Improved Functional Outcome After Peripheral Nerve Stimulation of the Impaired Forelimb Post-stroke

Lack of blood flow to the brain, i.e., ischemic stroke, results in loss of nerve cells and therefore loss of function in the effected brain regions. There is no effective treatment to improve lost function except restoring blood flow within the first several hours. Rehabilitation strategies are widely used with limited success. The purpose of this study was to examine the effect of electrical stimulation on the impaired upper extremity to improve functional recovery after stroke. We developed a rodent model using an electrode cuff implant onto a single peripheral nerve (median nerve) of the paretic forelimb and applied daily electrical stimulation. The skilled forelimb reaching test was used to evaluate functional outcome after stroke and electrical stimulation. Anterograde axonal tracing from layer V pyramidal neurons with biotinylated dextran amine was done to evaluate the formation of new neuronal connections from the contralesional cortex to the deafferented spinal cord. Rats receiving electrical stimulation on the median nerve showed significant improvement in the skilled forelimb reaching test in comparison with stroke only and stroke with sham stimulation. Rats that received electrical stimulation also exhibited significant improvement in the latency to initiate adhesive removal from the impaired forelimb, indicating better sensory recovery. Furthermore, axonal tracing analysis showed a significant higher midline fiber crossing index in the cervical spinal cord of rats receiving electrical stimulation. Our results indicate that direct peripheral nerve stimulation leads to improved sensorimotor recovery in the stroke-impaired forelimb, and may be a useful approach to improve post-stroke deficits in human patients.

Histological Assessment of Wallerian Degeneration of the Rat Tibial Nerve Following Crush and Transection Injuries

BACKGROUND

 Wallerian degeneration (WD) following peripheral nerve injury (PNI) is an area of growing focus for pharmacological developments. Clinically, WD presents challenges in achieving full functional recovery following PNI, as prolonged denervation of distal tissues for an extended period of time can irreversibly destabilize sensory and motor targets with secondary tissue atrophy. Our objective is to improve upon histological assessments of WD.

METHODS

 Conventional methods utilize a qualitative system simply describing the presence or absence of WD in nerve fibers. We propose a three-category assessment that allows more quantification: A fibers appear normal, B fibers have moderate WD (altered axoplasm), and C fibers have extensive WD (myelin figures). Analysis was by light microscopy (LM) on semithin sections stained with toluidine blue in three rat tibial nerve lesion models (crush, partial transection, and complete transection) at 5 days postop and 5 mm distal to the injury site. The LM criteria were verified at the ultrastructural level. This early outcome measure was compared with the loss of extensor postural thrust and the absence of muscle atrophy.

RESULTS

 The results showed good to excellent internal consistency among counters, demonstrating a significant difference between the crush and transection lesion models. A significant decrease in fiber density in the injured nerves due to inflammation/edema was observed. The growth cones of regenerating axons were evident in the crush lesion group.

CONCLUSION

 The ABC method of histological assessment is a consistent and reliable method that will be useful to quantify the effects of different interventions on the WD process.

Stimulation of abdominal and upper thoracic muscles with surface electrodes for respiration and cough: Acute studies in adult canines

OBJECTIVE

To optimize maximal respiratory responses with surface stimulation over abdominal and upper thorax muscles and using a 12-Channel Neuroprosthetic Platform.

METHODS

Following instrumentation, six anesthetized adult canines were hyperventilated sufficiently to produce respiratory apnea. Six abdominal tests optimized electrode arrangements and stimulation parameters using bipolar sets of 4.5 cm square electrodes. Tests in the upper thorax optimized electrode locations, and forelimb moment was limited to slight-to-moderate. During combined muscle stimulation tests, the upper thoracic was followed immediately by abdominal stimulation. Finally, a model of glottal closure for cough was conducted with the goal of increased peak expiratory flow.

RESULTS

Optimized stimulation of abdominal muscles included three sets of bilateral surface electrodes located 4.5 cm dorsal to the lateral line and from the 8^th intercostal space to caudal to the 13^th rib, 80 or 100 mA current, and 50 Hz stimulation frequency. The maximal expired volume was 343 ± 23 ml (n=3). Optimized upper thorax stimulation included a single bilateral set of electrodes located over the 2^nd interspace, 60 to 80 mA, and 50 Hz. The maximal inspired volume was 304 ± 54 ml (n=4). Sequential stimulation of the two muscles increased the volume to 600 ± 152 ml (n=2), and the glottal closure maneuver increased the flow.

CONCLUSIONS

Studies in an adult canine model identified optimal surface stimulation methods for upper thorax and abdominal muscles to induce sufficient volumes for ventilation and cough. Further study with this neuroprosthetic platform is warranted.

Respiratory responses to stimulation of abdominal and upper-thorax intercostal muscles using multiple Permaloc electrodes

Stimulation of abdominal and upper-thoracic muscles was studied with the long-term goal of improved respiratory care for spinal cord injury (SCI) patients. A 12-channel stimulator and multiple surface and implanted Permaloc electrodes were evaluated in five anesthetized canines. Abdominal stimulation with 100 mA using four bilateral sets of surface electrodes placed on the midaxillary line at the 7th through 13th intercostal spaces and with a closed airway at a large lung volume produced an expiratory tracheal pressure of 109 +/- 29 cm H2O (n = 2, mean +/- standard error of the mean). Similar high pressures were induced with implanted electrodes at the same locations. Upper-thoracic stimulation with 40 mA and four sets of implanted electrodes ventral to the axilla induced inspiratory pressures of -12 +/- 2 cm H2O (n = 5). Combined extradiaphragmatic pacing with an open airway produced a tidal volume of 440 +/- 45 mL (n = 4). The robust respiratory volumes and pressures suggest applications in SCI respiratory care.

Hypomagnesemia in hemodialysis patients: role of proton pump inhibitors

BACKGROUND

Recent observations have associated hypomagnesemia with increased risk of cardiovascular morbidity and mortality in hemodialysis patients.

METHODS

We did a 3-month chart review of 62 chronic hemodialysis patients at a single US hospital. All were dialyzed using a dialysate [Mg] of 0.75-1.0 mEq/l. Patients were divided into two groups: hypomagnesemic (mean predialysis plasma [Mg] <1.5 mEq/l) and non-hypomagnesemic (mean predialysis plasma [Mg] ≥1.5 mEq/l).

RESULTS

All patients were male; mean age was 64.3 ± 8.7 years and the majority (73%) diabetic. 24 patients (39%) had hypomagnesemia and 38 (61%) were not hypomagnesemic. There were no significant differences between the two groups in age, diabetes status, blood pressure, duration of dialysis, plasma calcium, phosphorus, albumin, intact parathyroid hormone (PTH), dialysis adequacy (Kt/V), or dietary protein intake (as estimated by normalized protein catabolic rate, nPCR). However, use of proton pump inhibitors (PPIs) was significantly associated with hypomagnesemia (plasma [Mg] 1.48 ± 0.16 mEq/l in the PPI group vs. 1.65 ± 0.26 mEq/l in the non-PPI group, p = 0.007). Adjustment for age, diabetes status, duration of dialysis, plasma albumin, Kt/V, nPCR, and diuretic use did not affect the association between PPI use and hypomagnesemia.

CONCLUSIONS

Use of PPIs in patients dialyzed using a dialysate [Mg] of 0.75-1.0 mEq/l is associated with hypomagnesemia. We suggest monitoring plasma [Mg] in patients taking PPIs, with discontinuation of the medication if possible and/or adjustment of dialysate [Mg] to normalize plasma [Mg].

Hypertrophy of neurons within cardiac ganglia in human, canine, and rat heart failure: the potential role of nerve growth factor

Background

Autonomic imbalances including parasympathetic withdrawal and sympathetic overactivity are cardinal features of heart failure regardless of etiology; however, mechanisms underlying these imbalances remain unknown. Animal model studies of heart and visceral organ hypertrophy predict that nerve growth factor levels should be elevated in heart failure; whether this is so in human heart failure, though, remains unclear. We tested the hypotheses that neurons in cardiac ganglia are hypertrophied in human, canine, and rat heart failure and that nerve growth factor, which we hypothesize is elevated in the failing heart, contributes to this neuronal hypertrophy.

Methods and Results

Somal morphology of neurons from human (579.54±14.34 versus 327.45±9.17 μm²; P<0.01) and canine hearts (767.80±18.37 versus 650.23±9.84 μm²; P<0.01) failing secondary to ischemia and neurons from spontaneously hypertensive rat hearts (327.98±3.15 versus 271.29±2.79 μm²; P<0.01) failing secondary to hypertension reveal significant hypertrophy of neurons in cardiac ganglia compared with controls. Western blot analysis shows that nerve growth factor levels in the explanted, failing human heart are 250% greater than levels in healthy donor hearts. Neurons from cardiac ganglia cultured with nerve growth factor are significantly larger and have greater dendritic arborization than neurons in control cultures.

Conclusions

Hypertrophied neurons are significantly less excitable than smaller ones; thus, hypertrophy of vagal postganglionic neurons in cardiac ganglia would help to explain the parasympathetic withdrawal that accompanies heart failure. Furthermore, our observations suggest that nerve growth factor, which is elevated in the failing human heart, causes hypertrophy of neurons in cardiac ganglia.

Respiratory muscle pacing with chronically implanted intramuscular Permaloc electrodes: A feasibility study

We tested the feasibility of stimulating upper-intercostal and abdominal muscles plus the diaphragm by using chronically implanted intramuscular electrodes.During two survival surgeries with six dogs, intramuscular electrodes were implanted bilaterally in the three respiratory muscles. Standard stimulation of the diaphragm was conducted. The dorsolateral and ventrolateral abdominal wall areas were stimulated with a 25 mA current. The second to fourth intercostal spaces were stimulated to elicit the largest tidal volume associated with the least coactivation of the serratus and latissimus muscles. Lone diaphragm and upper-intercostal muscle pacing produced inhaled tidal volumes (mean +/- standard error of the mean) of 293 +/- 36 mL and 59 +/- 17 mL, respectively. Lone abdominal muscle pacing produced an exhaled volume of 55 +/- 17 mL. Combined pacing of diaphragm and intercostal muscles increased the inhaled volume to 389 +/- 39 mL. The addition of abdominal pacing following the combined stimulation of diaphragm and intercostals increased the exhaled volume to 472 +/- 54 mL. During autopsy, dislodgement of the electrodes overlying the ribs was a concern and probably resulted from loose animal jackets. Chronic intramuscular Permaloc electrodes can be implanted in several respiratory muscles and increase tidal volumes more than diaphragm stimulation alone.

Stimulating multiple respiratory muscles with intramuscular Permaloc electrodes

OBJECTIVE

To test the feasibility of implanting intramuscular electrodes (Permaloc, Synapse Biomedical Inc, Oberlin OH) with self-securing polypropylene anchors to stimulate upper-intercostal and abdominal muscles plus the diaphragm.

METHODS/RESULTS

In 6 anesthetized dogs, 12 Permaloc electrodes were implanted in the 3 respiratory muscles (4 in each muscle group). Tidal volume with diaphragmatic stimulation was 310 +/- 38 mL (mean +/- SE); with upper intercostal stimulation, it was 68 +/- 18 mL; and with combined diaphragm intercostal stimulation, it was 438 +/- 78 mL. By study design, stimulation in the upper intercostal muscles was limited to not more than slight/moderate contraction of the serratus and latissimus muscles overlying the ribs. Abdominal muscle stimulation produced exhaled volumes of 38 +/- 20 mL (this stimulation was limited by the maximal output of the stimulator of 25 milliamperes). Combined diaphragm intercostal stimulation followed by abdominal muscle stimulation increased exhaled volumes from 312 +/- 31 mL to 486 +/- 58 mL (P = 0.024).

CONCLUSIONS

Permaloc electrodes can be successfully implanted in upper intercostal and abdominal muscles in addition to the diaphragm. Combined diaphragm intercostal stimulation followed by abdominal muscle stimulation increased the exhaled volumes recorded with diaphragmatic stimulation alone.

Balloon-tipped catheter for measuring urethral pressures

BACKGROUND

Better methods are needed for recording urethral function for complex urologic problems involving the bladder, urethra, and pelvic floor.

OBJECTIVE

To evaluate a balloon catheter for recording urethral pressure and function using bench-top testing and evaluation in an animal model.

METHODS

Balloon pressure-recording methods included slightly inflating the balloon with water and placing the pressure transducer on the distal end of the catheter. For bench-top testing, manual procedures and a silastic tube with a restriction were used. In 3 anesthetized dogs, pressure recorded from the skeletal urethral sphincter was induced with electrical stimulation of the sphincter. Anal sphincter pressure was also recorded.

RESULTS

Bench-top testing showed good pressure recordings, including a confined peak at the tube restriction. Animal tests showed urethral pressure records with rapid responses when electrical stimulation was applied. Peak pressure at the urethral skeletal sphincter was 55.7 +/- 15 cmH2O, which was significantly higher than the peak pressure recorded 2 cm distally in the proximal urethra (3.3 +/- 2.3 cmH2O). Peak anal pressures were smaller and unchanged for the 2 stimulations.

CONCLUSIONS

Balloon-pressure recordings showed rapid responses that were adequate for the tests conducted. In the animal model, high-pressure contractions specific to the skeletal urethral sphincter were shown. Balloon-tipped catheters warrant further investigation and may have applications for the evaluation of detrusor-sphincter dyssynergia after spinal cord injury or for stress urinary incontinence.

Effective methods of pelvic plexus nerve and bladder stimulation in anesthetized animal model

Urinary retention is a serious urological problem associated with spinal cord injuries (SCIs) and other pelvic disorders. Effective methods of pelvic nerve stimulation were investigated for this problem. Following anesthesia in five dogs, the bladder was surgically exposed. Bladder and anal sphincter pressures were recorded. Testing was first conducted with probe electrodes. Barb electrodes were then implanted with a needle near the pelvic plexus nerves and the bladder wall. We tested different electrode arrangements and stimulating parameters to induce bladder contractions without skeletal muscle stimulation. The pelvic plexus nerves near the bladder were identified, and the barb electrodes were effectively implanted. Stimulation with bipolar and bilateral electrodes induced pressures over 30 cmH(2)O without skeletal muscle activation. Common stimulation parameters were 40 pps, 400 microseconds pulse duration, and 15 to 25 mA stimulating current applied for 3 s. Effective electrode implantation methods were shown. Also identified were electrode arrangements and stimulating parameters that induced strong bladder contractions without skeletal muscle activation. However, voiding studies were not conducted. Further studies with barb electrodes are warranted, and these methods may have applications for bladder stimulation following SCI.

A 24-hour feasibility study of intraurethral valved catheter for bladder management in males with spinal cord injury

This feasibility study was conducted to evaluate design features of the novel intraurethral valved catheter, Surinate (Urovalve, Inc; Newark, New Jersey). The device extends from the bladder neck to just beyond the external sphincter and contains a valve that can be activated by an external magnet for bladder emptying. Five patients were recruited from the Edward Hines Jr Department of Veterans Affairs Hospital spinal cord injury population. We conducted cystometry and cystoscopy to evaluate the lower urinary tract. Then, the device was inserted for 24 hours with careful monitoring. The catheter was removed from the first patient because he developed autonomic dysreflexia during implantation. The next four patients used the catheter overnight and tolerated it well: one with independent use and two with increased abdominal pressure. Emptying time was 208 +/- 99 s, residual was 42 +/- 33 mL, and the first-stream flow rate was 1.8 +/- 0.7 mL/s. The safety tether was used in three patients because the extraction device did not work. Results showed effective implantation and stability of the device in the urethra. However, objectives for use and extraction were not met. This feasibility study provided important information that will help guide design improvements for the intraurethral valved catheter.

Characteristics of persons with spinal cord injury as documented by use of an interactive data system

RATIONALE

Physicians need information about their rehabilitation practices that shows the types of patients being seen and the outcomes for their rehabilitation programs. In order to obtain more information on secondary medical complications and prevention programs, and to provide the information to the spinal cord injury (SCI) rehabilitation team, an interactive data management system was developed.

RESULTS

Initial findings for the first 99 patients with SCI were presented for staff review. Demographic information indicated that patients typically lived in private residences, had at least a high school education, and had annual incomes < $20,000. There were nearly equal numbers of paraplegic and tetraplegic patients; 63% of patients were more than 50 years of age and 69% were more than 10 years post-injury. Over 80% of the patients reported satisfactory health, were physically active, and had adequate transportation. Paraplegic and tetraplegic patients had similar profiles for secondary complications.

CONCLUSIONS

The SCI staff was surprised that greater than 35% of patients with SCI reported current problems with spasticity, pain, and pressure ulcers. The staff was interested in obtaining additional patient-perception information including the severity of each problem, how the problem interfered with daily activity, and the desire for additional care. The staff felt that patients were reporting problems more often to the interviewer than to their physician. There was unanimous support for the ongoing collection of patient-perception information.

Research priorities for urological care following spinal cord injury: recommendations of an expert panel

OBJECTIVE

A multidisciplinary panel of experts from Canada and the United States was convened by the Ontario Neurotrauma Foundation (ONF) to establish research priorities in the area of urological care following spinal cord injury (SCI).

DESIGN

The panel reviewed a synthesis of published literature in five areas of urology, identified emerging opportunities in the private and public sector, and used a modified Delphi approach to reach consensus on priorities for funding.

RESULTS

The panel recommendations included: clinical trials of the safety and efficacy of M3 receptor specific anti-muscarinic agents for bladder hyperactivity in SCI patients; development and testing of protocols for sacral nerve electrostimulation without sacral afferent neurectomy for management of micturition - including selective stimulation of sacral nerve fibers, high frequency blocking of the pudendal nerve to minimize the risk of urethral sphincter co-contraction and genital nerve stimulation for bladder inhibition and incontinence management; clinical trials of the efficacy and safety of intra-urethral valve catheters; trials of the efficacy of probiotics for bacterial interference i.e. to reduce colonization by uropathogens and manage the dual problems of infection and pathogen resistance to anti-microbials: innovations in the prevention or treatment of stone disease (ureteral, bladder and kidney).

CONCLUSIONS

The recommendations form the strategic priorities of the ONF SCI grants program for Ontario-based investigators and their partnerships with out-of-province collaborators and organizations.

Microstimulators and intramuscular hook electrodes for the stimulation of respiratory muscles

BACKGROUND/OBJECTIVES

We determined the feasibility of stimulating the major muscles of respiration with different types of electrodes. Intramuscular hook electrodes, model microstimulators (M-Micro) developed in our laboratory, and commercial radiofrequency microstimulators (RFM) (Alfred Mann Foundation, Valencia, CA), were employed in this investigation.

METHODS

In 8 anesthetized dogs, M-Micro were placed bilaterally on the diaphragm and in the abdominal muscles, and hook electrodes were placed in the 3rd and 5th intercostal regions adjacent to the intercostal nerves known to support inspiration. In 3 of the 8 animals, RFMs (Alfred Mann Foundation) in addition to the M-Micros were sutured to each hemidiaphragm at the same optimal site for phrenic nerve stimulation. During a hyperventilation-induced apnea, 2-second stimulations were applied to the diaphragm and with various combinations of diaphragm plus supporting muscles, both thoracic and abdominal.

RESULTS

Diaphragm stimulation alone provided tidal volumes adequate for basal alveolar ventilation. However, implantation of the RFM required greater contact with the muscle. Stimulating other respiratory muscles along with the diaphragm further increased tidal volumes. The hook electrodes, M-Micro, and RFM performed equally well.

CONCLUSIONS

In the acute dog model, M-Micro and hook electrodes can provide an implant system for the maintenance of ventilation. Support of the intercostal and abdominal muscles has the potential to reduce the contraction requirements of the diaphragm with decreased likelihood of diaphragm fatigue and hypoventilation. Whether the electrodes under investigation could provide an implant system for long-term ventilation needs to be determined.

A spinal cord injured animal model of lower urinary tract function: observations using direct bladder and pelvic plexus stimulation with model microstimulators

BACKGROUND

Microstimulators are new devices that should be considered for management of lower urinary tract problems following spinal cord injury (SCI) such as urinary retention. These devices are small (less than 25 mm by 5 mm) with the electrodes located on the ends of the stimulator. However, it is not known whether the small electrodes on these devices would be effective in stimulating the plexus of nerves that innervate the bladder. The aim of the present study was to provide preliminary observations with model microstimulators (M-Micro) for inducing bladder contractions in an SCI animal model. Bladder wall and pelvic plexus stimulation sites were compared. Additional investigations evaluated parameters such as stimulation polarity, frequency, and period as well as bladder filling volume.

METHODS

In an initial survival surgery, bilateral M-Micros were implanted on the bladder wall and the pelvic plexus along the urethra in 3 female cats. A second survival surgery was conducted 3 to 5 weeks later to produce a T1 0 SCI. Studies are reported following the second survival surgery. These studies included the effects of stimulation and bladder filling.

RESULTS

The postmortem location of the implanted pelvic plexus M-Micro was previously described as near the bladder neck. Therefore, the pelvic plexus location is described in this report as "pelvic plexus (bladder neck)" stimulation. The observations showed effective stimulation with pelvic plexus (bladder neck) stimulation and voiding in some cases. Stimulation was limited by side effects of increased abdominal pressure and leg movement. Other factors also affected the response to stimulation, including the initial bladder volume and stimulating parameters. Fluoroscopy showed that when stimulation did not induce voiding the striated urethral sphincter was closed.

CONCLUSIONS

This case series of 3 SCI animals showed that the small electrodes on the M-Micro could be used to stimulate the bladder with contractions and voiding in some cases. The pelvic plexus (bladder neck) location for the M-Micro may be a better location than higher on the bladder wall. Limiting side effects of stimulation included leg movement and increased abdominal pressure. Additional important factors included the stimulation parameters, initial bladder volume, and the function of the skeletal urethral sphincter.

Chronic instrumentation with model microstimulators in an animal model of the lower urinary tract

BACKGROUND

Microstimulators are a new type of neuroprosthetic device that should be considered for applications such as micturition control after spinal cord injury (SCI). These devices are small (less than 25 mm by 5 mm) and the electrodes are located on the ends of the stimulator. The aim of the current study was to develop methods for chronic implantation of model microstimulators (M-Micro) on the bladder wall and pelvic plexus of female cats. A postmortem evaluation of the effects of 3 months of implantation is reported.

METHODS

Techniques to produce the M-Micro are described. Four of these devices were implanted in 4 female cats and maintained after the initial instrumentation surgery and a second survival surgery for SCI (at T10). Using a single suture tied around the M-Micro, these devices were secured to the bladder wall or the fat pads adjacent to the pelvic plexus. Additional instrumentation was implanted, including 2 catheters in the bladder, 1 abdominal balloon, and electromyography electrodes in the urethral and anal sphincters. Postmortem observations of the location of the M-Micro on the bladder wall were conducted after fixation.

RESULTS

The animals' conditions were good. One animal was sacrificed early because of a skin infection. A single suture was sufficient to anchor the M-Micro. However, during the surgical implantation the pelvic plexus M-Micro ended up close to the bladder neck. Extensive fibrous connective tissue formed around the M-Micro and implanted catheters on the bladder wall. This appeared to result, in part, from multiple devices implanted on or near the bladder wall.

CONCLUSIONS

These pilot studies showed that the M-Micro could be easily constructed and secured to the bladder wall or fat pads close to the pelvic plexus. There was a concern that the pelvic plexus location for the M-Micro ended near the bladder neck during the surgical implantation; however, these devices did not appear to migrate over this short, 3-month implantation period. The extensive connective tissue responses of the bladder wall to the tubes, wires, and M-Micro was a major concern. The M-Micro appears to be a good device to assess the potential of commercial microstimulators for use in micturition control.

Bladder-wall and pelvic-plexus stimulation with model microstimulators: Preliminary observations

Severe urinary retention is not a common condition, but may occur following some pelvic surgeries or other medical conditions. Electrical stimulation of the bladder has been examined as a means of managing this difficult problem. We conducted preliminary investigations in cats to prove the hypothesis that pelvic-plexus (bladder-neck) stimulation would produce greater micturition response with reduced side effects, such as animal movement or discomfort, than bladder-wall stimulation with electrodes implanted higher on the bladder wall. We used model microstimulators that mimic the look and function of commercial microstimulators, but that we constructed. We instrumented four female cats during a survival surgery. Animals recovered well and studies were conducted over a 1-month period in the conscious animal and under anesthesia. We performed a variety of studies with different stimulation parameters and electrode locations to evaluate our hypothesis. In the active animal, we supplied only low currents, but two animals responded to stimulation with bladder contractions and voiding. Following anesthesia, higher stimulating currents resulted in greater bladder contractions during stimulation in two of the three animals. In two cases, pelvic-plexus (bladder-neck) stimulation induced greater micturition responses than direct bladder-wall stimulation. In conclusion, we learned from these preliminary observations that stimulation at the pelvic plexus (bladder neck) may induce a better micturition response than stimulation higher on the bladder-wall. Newly available commercial microstimulators should be further studied for the treatment of urinary retention.

Preliminary observations of a synergistic bladder-sphincter relationship following spinal cord injury in a quadruped animal

BACKGROUND/OBJECTIVES

High urethral resistance or detrusor-sphincter dyssynergia (DSD) is characterized by obstructed voiding during bladder contractions. DSD is caused by an exaggerated pelvic floor reflex resulting from sensory input from elevated pressure in the bladder that produces reflex constriction of the urethral sphincter. The objective of this study was to determine whether sensory input from the bladder produced synergistic or dyssynergic pelvic floor reflexes following SCI in an animal model.

METHODS

A pelvic floor reflex that shares the same motor pathway with DSD is the bulbocavernosus (BC) reflex. The BC reflex was elicited with electrical stimulation in 4 male cats with T1 spinal injury, and recorded as an anal sphincter contraction. Recordings were obtained during control and elevated bladder pressures. Increased bladder pressure was induced with either manual pressure (Crede procedure) or spontaneous contractions resulting from bladder filling.

RESULTS

During the control period, the BC reflex indicated by the peak anal pressure response was 23 +/- 6 cmH2O. During elevated bladder pressure of 34 +/- 18 cmH2O, the BC response decreased to 10 +/- 3 cmH2O (not significant), showing a synergistic relationship. Anal sphincter tone between BC reflex tests showed a dyssynergic response. All 4 animals showed increased tone during elevated bladder pressures that averaged 9 +/- 5 cmH2O. Because abdominal pressure was not recorded, the significance is not clear. However, there was further support of a dyssynergic relationship based on increases in the anal and urethral electromyography recordings and some pelvic floor spasms during the elevated bladder pressure.

CONCLUSIONS

Because 2 different pelvic floor activities were observed during increased bladder pressures, this animal model may be described best as a mixed model. This model shows both synergistic and dyssynergic relationships between the bladder and the BC contractions. Although observed changes were not significant, the unique observations of synergistic bladder-sphincter activity shown by the inhibited BC reflex is in marked contrast to the strictly dyssynergic bladder-sphincter relationship seen in SCI patients.

Predicting urethral area from video-urodynamics in women with voiding dysfunction

AIMS

Mathematical models are useful for developing predictive parameters for characterizing the biomechanics of voiding dysfunction. The goal of this project was to test a one-dimensional steady flow model used to predict the minimum cross-sectional urethral area from urodynamic data.

METHODS

Nine adult female subjects underwent video-urodynamic testing. By using Bernoulli's formula and the Torricelli theorem, the minimum urethral area was predicted from pressure and flow rate at the moment of maximum flow rate during voiding. This prediction was compared with the minimum cross-sectional area of the urethra, which was calculated from minimum urethral diameter as measured from fluoroscopy, assuming a circular cross-section.

RESULTS

The maximum flow rate during voiding was 14.4 +/- 3.0 mL/sec. Mean bladder, abdominal, and detrusor pressures simultaneous with maximum flow rate were 63 +/- 7, 29 +/- 6, and 33 +/- 6 cm H(2)O, respectively. Mean minimum cross-sectional area of the urethra from fluoroscopy was 8.0 +/- 2.0 mm(2). Mean minimum cross-sectional area of the urethra predicted by the mathematical model was 5.0 +/- 1.0 mm(2) using bladder pressure and 7.0 +/- 2.0 mm(2) using detrusor pressure. There were no significant differences between the three cross-sectional area measures. However, when area predictions were expressed as percentage of fluoroscopic measurements, the estimate from detrusor pressure (97 +/- 13%) was significantly larger than the estimate from bladder pressure (69 +/- 7%).

CONCLUSIONS

A steady flow model is accurate enough on average to describe urine flow in the urethra. However, it may not be sufficiently accurate to aid in diagnosis of individuals.

Bladder pressure monitoring during intermittent catheterization: a comparison of gauges and methods

AIMS

We previously have investigated a technique for serial bladder pressure measurements in patients with spinal cord injury (SCI) using intermittent catheterization. In the current study, we compared an FDA-approved digital gauge with the previously studied analog gauge and studied the effects of hydrostatic pressure differences.

METHODS

Either a digital or an analog pressure gauge was attached to each subject's catheter just before bladder catheterization. Both immediate and stable pressures were recorded. The bladder was then drained until nearly empty and pressure was again recorded (almost empty bladder pressure). Detrusor pressure was estimated as full minus almost empty bladder pressure. Bladder pressures greater than 40 cm H2O were presumed to represent bladder contractions. To investigate the effects of hydrostatic pressure, additional measurements, adjusting the level of the air-urine meniscus, were obtained in three subjects.

RESULTS

Recordings were made from nine SCI subjects using both gauges. Estimates of detrusor pressure, with and without bladder contractions, and associated bladder volumes, were not significantly different between digital and analog gauges. In the absence of bladder contractions, detrusor pressure with the meniscus at the end of the catheter (5 +/- 1 cm H2O) was significantly lower than that recorded with no adjustment of the urine meniscus (12 +/- 1 cm H2O).

CONCLUSIONS

Standardizing measurement techniques to equalize hydrostatic pressures should facilitate reliable estimates of detrusor pressure. Frequent monitoring of bladder pressure using this technique may assist with the urological care of SCI patients.

A database of self-reported secondary medical problems among VA spinal cord injury patients: its role in clinical care and management

An interactive data management (IDM) system for the Spinal Cord Injury (SCI) Service was developed to collect self-reported patient data related to secondary medical complications and to provide feedback to the SCI rehabilitation team. The long-term objective is to improve clinical care through a process of staff review of current rehabilitation programs in the areas of prevalence, prevention, and management. Based on data from the first 99 SCI patients visiting the clinic and hospital after the installation of the IDM system, SCI patients reported high rates of current problems with spasticity (53 percent), pain (44 percent), and pressure ulcers (38 percent). Respiratory (12 percent) and bowel (14 percent) problems were less common current problems. The SCI staff questioned the reportedly high spasticity rates. They thought that the patients' answers might have indicated simply the occurrence of spasticity, rather than the more important issue of severe spasticity that interferes with daily activities. The staff suggested several additional spasticity questions to add to the study. In other areas, only a small percentage of patients wanted to talk with a therapist about prevention of pressure ulcers. Patients who had urinary problems consistently reported five urinary signs (e.g., cloudy urine). The clinical staff found these data informative and stated that they should continue to be collected.

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.

Use of a neuromuscular stimulator to increase anal sphincter pressure

OBJECTIVES

The objective of this study was to determine if short periods of electrical stimulation with perianal electrodes could increase anal pressures.

MATERIAL AND METHODS

Anorectal responses to electrical stimulation were evaluated in five healthy SCI patients. Anorectal pressures were recorded with a small pressure-recording balloon before, during, and immediately following stimulation. A battery-powered stimulator with self-adhering surface electrodes, two inches in diameter was used. Stimulating parameters consisted of 300 micros pulse duration, 35 Hz stimulating frequency. A current response study was conducted by using short periods of electrical stimulating with currents from 0-100 mA until a maximal pressure was recorded. Each current setting was conducted for 13.2+/-9.7 s before increasing to the next higher current, and fatigue was reduced by including a 5-minute rest between stimulations.

RESULTS

Four of the five subjects had strong anal contractions with perianal stimulation. Increases in pressure ranged from 38 to 125 cm H2O based on maximal responses at currents ranges of 60 to 100 ma. Even during the short periods of stimulation used here, fatigue was apparent. There was an average drop of 11% in anal pressure over the 13 s of stimulation. Rectal pressures were unchanged with perianal stimulation.

CONCLUSIONS

Perianal stimulation with surface electrodes is an approach that might be considered in the future for management of fecal incontinence in individuals with spinal cord injury. Further studies are needed to assess the feasibility of using chronic perianal surface electrical stimulation to sustain anal sphincter contractions.

Indications for a home standing program for individuals with spinal cord injury

Additional analyses were conducted on a recently published survey of persons with spinal cord injury (SCI) who used standing mobility devices. Frequency and duration of standing were examined in relation to outcomes using chi square analyses. Respondents (n = 99) who stood 30 minutes or more per day had significantly improved quality of life, fewer bed sores, fewer bladder infections, improved bowel regularity, and improved ability to straighten their legs compared with those who stood less time. Compliance with regular home standing (at least once per week) was high (74%). The data also suggest that individuals with SCI could benefit from standing even if they were to begin several years after injury. The observation of patient benefits and high compliance rates suggest that mobile standing devices should be more strongly considered as a major intervention for relief from secondary medical complications and improvement in overall quality of life of individuals with SCI.

Modified alpha wrap techniques for dynamic urethral graciloplasty in an animal model

Urethral sphincter reconstruction with a stimulated skeletal muscle flap has been used for treatment of severe intrinsic sphincter deficiency. Urethral strictures and failures were reported in some of the initial experiences. The etiology of these problems is not known, but elevated resting urethral pressures and excessive urethral displacement with stimulation are possible causes. We modified two operative techniques in forming dynamic urinary graciloplasty (DUG) in an attempt to minimize resting urethral pressure without stimulation and urethral mobility during stimulation. Two types of DUG were used. In the first group, a small flap (partial muscle wrap) from the gracilis muscle with an attachment site on the muscle was constructed in four dogs. In the second group, three dogs with a modified alpha wrap and proximal attachments were used. All of the gracilis muscle wraps were stimulated using an implanted programmable pulse stimulator with electrodes attached over the motor nerve. Following a 2-week, postrecovery period, urethral pressure measurements were obtained with and without stimulation. Five weeks were used for stimulation to condition the muscle. This was followed by 4 weeks of continuous stimulation. Thus, devices were implanted for 11 weeks. Before conditioning of the muscles was initiated, the partial muscle wrap pressure at rest was 42 +/- 27 cm H2O, which was higher than the incomplete alpha wrap resting pressure of 20 +/- 4 cm H2O. Stimulated partial flap pressure was 161 +/- 50 cm H2O, and stimulated modified alpha wrap pressures was 71 +/- 27 cm H2O. After conditioning with the modified alpha wrap, the resting and stimulated pressures were unchanged from before conditioning. Technical problems precluded collection of data during the conditioning period in dogs with partial flaps. During stimulation, the partial muscle wrap demonstrated marked deviation, whereas the modified alpha wrap had minimal urethral movement. Postmortem evaluation indicated no urethral stricture or fistula formation with either of the two types of wraps. The modified alpha wrap had several positive features. Advantages over the partial wrap were minimal resting pressures, reduced urethral mobility, and adequate sustained pressures during stimulation. Therefore, in contrast to the partial gracilis muscle wrap, aspects of the incomplete alpha wrap should be considered further for DUG.

Estimating detrusor pressure at home in pediatric patients with myelomeningocele

PURPOSE

We evaluated a method of estimating detrusor pressure at home in patients with myelomeningocele who perform clean intermittent catheterization to empty the bladder.

MATERIALS AND METHODS

Patients with myelomeningocele who perform clean intermittent catheterization underwent cystometry. At home they determined bladder pressure before draining a full bladder and after partial draining with the bladder almost empty. Home estimate of detrusor pressure was calculated using the formula, full bladder pressure - almost empty bladder pressure.

RESULTS

A total of 4 boys and 5 girls with a mean age plus or minus standard deviation of 9.6+/-7.9 years who were enrolled in our study made 16.9+/-15.2 home bladder pressure and volume recordings weekly each during a mean of 5.8+/-4.3 months. Mean bladder capacity determined at home was significantly greater than cystometric capacity (354+/-185 versus 250+/-146 ml.). At a mean home and cystometric volume of 190+/-110 ml. full bladder pressure at home was not significantly different from cystometric vesical pressure (31.0+/-8.8 versus 27.5+/-7.5 cm. water). At a mean volume of 23+/-15 ml. mean home almost empty bladder pressure was not significantly different from cystometric abdominal pressure at full and almost empty volumes (14.1+/-5.5 versus 17.0+/-7.4 and 15.5+/-5.8 cm. water). Mean home estimate of detrusor pressure was not significantly different from cystometric detrusor pressure (17.0+/-6.3 versus 10.2+/-9.2 cm. water).

CONCLUSIONS

Estimation of detrusor pressure at home is reliable and accurate in patients who perform clean intermittent catheterization. These pressure determinations may be used as a baseline for rapid identification of changes in bladder function.

Evaluation of a suture electrode for direct bladder stimulation in a lower motor neuron lesioned animal model

The purpose of this study was to evaluate a "suture" type electrode for direct bladder stimulation in an animal model of a lower motor neuron lesion. During an initial surgery, five male cats were instrumented under anesthesia using multistranded, 316 LVM, stainless-steel, wire electrodes implanted on the bladder wall serosa above the trigone area. Electrodes were constructed with a needle attached to the end that was removed after suturing the electrode in place. Additional instrumentation included urinary bladder catheters (tubes) for pressure recording and filling, and hook type electrodes for leg and pelvic floor electromyography recording. Chronic bladder filling and stimulation studies were conducted in tethered animals three to four weeks following surgery. To test these electrodes in a spinal cord injury model, a lower motor neuron lesion was performed including the sacral cord and complete nerve roots at L6 and below. These animals were evaluated during weeks 3 and 10 after injury. Direct bladder stimulation induced active contractions and voiding both before and after spinal cord injury. Effective stimulation parameters consisted of 40 pulses per s, 300 micros to 1 ms pulse duration, a stimulation period from 3 to 4 s, and a stimulation current from 10 to 40 mA. Fluoroscopy revealed an open membranous urethra during stimulation and following stimulation. A small diameter penile urethra was observed to limit flow. Postmortem evaluation of the suture electrode revealed no abnormalities such as corrosion, migration into the bladder lumen or displacement. These findings indicate that suture electrodes are suitable and effective for short-term implantation in the lower motor neuron animal model.

Follow-up assessment of standing mobility device users

The use of standing devices by spinal cord-injured subjects was investigated through a national survey of a sample of individuals who returned their manufacturer's warranty card to two companies. We obtained a 32% response rate (99/310). The majority of respondents were male (87%) with a median age between 41 and 50 years. Seventy-seven percent were paraplegic and 21% were quadriplegic. Forty percent had between 1 and 5 years experience with their device, and 84% of those responding were currently using their standing device. Forty-one percent used their standing device one to six times a week; two-thirds stood between 30 minutes and 1 hour for each use. Less than 10% of subjects experienced any side effects, such as nausea or headaches, from standing. Twenty-one percent of subjects reported being able to empty their bladder more completely. There was also a favorable response by some individuals on the effects of the standing devices on bowel regularity, reduction of urinary tract infections, leg spasticity, and number of bed sores. Finally, 79% of subjects highly recommended use of standing devices to other people with spinal cord injury. The positive responses of individuals using standing devices is a strong recommendation for the assistive technology community to make these devices more available to individuals with spinal cord injury.

Urodynamic verification of noninvasive back-pressure recordings from the urinary bladder

Obstructive voiding is best evaluated with urodynamics, especially simultaneous measurement of bladder-pressure and urine flow rates. As an alternative to catheterization for urodynamics, noninvasive back-pressure methods using an external condom system have been introduced. This device uses one side tube in the condom for pressure recording and an outlet tube that is clamped for short periods of time during voiding. However, there have been problems with accurate back-pressure recording, including leaking, clamping techniques, hydrostatic pressures associated with pressure recording below the level of the symphysis pubis, and assessment of back pressures in relation to bladder and detrusor pressures. To address these issues, we have modified the condom for passing a catheter into the urethra for simultaneous direct bladder and back-pressure recording. The clamping device on the outlet tube also has been modified to produce back flushing of urine in addition to clamping. Hydrostatic issues have been addressed by making pressure recordings at the level of the symphysis pubis. Seven patients with obstructive symptoms were evaluated using these new devices. Back pressures were not statistically different than detrusor pressures recorded with a urethral catheter. Thus, the modifications have improved back-pressure recording techniques. The use of noninvasive back-pressure recording may be an important adjunct in the evaluation of obstructive uropathy.

Home bladder pressure monitoring in children with myelomeningocele

PURPOSE

We evaluate a pressure gauge used at home for patients with myelomeningocele on clean intermittent catheterization to provide a system for inexpensive frequent monitoring of bladder pressures.

MATERIALS AND METHODS

Subjects with myelomeningocele using clean intermittent catheterization underwent cystometry in the laboratory. At home they obtained weekly volumes and bladder pressures before and after emptying. Home estimate of detrusor pressure was defined as full bladder pressure minus empty bladder pressure. Medication changes, subject position and urinary tract symptoms were noted.

RESULTS

A total of 11 subjects 10.5+/-7.3 years old have been enrolled and have made 16.7+/-12.6 weekly home bladder pressure and volume recordings in 4.7+/-3.1 months. Bladder capacities measured at home were 132+/-47% of cystometric capacities. At volumes of data overlap home full pressures (31+/-10 cm. water) were not statistically different from cystometric vesical pressures (25+/-9 cm. water). Home empty pressures (7+/-4 cm. water) were similar to cystometric abdominal pressures (14+/-8 cm. water). Home estimates of detrusor pressures (23+/-7 cm. water) magnified differences in full and empty pressures, and were significantly greater than cystometric detrusor pressures (11+/-11 cm. water). In 2 subjects significant increases in home full pressures occurred, which were associated with cessation of anticholinergic medication and infection.

CONCLUSIONS

Home monitoring of bladder pressure is a simple, inexpensive and accurate method of obtaining frequent bladder pressures in patients with myelomeningocele. These pressures are consistent over a large range of volumes and times, and could potentially be used to identify quickly changes in patient condition.

Botulinum toxin injections for voiding dysfunction following SCI

Botulinum toxin (BT) injections have been used successfully to treat spastic muscle conditions, including detrusor-sphincter dyssynergia (DSD) seen in spinal cord injury (SCI) patients. In our urology clinic, we used BT to treat three SCI patients who had voiding dysfunction, using a transperineal needle with electromyographic (EMG) monitoring. Two of the patients reported excellent results following the treatment. One patient, with whom the staff had difficulty doing intermittent catheterization (IC), improved significantly. The other patient had improved voiding with an external catheter and minimal urinary residual. The third patient had no improvement of leg spasms with his voiding dysfunction and required a sphincterotomy. Although patients may need repeat injections, BT is minimally invasive and easy to administer with no side effects. Overall, BT injection is an excellent method of managing voiding in SCI patients, especially those on continuous external catheters and with IC management who refuse or are not good candidates for surgery.

Optimization of sacral ventral root stimulation following SCI: two case reports with six-month follow-up

Sacral ventral root stimulation in conjunction with sacral dorsal rhizotomy has been effective in promoting voiding in individuals with upper-motor-neuron spinal cord injury. We report on two patients who had variable voiding responses to stimulation during the first six months after electrode implantation. We used videourodynamic records and daily voiding records to characterize their voiding difficulties. Different methods were used to improve voiding, including seating adjustments and changes in stimulation parameters. The first patient was unable to empty his bladder on a regular basis with stimulation using 24 pulses per sec stimulating frequency for the first two months after implantation. Voiding was substantially improved by using 35 pulses per sec. At the end of six months, he is regularly emptying his bladder with stimulation and is on an every-second-day bowel program. However, his bowel program has been irregular. The second patient had very good voiding when stimulation was applied in bed, but he had poor voiding with high residual volumes when sitting in his wheelchair. Voiding was improved when he used a wheelchair cushion that was cut out in the back or lifted his buttocks off the chair. These procedures appeared to reduce perineal pressures. This patient has bowel care on alternate days and his bowel care time has been reduced following implantation of the device. Neither of the patients experienced an erection with the device. Both patients feel positive about their implant experience.

Home monitoring of bladder pressure and volume in individuals with spinal cord injury and multiple sclerosis

Individuals with spinal cord injury and multiple sclerosis are at high risk for developing kidney dysfunction due to high bladder pressures. We have developed a device for frequent monitoring of bladder pressures at home in those patients who use intermittent catheterization to empty their bladders. Of eight subjects enrolled in the study, only five conducted home recording of pressure. Vesical and abdominal pressures measured at home were significantly lower than clinical cystometric pressures. However, subtracted detrusor pressures obtained from home records and cystometric records were not significantly different. The home detrusor pressures were consistent over a large time and volume range. Therefore, the home monitoring method could be used to establish a normal range of bladder pressures at home and to rapidly identify high bladder pressures in advance of upper urinary tract deterioration.

Short-term bladder-wall response to implantation of microstimulators

This study examined the histological response of the bladder wall serosa to the implantation of wireless microstimulators secured with a single polypropylene suture. Two to three microstimulators were implanted in each of three casts for an eight week implantation period to allow sufficient time for a bladder-wall injury-response to develop. Gross observation revealed encapsulation of the microstimulators with no perforation to the bladder lumen or migration from the bladder wall. Histological evaluation confirmed that all the microstimutators were encapsulated with a thin connective tissue sheath and a thickened subserosal layer. There was no remarkable difference in tissue morphology compared with normal bladder wall sections for five of seven stimulators. Two microstimulators in one cat revealed a moderate to severe inflammatory response confined to a small area around the stimulator. In a second cat, a suture extended through the bladder wall. The microstimulators were observed with a scanning electron microscope after explantation. The electrode surfaces, bonding interface between silicon and glass and insulating films that were exposed to biological fluids were carefully inspected. All these observations indicate that the glass capsule reliably protected the sealed cavity of the microstimulators from moisture. These results indicate the microstimulator should be considered for further studies such as effects of stimulation and long-term implantation.

Multielectrode nerve cuff stimulation of the median nerve produces selective movements in a raccoon animal model

In this study, an electrode system consisting of twelve small platinum dot electrodes imbedded in a spiral silicone rubber insulating cuff was used to investigate the feasibility of selective (regional) stimulation of the median nerves of the raccoon. Acute experiments in four raccoons consisted of functional responses observations, isometric force recordings from tendon attachments and postmortem fascicular mapping. Functional responses (elbow, wrist and/or digit flexion, pronation and/or thumb abduction) to selective stimulation were noted as dependent upon cuff electrode configuration (longitudinal tripole with and without field steering, as well as a transverse bipolar arrangement) and current level (threshold, 1/2 maximal, maximal). Muscle force recruitment curves (force as a function of stimulus amplitude) were plotted for flexor digitorum superficialis, flexor digitorum profundus, flexor carpi radialis, palmaris longus and pronator teres of three raccoons. Fascicular maps at the level of the nerve cuff were created indicating the approximate position of innervation to each of the aforementioned muscles, as well as other innervation such as paw fascicles, sensory fascicles, and elbow innervation (such as coracobrachialis). The greatest selectivity was observed at or near threshold current levels. In all four raccoons studied, a threshold electrode choice and stimulation strategy could be identified enabling selective production of either digit flexion, wrist flexion and/or digit and wrist flexion. It was possible to elicit a selective pronation response at threshold in three of the four animals. Selective elbow flexion at threshold could be produced in all four experiments. With stronger currents, additional movements were usually induced. The raccoon therefore appears to be a suitable, if challenging, animal model for further development of not only nerve cuff electrode approaches but perhaps other stimulation electrode technologies prior to human neuroprosthetic studies.

Testing peripheral somatosensory neuroprostheses by recording from raccoon cortex

A topologically organized representation of the body surface exists within the mammalian somatosensory cortical areas such that stimulation of a part of the body surface will produce a response in a localized region of the contralateral somatosensory cortex. Because of this topography, we propose that the selectivity of a peripheral somatosensory neuroprosthetic electrode array can be tested by noting whether the locus of maximum activation in the cortex moves in a consistent manner when differing portions of the array are stimulated. We further propose that the raccoon might well be the ideal animal in which to test this hypothesis, since the raccoon has a rather unique cortical somatosensory area where each digit is represented in individual subgyri around the tri-radiate sulcus. To demonstrate the feasibility of this concept, a pilot study was carried out in one raccoon under barbiturate anesthesia. The median nerve was stimulated via selective quadrants of a nerve cuff array of four tripolar electrodes implanted around the nerve. Cuff stimulation produced short-latency evoked surface potentials in the digit areas of the raccoon first somatosensory cortex. Response selectivity could be demonstrated, as could a separation between thresholds for producing movement or producing cortical evoked potentials. The sensory and motor responses elicited were consistent with the orientation of the median nerve within the cuff as determined by a postmortem identification of the muscle innervation pattern of the nerve.

Feasibility of implant driven micturition in paraplegic dogs

OBJECTIVE

This study evaluates the feasibility of using existing technology for implant driven micturition in paralyzed dogs (part I) and also examines a less invasive technique for implant driven micturition (part II).

STUDY DESIGN

Part I. Sacral nerve root dimensions and bladder and urethral pressure responses to intradural and extradural sacral nerve root stimulation were measured to determine the optimal location and size for sacral nerve root electrodes. Part II. Sacral nerve roots were stimulated via wire electrodes introduced into the S2 foramina.

ANIMALS OR SAMPLE POPULATION

Ten dogs (five dogs in part I and five dogs in part II).

METHODS

Part I. Microtip pressure transducers were used to monitor bladder and urethral pressure responses to sacral nerve root stimulation with tripolar hook electrodes. After euthanasia, sacral nerve root, and spinal canal dimensions were measured. Part II. Bipolar electrical stimulation of the sacral nerve roots was performed by introducing wire electrodes into the S2 foramina. Bladder and urethral pressures were recorded as in part I.

RESULTS

Part I. Stimulation of SI produced an increase in urethral, but not bladder, pressure. Stimulation of S2 or S3 produced increases in bladder pressure and decreases in urethral pressure. Intradural and extradural nerve roots were not significantly different with respect to nerve dimensions or effects on nerve stimulation. Part II. High bladder pressures were achieved, but effective voiding could not be produced, primarily because of urethral resistance.

CONCLUSIONS

Part I. Extradural implantation was determined to be the most appropriate site based on ease of dissection, nerve root dimensions, and decreased risk of iatrogenic trauma. Enough space is available to implant two to four tripolar spiral nerve cuffs. Part II. Transforaminal sacral nerve root stimulation did not effectively empty the bladder.

CLINICAL RELEVANCE

Clinical trials in paraplegic dogs are necessary to evaluate the number of sacral nerve cuff electrodes necessary to produce effective bladder emptying.

Direct bladder stimulation with suture electrodes promotes voiding in a spinal animal model: a technical report

To determine the efficacy of a new electrode for direct bladder stimulation, five male cats were instrumented during anesthesia. Multistranded, 316LVM, stainless-steel, wire electrodes were implanted on the bladder wall serosa above the trigone area. The electrodes were made with a needle attached to the end that was cut off after suturing the electrode in place. Additional instrumentation included tubes for pressure recording and filling, and hook electrodes for leg and pelvic floor EMG recording. Bladder filling and stimulation studies were conducted in tethered animals 1 to 2 weeks following recovery. Chronic studies were conducted following recovery in tethered animals. To test these electrodes in a spinal cord injury (SCI) model, a T-1 level complete lesion was performed on the above instrumented animals. Spinal animals had successful direct bladder stimulation that induced active contractions and voiding both before and after SCI, but voiding rates were higher more than 2 weeks after SCI and at larger initial bladder volumes. Optimum stimulation parameters consisted of 40 pulses per second, 300 microseconds to 1 ms pulse duration, a stimulation period of 3 to 4 s, and 10 to 40 mA. Urethral resistance, indicated by a urethral function measure, showed that stimulation had no adverse effect on urethral function, and fluoroscopy showed an open membranous urethra during stimulation and voiding. The cat has a small penile urethra that is the flow rate controlling zone. The suture electrode did not corrode, erode into the bladder, or become dislodged, and appears suitable for chronic implantation.

Do direct current electric fields enhance micturition in the spinal cat?

Changes in micturition behavior and motoneuron ultrastructure were studied in spinal cats to determine the effects of direct current (DC) electric field treatment. Adult cats received a complete injury at T8. A treatment group with an implanted 15 microA DC source and electrodes positioned near the lesion site was compared with non-treatment groups that were either operated or unoperated. Both bladder emptying with Crede and the withdrawal reflex were improved in the treatment group compared with the non-treatment group. Urodynamic procedures showed that high urethral resistance and pelvic floor activity following spinal injury was partially reduced in the stimulated cat, indicating inhibition of the urethral sphincter. The ultrastructural analysis of Onuf's nucleus suggested a similar synaptic input in all three groups. In conclusion, possible activation of inhibitory processes and/or neural plasticity best explain the early improvement of bladder function seen following electrical stimulation.

The raccoon as an animal model for upper limb neural prosthetics

The raccoon was evaluated as an animal model for upper limb neural prosthetics. This animal was selected primarily because the functional use of its forelimb mimics in many ways the usage in humans and because of its optimal size and commercial availability. Eight cadaver and fresh specimen forearms were dissected. Important characteristics of the raccoon forearm were: 1) large muscles in the volar forearm, 2) large digits in the paw that appear more similar to humans than to other species such as cat or dog, 3) persistence of two median nerve cords into the forearm, 4) no separation of individual tendons of flexor digitorum superficialis and flexor digitorum profundus in the carpal tunnel, 5) a small thumb digit with little function and 6) a primary origin of flexor policis longus on the proximal ulna with a secondary origin on the radius. Four animals were anesthetized and responses of the forearm and paw to stimulation of the volar forearm muscles with percutaneous electrodes were evaluated. A pair of stimulating electrodes was placed in each of four muscles or muscle groups. Recording electrodes were placed in two muscles which showed the greatest separation of muscle movements to stimulation. Stimulation currents just above threshold produced discrete motion as well as recordable EMG M-waves. Incremental increases in stimulation current produced an increase in M-wave amplitude up to a maximal stimulating current. Torque recordings for pronation, wrist flexion and finger flexion showed graded and selective responses. These results including anatomical descriptions indicate both the limitations of this animal model and its potential use in the development of upper limb neural prosthetics. We conclude that the raccoon model may be superior to other nonprimate animal models such as the cat because of its extensive forearm and paw movements.

Effects of low charge injection densities on corrosion responses of pulsed 316LVM stainless steel electrodes

The safe charge injection density for pulsing of 316LVM electrodes has been reported to be 40 microC/cm2. However, only 20 microC/cm2 is available for nonfaradic charge transfer and double layer charge injection. Therefore, we evaluated long term pulsing at 20 microC/cm2 with capacitor coupling.

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.

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.

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.

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.

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.

Comparison of electrical transients and corrosion responses of pulsed MP35N and 316LVM electrodes

Functional neuromuscular stimulation (FNS) is often limited by electrode malfunctions such as corrosion and breakage, particularly for intramuscular and epimysial type electrodes. As a result, the electrochemical charge injection characteristics and corrosion responses of single strand 316LVM stainless steel and MP35N nickel-cobalt alloy electrodes were evaluated in vitro. For charge balance, capacitor coupled monophasic protocols with varying charge injections were employed. Electrodes were evaluated with either positive-first or negative-first pulses, 60 Hz, 100 microsec pulse duration, and stimulation periods from 100 to 240 hours. Charge injection densities ranged from 20 to 80 microC/cm2. For both anodic-first and cathodic-first pulsing, the potential transients for the MP35N electrodes were more extreme than for the 316LVM electrodes over the test period, and increased corrosion was apparent on the MP35N electrodes from both optical and scanning electron microscopy. Therefore, 316LVM, but not MP35N, may be suitable for FNS applications with charge injection densities less than 40 microC/cm2.

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.