PubMed Health⌕ Search

Biomedical subjects

B Waldman

Publications and source records attributed to B Waldman.

13 recordsLinked to original sources
PubMed2006

Polymorphism, natural selection, and structural modeling of class Ia MHC in the African clawed frog (Xenopus laevis).

In the African clawed frog (Xenopus laevis), two deeply divergent allelic lineages of multiple genes of the class I MHC region have been discovered. For the MHC class I UAA locus, functional differences and the molecular basis for lineages maintenance are unknown. Alleles of linked class I region genes also exhibit strong disequilibrium with specific MHC alleles, but the underlying cause is not clear. We use MHC class Ia sequence data to estimate substitution rates and investigate structural differences between allelic lineages from protein models. Results indicate the operation of natural selection, and differences in the steric properties in the F pocket of the peptide-binding region among lineages. Variability in this pocket likely enables allelic lineages to bind very different sets of peptides and to interact differently with MHC chaperones in the endoplasmic reticulum. These results constitute evidence of the molecular evolutionary basis for 1) the maintenance of allelic lineages, 2) functional differences among lineages, and 3) strong linkage disequilibrium of allelic variants of class I region genes in X. laevis.

Amino Acid Sequence↗
PubMed2000

Characteristics and natural history of transient postoperative pseudosubluxation after total hip arthroplasty.

A series of 13 total hip arthroplasties (THAs) in which immediate postoperative radiographs revealed axial subluxation were reviewed, and the timing, incidence, and subsequent natural history of this phenomenon were determined. Each patient had received perioperative epidural anesthesia and was placed in an abduction splint before transfer to the postoperative care unit. All initial radiographs were taken while the patient was still under the effect of the epidural anesthetic agent (average, 54 minutes; range, 37-80 minutes) postoperatively. In each case, radiographs taken after anesthetic recovery and without limb manipulation revealed reduced components. The balance of the postoperative care and rehabilitation was uncomplicated; patients were followed at least 36 months postoperatively, and in only 1 patient did a subsequent hip dislocation occur. Over a 6-month period, the postoperative films of all THAs were studied, and postoperative subluxation was identified in about 3% of the cases. Postoperative subluxation is likely to be noted when the radiograph is obtained within 1 hour of transfer to the postoperative care unit. It does not appear to have a dramatic effect on the rate of postoperative dislocation, however. This radiographic finding probably is due to the continued effects of regional anesthesia, and reduction occurs as muscle tone returns. If transient subluxation is identified, no change in postoperative care is necessary.

Adult↗
PubMed1997

Multiple irrigation, debridement, and retention of components in infected total knee arthroplasty.

The results of 24 infected total knee arthroplasties (22 patients) that were treated by irrigation, debridement, and retention of the prosthetic components were prospectively studied. Strict criteria were used for the selection of this method of treatment. Patients had to be less than 30 days after index arthroplasty (postsurgical group) or had to have less than 30 days of knee symptoms (hematogenous group). In addition, there had to be no radiographic signs of osteitis or evidence of a loose prosthetic component. Patients had one to three irrigation and debridement procedures depending on systemic signs, knee symptoms, or the results of knee aspirations. All of the immediate postsurgical infections (10 knees) and 10 of the 14 (71%) late hematogenously infected knees retained the prosthesis without further evidence of infection at the final follow-up visit at 48 months (range, 24-140 months). This study shows that in selected circumstances, irrigation, debridement, and retention of the components can result in low morbidity with high success rates.

Aged↗
PubMed1997

Ankle fractures. The Lauge-Hansen classification revisited.

Rational treatment of ankle fractures requires knowledge of the extent of bone and soft tissue injury. Although the Lauge-Hansen classification attempts to do this by relating specific fracture patterns to injury mechanism, the experimental underpinning for this classification has not been reexamined rigorously using modern experimental methods. This study examines the hypothesis that the clinically occurring supination and external rotation injury pattern does not result from the mechanism described by Lauge-Hansen. Thirty-two anatomic specimen ankles were mounted on an MTS machine for combined axial loading with external rotation to failure testing. A foot plate supinated the foot 25 degrees. Testing was performed with the ankle at neutral, 25 degrees plantar flexed, 10 degrees to 15 degrees dorsiflexed, and in 6 degrees to 8 degrees leg valgus. Pure supination and external rotation with the ankle in neutral did not result in the Lauge-Hansen supination and external rotation type fractures. This outcome was not altered if the ankle specimens initially were placed in plantar flexion or dorsiflexion. The addition of a valgus load, which pushes the talus laterally against the fibula, resulted in the classic Lauge-Hansen supination and external rotation type fracture. All specimens had an isolated lateral injury or a lateral injury that preceded medial injury.

Aged↗
PubMed1996

An axially loaded model of the ankle after pronation external rotation injury.

Using a testing apparatus that allows axial loading and displacement in the sagittal, axial, and coronal planes, 6 ankles were tested under experimental conditions intended to model the Lauge-Hansen pronation external rotation injury. All specimens were rotated through a continuous range of sagittal motion with the ankle under 300 N of axial load as the coupled motion of the ankle in the coronal and axial axes was recorded. Combinations of fibular osteotomy, disruption of the syndesmosis up to 6 cm above the plafond, and deltoid transection were tested to mimic Stages I to III of the pronation external rotation ankle fracture. The effects of stabilization of the fibula and syndesmosis also were examined. Neither fracture of the fibula 4 cm above the plafond nor disruption of the syndesmosis to 6.0 cm resulted in a significant change in coupled motion of the talus. When the superficial deltoid was sectioned, the ankle had increased external rotation in plantar flexion. When the deep deltoid was sectioned, the ankle dislocated in plantar flexion unless the fibula was stabilized. This prevented dislocation but failed to restore normal talar kinematics. This study found no biomechanical support for placement of a syndesmotic screw unless the medial side cannot be stabilized anatomically.

Adult↗
PubMed1992

Embryonic olfactory learning in frogs.

We examined the effect of embryonic olfactory experiences on behaviour after hatching in two species of anuran amphibians, Rana temporaria and Rana sylvatica. Odorants (orange and citral) injected into the egg were "learned" by the embryo and subsequently preferred by tadpoles after hatching. The observed preferences were specific to the odours experienced prior to hatching, and tadpoles discriminated between the odour experienced as embryos and a novel odour. The acquired preference was maintained after metamorphosis for those individuals that exhibited a preference as tadpoles. Preferences of tadpoles were also influenced "naturally" by odours present in the water surrounding the developing embryos. The experimentally induced olfactory preferences did not appear to influence the exhibition of sibling recognition abilities. The study represents the first demonstration of "embryonic" learning in amphibians, and the functions and importance of early olfactory learning for amphibians are discussed.

Animals↗
PubMed1992

A review of sutures and suturing techniques.

The ideal suture is strong, handles easily, and forms secure knots. It causes minimal tissue inflammation and does not promote infection. It stretches and accommodates wound edema. Although no single suture possesses all of these features, proper selection of sutures helps achieve better results in skin surgery. Proper suturing technique is essential for obtaining good cosmetic results and avoiding scarring and poor wound healing. Techniques that must be mastered include good eversion of skin edges, avoiding suture marks, maintaining uniform tensile strength along the skin edges, and precise approximation along skin edges.

Humans↗
PubMed1977

Economic and racial disadvantage as reflected in traditional medical school selection factors.

Medical College Admission Test scores and undergraduate grade-point averages show that both lower income applicants in general and minority applicants in particular are at a competitive disadvantage in gaining admission to medical school. This study examines the extent to which income and race, viewed independently of one another, affect these selection factors. By analyzing data collected by the Association of American Medical Colleges on applicants to the 1976-77 entering class, factors associated with race were found to have a far more significant influence on applicants' credentials than factors associated with lower family income. An admissions policy based exclusively on GPAs and/or MCAT scores would proportionately exclude minority applicants from medical education but would have no similar effect on lower income white applicants.

Black or African American↗