Preliminary experience with percutaneous laser disc decompression in the treatment of sciatica.

OBJECTIVE: To examine the usefulness of percutaneous laser decompression of a herniated lumbar intervertebral disc. DESIGN: A case series. SETTING: A university-affiliated hospital. PATIENTS: Sixteen patients with clinical and radiologic evidence of herniated lumbar intervertebral discs. INTERVENTIONS: Percutaneous introduction of a fine optical fibre into a herniated lumbar disc and delivery of short pulses of laser energy. MAIN OUTCOME MEASURE: The relief of intractable leg pain. RESULTS: Nine of 14 patients with intractable leg pain experienced total relief after percutaneous laser disc decompression. Four patients required subsequent microsurgical discectomy, and one required a decompressive laminectomy. Of the two patients who had back pain as their major complaint, one required microsurgical discectomy after laser disc decompression. CONCLUSIONS: Percutaneous laser disc decompression can relieve sciatica caused by a herniated intervertebral disc. The technique requires limited use of health resources. Preliminary results suggest that an early return to work can be expected in patients successfully relieved of their leg pain.

Neurocardiac responses to vagoafferent electrostimulation in humans.

UNLABELLED: To determine if cardiac vagal tone is enhanced by vagal electrostimulation (VES), we examined the heart rate autospectrum (HRA) in eight patients with implanted stimulators for complex partial seizures. In four patients the VES was activated at 30 Hz and 500-msec pulse (HiStim group) compared to 2 Hz and 130-msec pulse for the LoStim group (n = 4). Continuous ECG and respiratory waveforms were recorded for 45 minutes every 8 hours (7-8 AM; 3-4 PM 11-12 PM) during resting supine wakeful epochs both before and 15 days after surgical implantation. From the HRA cardiac sympathovagal balance was expressed as the ratio of the low frequency (LF) power to the high frequency (HF) power. RESULTS: There were no presurgical differences between the groups in heart rate, its variance, or the energies contained in any autospectral band. The LoStim group showed no significant change in heart rate (HR), HF peak power, or LF:HF ratios during 2 weeks of VES. Conversely, in the HiStim group, the LF:HF peak power ratio (an expression of sympathetic dominance) decreased from 2.5 +/- 1.5 preimplant to 1.5 +/- 0.49 (P < 0.02) with VES. During VES there was a significantly higher HF power in the HiStim compared to LoStim group. No diurnal variations in HRA values were seen for either group. CONCLUSIONS: (1) A relationship exists between selective vagal nerve electrostimulation and the HRA; and (2) high stimulation frequency of the vagus nerve in man is associated with sustained augmentation of cardiac vagal tone throughout a 24-hour cycle.

Effects of chronic left vagal stimulation on visceral vagal function in man.

We examined the effects of chronic left vagal electrostimulation on afferent and efferent gastrointestinal vagal function in eight patients. Afferent function was assessed using cortical evoked responses to electrical stimulation of the esophagus and to direct vagal stimulation using the implanted left vagal electrode. Efferent gastrointestinal vagal function was measured by examining the basal, maximal, and sham fed stimulated gastric acid output prior to and with chronic left vagal electrostimulation. Esophageal electrostimulation produced a cortical evoked response consisting of three negative and three positive peaks within 400 msec after stimulation. Prior to vagal electrostimulation the mean conduction velocity of the afferent signal was measured at 8.72 +/- 3.39 m/sec, compatible with A-delta fibers involvement. Basal, maximal, and sham fed acid output were 1.11, 21.87, and 9.37 mmol/hour, respectively. The evoked response to esophageal electrical stimulation was not changed with chronic left vagal electrostimulation. Direct vagal stimulation also produced evoked potentials that were comparable to those obtained with esophageal stimulation. The mean conduction velocity was 6.26 +/- 2.72 m/sec (NS) so that there was no evidence of loss of myelinated fibers with chronic stimulation. No differences were detected in basal (1.29 mmol/h), maximal (21.64 mmol/h), or sham fed stimulated (8.03 mmol/h) acid output, showing that vagal electrostimulation has no effect on either total or vagally mediated acid output, an efferent vagal function. In conclusion, chronic left vagal electrostimulation has no significant adverse effect on gastrointestinal vagal function.

Effect of vagal nerve electrostimulation on the power spectrum of heart rate variability in man.

The power spectrum of heart rate variability contains low frequency (LF = 0.08-0.12 Hz) and high frequency (HF = 0.18-0.30 Hz) components said to represent neurocardiac rhythms. To verify whether such a relationship exists we report a unique study where the heart rate autospectrum was determined in a 28-year-old epileptic male patient with an implanted vagal electrical stimulator. The stimulator was activated at 20 Hz, 300 microseconds pulse, and 1.25 V. Continuous ECG and respiratory waveform records were obtained over 45 minutes every 8 hours (7-8 AM; 3-4 PM; 11-12 PM) with the stimulator ON, then 24 hours OFF and then 24 hours ON again. The overall LF:HF peak ratio increased from 0.64 to 1.99 (P less than 0.001) after the stimulator was turned OFF. There was a dramatic increase in the LF peak power (greater than 60%) and a corresponding decrease in the HF peak power (greater than 65%) when the stimulator was turned OFF. These values were reversed when the stimulator was turned ON again. In the early morning and late evening hours, there was a significant rightward shift in the LF peak power frequency (average 0.057 to 0.075 Hz) whenever the stimulator was ON. Otherwise, there were no significant circadian variations in any of the autospectral components. The results demonstrate an unequivocal relationship between selective vagal nerve electrostimulation and alterations in the heart rate autospectrum.

Secondary erythrocytosis due to a cerebellar hemangioblastoma: demonstration of erythropoietin mRNA in the tumor.

Cerebellar hemangioblastoma is a rare cause of secondary erythrocytosis. Although the erythrocytosis is a result of erythropoietin (Ep) stimulation, direct evidence of Ep synthesis by the tumor has been lacking. In an erythrocytotic patient with a cerebellar hemangioblastoma we found elevated levels of Ep in the tumor cyst fluid and for the first time demonstrated Ep mRNA in the tumor by Northern blotting. This finding confirms cerebellar hemangioblastoma as a site of ectopic Ep production.

The effect of intrathecal baclofen on the lower urinary tract in paraplegia.

The effect of intrathecal baclofen on urethral pressure was investigated in 6 spinal cord injured patients. Although the response was inconsistent, and further studies are necessary to define its role more clearly in the bladder management of these patients, its possible application as an alternative to sensory rhizotomy to improve bladder emptying in patients having sacral nerve stimulation procedures is discussed.

Intrathecal baclofen and the H-reflex.

Baclofen was given intrathecally to six patients with severe lower limb spasticity due to traumatic spinal cord injury. The effects of the drug on spasticity and the ratio between the maximum amplitude of the H reflex and the M response from the soleus (Hmax/Mmax ratio) were assessed. In each patient, spasticity was reduced following intrathecal baclofen and in four patients there was a reduction in the amplitude of the H reflex and Hmax/Mmax ratio. These results suggest that the Hmax/Mmax ratio may be helpful in establishing optimum drug dosage, particularly when the drug is used on a chronic basis.

FES for bladder: direct or indirect means?

Efforts to restore function to the neurologically disabled lower urinary tract by direct electrical stimulation of the bladder wall have met with only very limited success. This has been due to pain and cocontraction of bladder outlet mechanisms caused by presumed spread of the large currents required to effectively directly stimulate the detrusor muscle. Stimulation at the four anatomical sites of the sacral neural outflow on the other hand has been more successful. Conus medullaris stimulation has resulted in "good results" in just over half of the 28 patients so treated. Acceptance of this technique has been limited by the poor selectivity of the intramedullary electrodes in stimulating only the target motor neurons and the resultant clinical problems with the consequent stimulus current spread. Sacral anterior root stimulation has been used in at least 88 patients with generally good results. Cocontraction of the detrusor and external urethral sphincter are circumvented by the use of an intermittent pattern of stimulation. The primary disadvantage of this technique is the obligatory placement of the electrodes within the cerebrospinal fluid compartment. Clinical experience with stimulation of the extradural sacral mixed nerves is limited. Experimental studies indicate that success with this technique requires dorsal rhizotomy and pudendal neurotomy. Preliminary clinical experience suggests that these surgical manipulations may not be necessary for a successful outcome. The literature on clinical application of pelvic nerve stimulation is too limited for detailed comment on this technique. A definitive technique for restoration of bladder function by electrical stimulation remains to be developed.