PubMed Health⌕ Search

Biomedical subjects

J H Barker

Publications and source records attributed to J H Barker.

At least 19 recordsLinked to original sources
PubMed2001

Dynamic rectus abdominis muscle flap for intestinal stomal continence: a systematic approach.

Several attempts to create a continent stomal sphincter using dynamic myoplasty with limited success have been reported. Denervation atrophy and early muscle fatigue have plagued all reported attempts to make a continent stoma a reality. To address this problem in a series of experiments, we designed a stomal sphincter using the most caudal segment of the rectus abdominis muscle. Then, we performed a study to determine whether a sphincter created with a rectus abdominis muscle island flap could maintain stomal continence in the short term. We found that when stimulated using two different electrical stimulation protocols, in all cases the rectus abdominis muscle sphincter generated peak pressures well above those needed to maintain stomal continence (60 mm Hg). All sphincters were able to maintain stomal continence at all intraluminal bowel pressures tested. We found one of these protocols to be far superior and reached 4 hours of stomal continence after 8 to 10 weeks of electrical stimulation.

Abdominal Muscles↗
PubMed2001

Multi-channel orbicularis oculi stimulation to restore eye-blink function in facial paralysis.

Facial paralysis due to facial nerve injury results in the loss of function of the muscles of the hemiface. The most serious complication in extreme cases is the loss of vision. In this study, we compared the effectiveness of single- and multiple-channel electrical stimulation to restore a complete and cosmetically acceptable eye blink. We established bilateral orbicularis oculi muscle (OOM) paralysis in eight dogs; the OOM of one side was directly stimulated using single-channel electrical stimulation and the opposite side was stimulated using multi-channel electrical stimulation. The changes in the palpebral fissure and complete palpebral closure were measured. The difference in current intensities between the multi-channel and single-channel simulation groups was significant, while only multi-channel stimulation produced complete eyelid closure. The latest electronic stimulation circuitry with high-quality implantable electrodes will make it possible to regulate precisely OOM contractions and thus generate complete and cosmetically acceptable eye-blink motion in patients with facial paralysis.

Animals↗
PubMed2001

Gracilis muscle neosphincter for treating urinary incontinence.

The purpose of this study was to test the anatomical and functional feasibility of using a gracilis muscle free flap to create a urinary sphincter. Anatomical studies were performed in 12 human cadavers and short-term (n = 7) and long-term (n = 8) functional studies were performed in dogs. In the short-term functional studies, the left gracilis muscle was transferred into the pelvis and wrapped around the urethra and the right gracilis muscle was wrapped around a stent. A cuff electrode was placed on the muscle's nerve pedicle and used to stimulate the neosphincter while peak pressure, fatigue rate, and perfusion measurements were performed. In the long-term functional studies, intramuscular electrodes were inserted into the neosphincter to stimulate the flap. The flaps were wrapped around the urethra and dogs were followed for 16 weeks, during which time urodynamic measurements were performed. Our anatomical studies demonstrated that the gracilis muscle free flap could be transferred into the pelvis to create a urinary neosphincter. Our short-term functional study demonstrated that gracilis muscle free-flap function and perfusion were not compromised by transfer. In our long-term functional study, all neosphincters provided bladder outlet resistance pressures consistent with continence. Our anatomical, short-term, and long-term functional studies indicate that a gracilis muscle free-flap neosphincter is an effective procedure for treating urinary incontinence.

Animals↗
PubMed2001

Respect for persons, informed consent and the assessment of infectious disease risks in xenotransplantation.

Given the increasing need for solid organ and tissue transplants and the decreasing supply of suitable allographic organs and tissue to meet this need, it is understandable that the hope for successful xenotransplantation has resurfaced in recent years. The biomedical obstacles to xenotransplantation encountered in previous attempts could be mitigated or overcome by developments in immunosuppression and especially by genetic manipulation of organ source animals. In this essay we consider the history of xenotransplantation, discuss the biomedical obstacles to success, explore recent developments in transgenic sourcing of organs and tissues, and analyze the problem of infectious disease resulting from xenotransplantation (xenosis). We then apply a model of risk analysis to these risks. The conclusions of this risk analysis are used in an ethical evaluation of informed consent in xenotransplantation, with an ethical foundation in Kantian autonomy and Levinasian heteronomic alterity. Our conclusion is that individual and collective informed consent to the infectious disease risks of xenotransplantation requires an open, participatory and dialogical public policy process not yet seen in the United States and Europe. Until that process is created, we propose caution in xenotransplantation in general and a postponement of solid organ xenotransplants in particular.

Animals↗
PubMed2001

Microsatellite analysis of the inbreeding grass weed Barren Brome (Anisantha sterilis) reveals genetic diversity at the within- and between-farm scales.

Nine microsatellites were used to screen 131 samples of Barren Brome (Anisantha sterilis: synonym Bromus sterilis) collected from within the fields of three English farms [from Oxfordshire (Oxon), Leicestershire (Leics) and Wiltshire (Wilts)] and eight seeds taken from samples of each of 10 farms across England, UK. Most individuals (approximately 97%) were homozygous. Polymorphism occurred at all nine loci in all three farms sampled at the field scale, and at most loci for nine of the other 10 farm samples. Between three and 11 alleles were found per locus. Gene diversity (D = 1 - summation operator p(i)2) ranged from 0.088 to 0.760. Polymorphism occurred among individuals within and among fields, and farms. Some alleles were found in only one farm. On the basis of the alleles at all nine loci in the 211 sampled plants, a total of 92 (44%) different genotypes was identified. Clustering analysis using the unweighted pair group method with arithmetic averages (UPGMA) for the combined Oxon, Wilts and Leics samples did not cluster them into their respective farms. Similarly, a phenogram of samples from all 10 farms showed considerable mixing of individuals with respect to farm origins. Identification of genotypes on field plans showed evidence of both spatial localization and mixing. Previous reports have suggested that A. sterilis is strictly inbreeding with little intrapopulation variation at the genetic level. Our data reveal that A. sterilis exists as numerous separate and genetically different lines, which are maintained by inbreeding but which very occasionally outcross. Possible explanations for this pattern of high genetic diversity are discussed.

Alleles↗
PubMed2001

Dynamic rectus abdominis muscle sphincter for stoma continence: an acute functional study in a dog model.

Fecal stomal incontinence is a problem that continues to defy surgical treatment. Previous attempts to create continent stomas using dynamic myoplasty have had limited success due to denervation atrophy of the muscle flap used in the creation of the sphincter and because of muscle fatigue resulting from continuous electrical stimulation. To address the problem of denervation atrophy, a stomal sphincter was designed using the most caudal segment of the rectus abdominis muscle, preserving its intercostal innervation as well as its vascular supply. The purpose of the present study was to determine whether this rectus abdominis muscle island flap sphincter design could maintain stomal continence acutely. In this experiment, six dogs were used to create eight rectus abdominis island flap stoma sphincters around a segment of distal ileum. Initially, the intraluminal stomal pressures generated by the sphincter using different stimulation frequencies were determined. The ability of this stomal sphincter to generate continence at different intraluminal bowel pressures was then assessed. In all cases, the rectus abdominis muscle sphincter generated peak pressures well above those needed to maintain stomal continence (60 mmHg). In addition, each sphincter was able to maintain stomal continence at all intraluminal bowel pressures tested.

Animals↗
PubMed2001

Construction of a linkage map of the Rennell Island Tall coconut type (Cocos nucifera L.) and QTL analysis for yield characters.

AFLP and SSR DNA markers were used to construct a linkage map in the coconut (Cocos nucifera L.; 2n = 32) type Rennell Island Tall (RIT). A total of 227 markers were arranged into 16 linkage groups. The total genome length corresponded to 1971 cM for the RIT map, with 5-23 markers per linkage group. QTL analysis for yield characters in two consecutive sampling periods identified nine loci. Three and two QTLs were detected for number of bunches and one and three QTLs for number of nuts. The correlation of trait values between characters and evaluation periods is partially reflected in identical QTLs. The QTLs represent characters that are important in coconut breeding. The cosegregation of markers with these QTLs provides an opportunity for marker-assisted selection in coconut breeding programmes.

Chromosome Mapping↗
PubMed2000

Successful hand transplantation. One-year follow-up. Louisville Hand Transplant Team.

BACKGROUND: On the basis of positive results in studies of the transplantation of pig extremities and the information exchanged at an international symposium on composite tissue transplantation, we developed a protocol for human hand transplantation. METHODS: After a comprehensive pretransplantation evaluation and informed-consent process, the left hand of a 58-year-old cadaveric donor, matched for size, sex, and skin tone, was transplanted to a 37-year-old man who had lost his dominant left hand 13 years earlier. Immunosuppression consisted of basiliximab for induction therapy and tacrolimus, mycophenolate mofetil, and prednisone for maintenance therapy. RESULTS: The cold-ischemia time of the donor hand was 310 minutes. There were no intraoperative or early postoperative complications. Moderate acute cellular rejection of the skin of the graft developed 6, 20, and 27 weeks after transplantation. All three episodes resolved completely after treatment with intravenous methylprednisolone and topical tacrolimus and clobetasol. Temperature, pain, and pressure sensation had developed in the hand and fingers by one year. At one year, the patient had regained the ability to perform many functional activities with his left hand that he had not been able to perform with his prosthesis, such as throwing a baseball, turning the pages of a newspaper, writing, and tying his shoelaces. CONCLUSIONS: Early success has been achieved in hand transplantation with the use of currently available immunosuppressive drugs.

Adult↗
PubMed2000

Osteomyocutaneous flap as a preclinical composite tissue allograft: swine model.

Composite tissue allotransplantation (CTA) constitutes one of the last frontiers of microsurgery. Prior to its clinical application, the long-term efficacy of modern immunotherapy must be tested in a pre-clinical CTA model. Based on the concept of osteomyocutaneous forearm flap, we developed a CTA flap model in swine. After identifying the vascular territory of the flaps in six pigs (vascular casting), flaps were transplanted from mismatched donor to recipient pigs (n = 6). Rejection was assessed daily by visual inspection and histopathology of biopsy specimens. Recipient pigs were able to ambulate immediately following surgery. There were no flap failures owing to technical or surgical complications. Rejection occurred over a period of 7 days as manifested by edema, cellular infiltration, epidermalysis, and thrombosis. This pre-clinical flap model is excellent for evaluating the effectiveness of modern immunotherapy because it is anatomically and immunologically relevant and because the minimal morbidity caused to the animal permits long-term studies.

Animals↗
PubMed2000

Hand transplantation: comparisons and observations of the first four clinical cases.

Twenty, 15, and 8 months after the first four successful human hand transplant procedures were performed in Lyon (France), Louisville (U. S.), and Guangzhou (China), the transplant teams convened in Louisville, Kentucky, to share their experiences at the Second International Symposium on Composite Tissue Allotransplantation. This article presents reconstructive and immunological data from these landmark procedures in tabular format, in an attempt to answer some key questions about early outcomes of clinical hand transplantation. On the basis of these data, the initial outcomes of the first four hand transplants are encouraging and warrant proceeding with additional hand transplantations.

Adult↗
PubMed2000

Swine composite tissue allotransplant model for preclinical hand transplant studies.

Our laboratory previously developed and used an orthotopic radial forelimb osteomyocutaneous flap in the pig as a preclinical composite tissue allograft (CTA) model. To ensure that it mimicked the clinical situation as closely as possible we developed this model taking many immunologic and reconstructive considerations into account. While our original pig CTA model was ideal for studying the methods of preventing skin, muscle, bone, vessel and nerve rejection, and systemic toxicity, it did not include specialized tissues/structures of a joint and digit. Therefore, we were unable to evaluate rejection of these specialized tissues and their functional properties. Recognizing the importance of assessing joint rejection and function in hand transplantation research we developed a new swine forelimb CTA model that included the animal's medial digit. The present study describes the anatomy and the transplantation technique used in this new preclinical CTA model. We transplanted a radial osteomyocutaneous flap that included the medial digit between two size- (17-21 kg) and age- (6-8-week) matched farm pigs. We removed the digit from the recipient pig's forelimb in continuity with a section of the radial bone and replaced it with the same structure transplanted from a donor pig. After transplantation, a full-length cast was placed on the recipient pig's operated limb and changes in flap color, temperature and the presence of edema were monitored continuously for 6 h, and then regularly at predetermined intervals over 4 days. No weight bearing restrictions were placed on the animal's operated limb. After 4 days, the animal was euthanized. Direct visual monitoring of the allograft during 4 days revealed it was viable with no signs of graft failure due to technical complications associated with the transplant procedure. Upon waking from anesthesia, the animal stood and wandered freely about its cage with no apparent difficulty. Based on the animal's high level of activity at this time, we concluded that the procedure caused it minimal morbidity. At 4 days after the operation, early signs of rejection (skin erythema and edema) were observed. By incorporating a digit into our original CTA pig forelimb model we have made it a better model for performing preclinical hand transplant studies. The added advantage of being able to assess methods of preventing rejection in the specialized joint/digital tissues (articular cartilage, digital flexor and extensor systems, the nail complex) and assess long-term function of these structures is important. The fact that the procedure does not cause major morbidity to the animal makes it possible to conduct long-term graft survival and functional studies.

Animals↗
PubMed2000

Immunosuppressive agents in transplantation: mechanisms of action and current anti-rejection strategies.

Over the past century, the concept of interfering with the immune response at various sites by blocking the formation, stimulation, proliferation, and differentiation of lymphocytes has led to relentless development of new immunosuppressive drugs. These agents are associated with reduced risk of short- and long-term toxicity and have dramatically improved allograft and patient survival, especially in recipients of solid organ transplants. Current protocols in such patients are nearly all calcineurin-inhibitor based, using cyclosporine or tacrolimus, as part of dual, triple, or sequential therapy. This review focuses on agents currently in clinical use at transplant centers in United States. The drugs are described in terms of their basic mechanisms of action, therapeutic uses, clinical studies, and adverse effects. In addition, the efficacy and toxicity of a few promising new therapeutic approaches are examined. Finally, important challenges regarding pharmacological immunosuppression as it relates to solid organ and composite tissue allotransplantation are discussed.

Drug Therapy, Combination↗
PubMed2000

Mixed allogeneic chimerism and tolerance to composite tissue allografts.

The development of effective immunosuppressive drugs has made solid organ allotransplantation the preferred approach for treatment of end-organ failure. The benefits of these immunosuppressants outweigh their risks in preventing rejection of lifesaving solid-organ allografts. On the contrary, composite tissue allotransplants are non-lifesaving and whether the risks of immunosuppressants justify their benefits is a subject of debate. Hence, composite tissue allografts (CTA) have not enjoyed widespread clinical application for reconstruction of large tissue defects. Therefore, a method of preventing rejection that would eliminate the need for toxic immunosuppressants is of particular importance in CTA. Bone marrow transplantation (BMT) to establish mixed chimerism induces tolerance to a variety of allografts in animal models. This article reviews mixed chimerism-based tolerance protocols. Their limitations and their relevance to CTA are discussed, highlighting some unique characteristics (high antigenicity and the presence of active bone marrow) that make CTAs different from solid organ allografts.

Animals↗
PubMed2000

A computer analysis of reflex eyelid motion in normal subjects and in facial neuropathy.

OBJECTIVE: To demonstrate how computerized eyelid motion analysis can quantify the human reflex blink. DESIGN: Seventeen normal subjects and 10 patients with unilateral facial nerve paralysis were analyzed. BACKGROUND: Eyelid closure is currently evaluated by systems primarily designed to assess lower/midfacial movements. The methods are subjective, difficult to reproduce, and measure only volitional closure. Reflex closure is responsible for eye hydration, and its evaluation demands dynamic analysis. METHODS: A 60Hz video camera incorporated into a helmet was used to analyze blinking. Reflective markers on the forehead and eyelids allowed for the dynamic measurement of the reflex blink. Eyelid displacement, velocity and acceleration were calculated. The degree of synchrony between bilateral blinks was also determined. RESULTS: This study demonstrates that video motion analysis can describe normal and altered eyelid motions in a quantifiable manner. CONCLUSIONS: To our knowledge, this is the first study to measure dynamic reflex blinks. Eyelid closure may now be evaluated in kinematic terms. This technique could increase understanding of eyelid motion and permit more accurate evaluation of eyelid function. Dynamic eyelid evaluation has immediate applications in the treatment of facial palsy affecting the reflex blink. Relevance No method has been developed that objectively quantifies dynamic eyelid closure. Methods currently in use evaluate only volitional eyelid closure, and are based on direct and indirect observer assessments. These methods are subjective and are incapable of analyzing dynamic eyelid movements, which are critical to maintenance of corneal hydration and comfort. A system that quantifies eyelid kinematics can provide a functional analysis of blink disorders and an objective evaluation of their treatment(s).

Acceleration↗