Fine structures in denaturation curves of bacteriophage lambda DNA. Their relation to the intramolecular heterogeneity in base compositon.

Precise recording of polyphasic optical melting curves was carried out for three kinds of bacteriophage lambda DNA differing in length (lambdac1857s7, lambdacIb2 and lambdacIb2b5). Each of denaturation steps in melting profiles was characterized by two parameters, the melting temperature and the relative size. Any difference in fine structures in melting profiles was not recognized between the intact lambdacI857s7DNA and the DNA fragmented into halves. The change in fine structures in melting profiles caused by the deletions of the b2 and b5 region agreed qualitatively well with the prediction based on the physical and the genetical maps of phage lambda chromosome. The combined results indicate that, first, the well-known linear relationship between melting temperature and G+C content may apply also to each of denaturation steps in polyphasic melting curves due to heterogeneity of nucleotide distribution in a single DNA species, and, second, the effect of molecular ends on melting fine structures can be neglected at moderate salt concentration (0.01 M less than or equal to Na+ less than or equal to 0.2 M) for such a high molecular weight DNA. The heterogeneous distribution of nucleotides was derived for lambdaDNA and for its b2 and b5 regions.

Modifications to a carbon paste glucose-sensing enzyme electrode and a reduction in the electrochemical interference from L-ascorbate.

A glucose-sensing enzyme electrode was prepared by incorporating polyethylene glycol-modified glucose oxidase, horseradish peroxidase and 1,1'-dimethylferrocene into a carbon paste. The modification of glucose oxidase with polyethylene glycol was effective for increasing the enzyme activity in the carbon paste owing to the enhanced affinity of the polyethylene glycolmodified enzyme for the hydrophobic carbon paste matrix. In contrast, however, the enzyme activity of the polymer-modified peroxidase was lower than the unmodified peroxidase in the carbon paste matrix because of a severe loss of the enzyme activity during the modification with polyethylene glycol. Hence, the enzyme pair of polyethylene glycol-modified glucose oxidase and unmodified peroxidase was used for preparing the enzyme electrode. The reductive current response of the electrode to glucose was recorded at -0.2 V vs. Ag/AgCl. After the addition of glucose (100 microM), the current increased immediately and reached a plateau (delta = -0.12 microA) within 30 s. The current response was linear up to a glucose concentration of 500 microM and the detection limit was 20 microM (S/N = 5). Interference from ascorbate was very small: the current response to 1 mM glucose (-1.1 microA) was slightly reduced to -0.9 microA when 1 mM ascorbate was added to the glucose-containing solution. In biological and food samples, the concentration of ascorbate is generally quite low compared with the glucose concentration. The interference from ascorbate could actually be ignored for the purpose of determining glucose in soft drinks.

Flow injection analysis for glucose using an amperometric enzyme electrode based on lipid-modified glucose oxidase as the detector.

The concentration of glucose is determined by a combination of flow-injection analysis with amperometric enzyme sensor detection. The enzyme sensor is prepared by coating a glassy carbon electrode with a layer of lipid-modified glucose oxidase and Nafion: first, a benzene solution of the modified enzyme is placed on the glassy carbon electrode and dried, then a Nafion solution is placed on the electrode and dried. The sensor-based system exhibited a linear response for glucose concentration up to 10 mM with a sampling rate of 250 sample/h, and is stable for 12 weeks after 2000 glucose injections.

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.

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.

Cold-induced dysaesthesia in acute idiopathic polyneuritis.

Two cases are reported of cold-induced dysaesthesia occurring during an attack of acute idiopathic polyneuritis. Two similar cases found in the literature are reviewed. It is suggested that the dysaesthesia may be a localized symptom of cold sensitivity, with an initiating trigger in common with acute idiopathic polyneuritis.

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.

Nerve root infiltration and sympathetic block. An experimental study of intraradicular blood flow.

STUDY DESIGN: The nerve root of L7 was exposed, and a clamp was applied to simulate radiculopathy. Intraradicular blood flow was measured at the takeoff point of the nerve root and at the distal to the dorsal root ganglion before and after nerve root infiltration with 2% lidocaine or physiological saline solution (control group), or sympathetic ganglion block with 2% lidocaine. OBJECTIVES: To investigate one of the mechanisms of the therapeutic effect of nerve root infiltration by assessing changes in intraradicular blood flow. SUMMARY OF BACKGROUND DATA: Increased intraradicular blood flow was noted both proximal and distal to the clamp after nerve root infiltration or sympathetic ganglion block with 2% lidocaine. No increase was seen after nerve root infiltration with saline solution. Macroscopic and microscopic examination showed that dye after nerve root infiltration did not spread beyond the clamped region to the proximal site. METHODS: Intraradicular blood flow was measured with a tissue blood flowmeter using the electrolytic hydrogen clearance method before and after nerve root infiltration with 2% lidocaine or physiologic saline solution (control group), or sympathetic ganglion block with 2% lidocaine. RESULTS: Increased intraradicular blood flow was noted both proximal and distal to the clamp after nerve root infiltration or sympathetic ganglion block with 2% lidocaine. No increase was seen after nerve root infiltration with saline solution. CONCLUSIONS: An increase in intraradicular blood flow is related to one of the mechanisms of the therapeutic effect of nerve root infiltration. This effect may be mediated by the sympathetic nervous system.

Positions of dorsal root ganglia in the cervical spine. An anatomic and clinical study.

STUDY DESIGN: The authors investigated the positions of dorsal root ganglia and the relation of the location to symptoms and to the effects of nerve root infiltration in the cervical spine anatomically and clinically. OBJECTIVES: To clarify normal variation of positions of dorsal root ganglia and the relation of the location of dorsal root ganglia to symptoms and to the effects of nerve root infiltration. SUMMARY OF BACKGROUND DATA: The dorsal root ganglia of the spinal nerve has attracted much attention as an important structure in the mechanisms of radicular symptoms in the lumbar spine. Although the position of the dorsal root ganglia in the lumbar spine has been classified recently, there are few reports regarding the dorsal root ganglia in the cervical spine. METHODS: The positions of dorsal root ganglia were divided into two types: proximally situated and distally situated. The positions of dorsal root ganglia in the anatomic and clinical cases were compared. The relation of the positions of dorsal root ganglia to symptoms and to the clinical effects of nerve root infiltration were analyzed. RESULTS: There was no statistically significant difference in positions of dorsal root ganglia in C6 nerve roots between anatomic and clinical cases. In addition, there was no relation between symptoms and the positions of dorsal root ganglia in clinical cases. However, there was a significant difference in positions of dorsal root ganglia in C7 nerve roots between anatomic and clinical cases. Nerve root infiltration was significantly more effective in the distally situated type of dorsal root ganglia. CONCLUSIONS: This study defined the normal variation of the positions of dorsal root ganglia. The results strongly suggest that some attention should be paid to the position of dorsal root ganglia in the diagnosis and treatment of cervical radiculopathy.

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.

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.

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.

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.

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.

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.

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.

A model for acute, chronic, and delayed graded compression of the dog cauda equina. Presentation of the gross, microscopic, and vascular anatomy of the dog cauda equina and accuracy in pressure transmission of the compression model.

STUDY DESIGN: A new model for controlled, graded compression of the dog cauda equina was developed using the dog lumbar spine. The model was defined regarding macroscopic, microscopic, and vascular anatomy and regarding accuracy in pressure transmission. OBJECTIVES: The study was performed to develop a model for controlled, graded compression that would allow for acute, chronic, and delayed compression. SUMMARY OF BACKGROUND DATA: There has been an increasing interest for the reactions of the spinal nerve roots to mechanical deformation. The previously used models have had limitations regarding the duration and the onset of the compression and possibilities for a controlled variation of the compression pressure on chronically compressed nerve roots. METHODS: Macroscopic examination, light microscopy, and ink injection of the vasculature was used to assess the anatomic characteristics of the nerve tissue and the vasculature of the cauda equina in the dog lower lumbar spine. The relation between known pressures in the compression balloon used to compress the cauda equina and the pressure in the central thecal sac was assessed by measuring the pressure in an artificial thecal sac with a pressure transducer. RESULTS. The neural and vascular anatomy was found to have a close resemblance to the human cauda equina. The pressure in the thecal sac was within 5% of the pressure in the compression balloon at various pressures between 0-200 mm Hg. CONCLUSION: The presented model provides a good pressure transmission to the dog cauda equina, which has an anatomy that closely resembles the human cauda equina. The model may be well suited for physiologic studies of cauda equina compression. A double-balloon system may provide unique opportunities to induce chronic compression and delayed compression, i.e., additional compression after a certain time of chronic compression to resemble the changes in pressure that are characteristic for neurogenic claudication.

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.

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.

A model for acute, chronic, and delayed graded compression of the dog cauda equina. Neurophysiologic and histologic changes induced by acute, graded compression.

STUDY DESIGN: The results of acute compression on nerve function and morphology were analyzed in a recently developed model for graded cauda equina compression in the dog. OBJECTIVES: The model was developed to better mimic the clinical situation of cauda equina compression in association with spinal canal stenosis. SUMMARY OF BACKGROUND DATA: The compression of the cauda equina has been induced by metal clips, plastic bands, constrictors, and inflatable balloons. No model has used the intact spinal canal and induced compression by increasing the pressure per se in the canal. METHODS: An inflatable balloon with a diameter exceeding the diameter of the spinal canal was placed under the lamina of the L7 vertebra in the dog. The balloon was inflated to various pressures, and muscle action potential area and nerve conduction velocity were monitored during 2 hours of compression and 1.5 hours of recovery. Nerve root specimens were processed for light microscopic examination. RESULTS: There was a progressive reduction of muscle action potential area and nerve conduction velocity that was proportional to the applied pressure. Histologic evaluation revealed no nerve fiber damage but a slight intraneural edema after compression at 200 mg Hg. CONCLUSIONS: The presented model may provide reproducible results regarding neurophysiologic and morphologic effects after acute, graded compression of the dog cauda equina. Two additional conclusions can be made from this study. First, the area measurement of the MAP is probably well suited for recordings and analyses of changes in muscle action potentials. Second, the specific onset rate of this study, in relation to previous studies, indicates that there is a threshold for the compression onset rate for inducing additional nerve injury located in the interval 0.1-0.8 seconds. The results from the present study provides important baseline data for the continued studies on chronic and intermittent compression with the compression model.