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Biomedical subjects

D Simons

Publications and source records attributed to D Simons.

33 records · Page 2Linked to original sources
PubMed1994

Can total thyroidectomy be performed as safely by general surgeons in provincial centers as by surgeons in specialized endocrine surgical units? Making the case for surgical training.

OBJECTIVE: To determine whether surgeons who had received appropriate training in the technique of total thyroidectomy could continue to perform the procedure with minimal morbidity after moving to a provincial surgical practice. DESIGN: Comparison of the complication rates from total thyroidectomy between a specialized endocrine surgical unit and provincial centers. SETTING AND PATIENTS: Six hundred fifty patients undergoing total thyroidectomy by two surgeons over a 5-year period in the endocrine surgical unit at Royal North Shore Hospital, St Leonards, Australia, were compared with 120 patients undergoing total thyroidectomy by seven provincial surgeons who were former trainees in the unit. MAIN OUTCOME MEASURES: Indications for surgery and specific complications of thyroidectomy including recurrent laryngeal nerve palsy, permanent hypoparathyroidism, and postoperative bleeding. RESULTS: Each of the seven surgeons in provincial practice performed only between two and 16 thyroidectomies annually. The percentage of total thyroidectomies for benign and malignant disease was identical for both the endocrine surgical unit and provincial center groups (44%). There was no difference in the incidence of recurrent laryngeal nerve palsy, permanent hypoparathyroidism, or postoperative bleeding between the two groups. CONCLUSION: Total thyroidectomy is an operation that always engenders controversy relating to the morbidity of recurrent laryngeal nerve and parathyroid injury. Surgeons who have completed a well-designed training program and who have become proficient at total thyroidectomy as trainees will remain proficient at the procedure despite practicing in a provincial center. Achieving a low morbidity rate demands meticulous attention to operative technique and anatomical detail.

Clinical Competence↗
PubMed1994

Occurrence of domoic acid in Washington state razor clams (Siliqua patula) during 1991-1993.

The presence of domoic acid in aquatic species was reported for the first time in the United States in the late summer of 1991 in Monterey Bay, California. By October of 1991, domoic acid was found in razor clams (Siliqua patula) and in the viscera of Dungeness crab (Cancer magister) along the coasts of Washington and Oregon. In response to this outbreak, the National Marine Fisheries Service, in cooperation with the Washington State Department of Fisheries began analysis of Washington State razor clams for the period from November 1991 to June 1993. This survey indicated that domoic acid levels in the edible portion of the razor clams peaked in December of 1991 (average of all Washington state coastal sites: 106 ppm) and followed a slow decline to the present day low levels (< 5 ppm). Sixteen months after the maximum level, domoic acid has not completely disappeared from the razor clams from the Washington State beaches. Unlike mussels (Mytilus edulis), where the toxin is found only in the viscera, domoic acid distributes itself throughout the various body parts of the razor clam. The highest concentration occurs in the foot or "digger" and the lowest in the siphon or "neck." The concentration of domoic acid in the razor clam foot reached a high of 230 ppm.

Animals↗
PubMed1993

Effects of nimodipine on two neurologic measures sensitive to sensorimotor cortex damage.

Seventeen rats with lesions involving the sensorimotor forepaw and hindpaw regions were tested for the ability to run along a narrow bridge without slipping and to hold on to a small-diameter dowel suspended above the ground. Nine of the animals received the calcium channel blocker, nimodipine, once per day for the first 2 weeks after surgery, while the remaining eight rats received vehicle alone. Repeated measurements over the first 3 postoperative weeks showed deficits among the rats with lesions on both tasks. The animals treated with nimodipine, however, showed much better recovery, especially after the initial testing sessions.

Analysis of Variance↗
PubMed1989

Chordal geometry determines the shape and extent of systolic anterior mitral motion: in vitro studies.

In patients with hypertrophic cardiomyopathy, the mitral valve moves anteriorly and assumes a unique shape, with mitral-septal contact centrally and preserved valve orifice area laterally. This shape is not clearly predicted by the Venturi mechanism, which stresses flow above the valve as opposed to changes intrinsic to the valve. On the other hand, it has been suggested that displacement of the papillary muscles anteriorly and toward one another, as observed in this disease, can promote anterior mitral valve motion and produce this unusual shape. The purpose of this in vitro study was to test the hypotheses that anterior motion of a membrane in a flow field can be generated by altering the distribution or effectiveness of chordal tension tethering the membrane, and that the shape achieved by this membrane depends on the geometry of chordal tension. Accordingly, a horizontal leaflet mounted in a flow chamber was attached by chords at its distal end to a series of upstream screws. Chordal tension could be varied by turning the screws or redirected by shifting the screws anteriorly. Anterior leaflet motion having the same unusual configuration seen in patients was reproduced by decreasing central chordal restraint while tension on the leaflet edges was maintained. Directing chordal tension anteriorly caused greater degrees of anterior motion at earlier stages in the release of chordal restraint; increased flow rate had a similar but less marked effect. These studies suggest that primary geometric alterations in the papillary-mitral apparatus can play an important role in determining the presence and geometry of systolic anterior mitral motion. The nature of these alterations suggests a role for anterior and inward papillary muscle displacement in promoting such motion. The geometric factors embodied in this model can explain many observed features of this motion not adequately explained by the Venturi effect, such as early systolic onset and the importance of a distal residual leaflet. Finally, flow visualization studies emphasize the importance in this process of drag forces caused by interposing the leaflet into the flow stream, and of geometric factors that enhance such forces.

Cardiomyopathy, Hypertrophic↗
PubMed1986

Cognitive processes in Cebus monkeys (Cebus apella) when solving problem-box tasks.

Although monkeys are capable of solving problem-box tasks, they were said to perform without 'understanding the value of unlocking' and to use 'kinesthetic control' only [Kohts, 1928]. However, the cognitive processes are much more complex--at least in Cebus monkeys: the problem-solving process was conducted according to the position of the catch in relation to the edge of the door, i.e. our monkey learnt to use visual control. The main characteristics of the monkey's behavior were similar to those exhibited by children. Problem-box tasks proved to be a suitable method for the comparative analysis of cognitive processes in primates.

Animals↗
PubMed1979

Below-knee orthosis: a wrap-around design for ankle-foot control.

Control of foot and ankle positions with orthotic appliances is generally more difficult to accomplish in children with spastic than flaccid paralytic disorders. Our new design for a custom molded plastic ankle-foot orthosis has proven superior to other designs in most applications. The appliance is vacuum molded from very thin polypropylene plastic and innerfaced with a foam material (Aliplast). The limb is enclosed completely in plastic with an anterior opening secured by several Velcro straps. Although the material is soft and pliable, the circumferential support provides remarkably rigid control of the limb. The orthosis has been successfully applied to children with polio, meningomyelocele and all forms of spastic and athetoid cerebral palsy. In addition to superior limb control, another advantage appears to be reflex inhibition of abnormal motor tone in may spastic patients. Patients have preferred this orthosis to those previously worn probably due to greater comfort. The limitation of adjustability of dorsiflexion can be compensated by heel or sole shoe lifts. Excessive heat created by the "wrap-around" design can be reduced by a thin cotton sock extended above the orthosis.

Adult↗
PubMed1976

Effects of serial lesions of somatosensory cortex and further neodecortication on retention of a rough-smooth discrimination in rats.

Five groups of rats with bilateral lesions of the somatosensory cortex and one of animals sustained only sham operations were tested for retention of a rough-smooth discrimination. Two of the lesion groups had sequential unilateral ablations, in one case with interoperative testing, and three groups had one-stage bilateral lesions. The two groups of animals with serial lesions did not differ from each other or from sham operates in relearning the task. RAts with one-stage lesions and preoperative overtraining also performed well, but the other one-stage groups showed deficits relative to control and serial lesion groups. In the second experiment the sham operated rats from Experiment 1 experiences lesions anterior and posterior to the somatosensory zones. These lesions did not affect retention. Somatosensory cortex then was ablated in one operation and severe performance decrements were seen. Removal of additional neocortex in a sample of animals that had relearned the discrimination after one-stage somatosensory cortex lesions (Exp. 1) also affected retention. In contrast, retention was not impaired on some of the measures in those animals that originally had two-stage ablations. The findings from these two experiments show that some ablation effects can be circumvented with overtraining or serial lesion techniques. The data also indicate that non-somatosensory cortex may play a role in recovery after somatic cortex lesions, but that the substrates underlying recovery might not be the same after one-stage and two-stage ablations.

Animals↗
PubMed1976

["Counting" experiments with ravens using "matching-from-sample" methods. A contribution on problem-solving behavior in higher aniMALS].

The research goal is divided into two parts: 1. Detailed analysis of behavior in selection in a 6-choice matching-from-sample task. 2. Discussion of all observed preferences on the basis of the models of Sutherland and Mackintosh and of Miller, Galanter and Pribram. The experiments were run with 4 one-year-old ravens (Corvus corax); two of them were probably 2 males. The design is similar to Koehler's. In the task the correct responses were equally distributed between all stimuli and positions (random system). Although the task ("counting") was learned, a lot of relevant preferences for stimuli, positions, patterns etc. show that problem-solving in higher animals can be very complex. It could be shown that only a detailed analysis may clarify animal learning processes.

Animals↗
PubMed1975

Effects of serial lesions of somatosensory cortex and further neodecortication on tactile retention in rats.

Four groups of rats with bilateral lesions of somatosensory cortex and one of animals sustaining only sham operations were tested for retention of a difficult tactile discrimination. Two of the lesion groups had serial ablations, in one case with interoperative testing, and two had one-stage lesions. Bilateral ablations of somatosensory cortex severely retarded retention in all lesion groups relative to the control group and serial and one-stage groups did not differ from each other. The sham operated rats then experienced lesions of cortex anterior and posterior to the somatosensory areas. These lesions only marginally affected retention. Somatosensory cortex then was ablated and severe performance decrements were seen. Removal of additional neocortex in animals that previously had relearned the discrimination after somatosensory cortex lesions also resulted in very poor retention. These data demonstrate the importance of the somatosensory cortex in mediating tactile discriminations and suggest that non-somatosensory cortex may play a role in recovery after somatosensory cortical lesions.

Animals↗