Biomedical subjects
Publications and source records attributed to R A Schmidt.
The author reviews experience with genitourinary stimulation. Neurostimulation is of most benefit in spastic patients. Experience with sacral root stimulation is discussed. Complete bladder evacuation can be achieved with a combination of selectively placed neurectomies and strategically positioned electrodes.
We describe the microvascular repair of a traumatically lacerated penis (the fifth such case in the literature) and outline a uniform plan of management with which one can expect restoration of function and an adequate cosmetic appearance. Microvascular repair represents the most physiological method of reconstruction, with a lower incidence of urethral stricture disease, skin loss and sensory impairment.
Electrostimulation was used to study the neuroanatomy and physiology of penile erection in dogs and monkeys. The canine spinal nuclei responsible for penile erection, identified by the retrograde horseradish peroxidase transport technique after verification of the cavernous nerves with neurostimulation, were mediolateral autonomic neurons at T12-L3 and S1-S3. The erection induced by electrostimulation of the cavernous nerves is the result of increased arterial flow, relaxation of cavernous muscles, and venous outflow restriction. Study of electrostimulation in dogs and monkeys is invaluable for the understanding of the complex neurophysiology of human penile erection.
The term urethral syndrome reflects irritation in the external urethral (striated) sphincter. The cause of this condition may be as much poor voiding habits as it is infection or trauma. Treatment principles therefore involve retraining the voiding mechanism, as well as the judicious use of antibiotics, skeletal muscle relaxants, and an alpha-blocker. Neurostimulation has been used successfully to relieve symptoms in occasional refractory cases.
Previous studies have identified several cellular requirements for mevalonic acid that appear unrelated to cholesterol, dolichol, or ubiquinone. To search for other products of mevalonic acid that might account for these requirements we cultured Swiss 3T3 cells in the presence of mevinolin, an inhibitor of mevalonic acid biosynthesis, then labeled the cells with exogenous radioactive mevalonic acid. Upon analyzing the radioactive material formed, we found that 40-50% of it was not extractable into lipid solvents, and that most of the lipid-insoluble material behaved like protein when treated with sodium dodecyl sulfate:chloroform:phenol, RNase, or proteinase K. Further analysis by electrophoresis revealed that radioactivity was associated with a few specific proteins that had apparent molecular weights of 13,000-58,000. Control experiments indicated that authentic radioactive (R)-mevalonic acid was the active precursor. Other lines of evidence suggested that mevalonate was first converted to an isoprenoid compound, then covalently incorporated into proteins by way of a cycloheximide-insensitive mechanism. These results suggest that Swiss 3T3 cells possess novel metabolic products of mevalonic acid metabolism that are formed by post-translational incorporation of isoprenoids into specific cell proteins.
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Being able to induce erection by electrical stimulation of the cavernous nerves, we studied the hemodynamics of canine penile erection. Simultaneous recording of flow and pressure of the internal pudendal artery as well as pressure within the corpus cavernosum clearly demonstrated that increase of arterial flow preceded corporeal pressure increase. When saline was infused directly into the corpus cavernosum, with the aorta clamped, decreasing venous flow during erection could be demonstrated. Tumescence of the corpus cavernosum was found to be a result of active relaxation of sinusoidal spaces, active arteriolar dilatation, and active venous constriction. At full erection, there was still flow into and out of the corpus cavernosum, although it was reduced to only a fraction of a milliliter per minute.
The neuroanatomy of erection in men is not well defined. Recently, we isolated successfully the cavernous nerves for acute and chronic neurostimulation to induce penile erection in dogs and monkeys. We then investigated the anatomy of these nerves in humans by cadaveric dissection and serial histologic sectioning. Our experience in tracing the spinal nuclei responsible for vesical and urethral function by transportation of horseradish peroxidase enabled us to explore the location and organization of the spinal center for erection. Thus, systemic knowledge of the neuroanatomy of erection was accumulated. The spinal nuclei for control of erection are located in the intermediolateral gray matter at the S1 to S3 and T12 to L3 levels in dogs, and the S2 to S4 and T10 to L2 levels in humans. From these sacral nuclei axons issue ventrally and join the axons of the nuclei for the bladder and rectum to form the sacral visceral efferent fibers. These fibers emerge from the anterior root of S2 to S4, and join the sympathetic fibers to form the pelvic plexus, which then branches out to innervate the bladder, rectum and penis. The fibers innervating the penis (cavernous nerves) travel along the posterolateral aspect of the seminal vesicle and prostate, and then accompany the membranous urethra through the genitourinary diaphragm. These fibers are located on the lateral aspect of the membranous urethra and ascend gradually to the 1 and 11 o'clock positions in the proximal bulbous urethra. Some of the fibers penetrate the tunica albuginea of the corpus spongiosum, while others spread to the trifurcation of the terminal internal pudendal artery and innervate the dorsal, deep and urethral arteries. Shortly before the 2 corpora cavernosa merge the cavernous nerves penetrate the tunica albuginea along with the deep artery and cavernous vein. The terminal branches of these nerves innervate the helicine arteries and the erectile tissue within the corpora cavernosa. Because of the intimate relationship of the cavernous nerves to the rectum, prostate and urethra, they can be damaged easily during urological and pelvic procedures. This systemic knowledge of the human cavernous nerves from the spinal center to the erectile tissue should permit a better understanding of erection and impotence. Furthermore, with the aid of intraoperative neurostimulation, the cavernous nerves may be identified and preserved, thereby preventing iatrogenic impotence.
Backscatter from four commonly used metals (aluminum, lead, copper, and iron) was measured under diagnostic imaging conditions, using screen-film systems as detectors. The results indicate that for an 80-kV filtered beam and Par Speed/XRP system, backscatter increases as aluminum (Al) thickness increases until it reaches a plateau of approximately 12% at 50 mm Al. The amount of backscatter from any of these four metals increases as the tube voltage is raised from 60 to 115 kV. Measured backscatter depends strongly on the screens used, possibly due to their attenuation and energy response. Backscatter from aluminum was significantly greater than that from the other metals tested.
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For prosthetic use in genitourinary operations we investigated the feasibility of producing grafts from cultured smooth muscle cells on absorbable synthetic biomaterial. Biopsies of bladder wall muscle without mucosa were obtained from 20 rabbits for culture of smooth muscle cells; cultured cells were examined by light and electron microscopy. Those cells were grown in subculture on a microfiber mesh carrier woven from 35-denier polyglycolic acid fibers. As shown by scanning electron microscopy (SEM), complete coverage of the synthetic fabric was achieved after ten to fourteen days of subculture.
Surgical excision of fibrotic plaques and replacement of the defect by grafts may be necessary in advanced Peyronie disease. Synthetic, absorbable mesh for grafting the defect was used in 6 mongrel dogs. An area of tunica albuginea 1.5 by 2.5 cm was removed from the corpus cavernosum, thus exposing the spongy cavernous tissue. A Dexon mesh of the same dimensions, woven in our laboratory from polyglycolic acid fibers of 308 denier thickness, was sutured to the defect by 3-0 Dexon sutures. The mesh caused hemostasis and the animals' postoperative course was uneventful. Posterection cavernosograms showed no curvature of the penis, bulging of the operative area, or obstruction of the corpora cavernosa. Histologic studies at three weeks, and two, four, and six months after surgery showed complete healing and gradual replacement of the Dexon mesh by fibrous connective tissue.
A new operative technique using synthetic, absorbable mesh for grafting a urethral defect was applied in 7 mongrel male dogs. The ventral half of the urethral circumference with its surrounding corpus spongiosum was excised for a length of 3 to 4 cm. A Dexon mesh of the same dimensions, woven in our laboratory from polyglycolic acid fibers, was sutured to the defective area. A perineal urethrotomy was established, and no splints were left behind. Dogs were studied between two and six months. Retrograde urethrography showed that the operative area healed without strictures or irregularities. Intravenous urography showed no back pressure effects, and cultured urine was always sterile. Histologic examination two months after surgery showed that the urothelium was completely healed, without inflammatory changes or disruption. Suburothelial tissues were replaced by dense collagenous connective tissue. The excised corpus spongiosum did not regenerate. After six months, the area of dense collagen described was diminished in size so that the operative area could be hardly identified except by the absence of corpus spongiosum.
Radical prostatectomy often is followed by erectile dysfunction. Various etiologies have been postulated--vascular, psychologic, or neurologic. Recently, we were able to isolate the cavernous nerves of the prostatic plexus, which innervate the erectile tissue of the corpora cavernosa, for electroerection in dogs. Acute and chronic experiments were then performed to examine the relationship between erectile impotence and radical prostatectomy. We conclude that erectile impotence after total prostatectomy is a result of injury to the cavernous nerves and that potency can be preserved if these nerves are identified and salvaged during surgery.
Being able to induce controlled erection in dogs and monkeys, we investigated the hemodynamics and mechanism of penile erection. 'Chronic' monkey models, having had electrodes implanted around the cavernous nerves for electroerection, were studied to evaluate the details of the hemodynamic changes. The studies included: 1) arterial blood flow, 2) corporeal pressure, 3) blood gases, 4) venous flow and 5) radiography. Tumescence of the corpora cavernosa was found to be a result of: 1) active relaxation of the sinusoidal spaces, 2) active arteriolar dilatation and 3) active venous outflow constriction. At full erection there is adequate but reduced blood flow into and out of the corpora cavernosa for metabolic exchange.
Physical properties of four radiographic cassettes were investigated in combination with various screen/film systems. These properties included (a) transmittance of monoenergetic x rays over 14-96 keV and comparison with predictions based on attenuation coefficients; (b) relative patient exposure from 60 to 120 kV (from phantom measurements) and correlation with predictions based on measured transmittance as well as average energies and angles of incident radiation; and (c) amounts of scatter from various cassette materials and comparison with Monte Carlo calculations. The results provide a model of performance based on quantitation of cassette effects on system speed and image contrast. Carbon-fiber cassettes required the lowest patient exposure, produced the least scatter, and (in low-scatter situations) were capable of increased image contrast.
To investigate the feasibility of chronic stimulation of the sacral nerves for control of sphincter and bladder function, we implanted bipolar electrodes in 10 dogs. These electrodes, of conventional cuff (4 dogs), as well as innovative spiral designs (6 dogs) were placed around the S2 roots of the 10 dogs and in 3 of them around the S1 root additionally. The electrodes were connected to subcutaneous radiofrequency receivers for external activation. Microsurgical techniques were employed to perform dorsal rhizotomy and ganglionectomy. 5 dogs, 3 kept as long as 8 months, were chronically stimulated to a cumulated time of 100-150 h each. Functional and histological results reveal that sacral root nerves can be stimulated safely on a chronic basis for effective control of the lower urinary tract.