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Biomedical subjects

R A Schmidt

Publications and source records attributed to R A Schmidt.

At least 145 records · Page 8Linked to original sources

Mammography as a radiographic examination: an overview.

The mammographic examination can be considered from many different perspectives, not the least of which include the complex diagnostic or public health issues that determine the place of this study in modern medical practice. There is, however, no finer example than mammography of the role of radiological science in radiography. It is important that radiologists remain ever cognizant of this role in order to maximize the benefit of the examination to their patients.

Breast Neoplasms↗

Granular cell tumor of the breast mimicking carcinoma in pregnancy.

A granular cell tumor of the breast in a 20-year-old black pregnant woman is reported. Malignancy had been suspected clinically, radiologically, and on gross pathologic examination. Frozen section provided the correct diagnosis and the lesion was excised, obviating more radical surgery.

Adult↗

Rapid movements with reversals in direction. I. The control of movement time.

Modifications to the underlying motor control of rapid reversal movements (flexion-extension of the elbow) to accommodate experimentally induced changes in the movement time (MT) with constant movement amplitude were examined in man. MT was altered between conditions via instructions and feedback, resulting in seven distinct MT levels (from 100 to 250 ms to the reversal point) with essentially constant movement amplitude. As MT was decreased, the large increases in acceleration were met by two changes in motor control: (a) two- to three-fold increases in the peak accelerations and peak amplitudes of the agonist and antagonist EMGs, and (b) a systematic "compression" of the temporal structure of the entire acceleration-time and EMG-time patterns. This temporal "compression" with increased velocity caused by shifts in MT (distance constant) are considerably different from the constant-duration EMG bursts found when velocity is altered by changing movement distance (where MT is nearly constant). Our findings indicate that MT is a determiner of the temporal structure of rapid actions, and suggest that MT should be regarded as an important controlled variable, and not simply as an emergent property of variations in velocity.

Acceleration↗

Rapid movements with reversals in direction. II. Control of movement amplitude and inertial load.

Transformations of the underlying movement control of rapid sequential (reversal) responses were examined as the movement amplitude (Experiment 1) and moment of inertia (Experiment 2) were altered, with constant movement time. Increases in amplitude and inertia were both met by sharply increased joint torques with a constant temporal structure, suggesting that the alterations may have been governed by a single gain parameter. The durations of various EMG bursts were essentially constant across changes in inertia, supporting a model in which the output of a fixed temporal representation is amplified to alter joint torques. The EMG amplitudes increased greatly with both amplitude and load. However, the fact that the EMG durations increased systematically with increases in distance provided difficulties for this model of amplitude control. The data suggest an economy in motor control in simple agravitational movements, whereby relatively simple transformations of an underlying representation can accommodate large changes in movement amplitude and moment of inertia.

Acceleration↗

Clinical significance of sacral and pudendal nerve anatomy.

The neuroanatomy and neurophysiology of the external urethral closure mechanisms still are under debate because the motor fibers that emanate from the sacral plexus and pudendal nerve to supply this segment have not been traced, nor has their functional interrelationship been established. Therefore, we dissected 3 male human cadavers (aged 31 to 69 years) by tracing the entire sacral plexus, particularly the pudendal nerve, from the cauda equina throughout the branching of the nerves to their final destination. The dissection demonstrated that the extrinsic urethral sphincter, formed by the rhabdosphincter around the membranous urethra as well as the levator ani muscle and pelvic floor (especially the transversus perinei muscle), is innervated by somatic nerve fibers that emanate primarily from sacral roots S2 and S3. In 5 patients with neurogenic lower urinary tract dysfunction electrostimulation of the sacral root and pudendal nerve markedly increased intraurethral closure pressures. Stimulation of the pudendal nerve or its transversus perinei branch alone resulted in an increase in intraurethral closure pressure to 60 to 70 cm. water--an increase similar to that produced by stimulation of the sacral root without neurotomy. By means of neurotomy and/or neural blockade with lidocaine we were able to differentiate between the contributions of each muscular element to the external sphincteric mechanism. Almost 70 per cent of the closure pressure of the external urethral sphincter is induced by stimulation of the S3 ventral root, while the other 30 per cent derives from S2 and S4 neuronal impulses.

Adult↗

The force/force-variability relationship under controlled temporal conditions.

Previously, an inverted U relationship between force and force variability was demonstrated in both static and dynamic responses. Recent research suggests that the inverted U function may be due to a lack of control of the temporal aspects of the response. To investigate this hypothesis, we examined the relationship between force and force variability in rapid movements under controlled temporal conditions. Subjects (N = 4) made rapid reversal responses with a horizontal lever (using elbow flexion and extension) such that the time to reversal (160 ms) and the distance to reversal (45 degrees ) were held constant in each of six load conditions (either 0,.260,.780, 1.040, or 1.560 kg added to the lever). When time to reversal and time to peak acceleration were held constant, a curvilinear relationship between force and force variability resulted, suggesting that the inverted U function is related to control of the temporal aspects of the response.

Journal Article↗

Variability in practice: facilitation in retention and transfer through schema formation or context effects?

The main purpose of the study was to examine whether the effects of variability in practice within a class of movements, that is, enhanced retention and transfer performance relative to constant practice, are due to the formation of motor schemata (Schmidt, 1975) or to contextual interference effects, as suggested by Lee, Magill, and Weeks (1985). Forty-eight subjects were tested on a sequential timing task. One group of subjects (Schema) received variable practice within one movement class, practicing the same phasing pattern with different absolute durations. Practice conditions of another group (Context) involved the same absolute movement durations, as well as a different phasing pattern for each task version. Thus, contextual interference was about the same for both groups but only one group experienced different movement variations of the same class. On a retention test performed on a task version that had been practiced by both groups before as well as on a transfer test with the same phasing pattern but a longer absolute duration, the Schema group performed more effectively than the Context group, thus supporting schema theory. On a transfer task with new phasing requirements, however, the Context group demonstrated performance superior to that of the Schema group. In this case, the Context practice condition seemed to be more transfer-appropriate.

Journal Article↗

Computer-aided detection of microcalcifications in mammograms. Methodology and preliminary clinical study.

The authors investigated the feasibility of using computer methods for automated detection of clustered microcalcifications on clinical mammograms. A new difference-image approach using a matched filter/box-rim filter combination effectively removed the structured background from the image. A locally adaptive gray-level thresholding technique was then used for extraction of the signals from the resulting difference image. Signal-extraction criteria based on the size, contrast, number, and clustering properties of microcalcifications were next imposed on the detected signals to distinguish true signals from noise or artifacts. The detection accuracy of the computer scheme was evaluated by means of a free response receiver operating characteristic (FROC) analysis. It was found that, for simulated subtle microcalcifications superimposed on normal mammograms, the difference-image approach with a matched filter/box-rim filter combination could yield a true-positive cluster detection rate of 80% at a false-positive detection rate of one cluster per image. In a study of 20 clinical images containing moderately subtle microcalcifications, the automated computer scheme obtained an 82% true-positive cluster detection rate at a false-positive detection rate of one cluster per image. These results indicate that the automated method has the potential to aid radiologists in screening mammograms for clustered microcalcifications.

Breast Diseases↗

Diagnosis of rhabdomyosarcomas with HHF35, a monoclonal antibody directed against muscle actins.

The authors have recently developed a monoclonal antibody, HHF35, that recognizes the muscle-specific isoforms of actin. To determine its potential usefulness in the differential diagnosis of "small, round, blue cell" tumors of childhood, they immunolabeled formalinor B-5-fixed tissue sections from known cases of rhabdomyosarcoma or rhabdomyoma (30), neuroblastoma (9), retinoblastoma (2), and Ewing's sarcoma (9) with HHF35 and with antibodies to creatine kinase M, myoglobin, vimentin, and neuron-specific enolase. HHF35 reacted with 29 of 30 cases of rhabdomyosarcoma, whereas antibodies to creatine kinase M and myoglobin were positive on only 12 and 7 tumors, respectively. HHF35 did not react with any case of neuroblastoma, retinoblastoma, or Ewing's sarcoma when the antibody diluent contained 50 mM EDTA. These results indicate that HHF35 is a highly sensitive and specific marker for myogenic differentiation and that it will be useful in the differential diagnosis of rhabdomyosarcomas.

Actins↗

Neuromuscular dysfunction in nonbacterial prostatitis.

Although chronic nonbacterial prostatitis is common, the condition remains poorly understood and refractory to treatment. Another approach, i.e., a urodynamic explanation, seems warranted. The underlying cause of the symptoms may be an inappropriate spasm of of the distal urethra/external sphincteric unit, leading to increased pressure in the prostatic urethra with a resultant reflux of urine into the prostatic ducts. The presence of urine (sterile or infected) could induce ductal and periductal inflammation, which could further aggravate spasm of the involved pelvic musculature, exacerbating the voiding dysfunction. We present 3 patients in whom this sequence of events was documented radiographically and urodynamically. Consequently, treatment involved modulation of the dysfunction of the distal urethra/external sphincteric unit: (1) reeducation by reassurance and biofeedback was the initial line of therapy; (2) pharmacologic manipulation using alpha-blockers (to affect smooth and striated muscle irritability) and striated muscle relaxants was next tried; (3) finally, in unremitting symptoms, we used selective sacral-root electro-stimulation, successfully fatiguing the involved muscles and relieving the voiding dysfunction.

Adult↗

Neuroanatomy and clinical significance of the external urethral sphincter.

Although the topographic muscular architecture of the pelvic floor is essentially understood, its nerve supply and functional anatomy remain controversial. We therefore dissected 3 male human cadavers by tracing the entire sacral plexus and the pudendal nerve from the cada equina down to their final destination. Our anatomic dissection demonstrated that the voluntary external urethral sphincter mechanism is augmented by two separate muscular components: the levator ani and the transversus perinei muscle. Urodynamic findings with sacral neurostimulation support our anatomic description.

Adult↗

Polyglycolic acid mesh in repair of renal injury.

To evaluate the use of a polyglycolic acid (PGA) mesh graft for partial nephrectomy, we replaced the upper pole of the left kidney in 12 New Zealand white rabbits with a free omental fat graft and the lower pole with PGA mesh. The mesh stopped the bleeding immediately during the operation. At forty-eight hours, the fibers were still intact, with an organized clot on the surface of the mesh. Between two weeks and two months, the fibers had begun to be digested by histiocytes, with formation of giant cells and fibroblastic proliferation with collagen deposition around the mesh. At three months, there was complete resorption of the PGA mesh and formation of a new fibrous capsule. There was no renal reaction and no difference between the PGA mesh and the omental fat graft. We believe that PGA mesh can be helpful in repairing injured kidneys by securing hemostasis and serving as a scaffold for the formation of a new capsule.

Animals↗

Functional evaluation of penile veins by cavernosography in papaverine-induced erection.

Of 49 patients in whom cavernosography was performed after papaverine-induced erection 38 had abnormal venous leakage to various drainage systems (corpus spongiosum, cavernous vein or superficial and deep dorsal veins). Because the effect of papaverine on penile arteries, sinusoids and veins is similar to that caused by electrostimulation, we believe that this technique is better than other reported means of evaluating the functional status of the penile veins. However, we recommend that only patients with a normal arterial response but poor erection after papaverine injection be considered candidates for erection cavernosography, since they most likely will benefit.

Adult↗

Kinematics properties of rapid aimed hand movements.

Generalized motor program theory and the models of Schmidt, Zelaznik, and Frank (1978), and Meyer, Smith, and Wright (1982) of speed-accuracy relationships in aimed hand movements require that the underlying acceleration-time patterns exhibit time rescalability, in which all acceleration-time functions in an aimed hand movement are generated from one rescalable pattern. We examined this property as a function of movement time in Experiment 1, and as a function of movement time and movement distance in Experiment 2. Both experiments failed to demonstrate strict time rescalability in acceleration-time patterns, with the time to peak positive acceleration being invariant across movement time. This suggests that time rescalability is not a necessary condition for the linear relation between speed and spatial variability. A second major finding was that the variability in distance traveled at the end of positive acceleration was independent of movement time, contrary to the symmetric-impulse-variability model of Meyer et al. (1982). The findings of both experiments suggest that the processes involved in decelerating the limb play an important, but yet to be understood, role in determining the linear speed-accuracy trade-off. Finally, these results suggest that generalized motor programs are not based on simple, time-rescalable acceleration patterns.

Journal Article↗

Functional pattern of sacral root stimulation: III. Erection.

The mechanism of canine penile erection was studied in 6 'chronic' and 15 'acute' male dogs by means of sacral root stimulation combined with pharmacologic studies. The basic mechanism of erection cannot be explained by a pure increase in arterial perfusion of the cavernous spaces due to neural vasomotor regulation. The vasomotor mechanism, whether pure arteriolar vasodilation, or venous drainage impairment, or secondary to as yet undefined behavior of the corporal smooth muscle, can be activated by stimulation of the parasympathetic outflow. Those preganglionic fibers may synapse to noncholinergic and non-beta-adrenergic neurons, which release a yet unidentified vasodilator neurotransmitter mediating the neurovascular effect.

Animals↗