Biomedical subjects

K Olmarker

Publications and source records attributed to K Olmarker.

13 recordsLinked to original sources

PubMed1992

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.

Action Potentials↗

PubMed1992

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.

Action Potentials↗

PubMed1991

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.

Animals↗

PubMed1991

Spinal nerve root compression. Nutrition and function of the porcine cauda equina compressed in vivo.

A model for experimental studies of acute, graded compression of the cauda equina in pigs was presented (Olmarker et al. 1991a). Detailed analyses of the neural and vascular anatomy demonstrated a close resemblance to the human cauda equina. There were structural and vascular differences between spinal nerve roots and peripheral nerves that could contribute to differences in compression susceptibility between these two parts of the nervous system. The pressure transmission from the balloon to the nerve roots showed to have a high accuracy. The occlusion-pressures for the arterioles, capillaries and venules of the cauda equina were determined (Olmarker et al. 1989a). Arteriolar blood flow was stopped at a pressure close to the mean arterial blood pressure. Capillary blood flow was found to be dependent upon flow in the connected venules. The blood flow in some venules was found to be stopped at 5-10 mm Hg. However, venular occlusion pressures ranged from 5 to 60 mm Hg. Compression up to 200 mm Hg for 2 hours did not induce a "no-reflow" phenomenon when the compression was ended. However, a transient hyperemia was noted at all pressure/time relations studied, indicating nutritional deficit in the compressed segment during compression. Signs of edema were seen in nerve roots exposed to compression for 2 hours at either 50 or 200 mm Hg. The nutritional supply to the cauda equina was found to be impaired at low pressure levels (less than 10 mm Hg; Olmarker et al. 1990a). Diffusion from adjacent tissues with a better nutritional supply, including the cerebrospinal fluid, could thus not compensate completely for compression-induced effects on the transport of nutrients. However, a certain nutritional supply to the compressed segment was present even at 200 mm Hg compression. There were more pronounced effects on the nutritional supply induced by a rapid (0.05-0.1 sec.) than a slow (20 sec.) compression onset rate. Nutritional impairment was noted both within and outside the compressed nerve segment. An increase in vascular permeability was induced by compression at 50 mm Hg for 2 minutes (Olmarker et al. 1989b). The magnitude of this permeability increase was dependent on both the magnitude and the duration of compression. The permeability increase was more pronounced for the rapid than for the slow compression onset rate at all pressure/time relations studied. Reduction of muscle action potential (MAP) amplitude in tail muscles, after stimulation cranial to the compression zone, was induced by compression at 100 and 200 mm Hg for 2 hours (Olmarker et al. 1990b).(ABSTRACT TRUNCATED AT 400 WORDS)

Acute Disease↗

PubMed1991

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.

Animals↗

PubMed1991

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.

Animals↗

PubMed1990

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.

Animals↗

PubMed1990

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.

3-O-Methylglucose↗

PubMed1990

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.

Animals↗

PubMed1989

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)

Animals↗

PubMed1989

Microvascular response to locally injected collagenase. An experimental investigation in hamsters and rabbits.

Collagenase was injected into the ears of rabbits and the cheek-pouches of hamsters. The acute and long-term microvascular effects were studied by vital microscopy and microangiography. The enzyme was injected at three different concentrations: 120 units/ml, 600 units/ml and 3,000 units/ml. The medium (600 units/ml) and high (3,000 units/ml) concentrations induced effects on the microcirculation such as blood flow impairment and microbleedings. The magnitude of these effects was related to the concentration of the enzyme. Generally, these microvascular effects were of low magnitude as compared with other substances tested using the same experimental models.

Animals↗

PubMed1989

Edema formation in spinal nerve roots induced by experimental, graded compression. An experimental study on the pig cauda equina with special reference to differences in effects between rapid and slow onset of compression.

Edema formation in spinal nerve roots of the pig cauda equina was studied following experimental compression at various pressure levels, durations, and rates of onset, using a fluorescence microscopic technique. The time-pressure thresholds for the occurrence of edema in the nerve roots were: following rapid onset of compression (0.05-0.1 seconds), 2 minutes at both 50 mm Hg and 200 mm Hg, and following slow onset of compression (the pressure was slowly increased during 15-20 seconds), 2 hours at 50 mm Hg and 2 minutes at 200 mm Hg. Generally, the edema formation was more pronounced after rapid than after slow onset of compression. The data in this study also indicate that intraneural edema might be more easily formed in nerve roots than in peripheral nerves after compression injury.

Animals↗

PubMed1987

Effects of epidural and intrathecal application of collagenase in the lumbar spine: an experimental study in rabbits.

An experimental model is described in which collagenase in different concentrations and volumes were applied epidurally or intrathecally in the rabbit lumbar spine. This made it possible to study the tissue effects in a situation similar to that of collagenase leaking from a disc or accidental epidural or intrathecal injection at chemonucleolysis. Epidurally applied collagenase, in higher concentration, caused a local thinning of the dura. This effect was reduced at lower concentrations and volumes. Intrathecally injected collagenase, even in small amounts, caused intrathecal hemorrhage and acute paraplegia in the hind limbs. Therefore, in the clinical situation, intrathecal injection of collagenase must be avoided.

Animals↗