Biomedical subjects

J S Walter

Publications and source records attributed to J S Walter.

At least 37 records · Page 2Linked to original sources

PubMed1996

Preliminary noninvasive back-pressure recordings of bladder pressure.

Obstructive voiding is best evaluated with urodynamics, including bladder pressure and urine flow rates. Until recently, the recording of bladder pressure required the use of a urethral catheter. In preliminary observations, a noninvasive back-pressure method using an external condom catheter has been introduced to determine bladder pressure. This device uses a side tube for pressure recording and an outlet tube that is clamped for short periods of time. We have investigated design criteria for back-pressure recording techniques. In the laboratory setting using a plastic model, we determined that a low compliance condom is needed. In addition, a back flow of fluid during the clamping procedure helps to obtain quick back pressures and facilitates evaluation of pressure when low flow rates are present. These modified condom devices were evaluated in four male subjects. Back pressures were not statistically different than bladder pressures recorded with a urethral catheter. The use of back pressures in the evaluation for obstructive uropathy can be enhanced by using a pressure and flow nomogram.

Humans↗

PubMed1995

Diaphragm and accessory respiratory muscle stimulation using intramuscular electrodes.

We tested the hypothesis that electrical stimulation of respiratory muscles can be obtained from intramuscular electrodes. In acute anesthetized dogs, suture-type intramuscular electrodes were placed in each hemidiaphragm and needle electrodes were placed in various intercostal regions of the thorax. During a hyperventilation induced period of apnea a 2-second stimulation was applied to the diaphragm or to the thoracic electrodes, followed by a combined thoracic-diaphragm stimulation period. Thoracic expansion and tidal volumes were measured as indices of inspiratory effort. We found that diaphragm stimulation produced tidal volumes between 104% and 180% of spontaneous breathing. Electrodes in the upper thorax produced chest expansion and when combined with diaphragm stimulation increased tidal volumes (p < .05). We conclude that intramuscular electrodes represent a feasible method for long-term electrogenic ventilation. Also, thoracic support for diaphragm pacing in quadriplegics could produce a more effective long-term system that is less prone to fatigue and failure.

Animals↗

PubMed1995

Evaluation of a thin-film peripheral nerve cuff electrode.

This is a study of the reaction of large nerves to implantation using a flexible, thin-film cuff electrode. Cuff electrodes were implanted on the sciatic nerve of three cats. An implantation period of six weeks allowed sufficient time for any injury responses in the nerve and connective tissue sheath around the cuff to develop. The electrode came off the nerve in one of the cats. In the remaining two cats, gross observation following explantation of the electrodes revealed encapsulation of the cuffs without swelling of nerve tissue. Histological evaluation did not demonstrate nerve injury. The nerve cuff electrodes, which are comprised of titanium and iridium coatings on a fluorocarbon polymer substrate, appeared unaffected by the implantation, and connective tissue encapsulation did not adhere to either the polymer substrate or metallization. Evaluation of the electrodes using activated iridium oxide charge injection sites in more extended studies is now being undertaken.

Animals↗

PubMed1995

Direct bladder stimulation with percutaneous electrodes and impedance monitoring of volume in an SCI animal model.

Bladder responses to percutaneous electrodes were investigated with stimulation in three male spinal cats. The animals had been spinalized (T1 level lesion) 10 weeks prior to these studies and had been instrumented with chronic bladder had been spinalized (T1 level lesion) 10 weeks prior to these studies and had been instrumented with chronic bladder wall electrodes and suprapubic bladder catheters for filling and pressure recording. percutaneous stimulation in tethered animals was conducted wit hook electrodes inserted with a needle in the abdomen bilaterally adjacent to the bladder trigone. Stimulation was conducted with 40 Hz pulse trains of 10 to 30 mA for three seconds. Stimulation with both percutaneous and chronic electrodes induced high bladder pressures and voiding. In addition, with chronically implanted electrodes, impedance monitoring of bladder volume was found to be an effective recording technique.

Animals↗

PubMed1994

Comparison of 316LVM and MP35N alloys as charge injection electrodes.

An In vitro comparison of the corrosion response of 316LVM stainless steel and MP35N (a CoNiCrMo alloy) electrodes under conditions appropriate to applications in functional electrical stimulation (FES) was made. Electrodes of both alloys were subjected to a cathodic 40 microC/cm2 charge injection protocol and the potential transient response was recorded over a 96 h period. The transient responses were compared with potentiodynamic polarization data used to establish the quasiequilibrium response of the alloys in the carbonate and phosphate-buffered saline electrolyte used in the study. The MP35N electrodes exhibited extensive pitting corrosion during charge injection, whereas little corrosion was observed on 316LVM electrodes. An explanation for the susceptibility of MP35N to corrosion during charge injection is found in the potentiodynamic polarization data, which reveal a breakdown potential (critical pitting potential) of 0.45 V (SCE) for MP35N compared with 1.05 V (SCE) for 316LVM. Factors that may influence corrosion response during charge injection from alloys exhibiting active-passive behavior are discussed.

Chromium Alloys↗

PubMed1994

Urodynamic measure of urethral cross-sectional area: application for obstructive uropathy.

A conductance formula was developed based on pressure (P) and flow (Q) data collected from rigid tubes with a cross-sectional area in the range of the flow controlling zone of the urethra. Curve fitting of data resulted in an exponential formula and a simple proportionality constant related tube of differing cross-sectional area. The resulting formula estimates cross-sectional area based on P and Q data and is in the form of a conductance ratio because Q is in the numerator and P is in the denominator. The formula is AEFm = 3.5 Q/P0.58, where AEFm is the area equivalent factor-male and Q is measured in ml/sec and P is cm H2O. To further introduce the estimate of cross-sectional area, urodynamics were retrospectively reviewed from 19 males over the age of 50 with complaints of prostatism. The AEFm was plotted on standard urodynamic records much like P and Q data. The onset of voiding was characterized by a rapid increase in urethral area. Maximal cross-sectional area obtained at maximal flow was 2.9 +/- 1.4 mm2. The maximal urethral area per unit of applied detrusor pressure, an estimate of urethral compliance, was 0.06 +/- 0.6 mm2/cm H2O. This latter measure may help to compare patients with widely different detrusor pressures. The urodynamic data from two young adult males is also presented for comparison. Their average maximal urethral cross-sectional area was 7.1 mm2. Their average area per unit of applied detrusor pressure was 0.15 mm2/cm H2O. These larger values contrast sharply with the BPH group. The AEFm clearly shows urethral function in terms of the principal factor regulating the urine flow rate, the urethral cross-sectional area.

Adult↗

PubMed1994

Management of incontinent SCI patients with penile stimulation: preliminary results.

We investigated dorsal penile stimulation for control of incontinence in nine spinal cord impaired (SCI) patients, using a battery-powered home-use stimulator connected to surface electrodes (Unipatch). The efficacy of the penile stimulation was assessed by urodynamic evaluation (NL-2, LifeTech) and surface electrodes (Unipatch); baseline and repeat cystometries (CMG) with and without stimulation were done. Stimulation for home use was begun at threshold parameters for inducing perineal contractions and, after two weeks, was adjusted based upon results. Two subjects successfully completed the study and became continent. One of these patient's CMG demonstrated hyperreflexia and his volume increased from 110 ml to 150 ml after the stimulation protocol. The most effective stimulating parameters were 5 pps, 250 microsec, pulse width and 40 ma current. The other patient also had a hyperreflexic bladder and improved on the protocol. The remaining seven patients did not complete the study for several reasons. Three patients had CMG's that demonstrated areflexia. Stimulation did not alter their bladder function and they dropped out of the program. Three other subjects withdrew because of bothersome sensations even at subthreshold levels and they complained that the technique was cumbersome. Finally, one patient with significant hyperreflexia and incontinence withdrew after trying unsuccessfully and diligently for 10 days. Our encouraging results in two patients with hyperreflexic bladders and decreased sensation suggest that this modality may be effective in this patient group.

Adult↗

PubMed1994

Dynamic bulbocavernosus reflex: dyssynergia evaluation following SCI.

High urethral resistance caused by detrusor-sphincter dyssynergia (DSD) occurs following spinal cord injury (SCI) and results in poor voiding. A major pelvic floor reflex that may be involved in DSD is the bulbocavernosus reflex (BC) and evaluation of this reflex during the micturition cycle may provide additional information regarding this role. The periodic BC observed during micturition via cystometry is described as a dynamic bulbocavernosus reflex (DBC). The DBC was induced in upper motor neuron SCI patients using periodic dorsal penile nerve stimulation; the evoked reflex response was recorded with an anal sphincter pressure sensing balloon. Stimulation of 15-50 mA was applied at the base and dorsal side of the penis with surface electrodes, pulsed at a rate of 0.25 Hz. By applying the stimulation during cystometry, the BC reflex could be evaluated throughout the entire micturition cycle. Results showed that the DBC increased during bladder filling and bladder contractions. These findings indicate that an enhanced BC reflex is a major factor causing increased urethral resistance during micturition.

Adult↗

PubMed1993

Inhibiting the hyperreflexic bladder with electrical stimulation in a spinal animal model.

Uninhibited bladder contractions are a problem in spinal cord injured patients. Accordingly, methods using electrical stimulation to inhibit the bladder were investigated in chronic spinal cord injured (C6-T1) male cats. In unanesthetized, restrained animals, spontaneous bladder contractions were observed after the bladder was filled above the micturition threshold. In 3 of the 5 cats studied, this bladder activity could be inhibited with stimulation of either sacral nerves or pudendal nerves. Pudendal nerve stimulation, however, was more selective than sacral nerve stimulation for inhibition with fewer side effects such as leg spasms. Tibial nerve stimulation was ineffective and caused leg spasms and increased bladder activity. Finally, high-frequency stimulation (1,000 Hz) of the sacral nerves was shown to block bladder contractions in 2 of 3 cats investigated. However, this method had adverse side effects such as leg flexion and secondary bladder contractions. We conclude that pudendal nerve/pelvic floor stimulation at low frequency is a relatively effective method in this model.

Animals↗

PubMed1993

Measurement of total urethral compliance in females with stress incontinence.

Urodynamic evaluation of stress incontinence has failed to result in consistent diagnostic parameters. Using retrospective female bladder pressure and urine flow data, we evaluated two parameters based on a conductance formula. This formula was derived from fitting a classical fluid dynamic equation to published data of voiding cystourethography. The Area Equivalent Factor-female at maximal flow represents maximal urethral opening and this value further divided by the pressure is the total urethral compliance. A stress incontinent group had a strong trend toward greater maximal urethral opening and total urethral compliance than a continent group. These parameters may, therefore, have potential in the evaluation and understanding of stress urinary incontinence.

Adult↗

PubMed1993

Evaluation of direct bladder stimulation with stainless steel woven eye electrodes.

Encouraged by recent clinical reports of micturition induced in patients by direct bladder stimulation, we conducted a study of optimum methods of direct bladder stimulation. During surgery six male cats received eight large surface-area woven eye electrodes sutured to the bladder wall serosa, four on the bladder dome and four adjacent to the trigone area. Two additional small surface-area single knot electrodes were sutured in the trigone area. Suprapubic and intraperitoneal tubes were placed for pressure recording and bladder filling. Leg and pelvic floor EMG electrodes were also used for tethered recordings. One to eight weeks after surgery, optimum stimulation methods were evaluated as the animal freely moved about a urodynamic recording cage. Electrodes in the trigone region were more effective than electrodes on the dome and induced bladder contractions and voiding similar to spontaneously induced voiding with bladder filing. Large surface area, woven eye electrodes, composed of multistranded 316LVM stainless steel wire, were more effective than smaller surface area single knot electrodes. High stimulating frequencies (40 Hz) were better than lower frequencies (10 to 20 Hz), and a 1 millisecond pulse duration was optimal. Pulsing with stimulating currents from 10 to 25 mA induced effective bladder contractions with voiding when applied for 3 seconds. However, lower currents using longer stimulation periods were also effective. Bipolar electrodes with both electrodes on the bladder wall were superior to monopolar arrangements with the positive ground electrode along the animal's back. We concluded that in the able-bodied cat model, bladder contractile activity for micturition can be induced with direct bladder stimulation and with little discomfort. An effective stimulation protocol consists of capacitor-coupled monophasic pulses with large surface area bipolar electrodes in the trigone region. Stimulating parameters of 40 Hz, 1 msec., 10 to 25 mA applied for 3 seconds were optimal. In addition, based on corrosion resistance observations, the electrodes are quite suitable for long-term studies.

Animals↗

PubMed1993

Urologic aspects of traumatic central cord syndrome.

Central cord syndrome (CCS) is a subset of spinal cord injury, characterized by more motor involvement of the upper extremities than the lower extremities and sacral sensory sparing. Patients with central cord syndrome have been reported to have a good rehabilitation and urologic outcome. Our purpose was to assess the urologic outcome in a group of patients with central cord syndrome. We reviewed 23 patients with central cord syndrome who were admitted to Hines VA Hospital between 1983 and 1991, 20 of whom were older than 50 years of age. Urodynamic studies showed detrusor hyperreflexia with a synergistic EMG in 15 patients and detrusor hyperreflexia with external urethral sphincter dyssynergia (DSD) in five patients. Three patients with no urologic problems were not tested. Bladder sensation was preserved during filling in all patients. At follow-up (median = 2-4 months), 16 patients (70 percent) were voiding, seven of whom required either occasional external or intermittent catheterization; nine were voiding independently. The seven other patients (30 percent) required either continuous external or intermittent catheterization (including the five with DSD). Urologic morbidity in the period after SCI included: urinary tract infections (12), renal (2) and bladder calculi (2), superficial bladder cancer (1), epididymitis (1) and none (6). Fifteen patients (65 percent) were ambulatory at follow-up while four patients needed wheelchairs. Data were not available for the other four patients. Urodynamic studies in three of the wheelchair-bound patients showed that two of them had DSD. Most patients with central cord syndrome have favorable urologic and rehabilitation outcomes and can be managed conservatively.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1992

Bladder inhibition by penile nerve stimulation in spinal cord injury patients.

Detrusor hyperreflexia causing voiding dysfunction in spinal cord injury patients is a difficult problem and is not always treated effectively by anticholinergic agents. We have been investigating electrical stimulation methods to inhibit hyperreflexia and dorsal penile nerve stimulation is the most promising. Six chronic suprasacral spinal cord injury men (average age 36 years) underwent stimulation testing with water cystometry before, during and after stimulation. Dorsal penile stimulation was done with carbon rubber butterfly electrodes (Medtronic) with parameters of 5 pulses per second, 0.35 msec. pulse duration, and current at a level above the threshold for pelvic twitching activity and adjusted for optimal bladder effect (range 25 to 70 mamp.). In all 6 patients the cystometrogram during stimulation showed an increase in bladder volume over the prestimulation cystometrogram (range 27 to 150%). In 2 patients there was no detrusor activity after filling to 500 cc. Stimulation was then stopped and a spontaneous contraction occurred. The cystometrogram conducted after the stimulus also had less volume than that performed during stimulation but it was larger than the prestimulation volume. Penile nerve stimulation was painless with no side effects. Penile nerve electrical stimulation is effective for inhibiting bladder hyperreflexia and should be easily adaptable for chronic home use as an alternative to current therapy.

Adult↗

PubMed1992

Comparison of direct bladder and sacral nerve stimulation in spinal cats.

Neuroprosthetic techniques have been used to facilitate voiding via electrical stimulation for bladder management following spinal cord injury (SCI), but high urethral resistance has been a problem. This problem was investigated here in the chronic, spinal, male cat (C6-T1) using direct bladder and sacral nerve stimulation. Direct bladder stimulation was only conducted during terminal procedures with an open abdomen and with four hook electrodes inserted into the bladder wall. Sacral stimulation was conducted daily during the 10 weeks post-SCI and during terminal procedures. Stimulation was conducted with both implanted epidural electrode and surface electrodes over the sacral bone. Both of these sacral methods stimulated anterior and posterior roots. However, these sacral methods were generally ineffective for inducing voiding during the study. In three of the five animals investigated, stimulation did not empty the bladder. In the remaining two animals, the bladder was emptied with sacral stimulation, but only after return of bladder reflex activity, 2 to 4 weeks post-injury. When poor voiding occurred in spite of high bladder pressures, it indicates high urethral resistance. This was confirmed using video cystourethrography where the membranous urethra was observed to remain closed following stimulation. Direct bladder stimulation was then compared to sacral nerve stimulation during terminal procedures. Direct bladder stimulation induced voiding at a high rate both during and after stimulation, whereas sacral nerve stimulation with implanted electrodes induced voiding at a lower rate and only after stimulation. A simple urethral resistance measure, the ratio of bladder pressure to voiding rate, was lower with direct bladder stimulation than sacral nerve stimulation. Stimulation-facilitated voiding has also been associated with the development of bladder wall hypertrophy. This problem was investigated by evaluating bladder wall thickness postmortem in three groups of animals: the first group was the spinal-stimulated animals detailed above; the additional two groups were a spinal-nonstimulated but instrumented group maintained for 10 weeks following injury, and an intact group of animals. The stimulated spinal cats tended to have the thickest bladder wall followed by the nonstimulated spinal cats. The wall thickness of intact animals served as a control.

Animals↗

PubMed1990

Female urinary retention.

The urodynamic results in 68 females with urinary retention were reviewed. There were two groups: 39 patients with neurologic causes for retention, and 29 patients in whom possible causes for retention included: psychological history (15 patients), gynecologic pathology, and urinary tract infection. Nine patients in the neurogenic group and 13 patients in the non-neurogenic group had undergone urethral dilatation with no improvement. Upper urinary tract evaluation was unremarkable. Detrusor failure was the prominent bladder pattern in both groups. In the neurogenic group, low pressure detrusor activity was also present in 10 patients, 3 of whom had sphincter dyssynergia. Flow rate, surface electromyography, and bethanechol supersensitivity test could not help differentiate neurogenic from non-neurogenic detrusor failure. The notation of abnormal bladder sensation did significantly differ between the groups, but was of limited accuracy as an indicator of neurogenic retention. Self-intermittent catheterization was the most effective treatment for both groups, with some patients voiding adequately in follow-up. Although no one test can accurately differentiate neurogenic from nonneurogenic female urinary retention, careful neurourologic evaluation will help guide us to more appropriate management.

Bethanechol↗

PubMed1989

Microinjection of interleukin-1 into brain: separation of sleep and fever responses.

Interleukin-1 (IL1) and muramyl peptides are somnogenic, pyrogenic, immune response modifiers, Their central nervous system loci of action with respect to sleep and body temperature in rabbits were examined in this study using microinjection techniques. Unilateral microinjection of IL1 into various basal forebrain or brain stem sites resulted in elevated colonic temperatures (Tc), but the duration of slow-wave sleep (SWS) was unchanged compared to results obtained after control injections. Injection of IL1 into posterior hypothalamic areas failed to elicit either sleep or temperature responses. In contrast to these results, injection of either IL1 or muramyl dipeptide into the Aqueduct of Sylvius was followed by enhanced SWS and Tc. These results show that IL1-induced sleep and fever responses can be separated. Somnogenic sites of action for IL1 and muramyl peptides remain unknown.

Animals↗

PubMed1989

Surface stimulation techniques for bladder management in the spinal dog.

Electrical stimulation of the bladder wall or sacral nerves may be effective for bladder management in the spinal cord injured patient. However, extensive surgery has been required for electrode implantation. We compared urodynamic responses using surface and minimally invasive epidural stimulating techniques in the chronic spinal male dog. Various surface stimulating techniques were effective: 1) sacral monopolar electrical stimulation with negative electrodes over S2 sacral foramina and positive electrodes on the legs, 2) sacral bipolar electrical stimulation with electrodes only over sacral foramina, 3) perineal monopolar electrical stimulation, and 4) perineal tactile stimulation. Urodynamic responses were similar to those for sacral epidural electrodes implanted adjacent to sacral nerves. Voiding was obtained both during stimulation and poststimulation. Stimulating parameters that were effective for daily voiding with sacral surface electrodes were 10 pps, 30 to 45 ma, 0.6 ms pulse duration, and 2 to 5 sec stimulation train duration.

Animals↗

PubMed1989

Urethral responses to sacral stimulation in chronic spinal dog.

Urethral activity was investigated in the awake chronic spinal-injured canine using urodynamic recordings, video cystofluoroscopy, and urethral pressure recordings without anesthesia. Bladder contractions and voiding were induced by electrical stimulation with epidural electrodes inserted into the sacral canal. Urethral pressure remained elevated during stimulation and for 1-3 s afterward. Poststimulation voiding occurred with three different patterns: 1) pulsatile voiding in which squirting of urine was associated with contractions in the membranous urethra; 2) "on and off" voiding in which pulsatile flow was interrupted for brief periods of time; and 3) steady-stream voiding in which nonpulsatile flow was followed by pulsatile flow. Viewing these voiding patterns with fluoroscopy indicated that the proximal membranous urethra was important in all of the patterns. We conclude that in the chronic spinal-injured canine the skeletal muscle within the membranous urethra (rhabdosphincter) is involved in responses to sacral stimulation and various voiding patterns.

Animals↗