Biomedical subjects
B Rydevik
Publications and source records attributed to B Rydevik.
Neurophysiology of cauda equina compression.
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Effects of acute graded strain on efferent conduction properties in the rabbit tibial nerve.
This study examines effects of acute stretch on electrophysiologic properties of rabbit tibial nerve. Compound motor action potentials (CMAP) were measured in 30 rabbits, during and after two hours of acute, graded strain. The rabbits were assigned to one of three groups defined by the degree of stretch (0%, 8%, or 15%) beyond original resting length. These groups were subdivided according to ankle position during nerve strain (ankle dorsiflexion or ankle plantar flexion). Two hours of 8% strain did not significantly decrease CMAP amplitude. Fifteen percent strain with the ankle in dorsiflexion produced a significant and profound drop (99%) in CMAP amplitude. These findings are clinically relevant to nerve stretch injuries and to surgical procedures that induce acute nerve strain.
The utility of portable nerve conduction testing for patients with carpal tunnel syndrome: a prospective clinical study.
The usefulness and accuracy of a portable instrument, the electroneurometer, for measuring distal motor latencies was determined in a prospective study of 28 patients (51 hands) with carpal tunnel syndrome and 10 controls (18 hands). There was a close correlation of distal motor latencies from the electroneurometer with those from formal electrodiagnostic testing. The average distal motor latency of controls was 3.3 +/- 0.4 msec, compared with a mean value of 5.2 +/- 1.8 msec in symptomatic hands. The sensitivity of the neurometer test alone was 69% (9 false-negatives); when combined with quantitative sensibility testing, sensitivity increased to 84%. Specificity of the neurometer test alone was 100% (no false-positives). The portable electroneurometer is a convenient, painless, inexpensive device for screening patients with carpal tunnel syndrome. Formal electrodiagnostic testing is indicated for differentiation of lesions present at different levels, for detection of subtle sensory changes, and for use in those patients in whom surface electrode usage is ineffective.
Local electrophysiologic stimulation in experimental double level cauda equina compression.
Double level compression of nerve roots has been known to exist for a long time, but only in recent years the clinical significance of such conditions has been discussed. In the current study, nerve root function in double level compression was analyzed by measurements of tail muscle electromyogram, after stimulations of 1) the intermediate segment between the compression sites and 2) cranial to the two compression sites in a pig model. The electromyogram-amplitudes were more reduced after intermediate, than cranial stimulation. This difference was suggested to be based on an additional increasing threshold to elicit an action potential within the intermediate segment due to a nutritional deficit at this location. The results further stress the importance of local changes within the intermediate segment in double level nerve root compression.
Pathophysiology of spinal stenosis.
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Single- versus double-level nerve root compression. An experimental study on the porcine cauda equina with analyses of nerve impulse conduction properties.
Double-level nerve root compression had a greater effect on nerve impulse conduction, recorded as tail muscle action potential amplitude, than single-level compression at both 10 and 50 mm Hg. If the distance between the two compression sites at 10 mm Hg compression was increased from one vertebral segment (10 mm) to two vertebral segments (30 mm), the reduction of muscle action potential amplitude was further enhanced. These observations may give new insight into the pathophysiology of cauda equina compression in spinal disorders such as stenosis.
Effects of chondroitinase ABC on intrathecal and peripheral nerve tissue. An in vivo experimental study on rabbits.
The enzyme chondroitinase ABC has recently been suggested for use in chemonucleolysis. The effects of 200 U ml of chondroitinase ABC were studied on intrathecal and peripheral nerve tissue in rabbits. After the intrathecal (subarachnoid) application of 0.2 ml of either the diluent in the control group (N = 2) or chondroitinase in the study group (N = 4), no neurologic deficit was detected. Compared with the control group, no morphologic changes at the light microscopic level were induced in the spinal cord by chondroitinase. No neurophysiologic differences were detected between tibial nerves after exposure to 1 ml of the diluent (control, N = 8) or chondroitinase (the other leg) for 4 weeks, nor did the study group, compared with the control group, show any morphologic changes in the tibial nerves. Because the concentration of chondroitinase ABC tested was approximately 40 times higher than might be used clinically for chemonucleolysis, the present study indicates a wide margin of safety for unwanted side effects on nerve tissue.
Experimental nerve root compression. A model of acute, graded compression of the porcine cauda equina and an analysis of neural and vascular anatomy.
Nerve root compression has been suggested as one important pathogenetic factor in low-back pain syndromes and sciatica. The underlying pathophysiologic mechanisms are, however, incompletely known, partly because of the lack of experimental data on this topic. In the present study, a model for experimental compression of the porcine sacrococcygeal cauda equina is presented. The model consists of surgical exposure of the cauda equina and compression of the cauda equina toward the ventral aspect of the spinal canal by an inflatable balloon fixed to the spine. This compression system was shown to have a high accuracy in pressure transmission from the balloon to the cauda equina. The gross and microscopic neural anatomy and the vascular anatomy of the porcine cauda equina were analyzed with light microscopic and ink-perfusion techniques. The porcine cauda equina showed a close anatomic resemblance to the human lumbosacral cauda equina. The presented model offers unique possibilities for experimental studies on nerve root compression injury because of the easy surgical exposure and the sufficient length of the nerve roots. In separate studies, this model, along with investigations of solute transport to the nerve tissue and of impulse propagation, has been used to analyze the effects of acute, graded compression on blood flow and edema formation in the cauda equina. The porcine cauda equina would also be particularly suitable for chronic compression studies because any neurologic deficit acquired would be restricted to the tail.
Pathophysiology of sciatica.
The exact pathophysiologic mechanisms behind sciatica are incompletely known; however, compression of spinal nerve roots is known to be correlated to both pain and neural dysfunction in a segmental distribution of that specific nerve root. Compression per se may impair the transport of nutrients to the nerve tissue in such a way that affects the nerve root function. There also might be a local affect on nerve roots or root sleeves by substances leaking from the degenerated intervertebral discs.
Importance of compression onset rate for the degree of impairment of impulse propagation in experimental compression injury of the porcine cauda equina.
The effects of a rapid (0.05-0.1 seconds) and a slow (20 seconds) onset rate of cauda equina compression on impulse propagation, in terms of tail muscle electromyogram (EMG) amplitude, were analyzed in an experimental model of the pig cauda equina. Sham compression and compression at 50 mm Hg at either rapid or slow onset induced no or only minor functional impairment. Compression at 100 or 200 mm Hg induced impairment of the impulse propagation that was proportional to the applied pressure. The effects were more pronounced (P less than 0.01) for the rapid than for the slow onset of compression at both these pressure levels. An important factor for this observed difference in effects between the two employed onset rates seems to be the magnitude of intraneural edema formed outside the compression zone.
Cauda equina anatomy. I: Intrathecal nerve root organization.
The three-dimensional organization of the human cauda equina has not been described previously. This is partly due to the difficulties of dissecting individual, unfixed nerve roots. By the use of a newly developed in situ fixation and embedding technique on 15 fresh human cadavers, the cross-sectional anatomy of the cauda equina was defined from L2-L3 to L5-S1. A highly consistent cross-sectional pattern was observed in all specimens. The lower sacral (S2-S5) and coccygeal roots were located in the dorsal aspect of the thecal sac, whereas the lumbar and first sacral roots exhibited an oblique, layered pattern as they ascended. The motor bundle was situated anteromedial to its respective sensory bundle within each layer, Invaginations of arachnoid held the nerve roots in a fixed relationship to one another. This previously undescribed three-dimensional anatomy within the thecal sac may aid in the understanding and treatment of trauma, neurocompressive syndromes, and tumors of the cauda equina.
Diffusion from the cerebrospinal fluid as a nutritional pathway for spinal nerve roots.
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Compression-induced changes of the nutritional supply to the porcine cauda equina.
The effects of compression on the transport of 3H-labeled methyl glucose to spinal nerve roots were analyzed in an experimental model of the pig cauda equina. A rapid onset of compression (0.05-0.1 s) induced more pronounced effects than a slow onset (20 s) at corresponding pressure levels. There was evidence that this observed difference may be related to the magnitude of intraneural edema formed outside the compression zone. The results also indicate that the nutritional transport might be impaired at very low pressure levels and that diffusion from adjacent tissues with a better nutritional supply, including the cerebrospinal fluid, may not fully compensate for any compression-induced impairment of the intraneural blood flow.
1990 AcroMed Award in basic science. Cauda equina anatomy. II: Extrathecal nerve roots and dorsal root ganglia.
Inconsistent data exist regarding the anatomy of the spinal nerve roots lateral to the thecal sac. A newly developed in situ technique was used to precisely define anatomic parameters on 20 fresh human cadavers. The take-off angle of the nerve roots from the thecal sac decreases from a mean of approximately 40 degrees from L1-L5 to 22 degrees at S1. The motor bundles are directly ventral to the sensory fibers within individual roots extrathecally. Dorsal root ganglia size varies with vertebral level. The majority of ganglia lie directly beneath the vertebral pedicles and one third overlie a portion of the lateral intervertebral disc. These previously undescribed relationships may aid in the understanding of lumbosacral neurocompressive disorders and are important to note during pedicle screw insertion, posterolateral decompression for spinal trauma, and paravertebral approaches for lateral disc herniations.
Microvascular effects of chondroitinase ABC and chymopapain. An in vivo experimental study on hamsters and rabbits.
Immediate and long-term microvascular effects of chondroitinase ABC, 200 unit/ml, were analyzed in ten hamsters. The immediate effects on the microcirculation were studied by vital microscopy following local injection in the cheek pouch. There were no detectable effects on the microvascular blood flow during the 60 minutes of observation for chondroitinase ABC or the control. A therapeutic concentration (2000 pKat/ml) of chymopapain stopped the microcirculation in the injected area immediately, with numerous microbleedings at the border zone. Long-term effects were studied after subcutaneous injections in the ears of six rabbits. Chondroitinase ABC and the control did not cause any macroscopic or microangiographic effects. However, light microscopy showed a moderate inflammatory reaction in the subcutaneous layer for both chondroitinase ABC and the control. Chymopapain induced severe effects on the cartilage and surrounding tissues. Microangiography revealed a vessel-free zone at the injection site. Since 200 units/ml of chondroitinase ABC is four to eight times higher than the concentration that might be used for chemonucleolysis, i.e., dissolution of intervertebral discs by local enzyme injection, the present investigation suggests a wide margin of safety regarding the potential effects on blood vessels in tissues surrounding the disc.
Effects of experimental graded compression on blood flow in spinal nerve roots. A vital microscopic study on the porcine cauda equina.
Compression injuries of spinal nerve roots are very common. However, the basic pathophysiology of these conditions is not fully understood. In this study a model is presented for experimental graded compression of the nerve roots of the pig cauda equina, including a technique for vital microscopic studies on the microcirculation flow of the intrinsic vessels of the nerve roots during compression. With this model critical pressure levels for compression-induced occlusion of the arterioles, capillaries, and venules of the intrinsic vasculature of the nerve roots were determined. The study showed that the average minimum pressure in the inflated balloon required to stop the flow in the arterioles was 127 mm Hg (SD = 18, n = 11), in the capillaries 40 mm Hg (SD = 6, n = 12), and in the venules 30 mm Hg (SD = 10, n = 12). The average mean arterial pressure (MAP) was 150 mm Hg (SD = 14, n = 12). There was a statistically significant correlation (p greater than 0.001) between the MAP and the pressure required to stop the flow in the arterioles (r = 0.83, n = 14), but no correlation between MAP and capillary (r = 0.09 NS, n = 20) or venular (r = -0.28 NS, n = 34) occlusion pressure. After the nerve roots had been compressed at 50 or 200 mm Hg for 10 min or 2 h, the recirculation started immediately. There was a hyperemia during the first 10 min, with a dilatation of the vessels, particularly the venules. In nerve roots exposed to compression for 2 h at either 50 or 200 mm Hg, an intraneural edema developed.(ABSTRACT TRUNCATED AT 250 WORDS)