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Biomedical subjects

M W Walker

Publications and source records attributed to M W Walker.

50 records · Page 3Linked to original sources
PubMed1986

The effects of a calcium deficient diet on the mechanical properties and morphology of goose bone.

A control group of geese (Anser anser) on a normal calcium diet for egg laying poultry was compared to egg laying geese on a calcium deficient diet. The ultimate compressive strength and modulus of elasticity of femoral cortical bone from each group were determined by compressing right circular cylinders which were 2.4 mm in height and 0.8 mm in diameter. The bending strength and bending modulus of elasticity of tibial cortical bone were determined by three point bend tests on rectangular prisms which were approximately 25 mm by 0.8 mm by 0.8 mm. Bone calcium content and eggshell calcium content were determined by atomic absorption spectrophotometry. Blood samples were analyzed for free calcium ion concentration. Histological observations included studies of cross-sectional microradiographs, examinations of cross sections stained by a modified Masson's technique, and a determination of fractional area of voids by quantitative microscopy. The average compressive modulus for the control birds was 12.0 GPa (S.D.: 6.2 GPa) while the ultimate compressive strength was 165 MPa (S.D.: 27 MPa). Calcium deprived birds showed slight, but not statistically significant, decreases in both the compressive modulus and compressive strength. The tibial three point bending modulus for the control birds was 16.5 GPa (S.D.: 2.6 GPa) while the ultimate bending strength was 256 MPa (S.D.: 58 MPa). Once again, slight though not statistically significant decreases in the bending modulus and strength were seen in the geese on the calcium deficient diet. The average calcium content (wt%) of the femora of the control birds was 20.5% (S.D.: 4.3%) and 20.6% (S.D.: 4.8%) for the tibiae. No significant differences were noted in the calcium deprived birds. The average fractional void area for the control bird femoral bone was 12.0% (S.D.: 2.6%) and 9.8% (S.D.: 1.8%) for the tibial bone. Significantly greater fractional void areas were noted in the calcium deficient birds as were profound changes in the macrocellular structure of these bones.

Animals↗
PubMed1986

An experimental study of eight current arterial prostheses.

Eight currently used arterial prostheses with differing constructions and materials were implanted in the descending thoracic aorta of mongrel dogs. The prostheses were Gore-Tex (polytetrafluoroethylene), DeBakey Woven, Cooley Woven, Meadox Woven Double Velour, Cooley Knitted Double Velour, Microvel, Vasculour II, and Bionit II. Five series of these eight prostheses were serially implanted in heparinized subjects. During the 40 implantations, attention was focused on three major characteristics: preclotting efficiency, surgical handling characteristics, and healing. Gore-Tex is impervious to blood. The DeBakey and Cooley woven grafts are nearly so. The remaining prostheses required preclotting. The Meadox Woven Double Velour became impervious after two preclotting steps, the Cooley Knitted Double Velour and the Bionit II required three, and the Vasculour II and the Microvel required four. The surgical handling characteristics of the knitted prostheses clearly surpassed those of the DeBakey and Cooley woven and Gore-Tex prostheses. Although the Meadox Woven Double Velour prosthesis had better conformability than the nonveloured woven, the tendency of its cut edge to fray was more pronounced. Healing was much more advanced in the knitted and woven prostheses than in the Gore-Tex.

Animals↗
PubMed1986

Neuropeptide Y: a powerful modulator of epithelial ion transport.

Neuropeptide Y (NPY) is a major gut peptide localized in the intestinal mucosa of several mammalian species. Ileal mucosa from rabbit and guinea-pig was mounted in Ussing chambers in order to study the effect of NPY on short circuit current. Neuropeptide Y inhibited the short circuit current when applied to the serosal side of the tissue. The maximum change in short circuit current was -50 +/- 6 microA cm-2 in the rabbit ileum and -49 +/- 14 microA cm-2 in the guinea-pig ileum. The EC50 was 3 X 10(-8) M in both species. Pretreatment of rabbit ileum with the alpha 2-adrenoceptor antagonist, yohimbine (1 X 10(-6) M) for 10 min did not reduce the response of the tissue to neuropeptide Y (1 X 10(-7) M). When applied serosally to rabbit ileal mucosa, the related peptide YY caused a maximum change in short circuit current of -60 +/- 13 microA cm-2; the EC50 was 2 X 10(-9) M. Isotopic flux studies in rabbit ileum showed that 1 X 10(-7) M neuropeptide Y enhanced mucosal-to-serosal Na+ and Cl- fluxes and reduced serosal-to-mucosal Cl- flux. Replacement of chloride with gluconate on both sides of the tissue significantly reduced the change in short circuit current produced by neuropeptide Y (1 X 10(-7) M), as did a similar replacement of bicarbonate. It is concluded that neuropeptide Y and peptide YY are the most potent neurotransmitters or hormones so far described in their ability to attenuate electrogenic transport in the small intestine.

Animals↗
PubMed1986

The effect of predetermined thrombotic potential of the recipient on small-caliber graft performance.

This study was designed to establish the influence of the recipient's thrombotic potential on the patency of small-caliber prostheses and to evaluate the subsequent improvement of graft performance by medicinally altering the prostaglandin balance in subjects predisposed to graft occlusion. Mongrel dogs were pretested and classified as low and high responders according to their thrombotic potential, measured as prostaglandin metabolite balance and platelet aggregability. High responders were randomly divided into two groups. Those assigned to serve as the medicated subjects were pretreated 1 week before surgery with a single oral daily administration of combined dazmegrel (UK-38,485) and aspirin in equal dosages of 3 mg/kg. Medication was continued throughout the experiment. Dacron grafts were implanted bilaterally in the carotid artery site in all subjects. Following a 3-week implantation period, the patency rate for the group with low thrombotic potential was 100%. In the animals with high thrombotic potential the patency rate was 10% for nonmedicated subjects and 100% for medicated subjects. These data support the concept that the thrombotic potential largely determines the capacity of the recipient's blood to thrombose small-caliber prostheses. Effective medicinal alteration of prostaglandin balance results in exceptionally increased patency of synthetic grafts.

Animals↗
PubMed1986

Prevention of retrosternal adhesions after pericardiotomy.

Because repeat sternotomies are becoming much more prevalent with repeat coronary bypass operations, prevention of direct adhesions of the heart and grafts to the back of the sternum by use of synthetic or xenograft material to close the pericardiotomy has become a matter for investigation. In this study bovine and equine glutaraldehyde-processed xenografts were implanted bilaterally in dogs for implant intervals of 6 weeks and 3, 6, 9, and 12 months. The bovine and equine xenografts both performed well in resisting the adhesion of the heart to their inner surfaces and less well in resisting adhesion of the lung and chest wall to their outer surfaces. The bovine xenograft had a higher percentage of adhesion-free surface on all the surfaces evaluated; however, one of our 12-month bovine pericardial xenograft implants exhibited significant multifocal calcific degeneration. Although pericardial xenografts generally have performed well when implanted in the dog, Gallo, Artiñano, and Duran recently expressed concern about their performance in humans. Along with our finding of calcification, their concern suggests a cautious approach to clinical application.

Animals↗
PubMed1985

Glutaraldehyde preparation of coronary artery bypass bioprostheses.

A method for glutaraldehyde (GA) fixation of canine carotid arteries has been developed for the preparation of small caliber biologic prostheses for coronary artery bypass. The biologic grafts were preserved by a static inflation technique that proved to be more advantageous than the standard stenting method. The most suitable static inflation pressure was found to be 120 mm Hg. By means of colorimetric measurements the minimal tanning time and the amount of GA required for complete fixation for canine vascular tissue were established. Stabilization of the vessel collagen and confirmation of GA-collagen cross-linking were verified by evaluation of the elastic properties and shrinkage temperature of the grafts. Stress-strain measurements were evaluated to determine the number of cross-links introduced in the vascular tissue by GA. This number was shown to be proportional to the inflation pressure. Ethyl alcohol was chosen as the storage solution because it maintained the best physical, chemical, and histologic characteristics of the grafts. Biological evaluations were performed with carotid implants that were examined following acute low flow studies and implantations up to 112 days. All implantations have yielded 100% patencies.

Aldehydes↗
PubMed1985

Experience with the bipolar prosthesis in hip arthroplasty. A clinical study.

Hip arthroplasty using a bipolar prosthesis was performed in 73 patients (75 hips) with femoral neck fracture, osteoarthritis, rheumatoid arthritis, or degenerative arthritis. Bipolar hip arthroplasty is more conservative than conventional total hip arthroplasty, because methyl methacrylate usually is not needed to fix the bipolar prosthesis to bone. Overall results were 67.1% good to excellent, 20.5% fair, and 12.3% poor; among the arthritic patients, the results were 72.9% good to excellent, 19.1% fair, and 8.5% poor. Complications included one deep wound infection and one arterial embolus; no dislocations occurred.

Adult↗
PubMed1981

Use of services for the mentally retarded in the African-American community.

Mentally retarded individuals, their families, and professionals in the service delivery system in the African-American community were interviewed concerning the use of services for the mentally retarded. It was found that African-Americans underutilized available services. Reasons for this included aspects of the service delivery system and features of African-American Culture. Recommendations were made for increasing the use of services.

Black or African American↗
PubMed1980

Experimental comparison of the thrombogenicity of fibrin and PTFE flow surfaces.

Two types of 4 mm ID prostheses were studied in the carotid arteries of the dog. These were noncrimped polypropylene-supported filamentous velour knitted Dacron (PPSFV) and expanded polytetrafluoroethylene (e-PTFE, Gore-Tex). Thrombus-"Free" Surface TFS) areas and patency rates were determined at the end of the implant periods. One series of implants was subjected to controlled low flow rates for six hours; another was exposed to physiologic flow rates and observed at seven days, 14 days, and 12 weeks. At six hours the filamentous Dacron, preclotted according to a specific regimen utilizating heparin, performed as well as, and possibly better than, e-PTFE. The Gore-Tex developed surface coagulum in an irregular fashion which was related to graft wetting and blood soakage. Seven-day TFS scores and patency rates of the two graft types were comparable at physiologic flow rates. At two weeks, TFS scores and patency rates of the two graft types were comparable at physiologic flow rates. At two weeks, TFS scores and patency rates dropped. This was sufficiently marked in the case of e-PTFE that longer-term implants were not done. However, PPSFV grafts were implanted for 12 weeks, and all grafts examined at that time had closed. It appears that patency of 4 mm ID grafts of this construction will not be reliably attained in the dog carotid artery without the use of platelet-inhibitory drugs until complete healing has occurred.

Animals↗
PubMed1979

Current arterial prostheses. Experimental evaluation by implantation in the carotid and circumflex coronary arteries of the dog.

Five types of 4-mm diameter arterial prostheses (three Dacron, one expanded Teflon, one preserved umbilical vein) were studied in the dog to assess graft thrombogenicity. Separate experiments involving six hours of controlled blood flow, one-week carotid implantation, and aortocoronary implantation were performed. In general, graft thrombogenicity derived from controlled flow study was more predictive of a graft's long-term implantation success than were one-week implantation results. In order of increasing thrombogenicity, we ranked grafts studied as follows: noncrimped Dacron, expanded Teflon, crimped Dacron, umbilical vein. Results of 19 experimental left coronary artery implantations using Dacron or Teflon prostheses are reported that indicate grafts with low measured thrombogenicity are most likely to succeed in this site. Data presented in this report suggest there is reason to evaluate noncrimped, kink-resistant, porous Dacron grafts for use both in the left coronary artery and below the knee when there is compelling clinical indication and no autogenous vessels are available.

Animals↗
PubMedDate not supplied

Clinically significant gastroesophageal reflux in the at-risk premature neonate: relation to cognitive scores, days in the NICU, and total hospital charges.

OBJECTIVE: The principal objective of this retrospective, cohort study was to determine if clinically significant gastroesophageal reflux (GER) would impair the long-term cognitive and motor development of preterm infants. An additional objective was to determine the effects of clinically significant GER on the length of hospital stay and total hospital charges in preterm infants. STUDY DESIGN: The design was a retrospective, cohort study of 66 preterm infants, followed in the Neonatal Developmental Follow-Up Clinic of The Children's Hospital in Greenville, SC. Thirty-three premature infants with clinically significant GER met the following study criteria: birth dates, 1988 through 1994; lack of gastrointestinal anatomic defects; and lack of acute neurologic injury (defined as no intraventricular hemorrhage greater than Papile's grade I, no periventricular leukomalacia, no seizures, and no history of birth asphyxia). Clinically significant GER was defined as GER associated with moderate to severe apnea (n=29) or GER associated with moderate to severe feeding intolerance (n=4). The study patients were matched as closely as possible with 33 control premature infants for sex (except when twins were used), ethnicity, social risk, gestational age, birth weight, and Apgar scores at 1 and 5 minutes. Social risk was categorized using Hack's Social Risk Scale. Important covariates included apnea, home monitoring, and nasal continuous positive airway pressure. RESULTS: Neurodevelopmental test scores from 7 months of age through 2 years of age did not show any significant differences between premature infants with clinically significant GER and premature infants with no evidence of clinically significant GER. Total hospital charges were statistically different for the clinically significant GER infants and the nonclinically significant GER infants (median $112,916 versus median $63,928, p=0.01). Total neonatal intensive care unit length of stay measures were statistically different between the two groups (median 53 days versus median 40.5 days, p=0.01). CONCLUSION: Even though clinically significant GER may pose a substantial medical risk in premature infants, the long-term cognitive consequences appear to be negligible. Nevertheless, those premature infants with clinically significant GER do consume significantly more hospital resources than matched controls. Early diagnosis and intervention may possibly lessen the impact of medical costs and reduce length of hospital stay.

Cognition Disorders↗