Hyperemia, CO2 responsiveness, and autoregulation in the white matter following experimental spinal cord injury

Quantifying injury expansion in the cervical spinal cord with intravital ultrafast contrast-enhanced ultrasound imaging

Spinal cord injury is characterized by hemodynamic disruption at the injury epicenter and hypoperfusion in the penumbra, resulting in progressive ischemia and cell death. This degenerative secondary injury process has been well-described, though mostly using ex vivo or depth-limited optical imaging techniques. Intravital contrast-enhanced ultrasound enables longitudinal, quantitative evaluation of anatomical and hemodynamic changes in vivo through the entire spinal parenchyma. Here, we used ultrasound imaging to visualize and quantify subacute injury expansion (through 72 h post-injury) in a rodent cervical contusion model. Significant intraparenchymal hematoma expansion was observed through 72 h post-injury (1.86 ± 0.17-fold change from acute, p < 0.05), while the volume of the ischemic deficit largely increased within 24 h post-injury (2.24 ± 0.27-fold, p < 0.05). Histology corroborated these findings; increased apoptosis, tissue and vessel loss, and sustained tissue hypoxia were observed at 72 h post-injury. Vascular resistance was significantly elevated in the remaining perfused tissue, likely due in part to deformation of the central sulcal artery nearest to the lesion site. In conjunction, substantial hyperemia was observed in all perilesional areas examined except the ipsilesional gray matter. This study demonstrates the utility of longitudinal ultrasound imaging as a quantitative tool for tracking injury progression in vivo.

Genome-wide gene expression profiling of stress response in a spinal cord clip compression injury model

Background

The aneurysm clip impact-compression model of spinal cord injury (SCI) is a standard injury model in animals that closely mimics the primary mechanism of most human injuries: acute impact and persisting compression. Its histo-pathological and behavioural outcomes are extensively similar to human SCI. To understand the distinct molecular events underlying this injury model we analyzed global mRNA abundance changes during the acute, subacute and chronic stages of a moderate to severe injury to the rat spinal cord.

Results

Time-series expression analyses resulted in clustering of the majority of deregulated transcripts into eight statistically significant expression profiles. Systematic application of Gene Ontology (GO) enrichment pathway analysis allowed inference of biological processes participating in SCI pathology. Temporal analysis identified events specific to and common between acute, subacute and chronic time-points. Processes common to all phases of injury include blood coagulation, cellular extravasation, leukocyte cell-cell adhesion, the integrin-mediated signaling pathway, cytokine production and secretion, neutrophil chemotaxis, phagocytosis, response to hypoxia and reactive oxygen species, angiogenesis, apoptosis, inflammatory processes and ossification. Importantly, various elements of adaptive and induced innate immune responses span, not only the acute and subacute phases, but also persist throughout the chronic phase of SCI. Induced innate responses, such as Toll-like receptor signaling, are more active during the acute phase but persist throughout the chronic phase. However, adaptive immune response processes such as B and T cell activation, proliferation, and migration, T cell differentiation, B and T cell receptor-mediated signaling, and B cell- and immunoglobulin-mediated immune response become more significant during the chronic phase.

Conclusions

This analysis showed that, surprisingly, the diverse series of molecular events that occur in the acute and subacute stages persist into the chronic stage of SCI. The strong agreement between our results and previous findings suggest that our analytical approach will be useful in revealing other biological processes and genes contributing to SCI pathology.

Histologically proven venous congestive myelopathy without concurrent vascular malformation: Case reports and review of the literature

BACKGROUND

Venous congestive myelopathy is a progressive myelopathy that is generally caused by a spinal dural arteriovenous fistula.

CASE DESCRIPTION

We report a patient with histologically confirmed venous congestive myelopathy without concurrent vascular malformations in radiological and intraoperative findings.

CONCLUSIONS

The definitive underlying etiology of this congestive myelopathy was unclear. However, this case report highlights the possibility of venous congestive myelopathy with etiology other than a dural arteriovenous fistula. Further, a systematic and elaborate examination should be undertaken to explore the underlying pathology whenever this type of spinal parenchymal lesion is detected.

Delayed post-traumatic spinal cord infarction in an adult after minor head and neck trauma: a case report

INTRODUCTION

Delayed post-traumatic spinal cord infarction is a devastating complication described in children. In adults, spinal cord ischemia after cardiovascular interventions, scoliosis correction, or profound hypotension has been reported in the literature. However, delayed spinal cord infarction after minor head trauma has not been described yet.

CASE PRESENTATION

We report the case of a 45-year-old Hispanic man who had a minor head trauma. He was admitted to our hospital because of paresthesias in his hands and neck pain. A radiological workup showed cervical spinal canal stenosis and chronic cervical spondylotic myelopathy. Twelve hours after admission, our patient became unresponsive and, despite full resuscitation efforts, died. The autopsy revealed spinal cord necrosis involving the entire cervical spinal cord and upper thoracic region.

CONCLUSIONS

This case illustrates the extreme fragility of spinal cord hemodynamics in patients with chronic cervical spinal canal stenosis, in which any further perturbations, such as cervical hyperflexion related to a minor head injury, can have catastrophic consequences. Furthermore, the delayed onset of spinal cord infarction in this case shows that meticulous maintenance of blood pressure in the acute post-traumatic period is of paramount importance, even in patients with minimal post-traumatic symptoms.

Blood supply and vascular reactivity of the spinal cord under normal and pathological conditions

The authors present a review of spinal cord blood supply, discussing the anatomy of the vascular system and physiological aspects of blood flow regulation in normal and injured spinal cords. Unique anatomical functional properties of vessels and blood supply determine the susceptibility of the spinal cord to damage, especially ischemia. Spinal cord injury (SCI), for example, complicating thoracoabdominal aortic aneurysm repair is associated with ischemic trauma. The rate of this devastating complication has been decreased significantly by instituting physiological methods of protection. Traumatic SCI causes complex changes in spinal cord blood flow, which are closely related to the severity of injury. Manipulating physiological parameters such as mean arterial blood pressure and intrathecal pressure may be beneficial for patients with an SCI. Studying the physiopathological processes of the spinal cord under vascular compromise remains challenging because of its central role in almost all of the body's hemodynamic and neurofunctional processes.

Targeting microvasculature for neuroprotection after SCI

Spinal cord injury (SCI) is characterized by secondary degeneration, which leads to tissue loss at the epicenter and subsequent functional deficits. This review provides insight into the pathophysiology of microvascular dysfunction and endothelial cell loss, which are among the earliest responses during the first postinjury day. The enigmatic role of the angiogenic response in the penumbra around the lost tissue, which occurs during the first 2 weeks, is also discussed. The importance of stabilizing and rescuing the injured vasculature is now well-recognized, and several pharmacological and genetic treatments have emerged in the past few years. We conclude with suggestions for future experimental research, including development of vascular-selective treatments and exploitation of genetic models. In summary, vascular dysfunction following SCI is an important contributor to neurological deficits, as proposed long ago. However, there now appears to be new and potentially powerful opportunities for treating acute SCI by targeting the vascular responses.

Neuromonitoring during surgery for metastatic tumors to the spine: intraoperative interpretation and management strategies

Resection of metastatic tumors of the spine poses great technical challenges, with the potential of creating severe neurologic deficits. Several modalities of electrophysiologic monitoring, including SSEPs and MEPs, have evolved to aid in resection of these tumors. This review has presented additional techniques-such as mapping of the dorsal columns with antidromic-elicited SSEPs to plan the myelotomy and direct intra-medullary stimulation-that help to identify the extent of the tumor margin at its interface with functional tracts. Neuromonitoring can potentially minimize the sensory and motor damage that can occur during resection of metastatic tumors of the spine. Further experience with these techniques should allow improved results follow-ing surgical procedures in functionally eloquent are as of the spinal cord during the surgical management of metastatic tumors.

Venous hypertensive myelopathy as a potential mimic of transverse myelitis

STUDY DESIGN

Case report.

OBJECTIVE

We describe a patient who developed a myelopathy associated with a noncompressive herniated cervical intervertebral disc at the same level. We provide clinical and radiological evidence that reveals that even though the disc herniation did not compress the spinal cord, it diminished venous blood flow out of the spinal cord, possibly resulting in a venous hypertensive myelopathy (VHM).

SETTING

Baltimore, MD, USA.

CLINICAL PRESENTATION

A 29-year-old woman developed a cervical radiculopathy, followed by a slowly progressive cervical myelopathy associated with a herniated C5-C6 disc. Magnetic resonance imaging showed a noncompressive disc herniation, a swollen spinal cord with increased T2 signal most prominent at the site of the herniated disc, extending several levels above and below the disc. The patient was diagnosed with acute transverse myelitis (ATM) and was started on IV steroids. However, unlike most cases of transverse myelitis, spinal fluid analysis was noninflammatory. In contrast, several features suggested that the patient instead had VHM. We suggest that the disc herniation resulted in impaired drainage of blood from the spinal cord through compression of the venous plexus near the intervertebral foramen.

INTERVENTION

Although the patient did not recover function following high-dose steroid administration, she recovered completely following C5-C6 discectomy and fusion.

CONCLUSION

To our knowledge, this is the first report of likely VHM in the absence of a spinal arteriovenous malformation. We suggest that some patients diagnosed with ATM in the setting of extrinsic spinal column abnormalities may actually have a noninflammatory myelopathy associated with impaired spinal venous drainage.

Embryonic intermediate filament, nestin, expression following traumatic spinal cord injury in adult rats

Precursor cells in the ependyma of the lateral ventricles of adult mammalian brain have been reported in brain, and also in the spinal cord. The present study used antibody to the intermediate filament protein (nestin) as an immunohistochemical marker for neural stem cells and precursor cells in a rat model of spinal cord trauma. Male Sprague-Dawley rats (n=25) had a laminectomy at Thll-Thl2, and spinal cord contusion was created by compression with 30 g of force for 10 min. The rats were killed at 24 h, 1 week and 4 weeks after injury, and four levels of the spinal cord were examined: 5 mm and 10 mm, both rostral and caudal region to the injury center. Time- and region-dependent alterations of nestin immunoreactivity were analyzed. Revealed at 24 h post-injury, 5 mm rostral and caudal to the lesions, nestin expression was observed in ependymal cells and around the hemorrhagic and necrotic lesion located in dorsal spinal cord, peaking at 1 week after injury. Moreover, nestin expression was also observed in the white matter of ventral spinal cord, extending into arborizing processes centripetally from the pial surface toward the central canal. At 4 weeks after injury, nestin expression in ependyma decreased 10 mm from the injury site. But nestin expression in white matter increased dramatically with a 100-fold increase in nestin originating from the pial surface, and extension now to all the white matter. The latter was accompanied by glial fibrillary acidic protein positivity into very long arborizing processes, morphologically compatible with radial glia. The findings suggest two possible sources of precursor cells in adult mammalian spinal cord; ependyma of the central canal and subpial astrocytes. Subpial astrocytes may be associated with neural repair and regeneration after spinal cord injury.

Spinal cord contusion models

Most human spinal cord injuries involve contusions of the spinal cord. Many investigators have long used weight-drop contusion animal models to study the pathophysiology and genetic responses of spinal cord injury. All spinal cord injury therapies tested to date in clinical trial were validated in such models. In recent years, the trend has been towards use of rats for spinal cord injury studies. The MASCIS Impactor is a well-standardized rat spinal cord contusion model that produces very consistent graded spinal cord damage that linearly predicts 24-h lesion volumes, 6-week white matter sparing, and locomotor recovery in rats. All aspects of the model, including anesthesia for male and female rats, age rather than body weight criteria, and arterial blood gases were empirically selected to enhance the consistency of injury.

Influence of posttraumatic hypoxia on behavioral recovery and histopathological outcome following moderate spinal cord injury in rats

Pulmonary dysfunction leading to secondary hypoxia is a common complication of spinal cord injury (SCI). The purpose of this study was to clarify the behavioral and histopathological consequences of posttraumatic hypoxia in an established model of traumatic SCI. Forty-five female Sprague-Dawley rats were randomly assigned to one of four groups, including (1) laminectomy and normoxia (n = 10), (2) laminectomy and hypoxia (n = 11), (3) NYU weight-drop and normoxia (n = 12), and (4) NYU weight-drop and hypoxia (n = 11). For these studies, a moderate injury was induced by adjusting the height of the weight drop (10 g) to 12.5 mm above the exposed spinal cord (T10). Immediately after injury, PaO2 in the hypoxic rats was kept between 30 and 35 mm Hg for 30 min. PaO2 in the normoxic group was maintained over 100 mm Hg, while PaCO2 in all rats was maintained at 35-40 mm Hg. The behavior of the rats was checked every 7 days using the Basso, Beattie, and Bresnahan (BBB) locomotor rating scale. Rats were sacrificed at 8 weeks for quantitative histopathological analysis of lesion areas. During the hypoxic insults, the mean arterial blood pressure dropped in both sham control and weight-drop rats (p < 0.01). At the end of the 8-week monitoring period, BBB scores were 12.5 +/- 3.1 (mean +/- SEM) and 14.2 +/- 3.4 in the normoxic and hypoxic traumatized rats, respectively. No significant difference between the traumatized groups was documented with BBB monitoring. In contrast, the percent of gray matter necrosis at the impact epicenter was significantly increased in hypoxic versus normoxic SCI rats (p < 0.01). These data demonstrate that posttraumatic hypoxia complicated by mild hypotension aggravates the histopathological consequences of SCI and further emphasize the need to control for secondary hypoxic insults after experimental and clinical SCI. Potential explanations for the lack of a correlation between the behavioral and histopathological findings are discussed.

Efficacy of high dose amino acid solution on spinal cord injury induced by focal Nd:YAG laser irradiation

In this experimental study, a neodymium:yttrium-aluminium-garnet (Nd:YAG) laser was used to induce highly reproducible focal spinal cord lesions in anaesthetized guinea pigs. The efficacy of high dose amino acid solution (HDAAS) on this injury is investigated. Experiments were performed on 36 animals divided into three groups; sham operated controls, laser irradiated surgical controls, and amino acid groups. Acute responses to injury were evaluated with somatosensory (SSEP) and motor evoked potentials (MEP) and functional recovery was assessed for 8 weeks using the inclined plane technique. In the laser irradiated surgical control group, MEP disappeared one hour after the laser injury, but SSEP revealed changes of amplitude and latency. In this group, the average value of the inclined plane at 24 hours after the laser application was 45.3 +/- 1.4 degrees. In the amino acid group, at the sixth hour of injury, MEP and SSEP changes improved with infusion of HDAAS for 4 hours. This improvement was statistically significant (for latency of SSEP U = 140 p < 0.05). Inclined plane value at 24 hours after the laser application was 65.5 +/- 1.2 degrees in this group. This study showed that application of Nd:YAG laser irradiation on the spinal cord induced spinal cord injury which presented as paraparesis, HDAAS may provide significant therapeutic protection in secondary damage following this injury and may have a potential role in the treatment of acute spinal cord injury.

The effects of arterial blood gas values on lesion volumes in a graded rat spinal cord contusion model

The detrimental effects of extreme blood gas values are well documented. However, the range of normal values has not been rigorously defined. There is an ongoing debate concerning the need for ventilation and tight control of blood gas values in spinal cord injury models. Consequently, we performed a retrospective study of 84 rats using a graded rat spinal cord contusion model. Spinal cord ionic lesion volumes were calculated from Na and K shifts at 24 h after injury. Blood gas measurements were obtained 5 min before contusion. For pH values of 7.31-7.46, systemic acidosis was associated with a small but significant decrease in ionic lesion volumes in the 12.5 and 25 g.cm contusion groups (p < 0.05 and p < 0.03, respectively). pH had no effect on ionic lesion volumes in the 50 g.cm contusion group (p > 0.5). PaCO2 values from 23 to 53 mm Hg showed an effect only at 25 g.cm (p < 0.05). PaO2 values of 46-138 mm Hg and calculated HCO3 values of 13-28 mEq/L had no effect on ionic lesion volumes. Two conclusions may be derived from these data. First, mild systemic acidosis is associated with a small reduction in ionic lesion volumes after mild and moderate injury but not after severe injury. This suggests that secondary mechanisms play a greater role in mild injuries. Second, variations in arterial blood gases within clinically normal ranges do not strongly influence 24-h ionic lesion volumes in a graded spinal cord injury model. The effects of blood gas values on ionic lesion volumes are not statistically significant unless the data are adjusted for injury severity. Although blood gas values must be carefully monitored, ventilation may not be needed routinely in rat spinal cord injury models. We recommend maintaining pH values between 7.35 and 7.40, PaCO2 between 35 and 41 mm Hg, and PaO2 greater than 71 mm Hg.

Intraoperative measurement of spinal cord blood velocity using pulsed Doppler ultrasound. A Case report

Blood velocity in the anterior spinal artery was measured with a 20 MHz doppler ultrasound microvascular probe through a standard laminectomy during syringoperitoneal shunt placement. Velocity increased with increasing levels of pCO2, with dural opening, and with syrinx drainage. These observations support the use of the doppler signal as an index of arterial blood flow. Doppler measurements are easily performed, do not require dural opening, and may be performed repetitively without risk of tissue damage. Pulsed doppler techniques provide a rapid, safe method for intraoperative evaluation of spinal cord blood velocity and may emerge as a useful tool for assessment of spinal cord blood flow.

Omento-myelo-synangiosis in the management of chronic traumatic paraplegia: case report

A case of traumatic paraplegia, with almost complete motor and sensory loss up to the umbilicus, who had an operation for post traumatic arachnoiditis and diagnosed as having recurrence of arachnoiditis and traumatic syringomyelia and treated by a pedicled omental onlay graft to the spinal cord, is described. The patient made a remarkable recovery and 1 year after surgery he continues to maintain excellent progress. He is now able to walk with support and is completely independent. It is suggested that chronic paraplegics should be assessed for possible arachnoiditis and traumatic syringomyelia and if detected an omental transposition be considered as one means of increasing rehabilitation potential.

Increase in rat spinal cord blood flow with the calcium channel blocker, nimodipine

Nimodipine, a calcium channel blocker, is known to increase cerebral blood flow. In the present study, the authors investigated the effect of nimodipine on spinal cord blood flow in normal rats. Cardiovascular parameters, including mean systemic arterial blood pressure, cardiac output, and heart rate, were recorded during infusion of nimodipine in a dose-response fashion. The experiment was a randomized blind study in which four groups of five rats received different doses of nimodipine (0.001, 0.01, 0.05, and 0.10 mg/kg) intravenously over 30 minutes, and a control group of five rats received only the diluent. The hydrogen clearance and thermodilution techniques were used to measure spinal cord blood flow and cardiac output, respectively. The 0.05-mg/kg dose of nimodipine caused the largest increase in spinal cord blood flow, with a 40% increase over the preinfusion level, although there was a 25% reduction in mean arterial pressure. The 0.10-mg/kg dose did not increase spinal cord blood flow more than the 0.05-mg/kg dose, most likely due to the concomitant 37% reduction in mean arterial pressure. Cardiac output was significantly increased by the 0.05- and 0.10-mg/kg doses secondary to the drop in total peripheral resistance. The increase in spinal cord blood flow produced by nimodipine lasted approximately 20 minutes after the termination of the infusion. Thus, nimodipine at a dose of 0.05 mg/kg markedly increased blood flow in the normal spinal cord even though there were major changes in mean systemic arterial pressure and cardiac output. Further research is required to determine whether this drug might be beneficial in treating ischemic states of the spinal cord, such as posttraumatic ischemia.

Therapeutic trial of hypercarbia and hypocarbia in acute experimental spinal cord injury

Hypocarbia, normocarbia, or hypercarbia was maintained for an 8-hour period beginning 30 minutes after acute threshold spinal cord injuries in cats. No statistically significant differences in neurological recovery or histologically assessed tissue preservation were found among the three groups of animals 6 weeks after injury. No animal recovered the ability to walk. It is concluded that maintenance of hypercarbia or hypocarbia during the early postinjury period is no more therapeutic than maintenance of normocarbia. Mortality rates and tissue preservation data suggest, however, that postinjury hypocarbia may be less damaging than hypercarbia.

Failure of tetracaine to reverse spinal cord injury in the cat

Beginning 30 minutes after acute spinal cord injury, cats were treated by the administration of continuous spinal anesthesia for 8 hours. This was achieved by the intermittent injection of hyperbaric tetracaine into the subarachnoid space at the site of injury via an indwelling catheter. There were no significant differences in functional recovery or histologically assessed tissue preservation between treated cats and concurrently managed control animals. The indwelling subarachnoid catheter used for drug administration was found to have no significant effect on the spinal cord injury.

Dural arteriovenous malformations of the spine. Clinical features and surgical results in 55 cases

The clinical and angiographic findings of 55 patients with a spinal dural arteriovenous malformation (AVM) are reviewed, and the results of surgery assessed. The symptoms of dural AVM are usually gradual in onset, and hemorrhage from this type of AVM is less common than in true spinal cord angiomas. Other clinical features and the myelographic findings are similar to those of spinal cord angiomas. On angiography, the nidus of dural AVM's usually projected lateral to the spinal cord. Clipping of communicating vessels between the AVM and the coronal plexus was carried out in 50 patients, and decompressive laminectomy only in five cases. Surgery led to improvement of disturbed gait or arrest of a previously progressive course in 85% of those managed by clipping communicating vessels. The pathophysiology and surgical treatment of dural AVM's are discussed.

Local vascular response to change in carbon dioxide tension. Long term observation in the cat's brain by means of the hydrogen clearance technique

Thirty six small hydrogen sensitive electrodes were inserted into the brains of 6 cats to evaluate the local vascular response to change in PaCO2, of cortex, subcortical white matter, and caudate nucleus. Repeated measurements (617) of local cerebral blood flow (ICBF) were performed over a period of 12 weeks. Within a PaCO2 range from 19 to 96 mmHg the local response of CBF was linear in most of the regions measured. The absolute local CO2 reactivity (CO2-R) showed a positive correlation to ICBF at PaCO2 = 40 mmHg (ICBF40) with the regression line: absolute CO2-R = 0.02 ICBF40 + 0.22, r = 0.71 (p less than 0.01). Therefore relative ICBF change was calculated in relation to ICBF40 to make comparisons between the CO2 response of different measuring days and of different regions examined. No significant change in relative CO2-R was observed during the 12 weeks interval. Differences of relative CO2-R between investigated regions were insignificant. The uniformity of relative CO2 response might support the hypothesis of a direct effect of PaCO2 or pH on the vessel wall. For comparison of CBF, the individual determination of CBF40 and relative CO2-R would be necessary.

A reproducible spinal cord injury model in the cat

Allen's weight-drop method for producing experimental spinal cord injuries was improved by placing a curved stainless steel plate anterior to the spinal cord to provide a smooth, hard surface for the receipt of posterior cord impact. In addition, an electronic circuit was used to ensure that cord injury was produced by a single impact, thereby enhancing the reproducibility of the injury mechanism. Using a spinal cord injury model with these modifications, the author found that the recovery of hindlimb function and the histopathological appearance of the injured cord 6 weeks after upper lumbar injury were closely related to injury magnitude. The curve of functional recovery versus injury magnitude has a sharp transition centered at 10 gm X 15 cm, and indicates that an injury of 10 gm X 20 cm produces a "threshold" lesion suitable for the future evaluation of spinal cord treatment methods.

Control of blood flow in the cat spinal cord

Spinal cord blood flow (SCBF) and the effect of end-tidal CO2 concentration (ETCO2) on SCBF (CO2 reactivity) were studied in the lumbar spinal cord of cats by means of the hydrogen-clearance technique Hydrogen gas was administered by inhalation, and its level in spinal cord tissue was estimated amperometrically with small (75 micrometers) platinum electrodes. The average SCBF's at normocapnia (ETCO2 = 4%) of the ventral horn gray matter and of the white matter at several locations were 43.2 and 16.2 ml . 100 gm-1 . min-1, respectively. For gray and white matter, the values of CO2 reactivity, estimated by the coefficient of the regression of SCBF (ml . 100 gm-1 . min-1) on ETCO2 (ml . 100 ml-1) were 11.6 and 2.1, respectively. No differences in SCBF or CO2 reactivity were observed between intact animals kept under N2O-O2 ventilation and decerebrated animals with no anesthesia. After an acute spinal section, ventral horn SCBF and CO2 reactivity (measured eight segments below the cordotomy) were not altered, in spite of the profound neural depression present (that is, spinal shock). Orthodromic (dorsal root) stimulation of the ventral horn neurons induced an average increase in blood flow of 128% above control values. Antidromic (ventral root) motoneuron activation failed to produce any significant changes in ventral horn blood flow.

The effect of blood transfusion, dopamine, and gamma hydroxybutyrate on posttraumatic ischemia of the spinal cord

Posttraumatic spinal cord blood flow (SCBF) was assessed after elevating the mean systemic arterial pressure (mSAP) with a blood transfusion, or with an infusion of dopamine. The effect of the anesthetic agent, gamma hydroxybutyrate, was also assessed. Flows were measured using the 14C-antipyrine autoradiographic method. Animals were injured at T-1 by acute compression of the spinal cord with a clip exerting a pressure of 175 gm. Uninjured animals, with mSAP's of 120.0 +/- 17.0 mm Hg, had gray and white matter flows of 74.2 +/- 22.3 and 18.7 +/- 6.7 ml/100 gm/min, respectively, while injured untreated animals had mSAP's of 82.5 +/- 14.1 mm Hg and gray and white matter flows of 13.3 +/- 12.1 and 3.9 +/- 3.9 ml/100 gm/min, respectively, at the injury site. Blood transfusion raised the mSAP's to 127.5 +/- 13.7 mm Hg in the injured animals and doubled the flows in gray and white matter to 25.6 +/- 30.2 and 6.3 +/- 6.4 ml/100 gm/ml, respectively. Dopamine did not have as beneficial an effect as blood transfusion on either the mSAP (101.0 +/- 16.7 mm Hg) or the SCBF (gray and white matter flows of 18.4 +/- 12.4 and 5.8 +/- 5.9 ml/100 gm/min). Gamma hydroxybutyrate (GHB) had almost no effect on the mSAP or SCBF of normal animals, and in injured animals produced only a unilateral increase in flow on the less severely injured side, without affecting the mSAP.

The effects of ischemia on long-tract neural conduction in the spinal cord

In this experiment, the effects of ischemia on neural conduction in the monkey spinal cord were studied. In six monkeys generalized ischemia of the spinal cord was created by bleeding the animals to a hypotensive level below the lower limits of autoregulation in the spinal cord. The progressive development of spinal cord ischemia was documented by blood-flow measurement using the hydrogen clearance method. Physiological integrity of the spinal cord was monitored and recorded by the spinal evoked response. The spinal evoked response did not disappear until at least 10 minutes of profound ischemia. At levels of ischemia 20% to 25% of normal blood flow, the spinal evoked response was unchanged. It is concluded that long-tract neural conduction in the spinal cord is relatively resistant to the effects of ischemia.

Loss of autoregulation and posttraumatic ischemia following experimental spinal cord trauma

Blood flow in the dorsolateral funiculus of the cat thoracic spinal cord was studied after severe experimental cord injury, using a modification of the hydrogen clearance technique. Autoregulation was intact during the initial 60 to 90 minutes after cord injury, but was then lost coincident with the onset of ischemia. The data suggest that the ischemic response to spinal cord injury is mediated both by the loss of autoregulation and by relative vasoconstriction of the resistance vessels. Therapeutic intervention aimed at maintaining perfusion during the early posttraumatic period may prove of value in reversing or limiting some elements of dysfunction due to the secondary injury of ischemia.

Angiography of the spinal cord after vertebral trauma

Angiography of the spinal cord after trauma to the spine is reported in 14 new cases with neurological signs. Three types of angiographic signs are demonstrated: (1) arterial interruption of the anterior spinal artery, the ascending branch of the radiculomedullary arteries or the extravertebral arteries; (2) displacement of the anterior spinal artery without interruption; (3) hyperemia. The mechanism and significance of these signs are discussed.