Effects of lidocaine on blood flow and endoneurial fluid pressure in a rat model of herniated nucleus pulposus.

STUDY DESIGN: An experimental study was conducted to evaluate the effects of lidocaine on nucleus pulposus-induced pathophysiologic changes. OBJECTIVES: To investigate the effects of lidocaine on blood flow in the hind paws and endoneurial fluid pressure in the dorsal root ganglia in a rat model of herniated nucleus pulposus, and to clarify the therapeutic mechanisms of nerve root infiltration. SUMMARY OF BACKGROUND DATA: It has been shown experimentally that application of nucleus pulposus to the nerve roots increases endoneurial fluid pressure and decreases blood flow in the dorsal root ganglia and the corresponding hind paw. These changes are thought to be an important pathogenic mechanism associated with sciatica caused by disc herniation. Nerve root infiltration is one of the nonoperative effective therapies for radiculopathy caused by disc herniation. However, the therapeutic mechanisms still are unknown. METHODS: For this study, 21 Sprague-Dawley rats were used. Autologous nucleus pulposus was applied to the nerve root with a piece of Spongel containing lidocaine (lido group) or physiologic saline solution (control group). In Series 1 of this study (Blood Flow in the Hind Paw), blood flow in the corresponding hind paws was monitored continuously using a laser Doppler flowmeter before application of the test solutions, and every 5 minutes thereafter for an additional 3 hours in both the control (n = 5) and lido (n = 5) groups. In Series 2 of this study (Endoneurial Fluid Pressure in the Dorsal Root Ganglion), endoneurial fluid pressure was recorded with a servo-null micropipette system using glass micropipettes before and 3 hours after application of the test solutions in both the control (n = 6) and lido (n = 5) groups. After measurements, dorsal root ganglia were assessed for histology. RESULTS: In Series 1, blood flow in the corresponding hind paw in the control group showed significant reduction as compared with that of the Lido group, starting about 90 minutes after application (P < 0.01-0.05). Hind paw blood flow in the lido group did not show any reduction during measurements. In Series 2, the value of endoneurial fluid pressure in the lido group 3 hours after application was significantly lower than in the control group (P < 0.01). Interstitial (endoneurial) edema in the dorsal root ganglion in the lido group appeared to be qualitatively less than in the control group. CONCLUSIONS: The data indicate that lidocaine reduces the pathophysiologic changes in the dorsal root ganglion and hind paws induced by nucleus pulposus. These effects of lidocaine may relate to the mechanisms underlying the therapeutic effects of nerve root infiltration.

Prevention of compartment syndrome in dorsal root ganglia caused by exposure to nucleus pulposus.

STUDY DESIGN: An experimental study to clarify the effects of pentoxifylline, as an anti-tumor necrosis factor-alpha therapy on endoneurial fluid pressure in the dorsal root ganglion using an animal model of herniated nucleus pulposus. OBJECTIVES: To investigate the effects of anti-tumor necrosis factor-alpha therapy to nucleus pulposus-induced nerve root/dorsal root ganglion changes. SUMMARY OF BACKGROUND DATA: It has been reported experimentally that application of nucleus pulposus into epidural space induces morphologic and functional changes in the nerve roots and induces compartment syndrome in the dorsal root ganglia. Tumor necrosis factor-alpha has been considered a key pathogenic factor in the initiation and maintenance of neuropathic pain states. METHODS: A total of 11 adult, female Sprague-Dawley rats had their left L5 nerve roots and associated dorsal root ganglions exposed. Autologous nucleus pulposus was applied to the L5 nerve root just proximal to the dorsal root ganglion. A piece of Spongel (Yamanouchi Pharmaceutical Co., Tokyo) containing 20 microL of 1000 microg/mL pentoxifylline was applied with the nucleus pulposus (NP+PTX group). In control animals nucleus pulposus was applied with a piece of Spongel containing 20 microL of physiologic saline solution in a similar fashion (NP+PS group). Endoneurial fluid pressure was recorded with a servo-null micropipette system using glass micropipettes with tip diameters of 4 microm. Endoneurial fluid pressure in the dorsal root ganglion was measured before and 3 hours after application of test substances. After measurement of endoneurial fluid pressure, the nerve root and dorsal root ganglion were processed for histology and evaluated by light microscope. RESULTS: Values of endoneurial fluid pressure before application of test substances were as follows: 2.4 +/- 1.2 cm H2O in the NP+PS (control) group and 1.8 +/- 0.4 cm H2O in the NP+PTX group. There was no statistically significant difference between these two pretreatment measurements. However, values of endoneurial fluid pressure after application were as follows: 8.6 +/- 1.8 cm H2O in the NP+PS group and 2.9 +/- 0.8 cm H2O in the NP+PTX group. Values of endoneurial fluid pressure in the NP+PTX group were significantly lower compared with the NP+PS group. Histologic examination consistently showed only a slight degree of edema evident in the NP+PTX group compared with the NP+PS group. CONCLUSION: Pentoxifylline, an anti-tumor necrosis factor-alpha drug, prevented the dorsal root ganglion compartment syndrome caused by topical application of nucleus pulposus. Anti-inflammatory cytokine therapy may become an effective treatment of sciatica due to disc herniation.

Combined laminectomy and thoracoscopic resection of dumbbell-type thoracic cord tumor.

STUDY DESIGN: A study of five patients whose dumbbell or paraspinal tumors of the thoracic spine were managed by using thoracoscopic surgery is reported. OBJECTIVES: To report on the use of combined laminectomy and thoracoscopic resection for the management of dumbbell-type thoracic cord tumor. SUMMARY OF BACKGROUND DATA: Some posterior mediastinal tumors can be resected safely with video-assisted thoracic surgery. However, there are few reports on thoracoscopic resection of dumbbell and paraspinal tumors of the thoracic spine. METHODS: Five patients who received treatment for thoracic spine dumbbell tumors and paraspinal tumors were studied retrospectively. Three patients had dumbbell tumors, and two had paraspinal tumors of the thoracic spine. Preoperative evaluation of each patient included plain chest radiography, magnetic resonance imaging, and computed tomography. All patients underwent total resection by means of a combined posteroanterior approach, with thoracoscopic surgery for dumbbell tumors and thoracoscopic surgery alone for paraspinal tumors. In all patients, a gross total resection was achieved with this approach. All patients were observed for a minimum of 3 years. RESULTS: All patients regained their ability to walk 2 days after surgery, except for one patient who had a hemothorax. A gross total tumor resection, documented by magnetic resonance imaging, was performed on all patients. Follow-up imaging at 6 weeks, 1 year, 2 years, and 3 years after surgery did not show residual tumor or recurrence in any patient. To date, spinal instability has not developed in any patient. CONCLUSIONS: Combined laminectomy and thoracoscopic surgery may be a good alternative method for managing thoracic dumbbell tumors.

Amperometric determination of acetic acid with a trienzyme/poly(dimethylsiloxane)-bilayer-based sensor.

A trienzyme sensor for the amperometric determination of acetic acid was prepared by immobilizing acetate kinase (AK), pyruvate kinase (PK), and pyruvate oxidase (PyOx) on a poly(dimethylsiloxane) (PDMS)-coated electrode. AK catalyzes the phospho-transferring reaction between acetic acid and ATP to form ADP; PK, the phospho-transferring reaction between ADP and phosphoenolpyruvate to form pyruvic acid; and PyOx, the oxidation of pyruvic acid with oxygen. The oxygen consumption could be monitored by using the PDMS-coated electrode without interference from the PyOx reaction product, hydrogen peroxide. Thus, the concentration of acetic acid (5 microM-0.5 mM) could be determined from the decrease in the cathodic current at -0.4 V vs Ag/AgCl. This is the first example of a biosensor that can be used for the determination of acetic acid in ethanol-containing food samples. The acetate-sensing electrode could be used for more than one month.

Detection of monoclonal proteins by capillary electrophoresis using a zwitterion in the running buffer.

Some cases have been reported in which a small monoclonal protein (M-protein) cannot be detected by conventional cellulose acetate membrane electrophoresis (CAE) or capillary zone electrophoresis (CZE) using a short fused-silica capillary. This is probably because these methods do not have the necessary sensitivity or resolution. To overcome this problem, we improved the CZE system by using a longer capillary and adding a zwitterion to the running buffer (pH 10.0). A comparison of CZE and CAE demonstrated that with the exception of alpha(1)- and alpha(2)-globulin, the correlation was satisfactory in serum samples from 34 patients with M-proteins which had been detected by immunoelectrophoresis. In addition, a comparison of CZE electropherograms with those from CAE showed that small M-proteins that went undetected by CAE could be detected by CZE in four patients whose diseases included epipharyngeal carcinoma, solitary plasmacytoma, Crow-Fukase syndrome and macroglobulinemia. The improved resolution produced by a longer capillary may be effective for the detection of small M-proteins.

Application of nucleus pulposus to the nerve root simultaneously reduces blood flow in dorsal root ganglion and corresponding hindpaw in the rat.

STUDY DESIGN: An experimental study to clarify the effects of nucleus pulposus on blood flow in the dorsal root ganglion and hindpaws. OBJECTIVES: To investigate the effects of application of nucleus pulposus to nerve root on blood flow in the dorsal root ganglion and the corresponding hindpaw. SUMMARY OF BACKGROUND DATA: It has been reported experimentally that application of nucleus pulposus into the epidural space induces morphologic and functional changes in the nerve roots and induces compartment syndrome in the dorsal root ganglia. However, it has not been clarified which of these changes induces symptoms in the lower limbs. METHODS: Sixteen adult, female Sprague-Dawley rats had the left L5 nerve root and associated dorsal root ganglions exposed. Autologous nucleus pulposus was applied to the L5 nerve root, just proximal to the dorsal root ganglion (NP group). For control, the same volume of muscle tissue was applied similarly to the neural tissue (control group). Blood flow in the dorsal root ganglion, corresponding hindpaw, and the contralateral hindpaw was continuously monitored by two-channel laser Doppler flowmeter for 3 hours. After measurement of blood flow, the nerve root and dorsal root ganglion were processed for histology and evaluated by light microscope. RESULTS: Blood flow in the NP group was reduced, not only in the dorsal root ganglion, but also in the corresponding hindpaw. These reductions were statistically significant compared with the control group (P < 0.01). Edema was the principal pathologic finding seen consistently in the nerve roots and in many of the associated dorsal root ganglia from nucleus pulposus-treated animals. CONCLUSION: Application of nucleus pulposus to nerve root decreased blood flow in the dorsal root ganglion and corresponding hindpaw. These basic pathophysiologic changes are associated with compression injuries caused by herniated discs and are accepted neuropathologic mechanisms of injury associated with painful neuropathies. These acute observations in the dorsal root ganglion and the hindpaw may be important initial factors in the pathogenesis of radicular leg pain (sciatica) due to disc herniation.

[A case of stunned myocardium concomitant with endotracheal intubation].

"Stunned myocardium" was defined by Braunwald et al in 1982 as reversible postischemic myocardial dysfunction. We report a case of a 57-year-old woman for cholesystectomy who developed stunned myocardium during endotracheal intubation. She was free of any risks of heart disease. While the endotracheal tube was smoothly inserted after rapid induction, the blood pressure was remarkably elevated and electrocardiogram (ECG) showed ST segment elevations in leads I, aVL, as well as V2-V6, and ST segment depressions in leads II, III and aVF. The coronary angiography, performed 2 weeks later, revealed a normal coronary finding, but the left ventriculogram showed asynergy in its anterior and apical walls (AHA segments 2, 3 and 6). Left ventricular dysfunction in this case was possibly due to a direct effect of excessive cathecholamines secreted during an acute episode of hypertension triggered by intubation.

Vascular backache and consideration of its pathomechanisms: report of two cases.

We experienced two cases whose low back pain was improved after vascular reconstructive surgery for arteriosclerosis obliterans in the abdominal cavity. Based on these observations, we propose the term "vascular backache" and we discuss possible pathomechanisms underlying this condition. One patient had a stenotic lesion in the lower abdominal aorta and was operated transluminally; the other patient had a diffuse stenotic lesion from the abdominal aorta to the femoral arteries and had an axillofemoral bypass operation. After surgery, they experienced a reduction of backache along with an improvement of the vascular intermittent claudication. It is suggested that one factor leading to low back pain in some cases might be various degrees of ischemia of the extensor muscles in the lumbar spine.

Basic and update knowledge of intervertebral disc herniation: review.

Lumbar disc herniation is one of the most common causes of low back pain and/or sciatica. However, the pathogenesis of lumbar disc herniation, low back pain, and sciatica has not been fully understood. Inflammation in nerve root and dorsal root ganglia induced by nucleus pulposus may play an important role in the pathogenesis of spinal pain. I reviewed the basic and update papers regarding lumbar disc herniation. Herniated nucleus pulposus had been considered an enchondroma occurred from intervertebral disc, historically. At present, however, it is emphasized that nucleus pulposus has an inflammatogenic properties to affect the nerve root function, structure, vascular permeability, and pain.

Dorsal compartment syndrome of the upper arm. A case report.

A rare case of posttraumatic dorsal compartment syndrome of the upper arm is reported. This case was diagnosed by measuring the intracompartmental pressure. The patient was administered local anesthesia and immediately underwent surgery. The result was successful.

Effects of lidocaine on nucleus pulposus-induced nerve root injury. A neurophysiologic and histologic study of the pig cauda equina.

STUDY DESIGN: Application of autologous nucleus pulposus on nerve roots and treatment with local application of lidocaine in the pig. OBJECTIVES: Studies of the effects of lidocaine on nucleus pulposus-exposed nerve roots. SUMMARY OF BACKGROUND DATA: Nerve root infiltration may improve radicular symptoms beyond the pharmacologic duration of local anesthetics, but the mechanisms for this effect are not known. METHODS: Nucleus pulposus was harvested from a lumbar disc and placed onto the sacrococcygeal cauda equina in pigs. In Series 1, early lidocaine treatment of nucleus pulposus-induced nerve root injury, pigs received 2% lidocaine (n = 5) or saline (n = 5) before and after surgery. Nerve conduction velocity and histologic appearance were studied after 3 days. In Series 2, delayed lidocaine treatment of nucleus pulposus-induced nerve root injury, after 7 days 2% lidocaine was administered epidurally to nucleus pulposus-exposed (n = 4) and -nonexposed (n = 4) nerve roots. Nerve conduction velocity, muscle action potentials, and histologic appearance were assessed. RESULTS: In Series 1, early treatment with lidocaine limited the reduction in nerve conduction velocity. The epidural inflammation was less in lidocaine treated animals. In Series 2, nerve conduction velocity was lower in nucleus pulposus-exposed animals than in nonexposed animals. The initial reduction of nerve conduction velocity and muscle action potential was similar between the groups, but the recovery of muscle action potential was slower and less complete in nucleus pulposus-exposed nerve roots. There was minimal histologic nerve injury in both series and in both protocols. CONCLUSIONS: Early treatment with lidocaine may reduce nucleus pulposus-induced nerve root injury. Lidocaine induced a delayed recovery in nerve roots exposed to nucleus pulposus. Further studies are needed to clarify the therapeutic effects of nerve root infiltration and the pathophysiology of nucleus pulposus-induced nerve root injury.

Acute effects of nucleus pulposus on blood flow and endoneurial fluid pressure in rat dorsal root ganglia.

STUDY DESIGN: An experimental study to elucidate the initial factors in the pathogenesis of lumbar pain caused by disc herniation. OBJECTIVE: To evaluate the effects of autologous nucleus pulposus on blood flow and endoneurial fluid pressure in dorsal root ganglia. SUMMARY OF BACKGROUND DATA: Human sciatica is known to be associated with compression of lumbar nerve roots and dorsal root ganglia by herniated intervertebral discs. Recently, it has been shown that application of nucleus pulposus to nerve roots induces injury and pain-related behavior in experimental animals. In this study, the authors hypothesized that nucleus pulposus applied to a nerve root would cause increased intraneural edema and reduced blood flow in the corresponding dorsal root ganglia. Studies in peripheral nerves have shown that these initial pathophysiologic disturbances initiate complex events that exacerbate nerve injury and cause pain. METHODS: A total of 29 adult female Sprague-Dawley rats weighing 200 to 250 g had their left L5 nerve roots and associated dorsal root ganglia exposed. Autologous nucleus pulposus was harvested from the tail and applied to the L5 nerve root just proximally to the dorsal root ganglia (nucleus pulposus group). For control, the same volume of muscle was harvested from the surgical area in the back and applied similarly to the neural tissue (control group). Blood flow was continuously monitored using a laser Doppler flow probe for 3 hours (n = 10) or 4 hours (n = 8) in animals with indwelling cannulas for measurement of systemic arterial pressure. Endoneurial fluid pressures were recorded with a servonull micropipette system using glass micropipettes with tip diameters of 4 microns. Endoneurial fluid pressure in the dorsal root ganglia was measured before and 3 hours after application of nucleus pulposus (n = 7) or muscle (n = 4). After measurement of blood flow and endoneurial fluid pressure, the nerve root and dorsal root ganglia were processed for histology and evaluated by light microscope. RESULTS: Blood flow in the nucleus pulposus group was reduced by 10% to 20% from the initial value after 3 to 4 hours. This reduction was statistically significant compared with that of the control group (P < 0.01). Endoneurial fluid pressure was initially 2.6 +/- 1.2 cm H2O in the nucleus pulposus group, and 2.1 +/- 0.6 cm H2O in the control group. Three hours after application, endoneurial fluid pressure was 7.5 +/- 4.6 in the nucleus pulposus group (P > 0.05), and 2.0 +/- 0.8 in the control group (P > 0.05). Edema was the principal pathologic finding seen consistently in the nerve roots and in many of the associated dorsal root ganglia from animals treated with nucleus pulposus. CONCLUSION: Application of nucleus pulposus to nerve root increased endoneurial fluid pressure and decreased blood flow in the dorsal root ganglia. This study's acute observations in the dorsal root ganglia may thus help to explain why disc herniations without compression of neural tissue are sometimes painful because similar pathologic findings are observed after only nucleus pulposus application to the nerve root. The authors further suggest that exposure of nerve roots to nucleus pulposus may establish a "compartment syndrome" in the dorsal root ganglia.

High-throughput flow-injection analysis of glucose and glutamate in food and biological samples by using enzyme/polyion complex-bilayer membrane-based electrodes as the detectors.

The concentration of glucose was determined by a combination of flow injection analysis (FIA) with amperometric enzyme sensor detection. The enzyme sensor was prepared by immobilizing glucose oxidase on an electrode coated with a polyion complex layer consisting of poly-L-lysine and poly(4-styrenesulfonate). The inner, polyion complex layer was useful for preventing electrochemical interferents (e.g., L-ascorbic acid, uric acid and acetaminophen) from reaching the electrode surface, which was effective for reducing the interferential responses upon the injections of biological and food samples. The sensor-based system could be used for the determination of glucose from 10 microM to 3 mM with the sampling rate of 180 h-1, and was stable for more than 2 months. An FIA system for determining L-glutamic acid (3 microM-0.5 mM) was also prepared by using an enzyme electrode based on a glutamate oxidase/polyion complex-bilayer as the detector.

[A case of measles encephaloneuropathy in a pregnant women].

We reported a patient with measles encephaloneuropathy. A 26-year-old woman in her 15th week of gestation became febrile and developed cutaneous eruption typical of measles on July 1 1997. Five days after appearance of the rash, fetal death was identified and the fetus was removed. Following the operation, she became comatous. Neurological examination revealed neck stiffness, flaccid paralysis of the four limbs, and decreased sweating in the lower limbs. CSF protein was 143 mg/dl with cell count of 1365/mm3. Myelin basic protein in CSF was positive. High titers of antimeasles antibodies were found in the serum and the cerebrospinal fluid. EEG revealed a predominance of slow waves. In MRI obtained earlier in her illness, high signal intensity areas were noted to spread in the brain stem and external capsule on T2-weighted images. However, T1-weighted image was unremarkable. Serial electrophysiological studies suggested demyelination of the motor nerves. With combination of methylprednisolone and immunoglobulin therapy, she made a remarkable recovery without any neurologic sequelae. We believe that the measles encephalitis in our patient is predominantly demyelinating due to an immunologic reaction in a pathophysiological aspect. We should pay attention to coincident poly-radiculoneuropathy in the early stage of measles encephalopathy.

[Recovery from out-of-hospital cardiac arrest after mild hypothermia: report of two cases].

We report two patients with out-of-hospital cardiac arrest who recovered after hypothermia therapy. A 25-year-old man and a 16-year-old boy were transferred to our hospital after cardiopulmonary arrest due to idiopathic ventricular fibrillation and hypertrophic cardiomyopathy, respectively. We carried out hypothermia therapy using cooling blankets, and the patients were maintained at 32-33 degrees C for 96 and 36 h, respectively. After slow rewarming, they regained consciousness and recovered. During hypothermia, hypokalemia and arrhythmia occurred. Their arrest times (no spontaneous circulation and no CPR) were 10 min and 8 min, and CPR times (no spontaneous circulation while CPR was being performed) were 24 min and 20 min, respectively. In cases where the duration of ischemia is prolonged, the prognosis is expected to be poor. Therefore, we believe that hypothermia therapy is beneficial for such patients.

[Creutzfeldt-Jakob disease associated with ocular dipping--a case report].

We presented a case of Creutzfeldt-Jakob disease (CJD) associated with ocular dipping (OD). A 65-year-old woman was hospitalized with two months history of progressive ataxia and mental deterioration. On admission, she was bed-ridden and stuporous with rigidity of the four limbs. Her both eyes were noted to deviate downward slowly from midpossition, taking 1 to 3 seconds to reach the nadir and rapidly returned to midpossition. It was felt that these abnormal eye movements are compatible with OD. Findings of EOG were compatible with that of typical OD. Electroencephalogram obtained a few months later revealed periodic synchronous discharge. Magnetic resonance imaging of the brain which had demonstrated mild cerebral atrophy in the beginning subsequently revealed full-brown cerebral atrophy. Hence, she was diagnosed of having CJD. There has been no report of CJD associated with OD. The OD was observed to last as long as 110 days. When the above described abnormal eye movements were noted, there was no signs indicative of brain stem dysfunction present. Therefore, we feel that the present case suggest that a diffuse cerebral dysfunction involving the cerebral cortex and basal ganglia may underlie in the development of OD.

The effects of normal, frozen, and hyaluronidase-digested nucleus pulposus on nerve root structure and function.

STUDY DESIGN: Autologous nucleus pulposus was modified and applied to the cauda equina in pigs. Histology and neurophysiology were assessed after 7 days. OBJECTIVES: To assess if alterations of the nucleus pulposus would change the degree and distribution of the nerve injury induced by autologous nucleus pulposus. SUMMARY OF BACKGROUND DATA: It was reported recently that nucleus pulposus may induce structural and functional changes in nerve roots after epidural application. The basic mechanisms causing these changes are not fully understood. METHODS: Nucleus pulposus was harvested from lumbar discs and submitted to either of three treatments; 37 C for 24 hours (n = 5), -20 C for 24 hours (n = 5), or digestion by hyaluronidase for 24 hours (n = 6). In two additional pigs, nucleus pulposus was applied just after harvest as a control to verify previous observations. After 7 days, nerve conduction velocity was recorded, and specimens were processed for blinded light microscopic assessment. RESULTS: When nucleus pulposus was applied just after harvest, or when it had been kept at 37 C or digested by hyaluronidase for 24 hours, there was a significant reduction in nerve conduction velocity similar to previous observations. When nucleus pulposus had been kept at -20 C for 24 hours, however, there was no reduction in conduction velocity. There were no apparent differences between the groups at the histologic assessment. Staining of the nucleus pulposus showed that the cells in the nucleus pulposus exposed to -20 C were lysed, whereas the cells in the nucleus pulposus treated by the two other methods were mainly unaffected. CONCLUSIONS: Because freezing of the nucleus pulposus probably kills the cells but does not affect other components, one may assume that the biologic effects induced by the nucleus pulposus may be related to its cell population.

Voltammetric enzyme sensor for urea using mercaptohydroquinone-modified gold electrode as the base transducer.

A voltammetric urea-sensing electrode was prepared by combining a lipid-attached urease layer with a 2,5-dihydroxythiophenol-modified gold electrode. A self-assembled monolayer of dihydroxythiophenol was prepared on the gold surface by soaking the electrode into an ethanolic solution containing the modifier. A layer of the lipid-attached enzyme and that of acetyl cellulose overcoat were successively made on the dihydroxythiophenol-modified electrode by applying a dip-coating procedure. The addition of urea in a test solution (10 mM phosphate buffer, pH 7.0) brought about an increase of pH near the urease layer. The pH shift accompanied a negative shift of the anodic peak, which corresponded to the electro-oxidation of dihydroxyphenol moiety to form quinone, on the linear sweep voltammograms for the urease/dihydroxythiophenol electrode. The concentration of urea (0.2-5 mM) could be determined by measuring the electrode current at -0.05 V versus Ag/AgCl from the voltammogram. The electrode was applied to the determination of urea in human urine; the measurement of electrode current at such a low potential provided the urea determination without any electrochemical interference from L-ascorbic acid and uric acid.

Incision of the anulus fibrosus induces nerve root morphologic, vascular, and functional changes. An experimental study.

STUDY DESIGN: The effects on nerve root structure, vasculature, and function after incision of the adjacent disc was studied in a dog model. OBJECTIVES: To see if only incision of the disc per se is sufficient for inducing similar changes. SUMMARY OF BACKGROUND DATA: It is well known that nucleus pulposus will induce nerve root structural and functional changes in experimental situations. In these previous studies, relatively large amounts of nucleus pulposus were applied. METHODS: The left L7 nerve root was exposed and mobilized in 10 dogs. In five dogs, the adjacent L6-L7 disc was incised, and in five other dogs, the disc was not incised. After 7 days, nerve conduction velocity was recorded, and specimens were obtained for histologic evaluation. RESULTS: The nerve conduction velocity was significantly lower in the incision group (13 +/- 14 m/sec) compared with the nonincision group (73 +/- 5 m/sec). Structural changes of the axons were more pronounced in the incision group, however, the degree and distribution was too limited to fully account for the neurophysiologic reactions observed. There aims were obvious signs of capillary stasis with an increased number and diameter of the intraneural capillaries in the incision group. CONCLUSIONS: The present study indicated that incision of the anulus fibrosus is sufficient to induce significant morphologic and functional changes and that vascular mechanisms may be of importance for the observed changes. These experimental data suggest that leakage of nucleus pulposus material from anular tears, with injury to adjacent nerve roots, might be one pathophysiologic mechanism in patients with low back pain and sciatica but with no radiologic or surgical evidence of disc herniation.

Back muscle injury after posterior lumbar spine surgery. Topographic evaluation of intramuscular pressure and blood flow in the porcine back muscle during surgery.

STUDY DESIGN: Intramuscular pressure and blood flow of the back muscles were evaluated topographically during posterior lumbar spine surgery. The topographic damage of the back muscle after surgery was studied. OBJECTIVE: To investigate the relationship between intramuscular pressure or blood flow during posterior lumbar surgery and the back muscle injury after surgery. SUMMARY OF BACKGROUND DATA: Latrogenic back muscle injury in an animal and human model has been reported previously. Changes of intramuscular pressure and blood flow during surgery might be related to the muscle injury. No previous study on this issue has been published. METHODS: The contact pressure between the retractor blade and muscle tissue was monitored in 10 pigs during posterior surgery of the lumbar spine. On one side, intramuscular pressure at 5, 10, and 20 mm lateral to the retractor and on the other side blood flow of the back muscle at 5 and 20 mm during surgery were measured. Histologic changes of the back muscle at 5, 10, and 20 mm to the midline were evaluated 3 hours after surgery. RESULTS: The contact pressure decreased exponentially with time. Intramuscular pressure 5 mm lateral to the retractor was 114 +/- 31 mm Hg and was significantly higher than at 10 mm and 20 mm. Blood flow markedly decreased during surgery and recovered incompletely after releasing the retractor at 5 mm and 20 mm lateral to the retractor. Blood flow at 5 mm was significantly lower than at 20 mm throughout surgery. The muscle damage 3 hours after surgery was more severe near the retractor blade. CONCLUSIONS: The back muscles were exposed to pathophysiologic condition by a retractor during posterior lumbar spine surgery. External compression by a retractor increases intramuscular pressure to levels that impede local muscle blood flow. The muscle degeneration after surgery could be explained by direct mechanical damage and by the increased intramuscular pressure of muscle tissue by the retractor.