Transient conduction block following acute peripheral nerve ischemia

Neuromodulation accompanying focused ultrasound-induced blood-brain barrier opening

Burst-mode focused ultrasound (FUS) induces microbubble cavitation in the vasculature and temporarily disrupts the blood-brain barrier (BBB) to enable therapeutic agent delivery. However, it remains unclear whether FUS-induced BBB opening is accompanied by neuromodulation. Here we characterized the functional effects of FUS-induced BBB opening by measuring changes in somatosensory evoked potentials (SSEPs) and blood-oxygen-level dependent (BOLD) responses. Rats underwent burst-mode FUS (mechanical index (MI) of 0.3, 0.55 or 0.8) to the forelimb region in the left primary somatosensory cortex to induce BBB opening. Longitudinal measurements were followed for up to 1 week to characterize the temporal dynamics of neuromodulation. We observed that 0.8-MI FUS profoundly suppressed SSEP amplitude and prolonged latency, and this effect lasted 7 days. 0.55-MI FUS resulted in minimal and short-term suppression of SSEP for less than 60 minutes and didn’t affect latency. BOLD responses were also suppressed in an MI-dependent manner, mirroring the effect on SSEPs. Furthermore, repetitive delivery of 0.55-MI FUS every 3 days elicited no accumulative effects on SSEPs or tissue integrity. This is the first evidence that FUS-induced BBB opening is accompanied by reversible changes in neuron responses, and may provide valuable insight toward the development of FUS-induced BBB opening for clinical applications.

Biomechanical and functional variation in rat sciatic nerve following cuff electrode implantation

BACKGROUND

Nerve cuff electrodes are commonly and successfully used for stimulating peripheral nerves. On the other hand, they occasionally induce functional and morphological changes following chronic implantation, for reasons not always clear. We hypothesize that restriction of nerve mobility due to cuff implantation may alter nerve conduction.

METHODS

We quantified acute changes in nerve-muscle electrophysiology, using electromyography, and nerve kinematics in anesthetized Sprague Dawley rat sciatic nerves during controlled hindlimb joint movement. We compared electrophysiological and biomechanical response in uncuffed nerves and those secured within a cuff electrode using analysis of variance (ANOVA) and regression analysis.

RESULTS

Tethering resulting from cuff implantation resulted in altered nerve strain and a complex biomechanical environment during joint movement. Coincident with biomechanical changes, electromyography revealed significantly increased variability in the response of conduction latency and amplitude in cuffed, but not free, nerves following joint movement.

CONCLUSION

Our findings emphasize the importance of the mechanical interface between peripheral nerves and their devices on neurophysiological performance. This work has implications for nerve device design, implantation, and prediction of long-term efficacy.

Diurnal variation in clinical and electrophysiologic parameters associated with carpal tunnel syndrome

OBJECTIVE

Patients with carpal tunnel syndrome (CTS) often report aggravated symptoms in the early morning. In this study, we aimed to identify diurnal variations in clinical and electrophysiologic parameters of patients with CTS.

DESIGN

A cross-sectional clinical and electrophysiologic study was designed. First, electrophysiologic examinations were performed at 2 p.m. to confirm the diagnosis of patients who had been clinically labeled with CTS. Patients who were electrophysiologically and clinically diagnosed with CTS were included in the study, and electrophysiologic examinations were repeated at 7 p.m. and 7 a.m. A total of 64 hands with CTS (27 bilateral, 10 unilateral) and 40 control hands were studied. Grip and pinch strength of all the patients included in the study were measured using a hand dynamometer. Finally, a CTS clinical symptom severity scale and functional status scale were used to measure the symptoms and functional impairment, respectively.

RESULTS

The median motor nerve distal latency and median F-minimum latency were found to be prolonged in the CTS group in the morning, and the grip strength was also markedly reduced at this time. Similar results were obtained for the median palm mixed nerve conduction velocity and amplitude.

CONCLUSIONS

This study demonstrated that the clinical and electrophysiologic parameters of CTS patients were clearly different in the morning hours, with the symptoms of CTS manifesting at that time.

Quantitative sensory testing of cold and vibration perception during compression of median nerve at the wrist

We conducted a sequential study of quantitative sensory testing (QST) during compression-induced conduction block of the median nerve to determine relative vulnerability of the small and large myelinated nerve fibers. We tested cold (CPT) and vibratory perception thresholds (VPT) of the third digit in 15 healthy subjects during constant, localized compression for 30 min of the median nerve at the wrist. The orthodromic sensory nerve action potentials (SNAPs) recorded at wrist and elbow served to monitor the degree of associated conduction block. After the onset of nerve compression, it took 16 min for CPT to show the first change; VPT remained normal for 26 min. CPT recovered 2 min later than VPT after release of compression. The SNAP amplitude at the wrist diminished immediately at the start of compression and declined progressively, whereas the response at the elbow remained the same initially, showing no latency change for 20 min. A nearly identical time course of SNAP changes in the two experiments justified the comparison of separately tested CPT and VPT as a measure of modality-specific vulnerability. Contrary to the common belief, a focal compression sufficient to produce rapidly reversible conduction abnormalities affects the slow-conducting small myelinated fibers mediating cold perception before the fast-conducting large myelinated fibers transmitting vibration perception. The data document the order of modality-specific vulnerability of sensory nerve fibers to mild compression. The finding suggests that testing CPT, rather than VPT, provides a better QST to delineate rapidly reversible symptoms induced by compression.

Transient forearm conduction block in the median nerve

We present two cases referred for electrophysiological confirmation of carpal tunnel syndrome (CTS). Initial nerve conduction studies were normal. Approximately 20 min into the examination, both patients developed sensory symptoms and weakness in the distal median nerve territory while the elbow was extended and forearm supinated. Further studies demonstrated complete conduction block across the forearm in the median motor and sensory nerve fibers. When measurable, conduction velocities remained normal or were modestly slow. Complete clinical and electrophysiological recovery occurred within 2 min following forearm pronation, suggesting that dysfunction was probably due to focal transient ischemia. Patients describing increased sensory symptoms during routine electrophysiological assessments for CTS should be investigated to rule out the possibility of a more proximal abnormality.

Sequential changes of orthodromic sensory nerve action potentials induced by experimental compression of the median nerve at the wrist

OBJECTIVE

We studied sequential waveform changes associated with a progressive conduction block to elucidate the relative vulnerability of slow versus fast conducting fibers to a focal compression.

METHODS

In 12 healthy men, orthodromic compound sensory nerve action potentials (SNAPs) of the median nerve were recorded unipolarly at 4 sites over the forearm during a 30 min period of constant, localized compression of the nerve at the wrist.

RESULTS

Initial findings at the compression site consisted of nearly immediate reduction in size of the negative component accompanied by progressive enlargement of the initial-positive component. Recording at 2 cm proximal to the compression and at the elbow showed no change in onset latency initially, indicating at least partial preservation of the fast conducting fibers. Amplitude also remained unchanged for about 20 min, presumably because loss of negative and positive peaks compensated each other until conduction block began to involve a greater number of the fast conducting fibers.

CONCLUSIONS

The analysis of waveform changes and their time course suggests that a focal compression initially affects the slow conducting small diameter fibers. Partial conduction block gives rise to complex waveform changes depending on recording sites. A reduction in one polarity of constituent nerve fiber action potentials may enhance the other polarity of the SNAP.

"Pseudo-conduction block" in vasculitic neuropathy

The predominant electrophysiologic feature of vasculitic mononeuropathy multiplex is axonal loss. Electrophysiologic findings interpreted as conduction block have, however, also been reported to occur in neuropathy secondary to necrotizing vasculitis. We report 3 patients with mononeuropathy multiplex and biopsy proven vasculitis in whom eight nerves met criteria for conduction block. In each circumstance, serial study demonstrated conversion of the electrophysiologic findings to those most consistent with severe axonal loss. "Conduction block" in vasculitic mononeuropathy multiplex is secondary to focal axonal conduction failure presumably related to infarctive axonal injury. The term conduction block should be used with caution in this disorder and only if serial studies demonstrate findings consistent with this electrophysiologic diagnosis.

Peripheral neuropathy associated with ischemic vascular disease of the lower limbs

This paper deals with the possible identification of somatic and autonomic nerve damage in patients with peripheral obliterative arterial disease (POAD) at different stages of the disease, with a well-reproducible technique like electroneurographic evaluation of nerve conduction. In 64 patients with intermittent claudication, 19 patients with pain at rest, and 7 patients with trophic ulcers, electroneurographic evaluation of motor (tibial and peroneal) and sensory (superficial peroneal and sural) nerve conduction was performed. The median nerve (motor and sensory) was used as control. A severe impairment of sural and superficial peroneal nerve velocities was evident in many claudicant patients and in all patients with pain at rest and trophic ulcers, with a progression in the conduction abnormalities in advanced stages of the disease. Motor nerve conduction showed only minor reductions in patients with claudication and pain at rest, although some of them did show very poor velocity values. In 21 patients with intermittent claudication and sensory nerve abnormalities, the autonomic fibers activity, evaluated by the skin sympathetic response (SSR) test, was significantly depressed, thus suggesting an involvement of the local autonomic system in the ischemic disease. A correlation exists between the severity of the somatic nerve damage and the stage of the vascular insufficiency. However, in the group of claudicant patients, the evidence of similar ischemic threshold (claudication distance) may be associated with a marked difference in the amount of somatic nerve damage. The somatic and autonomic nerve alterations may play a relevant role in the progression of the disease toward critical limb ischemia.

Ischemic reperfusion causes lipid peroxidation and fiber degeneration

Although the neuropathology of ischemic fiber degeneration (IFD) is relatively well known, its pathogenesis is poorly understood. One putative mechanism of IFD is oxidative stress, causing a breakdown of the blood-nerve barrier (BNB) and lipid peroxidation. We evaluated the effect of ischemic reperfusion of rat sciatic-tibial nerve seeking biochemical and pathologic evidence of BNB disruption and lipid peroxidation. Ischemia, caused by the ligation of the supplying arteries to sciatic-tibial nerve, was maintained for 3 h, followed by reperfusion. Reperfusion resulted in an increase in nerve lipid hydroperoxides, greatest at 3 h, followed by a gradual decline over the next month. Nerve edema and IFD consistently became more severe with reperfusion, indicating that oxidative stress impairs the BNB (edema) and causes IFD. Reduced reperfusion was greatest over distal sciatic nerve and midtibial nerve at day 7. The most ischemic segment (midtibial), of nonreperfused ischemic nerves (duration 3 h), underwent both edema and IFD that was as pronounced as those of other segments after reperfusion, and underwent a smaller increase with reperfusion, suggesting that ischemia alone can also cause IFD and edema. The type of fiber degeneration was that of axonal degeneration.

Segmental median nerve conduction measurements discriminate carpal tunnel syndrome from diabetic polyneuropathy

Median nerve conduction has been compared in CTS, with or without diabetes, and diabetic polyneuropathy. Approximately 90% of hands were correctly predicted as CTS or diabetic polyneuropathy by a comparison including the median antidromic sensory nerve conduction velocities in the elbow-to-wrist segment, wrist-to-palm segment, palm-to-finger segment, and the amplitude of the sensory nerve action potential. CTS with diabetes could not be distinguished from CTS without diabetes. The association between proximal and distal nerve conduction velocities was similar in CTS and diabetic polyneuropathy. A study in motor fibers showed that the hands could be classified through a combination of M-wave latency and the more proximal motor nerve conduction velocity measurements. Independent of severity, motor and sensory nerve conduction was influenced to an equal degree in CTS and diabetic polyneuropathy. The hypothesis that both CTS and diabetic polyneuropathy can be associated with neural ischemia is discussed.

Expression of human immunodeficiency virus type 1 in the nervous system of transgenic mice leads to neurological disease

Patients infected with the human immunodeficiency virus type 1 (HIV-1) frequently develop central and peripheral nervous system complications, some of which may reflect the effect of the virus itself. In order to elucidate the pathogenic mechanisms of HIV in neurological disease in a small animal model, we generated transgenic mice expressing the entire HIV genome under control of the promoter for the human neurofilament NF-L gene. The transgene was predominantly expressed in anterior thalamic and spinal motor neurons. Animals developed a neurological syndrome characterized by hypoactivity and weakness and by axonal degeneration in peripheral nerves. These results provide evidence for a role of HIV in affecting both the central and peripheral nervous systems. This animal model may also facilitate the development of therapeutic agents against the human disease.

Biceps vs extensor carpi radialis recovery in Frankel grades A and B in spinal cord injury patients

Clinical literature suggests that the wrist extensors show a trend of achieving functional strength earlier than the biceps after spinal cord injury (SCI). Basic research, however, demonstrated that proximal muscles recover earlier than distal muscles after partial denervation. The purpose of this study was to compare biceps to extensor carpi radialis (ECR) recovery of muscle strength in 39 motor complete cervical SCI patients. Biceps (n = 19) and ECR (n = 20) with a 72 hour or 1 week motor grade of 1/5 were compared. Testing was performed weekly for 1 month, and again at 2, 3, 6 and 12 months post injury. The median recovery times to increase one motor grade were: biceps = 2 months and ECR = 2.5 months (p < 0.3). The median recovery times to increase two motor grades were: biceps = 2 months and ECR = 3 months (p < 0.4). In conclusion, there was no significant difference between the rates of recovery of the biceps and the ECR up to 12 months post SCI.

Nerve injuries

Sports medicine physicians should be able to recognize and manage peripheral nerve injuries in athletes. Most often, the injury is a result of repetitive microtrauma, linking peripheral nerve injury to other musculoskeletal injuries in athletes. As with other musculoskeletal injuries, rest and a modification of the athlete's regimen often lead to clinical improvement. If the physician is uncertain about the diagnosis, if the athlete develops a rapid worsening of symptoms and signs, or if the athlete is refractory to treatment, a physician who specializes in peripheral nerve injuries should be consulted.

Response of peripheral nerve to cyclic compression in a laboratory rat model

Repetitive cyclic loading of a nerve has been proposed as a pathogenic factor in the development of occupational compression neuropathies. Little is known about the basic response of peripheral nerve to cyclic compression. We investigated the hypothesis that cyclic compression is more detrimental to nerve function than constant compression. We measured the amplitudes and velocities of distally evoked action potentials in the presence of constant or cyclic compression of the tibial nerve in rats. Seven groups were subjected to constant or cyclic compression for 6 h by a computer controlled, hydraulically activated compression chamber. Nerves were compressed with 0 (control group), 30, 60, or 90 mm Hg of constant pressure or 0-30, 20-50, or 30-60 mm Hg of cyclic compression for approximately 20,000 compression cycles. Action potentials were recorded every 15 min. The effects of cyclic compression on nerve conduction were equivalent to the effects of constant compression at the average applied pressure. Cyclic loading itself does not appear to be an important pathogenic factor in the development of nerve conduction block.

Endoneurial blood supply to peripheral nerves is not uniform

Peripheral nerves are not uniformly susceptible to the effects of ischemia in human and experimental ischemic neuropathies. Since endoneurial blood flow is directly proportional to the number of endoneurial capillaries, we studied endoneurial capillary density at multiple levels of the peripheral nerves of normal rats. Capillary density was lowest in the sciatic and proximal tibial nerves and significantly higher in dorsal and ventral roots and distal tibial and plantar nerves. Endoneurial capillary density corresponds to the hierarchy of susceptibility to ischemic nerve damage in human and experimental ischemic neuropathies. These findings suggest that susceptibility of peripheral nerves to ischemia is determined, at least in part, by the density of endoneurial capillaries.

Reversible conduction block in human ischemic neuropathy after ergotamine abuse

Conduction block [a significant reduction in compound muscle action potential (CMAP) amplitude after proximal compared to distal stimulation] is often found in demyelinating neuropathies, including inflammatory neuropathies and degenerative neuropathies, such as "liability to pressure neuropathy." There is experimental evidence that a transient conduction block can occur in rats after ischemic lesions of peripheral nerves are induced either by ligation of arterial vessels supplying nerve trunks, or by injection of arachidonic acid into peripheral arterial vessels. Conduction block has also recently been described in cases with necrotizing vasculitis. To date, however, no example of a reversible conduction block has been reported in human ischemic neuropathy.

Effect of ischemia and reperfusion in vivo on energy metabolism of rat sciatic-tibial and caudal nerves

Our model of severe nerve ischemia consistently results in extinction of the compound nerve and muscle action potentials (NAP; CMAP) within 30 min. Since impulse transmission may depend on nerve energy metabolism (NEM), we studied the effects of ischemia with reperfusion on sciatic-tibial nerve NEM in vivo and compared these results with NEM of this nerve in deoxygenated Ringer's solution in vitro and postmortem. Ischemia for 30 min postmortem or in deoxygenated Ringer's solution resulted in marked depletion of adenosine triphosphate (ATP) and creatine phosphate (CP) and an increase in lactate (LAC) of sciatic-tibial nerve of adult male Sprague-Dawley rats. In vivo ischemia for up to 3 h to sciatic-tibial nerve was sufficient to extinguish CMAP but not NAP and did not deplete ATP, CP, or GLU nor did it increase LAC. Ischemia sufficient to extinguish NAP resulted in reduction of energy substrates to about 50% of resting. Muscle fails to conduct impulses before nerve and in vivo reductions of energy substrates are milder than in vitro changes. These changes are explainable in terms of energy requirements and supply. These findings support an energetic basis of ischemic conduction failure.

Acute peripheral arterial occlusion: electrophysiologic study of 32 cases

Thirty patients with 32 acute peripheral arterial occlusions underwent nerve conduction and electromyographic studies at a mean of 12.4 months after the vascular occlusion. Compound action potentials showed greater reduction than conduction velocity (26% to 75% vs 8% to 13% lower than normal). All changes were more prominent in the legs than arms, including fibrillation potentials (64% vs 28%). Short motor unit potentials were seen in 13% of patients; this group also had signs of severe nerve damage. The extent of abnormality varied with location of occlusion. Signs of nerve damage were significantly decreased in patients who had early revascularization. The electrophysiologic findings suggested axonal destruction rather than demyelination.

Involvement of thin afferents in carpal tunnel syndrome: evaluated quantitatively by argon laser stimulation

The thin afferent nerves were tested quantitatively by determining the thresholds of warmth and pricking pain to argon laser stimulation and by measuring the brain potentials related to pricking pain. In 27 patients with electrophysiologically verified carpal tunnel syndrome these parameters were measured from fingers 3 and 5 on both hands. All patients had had sensory symptoms ranging from 3 months to 25 years. Both the thresholds were elevated (P less than 0.05) at finger 3 compared to measurements from finger 5, and compared to finger 3 in a group of 39 controls. Four patients with symptoms for more than 7 years had thresholds below the control values. The power of the pain-evoked brain potentials elicited from finger 3 was lower (P less than 0.05) compared to finger 5, and compared to the control group (P less than 0.01). No correlations were found between the measured parameters and the clinical electrophysiological investigation. The findings support previous assumptions that chronic low-force compressions cause impairment of intraneural microcirculation, and hence can affect the function of the thin afferents.

Mononeuropathy in sickle cell anemia: anatomical and pathophysiological basis for its rarity

Peripheral neuropathy is a rare complication of sickle cell disease. We report a young black woman with sickle cell anemia who developed a proximal median mononeuropathy in the setting of sickle cell crisis. The clinical and electrodiagnostic features are consistent with an ischemic mechanism from the sickling process. The pathophysiological basis for the rarity of this complication may be related to the rich anastomotic microvasculature of peripheral nerve and the unique large size of the capillaries of this vascular network.

Optic nerve sheath decompression: a clinical review and proposed pathophysiologic mechanism

Surgical decompression of the intraorbital meningeal sheath of the optic nerve has undergone a recent resurgence of interest. Previously, the procedure had been reserved only for the most desperate cases of severe visual loss associated with chronic papilloedema. However, recent investigations have demonstrated the operation's efficacy not only for chronic papilloedema and pseudotumor cerebri, but also for the optic neuropathy associated with the acute retinal necrosis syndrome, traumatic subdural haematomas of the optic nerve and progressive nonarteritic ischaemic optic neuropathy. In this article, we review the previous literature concerning optic nerve sheath decompression, the indication for the procedure, its techniques and results. Finally, we propose that optic nerve sheath decompression may be effective for what appear to be very different optic neuropathies because the operation may reverse optic nerve ischaemia, a common pathophysiologic feature of all these disorders.

Conduction block in neuropathies with necrotizing vasculitis

Thirty-two patients with a mononeuropathy multiplex associated with a systemic necrotizing vasculitis were studied. The main abnormality was a loss of motor and sensory axons confirmed by electrophysiological and histological methods. A conduction block was observed in five patients, but only one was at a usual site of compression. Based on previous pathological studies and the experimental data in human and animals, the mechanism of the block is proposed to be ischemic. It is suggested that a conduction block in one nerve in a neuropathy with two or more individual nerves affected and with electrophysiological features of axonal degeneration may be due to a vasculitis.

Effects of sympathetic stimulation on C-fibre responses in rabbit

Unmyelinated C-fibre responses to electrical stimulation were recorded in common peroneal, sural and tibial nerves of rabbits. Three distinct C elevations, here called C1, C2 and C3, were recorded. C2 is probably of somatic origin because it was depressed due to collision by peripheral stimulation of cutaneous receptors. The conduction velocity of C3 corresponded to that of sympathetic post-ganglionic fibres. During sympathetic trunk stimulation the A-fibre responses were not significantly changed while C responses, especially C2, were reduced in amplitude and slightly delayed. The C-fibre responses were also influenced by intra-arterial infusion of noradrenaline. In most cases, the latency of the response was increased. The effect of sympathetic stimulation was completely blocked by hexamethonium, and partly blocked by phentolamine, an adrenergic alpha-receptor blocking agent which also blocked the effect of noradrenaline. The findings suggest that there are adrenergic receptors distributed along unmyelinated somatic afferent fibres. Sympathetic activity may release noradrenaline in the peripheral nerve, resulting in changed conductive properties in unmyelinated fibres transmitting sensory information.

Assessment of Sensory Nerve Conduction in Carpal Tunnel Syndrome before, during and after Operation

Sensory conduction velocities of the median nerve before, during and after operation were compared in nine patients with carpal tunnel syndrome and four controls, in order to evaluate the prognostic value of the pre-operative and intra-operative findings.

Sensory conduction velocity was higher after operation than before in all patients (mean difference 31.33%), but not in control subjects. One patient showed a dramatic increase of 157% immediately after decompression.

Comparing the intra-operative with the post-operative findings all patients but one showed an increase of antidromic sensory conduction velocity (mean 44.37%), while in control subjects again minimal changes were found (mean –4.25%).

The study confirms the high diagnostic value of the pre-operative antidromic sensory conduction velocity findings. However, the prognostic value of both pre-operative and intra-operative ASCV findings is low.

Conduction block without demyelination following acute nerve infarction

Incomplete infarction of the tibial nerve was produced in 37 rats by injecting arachidonic acid into the femoral artery. Sciatic-tibial motor nerve conduction studies were performed 1, 2, 3 and 7 days later. In all animals the evoked motor responses were of low amplitude and morphological examination showed axonal degeneration. In 20 rats the response elicited by proximal stimulation was of lower amplitude than the distal response indicating focal conduction block in a proportion of those axons which had survived the ischemia and were not degenerating distally. The conduction block resolved over several days and in all but one rat had disappeared by 7 days. Morphological examination of semithin sections and single teased myelinated axons revealed no evidence of segmental demyelination. The rapid resolution of conduction block and the lack of significant segmental demyelination suggest that it has a metabolic basis. We suggest that hypoperfusion of the subperineurial region of the proximal tibial nerve, the region surrounding the infarct through which surviving axons pass, may be sufficient to temporarily block impulse transmission in these surviving axons without producing morphological changes.

Enhanced 2-deoxyglucose incorporation in peripheral nerve during ischemia

We examined the effect of acute ischemia on peripheral nerve uptake of the glucose analog 2-deoxyglucose (2-DG). Endoneurial 2-DG incorporation was uniform at rest, but increased focally in areas subjected to moderate levels of ischemia which were not severe enough to impair nerve conduction. We believe these data are indicative of increased endoneurial glucose metabolism probably reflecting a compensatory shift to less efficient anaerobic glycolysis. This mechanism may in part account for peripheral nerve's ability to survive transient interruption of its blood supply.

Peripheral neurological complications of aortoiliac vascular disease

Six patients with an aortoiliac vascular disease and a peripheral neurological deficit are presented. Clinical and electromyographic findings revealed lumbosacral plexus, sciatic and femoral nerve lesions. A correlation is made between the level of the vascular lesion (aortic, aortoiliac or distally) and the type of peripheral nerve deficit observed. In a patient complaining of pain, weakness, or numbness in a leg, the differential diagnosis should include aortoiliac vascular disease. The peripheral neurological symptoms may be the initial manifestation of the vascular disease or may appear in the early post-operative period.

Transient focal conduction block following experimental occlusion of the vasa nervorum

Injection of low-dose arachidonic acid into the rat femoral artery occludes the vasa nervorum of the tibial nerve and produces focal and generalized ischemia with transient effects on nerve conduction. Across a severely ischemic segment of the proximal tibial nerve there is a marked fall in amplitude of the compound muscle action potential (CMAP), indicating focal conduction block. There is also significant slowing of maximal motor conduction velocity (MCV) through this nerve segment, but no dispersion of the proximally elicited response. Distally, in a region of less severe ischemia, there is mild slowing of MCV, but no further decrement in the CMAP amplitude. The conduction block begins 5-15 minutes after injection, reaches a nadir at 30 minutes, and persists in more severe cases for at least 2 hours. Despite these prolonged electrophysiologic abnormalities, there is no evidence of axonal degeneration or segmental demyelination.