidelines for operations or accreditation standards for sports medicine center were available and, at the time of this study, little information on the management and operation of sports medicine centers was available in the literature. The purpose of the study was to determine the management structure and function of selected sports medicine centers in the United States. Questionnaires were mailed to 200 randomly selected centers throughout the United State from a directory of sports medicine centers published in Physician and Sportsmedicine (1992) to gather descriptive information on eight areas, including 1) general background, 2) staffing, 3) services, facilities, and equipment, 4) billing, collections, and revenue, 5) clientele, caseloads, and referrals, 6) ownership and financing, 7) school and club outreach contracts, and 8) marketing strategies and future trends. A total of 71 surveys (35.5%) were returned in the allotted time frame. Data were analyzed using ranges, means, medians, modes, and percentages. Results yielded several conclusions about sports medicine centers. Nearly all (93%) of the centers employed physical therapists; physical therapists were clinical directors at 70.2% of centers; orthopaedists were most often medical directors; rehabilitation was the most frequently offered service (93%); physical therapy produced the highest revenue; sports injuries accounted for a mean 34.5% of patients, who were mostly recreational or high school athletes between 13-60 years of age; primary shareholders were most often physical therapists or physicians; most were involved in outreach services for schools; marketing strategies primarily involved communication with referral sources; and managed care was identified most frequently as a trend affecting the future of sports medicine centers. Findings identified common aspects of sports medicine centers and may assist in establishing guidelines for operations or accreditation of sports medicine centers.

Using hybrid magnetic bearings to completely suspend the impeller of a ventricular assist device

Clinically available blood pumps and those under development suffer from poor mechanical reliability and poor biocompatibility related to anatomic fit, hemolysis, and thrombosis. To alleviate these problems concurrently in a long-term device is a substantial challenge. Based on testing the performance of a prototype, and on our judgment of desired characteristics, we have configured an innovative ventricular assist device, the CFVAD4, for long-term use. The design process and its outcome, the CFVAD4 system configuration, is described. To provide unprecedented reliability and biocompatibility, magnetic bearings completely suspend the rotating pump impeller. The CFVAD4 uses a combination of passive (permanent) and active (electric) magnetic bearings, a mixed flow impeller, and a slotless 3-phase brushless DC motor. These components are shaped, oriented, and integrated to provide a compact, implantable, pancake-shaped unit for placement in the left upper abdominal quadrant of adult humans.

Evaluation of a hemostasis model for teaching basic surgical skills

The need for alternative methods of teaching veterinary medicine and surgery has increased in recent years because of increasing costs and changing public opinion. For these reasons a hemostasis model was developed that mimics the arteries and veins of the peripheral vascular system, and can be used to teach the basic skills involved in blood vessel ligation and division. This study evaluated the effectiveness of the fluid hemostasis model compared with using live animals for teaching these skills. Forty sophomore veterinary students participated in the study. Two groups of 20 students each received identical instruction in the basic techniques required for vessel ligation and division. The students then completed various exercises using inanimate models to objectively evaluate their psychomotor skills. Both groups then practiced the techniques for equal time periods; one group used the hemostasis model and the other performed a splenectomy on live dogs. After the practice session, the students were videotaped (for later evaluation), as they performed vessel ligations and divisions. The students then repeated the exercises using the inanimate models for evaluation of skills improvement. Questionnaire responses before and after the project were obtained to determine the students' views on the need for inanimate models for teaching purposes. Results of this study indicate that the hemostasis model was as effective as live animals for teaching the basic skills involved in blood vessel ligation. The students' opinions regarding the use of properly designed inanimate models for teaching these skills were dramatically changed.

Quantitative 1D saturation profiles on chalk by NMR

Quantitative one-dimensional saturation profiles showing the distribution of water and oil in chalk core samples are calculated from NMR measurements utilizing a 1D CSI spectroscopy pulse sequence. Saturation profiles may be acquired under conditions of fluid flow through the sample. Results reveal that strong saturation gradients exist in chalk core samples after core floods, due to capillary effects. The method is useful in analysis of corefloods, e.g., for determination of capillary pressure functions.

Cognitive and motivational determinants of academic achievement and behaviour in third and fourth grade disadvantaged children

While most studies on the determinants of learning deal with either cognition or motivation, there is a growing awareness that both should be considered. Our purpose was to examine the relative roles of cognitive and motivational factors for the scholastic achievement and behaviour of disadvantaged children. Cognition was conceptualised in terms of the psychosemantic theory that assesses cognitive processes by characteristics of the individual's meaning assignment (Kreitler & Kreitler, 1987a). Motivation was conceptualised in terms of the cognitive orientation (CO) theory which assumes that cognitive contents guide behaviour (Kreitler & Kreitler, 1982). Participants were 57 third and fourth graders of both genders, recommended for a remedial summer programme. They were administered the Meaning Test assessing cognitive abilities; the CO Questionnaire of Motivation for Learning assessing the disposition to learn; and the Metropolitan Achievement Test and the IOWA tests assessing verbal, mathematical and working skills. Teachers completed the Teacher-Child Rating Scale assessing six scholastic behaviours. Regression analyses showed that all dependent variables were predicted by the cognitive and motivational variables, better by specific than global predictors. Cognitive variables contributed more to the predictions, especially of academic achievements, and more in the case of verbal than mathematical abilities. In girls, motivational factors played a larger role than cognitive factors, absolutely and relative to boys. Implications for promoting scholastic achievements are discussed.

Cultural practices of Hispanics: implications for the prevention of AIDS

Specific cultural practices of Hispanics were assessed with regard to condom use as an AIDS prevention measure. The sample of 190 Hispanics, including 117 males and 73 females, were mostly young adults who had recently immigrated to the western part of the United States. Condom use was associated with the "one who buys the condoms, " who were mostly men, and machismo practices, such as protecting the woman by using condoms. Suggestions include directing prevention of AIDS messages to males, emphasizing the protection of women through the use of condoms. Religion was nota significant factor with regard to use of condoms even though over 85% of the subjects identified themselves as Catholic. Fate orientation with respect toAIDS also was not a significant factor. The extent adherence to traditional Hispanic cultural values was influenced by the degree of education and acculturation. It is suggested that both education and acculturation levels be assessed prior to the implementation of prevention programs.

MRI of a waterflood on a reservoir chalk sample

CSI of a waterflood experiment on a chalk sample from a North Sea hydrocarbon field has been performed. The method works well, giving separate maps of water and oil distributions. Difference images yield detailed information about fluid movements.

A review of the results of laparoscopic versus open appendectomy

Proponents of laparoscopic appendectomy emphasize the advantages of laparoscopic operation--decreased hospitalization, paralytic ileus, postoperative pain and wound complications, including infection. This study compared open laparoscopic appendectomy with laparoscopic appendectomy. To compare the two techniques, patients undergoing laparoscopic appendectomy at four hospitals were compared with patients undergoing open appendectomy during a six month period. Excluded were incidental appendectomies and patients with perforated appendicitis. An equal number of pediatric patients undergoing laparoscopic and open procedures were included in the analysis to avoid bias, because most of the laparoscopic appendectomies were performed in the adult patient population (age of more than 16 years). A University Medical Center, a Veterans Administration and two community hospitals were the settings. Patients undergoing laparoscopic appendectomy (n = 54) had an average age of 25.7 +/- 1.5 (range of six to 59 years). These patients were compared with 121 patients undergoing open appendectomy whose average age was 23.7 +/- 1.8 (range of three to 83 years). The race and gender distribution were similar in the two groups. Traditional open appendectomy was compared with a group of patients undergoing laparoscopic appendectomy. Variables evaluated were operating room time, number of patients who reported nausea, days until patient tolerated a regular diet, days of hospitalization, postoperative pain medication and wound infection rate. Results are expressed as the mean plus or minus standard error of the mean. Analysis of variance was used to compute continuous variables and Fischer's exact test was used for discrete variables. The laparoscopic approach was attempted in 61 patients and completed in 54 patients. Open appendectomy was performed upon 121 patients. Nineteen patients (18 who underwent open operation and one patient who underwent laparoscopic operation) were excluded from further analysis because of perforated appendicitis. The open procedure took less time (p < 0.05). However, there were more wound infections than in the laparoscopic group (seven of 103 versus zero of 53; p = 0.09). Patients with acute appendicitis recuperated more quickly from the laparoscopic procedure, as evidenced by the time until eating regular diet, period of hospitalization, incidence of nausea and pain medications on postoperative day one (p < 0.05). The absence of wound infections after laparoscopic appendectomy can be attributed to the practice of placing the appendix in a sterile bag or into the trocar sleeve before removal from the abdomen. Laparoscopic appendectomy reduces the period of hospitalization, postoperative ileus, nausea and postoperative pain in patients with acute appendicitis.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of desmopressin acetate on postoperative hemorrhage in patients receiving aspirin therapy before coronary artery bypass operations

It has been suggested that desmopressin acetate has been effective in reducing hemorrhage after coronary artery bypass grafting in patients receiving aspirin before operation. We conducted a prospective, randomized, placebo-controlled, double-blind trial to determine the effectiveness and safety of desmopressin in these patients. Sixty-five patients pretreated with aspirin within 7 days before their scheduled elective coronary artery bypass grafting were randomized to receive desmopressin (0.3 micrograms/kg) or placebo after cessation of bypass and reversal of heparin with protamine. The demographic characteristics and last dose of aspirin were similar in both groups. There was a significant reduction in postoperative blood loss noted between groups for both chest tube blood loss (833 +/- 311 ml for the 1-desamino-8-D-arginine vasopressin [desmopressin] group versus 1176 +/- 674 ml for the placebo group; p = 0.016) and total blood loss (1215 +/- 381 ml for the desmopressin group versus 1637 +/- 761 ml for the placebo group; p = 0.0097). Despite the differences in blood loss between the two groups, the red cell transfusions were not significantly different, but the use of platelets was less in the desmopressin group and almost achieved statistical significance (p = 0.053). Neither was there a difference in the occurrence of thrombotic complications between groups. It appears that desmopressin in this specific subgroup of patients receiving preoperative aspirin is effective as a prophylactic agent for reduction of postsurgical hemorrhage.