Norbert F. Kaula

The effect of magnetic resonance imagers on implanted neurostimulators.

This in‐vitro study was designed to investigate the safety of various implanted neurostimulators in magnetic resonance (MR) imagers. The effects of the static and changing magnetic fields and the radio frequency (RF) electromagnetic field generated by 0.35 and 2.5 T MR imagers on the voltage output of four models of implantable passive neurostimulafors and two models of implantable self‐powered neurostimulators was studied. The neurostimulators were mounted on a support and placed in the imagers. An oscilloscope monitored the voltages at the outputs of the neurostimulators. For an A very single‐channel stimulator, located at the isocenter, the amplitude of the output pulses induced by the 0.35 T imager was 6V; from a 1.5 T imager, it was 12 V. These amplitudes can cause discomfort and possible harm to a patient if the typical therapeutic value is 1–5 V. The amplitude of the stimulator receivers output decreased to relatively safe values beyond 40 cm from the isocenter. By contrast, there was no significant voltage output from the Medtronic SE‐4 receiver. For two models of self‐powered neurostimulators, the Medtronic Itrel and the Cordis MK If, the programmed stimulus parameters were not affected by the pulsed magnetic fields of the MR imagers. However, the RF fields at the isocenter heated the metal case of the stimulators. The rotational and linear forces produced by the fixed magnet on the Cordis MK II were judged to be too strong for a patient with this implant to be scanned. The study showed that patients with certain types of implanted neurostimulators can be scanned safely under certain conditions.

Intracavernous Pharmacotherapy for Impotence: Selection of Appropriate Agent and Dose

We performed a retrospective analysis of 101 impotent patients using intracavernous self-injections as primary therapy for vasculogenic impotence. A total of 70 patients used an average of 5.58 micrograms prostaglandin E1 (95% confidence interval 4.83 to 6.34 micrograms) as a single agent, and 31 injected 0.40 ml. (95% confidence interval 0.342 to 0.457 ml.) of a combination of papaverine (12 mg./ml.), phentolamine (1 mg./ml.) and prostaglandin E1 (9 micrograms/ml.). We describe the procedure to establish the dosage for home use and discuss the implications of the low dosages relative to previous reports.

Site of Deafferentation and Electrode Placement for Bladder Stimulation: Clinical Implications

Based on the clinical experience of treating neurogenic bladders by the electrical stimulation of the ventral sacral roots, neuroanatomical and neurophysiologic studies were designed to study the mechanism of detrusor-sphincter dyssynergia during electrical stimulation of the sacral roots. An experimental model was developed to decrease the stimulation response of the pelvic floor and external urethral sphincter muscles while preserving bladder contraction. The significance of the site of deafferentation and electrode implantation was evaluated under functional and clinical aspects. Our results indicate that a combination of intradural deafferentation and extradural electrode implantation may offer maximal deafferentation efficiency with minimal surgical risk. Intradural deafferentation is facilitated by a consistent arrangement of sacral roots with the dorsal roots running laterally to the ventral roots at the site of their exit from the dura. Detrusor-sphincter dyssynergia can be reduced by selective division of ventral sacral rootlets innervating the striated musculature of the pelvic floor and the urethral sphincter.

The Effect of Subatmospheric Pressure on the Simian Penis

The effects of subatmospheric pressure on the simian penis were studied in nine monkeys under anesthesia. A plastic cylinder was placed over the penis and suction applied until the gauge pressure was -100 to -200 cm. H2O. The intracavernous pressure decreased within one to three seconds to between -60 and -120 cm. H2O followed by a gradual increase as a result of blood flow into the corpora cavernosa. The intracavernous pressure recovery was 50% after 17 seconds and 100% by 30 to 60 seconds. These effects could also be observed when the penile base was partially constricted with a rubber band before applying the partial vacuum. Tumescence resulting from suction disappeared immediately when suction was terminated unless the base of the penis was constricted before and after the application of vacuum. In the latter case tumescence was prolonged (cavernous pressure between 60 and 120 cm. H2O) after suction. The cross-sectional area of the penis expanded to more than 150% of the flaccid state. The increase of intracavernous pressure from intracavernous papaverine injection was similar to that after suction with a constricting rubber band in place at the base of the penis. Subatmospheric pressure induces an expansion of the penis followed by increased blood inflow. The additional volume can be kept in the penis only if a constriction device is placed at the base of the penis. The tumescence induced by suction is passive, occurring without evidence of smooth muscle relaxation or release of neurotransmitters.

Intrathecal administration of substance P in the rat: The effect on bladder and urethral sphincteric activity

At the lumbosacral spinal cord level in the rat, substance P-positive neurons are present in dense concentration in the dorsal horn and the sacral parasympathetic nucleus. We undertook the present study to investigate the effect of intrathecal substance P (10 micrograms at the L6-S1 level) on urinary bladder and urethral sphincteric activity and to compare these effects with those of intravenous and intra-arterial administration. Three different bladder pressure responses were triggered by intrathecal substance P: (A) an immediate, strong bladder contraction (n = 5); (B) augmentation of the micturition reflex, as indicated by strong detrusor contractions in response to intravesical saline perfusion (n = 4); and (C) a slow, gradual increase to a high, steady peak (n = 8). The sphincteric electromyographic (EMG) activity was consistently increased. When substance P was given intravenously (n = 10) and intra-arterially (n = 3), the form, duration, and maximal amplitude of bladder contractions (owing to a direct smooth-muscle action) were comparable with those of Group A. The effects in intrathecal Groups B and C suggest that substance P provides a tonic influence on motor horn cells and on the preganglionic neurons in the sacral parasympathetic nucleus at the lumbosacral spinal cord level, where neuronal circuits controlling bladder and sphincteric activity are located.

The Latissimus Dorsi Muscle for Detrusor Assistance: Functional Recovery after Nerve Division and Repair

The treatment of choice for bladder atonia is clean intermittent catheterization. To eliminate the catheter-related morbidity and increase the quality of life for patients with an atonic bladder, the restoration of bladder contractility would be desirable. Based on our hypothesis that skeletal muscle might augment bladder contractility, we designed the present study to examine the ability of the latissimus dorsi muscle in situ to empty a bladder-like reservoir and to regenerate after division and repair of the supplying motor nerve. In 4 dogs, the left latissimus dorsi muscle was dissected, mobilized and wrapped around a bladder substitute (100-ml. silicone reservoir). Stimulation of the thoracodorsal nerve resulted in the evacuation of 63.8 +/- 6.2% of the reservoirs volume and a maximum pressure of 109.5 +/- 18.6 cm. H2O. Four months later, the thoracodorsal nerve supplying motor control to the muscle was transected and microsurgically reanastomosed. Using transcutaneous stimulation, we recorded the pressure generation and resulting evacuation at regular intervals for 8 months (that is, 12 months after the initial surgery). At the end of this period, the pressure was 79.3 +/- 12.1 cm. H2O (72.4% of the initial value), expelling 48.3 +/- 6.7% of total volume. This long-term study demonstrates: (1) the ability of the transposed latissimus dorsi muscle to evacuate a bladder-like reservoir; and (2) the regenerative potential of muscle and nerve after nerve transsection and repair. Use of skeletal muscle, which can be readily stimulated, may serve to facilitate bladder emptying and provide a treatment alternative to intermittent catheterization in the future.

The latissimus dorsi bladder myoplasty to assist detrusor function

Abstract The objective of this study was to evaluate whether an innervated skeletal muscle might augment detrusor function. In four dogs we performed the latissimus dorsi myoplasty, a transfer of the latissimus muscle as an innervated free flap wrapped around the bladder. Stimulation of the latissimus dorsi free flap initially achieved an average bladder pressure of 45.8 ± 8.41 cm H2O, sufficient for partial evacuation. After 4 months the muscle generated a maximal pressure of 82 cm H2O, resulting in an evacuation of 27.7%. For selected patients, the latissimus dorsi bladder myoplasty may provide an alternative to intermittent catheterization in the future.