Biomedical subjects

M Walkinshaw

Publications and source records attributed to M Walkinshaw.

11 recordsLinked to original sources

PubMed2001

Evaluation of capillary electrophoresis performance through resolution measurements.

The application of resolution measurements to an electrophoretic system can give a quantitative analysis of the health of that system. Capillary electrophoresis has become a routine method for the analysis of DNA and resolution measurements can be used to assess the resulting electropherogram. A number of methods are available to evaluate resolution and three methods are detailed in the current work. Parameters such as polymer concentration and column length were also examined in terms of resolution, and changes therein, if these parameters were modified.

DNA↗

PubMed2000

Selective boron-containing thrombin inhibitors--X-ray analysis reveals surprising binding mode.

Based on the structural comparison of the S1 pocket in different trypsin-like serine proteases, a series of Boc-D-trimethylsilylalanine-proline-boro-X pinanediol derivatives, with boro-X being different amino boronic acids, have been synthesized as inhibitors of thrombin. Among the novel compounds, a number of derivatives were synthesized which appeared to have side-chain variants too big to fit into the S1 pocket. Nevertheless, these compounds inhibited thrombin in the nM range. The X-ray structure of one of these inhibitors bound to the active side of thrombin reveals that a new binding mode is responsible for these surprising results.

Amides↗

PubMed1996

DNA profiling in two Alaskan Native populations using HLA-DQA1, PM, and D1S80 loci.

Two Native Alaskan populations were sampled and DNA profiles were generated for 201 individuals. Ninety two blood samples were collected from the North Slope Borough region of Alaska and the remaining 109 blood samples came from Native Alaskans in the Bethel and Wade Hampton areas. Allele and genotype frequencies were established for the HLA-DQA1, LDLR, GYPA, HBGG, D7S8, Gc, and D1S80 loci. Native Alaskans are slightly less polymorphic than Caucasians at the HLA-DQA1 locus. In contrast, the PM loci appear to be nearly as informative in the Native Alaskan populations as in Caucasians for identity testing. The data clearly demonstrate that all the loci tested are highly informative for the Alaskan populations and fall well within Hardy-Weinberg expectations. There is little evidence for departure from expectation of independence of alleles across loci. The data demonstrate that estimates of multiple locus profile frequencies can be obtained from Native Alaskan populations using the product rule under the assumption of independence of loci. In addition, Native Alaskan databases were more similar to each other and to other Native American databases than they were to U.S. Caucasians and African Americans.

Alaska↗

PubMed1993

Cyclosporins. Structure-activity relationships.

Cyclosporin A (Sandimmun) achieves immunosuppressive activity by complex formation with cyclophilin and subsequent binding of the binary complex to and inhibiting protein phosphatase 2B (calcineurin). Complexes of nonimmunosuppressive cyclophilin binding cyclosporin analogues do not inhibit protein phosphatase 2B, suggesting a crucial role for this enzyme in T cell activation. Binding of cyclosporin A to cyclophilins A, B, and C, respectively, results in complexes of significantly different inhibitory potency. The cyclosporin molecule thus has two functional domains, one mediating cyclophilin binding and a second one endowing affinity of the complex to calcineurin, thereby inhibiting its enzyme activity. Structure-activity studies and x-ray crystallography of cyclosporin-cyclophilin complexes indicate a crucial role of leucine side chains in positions 4 and 6 of the cyclosporin macrocycle for the calcineurin interaction.

Amino Acid Sequence↗

PubMed1992

Muscarinic activity of the thiolactone, lactam, lactol, and thiolactol analogues of pilocarpine and a hypothetical model for the binding of agonists to the m1 receptor.

Pilocarpine isosteres have been synthesized and characterized with regard to their in vitro muscarinic properties. The results indicate that the carbonyl oxygen of the lactone function of pilocarpine is of primary importance for agonist activity with the ether oxygen being of lesser or secondary importance. An X-ray structure determination for the hydrogen O,O'-ditoluoyltartrate salt of thiolactone pilocarpine isostere 2a has been performed. This compound has an unusual pharmacological profile exhibiting M1-agonist selectivity as well ass presynaptic antagonism. As a result this compound is also viewed as having therapeutic potential for Alzheimer's disease. A model for the binding of pilocarpine and other muscarinic agonists to the third transmembrane helix of the human m1 muscarinic receptor has been developed.

Animals↗

PubMed1988

Flow recovery and vasoconstriction following microvascular anastomosis.

A variety of factors may limit blood flow recovery in free flaps. In this study one of these factors, vasoconstriction, and its consequences was investigated. Blood flow recovery at the skin level following microvascular anastomosis was evaluated in the rat orthotopic groin free flap model using a laser Doppler velocimeter. In a study of 41 rats, measurements of external vessel diameter were made using a standard machinist's drum micrometer. After each flap was raised and the anastomoses performed, the field was flooded with either saline, 2% lidocaine, or 0.75% bupivacaine (Marcaine). The vascular clamps were released and measurements of flow were recorded as a percentage of the control value. In the saline-control group, it was found that flow gradually recovered to 91% of the preoperative value in an average time of 5.7 minutes. Six of 12 vessels in this group were found to have measurable spasm of the pedicle. In the lidocaine-treated group, flow recovered to 93% of the preoperative value in an average of 5.0 minutes. Two of 15 vessels had measurable spasm. In the Marcaine-treated group, flow recovered to 94% of the preoperative value in an average of 5.1 minutes. Three of 14 vessels showed measurable spasm. The final level of flow recovery showed no statistical difference in any of these groups whether or not spasm was present. We therefore conclude that, in this model, alteration in the diameter of the vascular pedicle as a consequence of performing a microvascular anastomosis affects only the time it takes to achieve ultimate recovery of flow but does not affect its final level.

Anastomosis, Surgical↗

PubMed1988

Ischemic injury to enteric free flaps: an experimental study in the dog.

Enteric free flaps have proven to be useful for reconstructing the cervical esophagus. Although jejunum is favored, the rationale for this is not at all clear. We have postulated that resistance to warm ischemia varies in different regions of the gut. An experiment was carried out in 10 mongrel dogs in which 10-cm segments of proximal, middle, and distal small bowel were isolated on single vascular pedicles. In each portion of the gut there were three segments: a control, a segment subjected to 60 minutes of warm ischemia, and a segment subjected to 120 minutes of warm ischemia. The following day each animal was reexplored, and the viability of bowel segments was assessed visually and with fluorescein. All control segments were viable at 24 hours. Twenty segments were subjected to 1 hour of warm ischemia, and all but two were viable. Nineteen gut segments were subjected to 2 hours of warm ischemia. Seven of eight proximal segments were viable, two of five midsegments were viable, and zero of six distal segments were viable. Survival in the distal portion compared to the proximal portion was significantly less (p less than 0.01). It appears from this study that isolated distal small bowel segments are less resistant to warm ischemia than proximal segments.

Adult↗

PubMed1987

Clinical evaluation of laser Doppler blood flow measurements in free flaps.

Adequate assessment of blood flow in free flaps with early detection of circulatory failure is an unresolved clinical problem. In 23 patients undergoing microvascular free tissue transfers, laser doppler blood flow measurements and clinical observations were made hourly for the first two postoperative days. There was 1 flap failure in 6 instances in which it was clinically necessary to intervene, by reexploration or draining a hematoma, to ensure the survival of the flap. It was hypothesized that the laser doppler measurements would predict future clinical events. However, it was found that although these measurements did correlate with clinical observations, they did not predict them and were actually less accurate in indicating the need for clinical intervention or the final outcome of the free flap procedure.

Adult↗

PubMed1985

The early use of free flaps in burns.

Fourth degree burns of the extremities, that is, burn wounds that go down to denuded bone or tendon, frequently necessitate either amputation of the involved limb or multistage reconstructive procedures involving prolonged hospitalization so that the limb may be salvaged. It is our belief that in these patients free flaps should be considered as a means of initial wound closure. Microvascular procedures under these circumstances may well represent the most expeditious means of salvaging an extremity even when more conventional techniques are available. Studies of a series of patients illustrating this point are presented.

Adult↗

PubMed1983

Vascularized omentum for facial contour restoration.

Our experience with the omental flap for facial soft-tissue augmentation in 7 patients is presented, along with our method of fixation of the graft to prevent gravitational descent. The history of the omental free flap, as well as the previously applied techniques for facial soft-tissue augmentation, is reviewed. It is our conclusion that the omental free flap is a safe, reliable technique. It can be readily molded to exactly conform to the patient's deformity and produces good results both in repose and during facial expression. We believe that gravitational descent of the graft can be prevented by the technique of multiple-suture fixation.

Adolescent↗

PubMed1980

Use of volume loading to obtain preferred levels of PEEP. A preliminary study.

Hemodynamic and oxygen transport measurements were made with successive increments of positive end-expiratory pressure (PEEP) in 14 episodes of ARDS in 11 patients who had normal or slightly increased blood volumes. "Preferred" or optimal PEEP was defined as the PEEP value associated with the greatest VO2 that did not compromise pulmonary function as determined by shunting (Qs/Qt). The preferred PEEP averaged 10.7 +/- 2.7 (SD) cm H2O in the patients who had appreciable reduction in cardiac index (CI) by the time this level of PEEP was reached. In 6 patients, the CI fell approximately 15%; then albumin, 25 g, was given. This restored CI, improved oxygen transport, and permitted us to give additional 10-15 cm H2O of PEEP, i.e., until 20--25 cm H2O was reached; this was achieved without hemodynamic impairment. The final preferred PEEP in these patients averaged 14.1 +/- 3.6 (SD) cm H2O. The authors conclude that the titration of PEEP as well as fluid therapy may be used to maximize VO2 in patients with early shock lung.

Adult↗