Spinal cord blood flow and pathophysiological changes after transient spinal cord ischemia in cats

Awake rabbit model of ischemic spinal cord injury with delayed paraplegia: The role of ambient temperature

BACKGROUND

Paraplegia after spinal cord ischemia is a devastating condition in the clinic. Here, we develop an awake rabbit model of spinal cord ischemia with delayed paraplegia and explore the influence of ambient temperature on the outcomes after injury.

METHODS

A total of 47 male rabbits were involved in the present study. Transient spinal cord ischemia was induced by occluding the infrarenal abdominal aorta of awake rabbits at different ambient temperatures. To find the optimal conditions for developing delayed paraplegia, hindlimb motor function after ischemia was evaluated between experiments.

RESULTS

The onset and magnitude of ischemic injury varied with the ambient temperature maintained during the peri-ischemia period. More serious spinal cord injury occurred when ischemia was induced at higher temperatures. At 18°C, 25-minute ischemia resulted in 74% of rabbits developing delayed paraplegia. At a temperature of 28°C or higher, most of the animals developed acute paraplegia immediately. While at 13°C, rabbits usually regained normal motor function without paraplegia.

CONCLUSION

This awake rabbit model is highly reproducible and will be helpful in future studies of delayed paraplegia after spinal cord ischemia. The ambient temperature must be considered while using this model during investigation of therapeutic interventions.

Effects of fluids vs. vasopressors on spinal cord microperfusion in hemorrhagic shock induced ischemia/reperfusion

OBJECTIVE

Spinal cord injury induced by ischemia/reperfusion is a devastating complication of aortic repair. Despite developments for prevention and treatment of spinal cord injury, incidence is still considerably high majorly impacting patient outcome. Microcirculation is paramount for tissue perfusion and oxygen supply and often dissociated from macrohemodynamic parameters used to guide resuscitation. Effects of fluids vs. vasopressors in the setting of hemodynamic resuscitation on spinal cord microperfusion are unknown. Aim of this study was to compare the effects of vasopressor and fluid resuscitation on spinal cord microperfusion in a translational acute pig model of hemorrhagic shock induced ischemia/reperfusion injury.

METHODS

We designed this study as prospective randomized explorative large animal study. We induced hemorrhagic shock in 20 pigs as a model of global ischemia/reperfusion injury. We randomized animals to receive either fluid or vasopressor resuscitation. We measured spinal cord microperfusion using fluorescent microspheres as well as laser-Doppler probes. We monitored and analyzed macrohemodynamic parameters and cerebrospinal fluid pressure.

RESULTS

Spinal cord microperfusion decreased following hemorrhagic shock induced ischemia/reperfusion injury. Both fluids and vasopressors sufficiently restored spinal cord microperfusion. There were no important changes between groups (percentage changes compared to baseline: fluids 14.0 (0.31-27.6) vs. vasopressors 24.3 (8.12-40.4), p = .340). However, cerebrospinal fluid pressure was higher in animals receiving fluid resuscitation (percentage changes compared to baseline: fluids 27.7 (12.6-42.8) vs. vasopressors -5.56 ((-19.8)-8.72), p = .003). Microcirculatory resuscitation was in line with improvements of macrohemodynamic parameters.

CONCLUSIONS

Both, fluids and vasopressors, equally restored spinal cord microperfusion in a porcine acute model of hemorrhagic shock induced ischemia/reperfusion injury. However, significant differences in cerebrospinal fluid pressure following resuscitation were present. Future studies should evaluate these effects in perfusion disruption induced ischemia/reperfusion conditions of microcirculatory deterioration.

Spinal Cord Parenchyma Vascular Redistribution Underlies Hemodynamic and Neurophysiological Changes at Dynamic Neck Positions in Cervical Spondylotic Myelopathy

Cervical spondylotic myelopathy (CSM) is a degenerative condition of the spine that caused by static and dynamic compression of the spinal cord. However, the mechanisms of motor and somatosensory conduction, as well as pathophysiological changes at dynamic neck positions remain unclear. This study aims to investigate the interplay between neurophysiological and hemodynamic responses at dynamic neck positions in the CSM condition, and the pathological basis behind. We first demonstrated that CSM patients had more severe dynamic motor evoked potentials (DMEPs) deteriorations upon neck flexion than upon extension, while their dynamic somatosensory evoked potentials (DSSEPs) deteriorated to a similar degree upon extension and flexion. We therefore generated a CSM rat model which developed similar neurophysiological characteristics within a 4-week compression period. At 4 weeks-post-injury, these rats presented decreased spinal cord blood flow (SCBF) and oxygen saturation (SO₂) at the compression site, especially upon cervical flexion. The dynamic change of DMEPs was significantly correlated with the change in SCBF from neutral to flexion, suggesting they were more sensitive to ischemia compared to DSSEPs. We further demonstrated significant vascular redistribution in the spinal cord parenchyma, caused by angiogenesis mainly concentrated in the anterior part of the compressed site. In addition, the comparative ratio of vascular densities at the anterior and posterior parts of the cord was significantly correlated with the perfusion decrease at neck flexion. This exploratory study revealed that the motor and somatosensory conductive functions of the cervical cord changed differently at dynamic neck positions in CSM conditions. Compared with somatosensory conduction, the motor conductive function of the cervical cord suffered more severe deteriorations upon cervical flexion, which could partly be attributed to its higher susceptibility to spinal cord ischemia. The uneven angiogenesis and vascular distribution in the spinal cord parenchyma might underlie the transient ischemia of the cord at flexion.

Duraplasty in Traumatic Thoracic Spinal Cord Injury: Impact on Spinal Cord Hemodynamics, Tissue Metabolism, Histology, and Behavioral Recovery Using a Porcine Model

After acute traumatic spinal cord injury (SCI), the spinal cord can swell to fill the subarachnoid space and become compressed by the surrounding dura. In a porcine model of SCI, we performed a duraplasty to expand the subarachnoid space around the injured spinal cord and evaluated how this influenced acute intraparenchymal hemodynamic and metabolic responses, in addition to histological and behavioral recovery. Female Yucatan pigs underwent a T10 SCI, with or without duraplasty. Using microsensors implanted into the spinal cord parenchyma, changes in blood flow (ΔSCBF), oxygenation (ΔPO₂), and spinal cord pressure (ΔSCP) during and after SCI were monitored, alongside metabolic responses. Behavioral recovery was tested weekly using the Porcine Injury Behavior Scale (PTIBS). Thereafter, spinal cords were harvested for tissue sparing analyses. In both duraplasty and non-animals, the ΔSCP increased ∼5 mm Hg in the first 6 h post-injury. After this, the SCP appeared to be slightly reduced in the duraplasty animals, although the group differences were not statistically significant after controlling for injury severity in terms of impact force. During the first seven days post-SCI, the ΔSCBF or ΔPO₂ values were not different between the duraplasty and control animals. Over 12 weeks, there was no improvement in hindlimb locomotion as assessed by PTIBS scores and no reduction in tissue damage at the injury site in the duraplasty animals. In our porcine model of SCI, duraplasty did not provide any clear evidence of long-term behavioral or tissue sparing benefit after SCI.

Effect of Spinal Shortening for Protection of Spinal Cord Function in Canines with Spinal Cord Angulation

Background

Posterior vertebral column resection (PVCR) has been widely used as a treatment for severe spinal deformity. By using the canine model of vertebral column resection, this study explored the effect of spinal shortening on blood flow and function of the spinal cord during spinal cord angulation.

Material/Methods

The canine model of L1 vertebral column resection was constructed with the PVCR technique. The canines were divided into 5 groups according to the degree of shortening: the 0/4 group, the 1/4 group, the 2/4 group, the 3/4 group, and the control group. Spinal cord blood flow, neuroelectrophysiology, HE staining, nitric oxide, and endothelin-1 were measured during the procedure of vertebral column resection and spinal cord angulation.

Results

The results showed that, in the 1/4 group and the 2/4 group, the blood flow of the spinal cord decreased by 16.5% and 10.6%, respectively, with no obvious damage in the spinal cord; in the 0/4 group and the 3/4 group, the blood flow decreased by 23.5% and 23.1%, respectively, with significant damage in the spinal cord.

Conclusions

When the spinal cord is shortened by 1/4 to 2/4, the tolerance of the spinal cord can increase and spinal cord injury resulting from angulation can be avoided. However, when the shortening reaches 3/4, it is harmful to the spinal cord. Proper shortening of the spinal cord by 1/4 to 2/4 may increase the tolerance of the spinal cord to the damage caused by angulation during PVCR.

Using Laser Doppler Imaging and Monitoring to Analyze Spinal Cord Microcirculation in Rat

Laser Doppler flowmetry (LDF) is a noninvasive method for blood flow (BF) measurement, which makes it preferable for measuring microcirculatory alterations of the spinal cord. In this article, our goal was to use both Laser Doppler imaging and monitoring to analyze the change of BF after spinal cord injury. Both the laser Doppler image scanner and the probe/monitor were being employed to obtain each readout. The data of LDPI provided a local distribution of BF, which gave an overview of perfusion around the injury site and made it accessible for comparative analysis of BF among different locations. By intensely measuring the probing area over a period of time, a combined probe was used to simultaneously measure the BF and oxygen saturation of the spinal cord, showing overall spinal cord perfusion and oxygen supply. LDF itself has a few limitations, such as relative flux, sensitivity to movement, and biological zero signal. However, the technology has been applied in clinical and experimental study due to its simple setup and rapid measurement of BF.

Changes in Pressure, Hemodynamics, and Metabolism within the Spinal Cord during the First 7 Days after Injury Using a Porcine Model

Traumatic spinal cord injury (SCI) triggers many perturbations within the injured cord, such as decreased perfusion, reduced tissue oxygenation, increased hydrostatic pressure, and disrupted bioenergetics. While much attention is directed to neuroprotective interventions that might alleviate these early pathophysiologic responses to traumatic injury, the temporo-spatial characteristics of these responses within the injured cord are not well documented. In this study, we utilized our Yucatan mini-pig model of traumatic SCI to characterize intraparenchymal hemodynamic and metabolic changes within the spinal cord for 1 week post-injury. Animals were subjected to a contusion/compression SCI at T10. Prior to injury, probes for microdialysis and the measurement of spinal cord blood flow (SCBF), oxygenation (in partial pressure of oxygen; PaPO₂), and hydrostatic pressure were inserted into the spinal cord 0.2 and 2.2 cm from the injury site. Measurements occurred under anesthesia for 4 h post-injury, after which the animals were recovered and measurements continued for 7 days. Close to the lesion (0.2 cm), SCBF levels decreased immediately after SCI, followed by an increase in the subsequent days. Similarly, PaPO₂ plummeted, where levels remained diminished for up to 7 days post-injury. Lactate/pyruvate (L/P) ratio increased within minutes. Further away from the injury site (2.2 cm), L/P ratio also gradually increased. Hydrostatic pressure remained consistently elevated for days and negatively correlated with changes in SCBF. An imbalance between SCBF and tissue metabolism also was observed, resulting in metabolic stress and insufficient oxygen levels. Taken together, traumatic SCI resulted in an expanding area of ischemia/hypoxia, with ongoing physiological perturbations sustained out to 7 days post-injury. This suggests that our clinical practice of hemodynamically supporting patients out to 7 days post-injury may fail to address persistent ischemia within the injured cord. A detailed understanding of these pathophysiological mechanisms after SCI is essential to promote best practices for acute SCI patients.

Ischemic preconditioning ameliorates spinal cord ischemia-reperfusion injury by triggering autoregulation

OBJECTIVE

The mechanism underlying ischemic preconditioning (IPC) protection against spinal cord ischemia-reperfusion (I/R) injury is unclear. We investigated the role of spinal cord autoregulation in tolerance to spinal cord I/R injury induced by IPC in a rat model.

METHODS

Sprague-Dawley rats were randomly assigned to four groups. IPC (P) group animals received IPC by temporary thoracic aortic occlusion (AO) with a 2F Fogarty arterial embolectomy catheter (Baxter Healthcare, Irvine, Calif) for 3 minutes. The I/R injury (I/R) group animals were treated with blood withdrawal and temporary AO for 12 minutes, and shed blood reinfusion at the end of the procedures. The P+I/R animals received IPC, followed by 5 minutes reperfusion, and then I/R procedures for 12 minutes. Sham (S) group animals received anesthesia and underwent surgical preparation, but without preconditioning or I/R injury. Neurologic function on postprocedure days 1, 3, 5, and 7 was evaluated by Tarlov scoring. Lumbar segments were harvested for histopathologic examination on day 7. To evaluate the role of autoregulation in IPC, spinal cord blood flow and tissue oxygenation were continuously monitored throughout the procedure duration.

RESULTS

The Tarlov scores in the I/R group were significantly lower than those in the S, P, and P+I/R groups on days 1, 3, 5, and 7 (P < .001). No significant differences were noted between the S, P, and P+I/R groups. The numbers of surviving motor neurons in the S, P, and P+I/R groups were significantly higher than those in the I/R group (P < .001); however, the number of surviving motor neurons did not differ between the S, P, and P+I/R groups. The P group exhibited higher spinal cord blood flow (P = .001-.043) and tissue oxygenation (P = .032-.043) within the first 60 minutes after reperfusion than the S group. The P+I/R group exhibited higher spinal cord blood flow (P = .016-.045) and tissue oxygenation (P = .001-.038) within the first 60 minutes after reperfusion than the I/R group.

CONCLUSIONS

IPC ameliorates spinal cord I/R injury in rats, probably mediated by triggering spinal cord autoregulation and improving local spinal cord blood flow and tissue oxygenation. This concept may be the new therapeutic targets in patients requiring aortic surgery.

Blood pressure changes alter tracheobronchial cough: computational model of the respiratory-cough network and in vivo experiments in anesthetized cats

We tested the hypothesis, motivated in part by a coordinated computational cough network model, that alterations of mean systemic arterial blood pressure (BP) influence the excitability and motor pattern of cough. Model simulations predicted suppression of coughing by stimulation of arterial baroreceptors. In vivo experiments were conducted on anesthetized spontaneously breathing cats. Cough was elicited by mechanical stimulation of the intrathoracic airways. Electromyograms (EMG) of inspiratory parasternal, expiratory abdominal, laryngeal posterior cricoarytenoid (PCA), and thyroarytenoid muscles along with esophageal pressure (EP) and BP were recorded. Transiently elevated BP significantly reduced cough number, cough-related inspiratory, and expiratory amplitudes of EP, peak parasternal and abdominal EMG, and maximum of PCA EMG during the expulsive phase of cough, and prolonged the cough inspiratory and expiratory phases as well as cough cycle duration compared with control coughs. Latencies from the beginning of stimulation to the onset of cough-related diaphragm and abdominal activities were increased. Increases in BP also elicited bradycardia and isocapnic bradypnea. Reductions in BP increased cough number; elevated inspiratory EP amplitude and parasternal, abdominal, and inspiratory PCA EMG amplitudes; decreased total cough cycle duration; shortened the durations of the cough expiratory phase and cough-related abdominal discharge; and shortened cough latency compared with control coughs. Reduced BP also produced tachycardia, tachypnea, and hypocapnic hyperventilation. These effects of BP on coughing likely originate from interactions between barosensitive and respiratory brainstem neuronal networks, particularly by modulation of respiratory neurons within multiple respiration/cough-related brainstem areas by baroreceptor input.

Contribution of supraspinal and spinal structures to the responses of dorsal spinal cord blood flow to innocuous cutaneous brushing in rats

Responses of dorsal spinal cord blood flow (SCBF) to innocuous mechanical cutaneous stimulation were investigated in anesthetized central nervous system intact (CNS-intact) and C2 spinalized rats. SCBF was recorded at the L4-L6 level with a laser Doppler flowmeter. SCBF increased with brushing of the ipsilateral proximal hindlimb and hindpaw, and there were no significant differences in the magnitudes of the responses in CNS-intact and spinalized animals. Brushing of the lower back had no effect on SCBF at the L4-L6 level in either cohort. Brushing stimulation produced no significant changes in systemic arterial blood pressure. The responses of SCBF to brushing in CNS-intact animals were diminished by pretreatment with phenoxybenzamine, an alpha-adrenoceptor blocking agent, but no such effects were seen in spinalized animals. These results indicate that innocuous mechanical cutaneous input can produce a segmentally-organized increase in regional SCBF, and that the responses are modulated, in part at least, by alpha-adrenergic receptors via supraspinal structures.

The effect of long-term reduction of aortic blood flow on spinal cord gray matter in the rabbit. Histochemical study of NADPH-diaphorase

1. The aim of this work was to study the influence of reduced aortic blood flow on NADPH-diaphorase (NADPH-d) staining in the gray matter of L4-S3 spinal cord segments. 2. Surgery was performed on the abdominal aorta of the rabbit. Spinal cord ischemia was introduced by infrarenal aortic constriction to 30% from the normal blood flow. Animals were allowed to survive 1 week, 1 month and 3 months after surgery. Neurological outcome was studied in relation to the duration of aortic occlusion. The NADPH-d histochemistry was used for the visualisation of spinal cord sections. 3. The most affected area of the spinal cord was pericentral region, and slight changes were seen in the NADPH-d activities of both dorsal and ventral horns. One week after surgery, NADPH-d positive pericentral neurons were almost unchanged in their shape and intensity of staining, the only difference was seen in slightly increased staining of the background around the central canal. One month following surgery neurons exhibited shrinkage or were swollen, NADPH-d staining was less intensive in the pericentral zone and positively stained vessels were present. 4. Three months of ischemia influenced the NADPH-d activity: (a) In the pericentral region were seen intensively NADPH-d stained neurons almost normal in shape of their bodies but with shortened processes or without them; (b) NADPH-d staining of neuropil was greatly enhanced mostly around the central canal and in the dorsal commissure; (c) Numerous vessels were present in the pericentral zone and in the location of the ventral horn. 5. It can be concluded that the reduction of blood flow in the abdominal aorta makes most changes in the pericentral region of the rabbit spinal cord. Increased NADPH-d staining of neuropil and the presence of positively stained vessels reflect increased NADPH-d/NOS production in the spinal cord gray matter after long-term incomplete aortic occlusion.

How many ligations of bilateral segmental arteries cause ischemic spinal cord dysfunction? An experimental study using a dog model

STUDY DESIGN

Segmental arteries were interrupted bilaterally for up to 7 levels to study the effects on spinal cord blood flow and neurologic function in dogs.

OBJECTIVE

To examine how many ligations of bilateral segmental arteries cause ischemic spinal cord dysfunction.

SUMMARY OF BACKGROUND DATA

Interruption of bilateral segmental arteries for up to 3 levels has been reported not to damage spinal cord function. However, to our knowledge, the effects of ligating more than 3 levels have not yet been clearly determined.

METHODS

There were 15 dogs divided into 5 groups: sham group, no ligation; group 1, ligation of bilateral segmental arteries at 3 levels (T11-T13); group 2, at 4 levels (T10-T13); group 3, at 5 levels (T10-L1); and group 4, at 7 levels (T9-L2). Spinal cord blood flow at T12 measured by laser Doppler flowmetry, and spinal cord-evoked and motor-evoked potentials were measured simultaneously until 10 hours after ligation. Neurologic function was assessed using a modified Tarlov grading system 1 week after operation in 20 other dogs divided into 4 groups (1, 2, 3, and 4).

RESULTS

Spinal cord blood flow was 99.3%, 80.7%, 71.5%, 44.3%, and 25.0% in the sham group, and groups 1, 2, 3, and 4, respectively, 10 hours after ligation. Abnormal spinal cord-evoked potentials were observed in 2 of 3 dogs in group 3 and all 3 in group 4. Abnormal motor-evoked potentials were observed in 1 of 3 dogs in group 3 and all 3 in group 4. Postoperative neurologic evaluation identified all 5 dogs in groups 1 and 2, respectively, and 3 in group 3 as having grade 5. There were 2 dogs in group 3 and 3 in group 4 that had grade 4, and 2 in group 4 had grade 3.

CONCLUSION

Interruption of bilateral segmental arteries at > or =5 consecutive levels risks producing a spinal cord ischemia capable of injuring the spinal cord.

Cerebrospinal fluid may mediate CNS ischemic injury

Background

The central nervous system (CNS) is extremely vulnerable to ischemic injury. The details underlying this susceptibility are not completely understood. Since the CNS is surrounded by cerebrospinal fluid (CSF) that contains a low concentration of plasma protein, we examined the effect of changing the CSF in the evolution of CNS injury during ischemic insult.

Methods

Lumbar spinal cord ischemia was induced in rabbits by cross-clamping the descending abdominal aorta for 1 h, 2 h or 3 h followed by 7 d of reperfusion. Prior to ischemia, rabbits were subjected to the following procedures; 1) CSF depletion, 2) CSF replenishment at 0 mmHg intracranial pressure (ICP), and 3) replacement of CSF with 8% albumin- or 1% gelatin-modified artificial CSF, respectively. Motor function of the hind limbs and histopathological changes of the spinal cord were scored. Post-ischemic microcirculation of the spinal cord was visualized by fluorescein isothiocyanate (FITC) albumin.

Results

The severity of histopathological damage paralleled the neurological deficit scores. Paraplegia and associated histopathological changes were accompanied by a clear post-ischemic deficit in blood perfusion.

Spinal cord ischemia for 1 h resulted in permanent paraplegia in the control group. Depletion of the CSF significantly prevented paraplegia. CSF replenishment with the ICP reduced to 0 mmHg, did not prevent paraplegia. Replacement of CSF with albumin- or gelatin-modified artificial CSF prevented paraplegia in rabbits even when the ICP was maintained at 10–15 mmHg.

Conclusion

We conclude that the presence of normal CSF may contribute to the vulnerability of the spinal cord to ischemic injury. Depletion of the CSF or replacement of the CSF with an albumin- or gelatin-modified artificial CSF can be neuroprotective.

Delayed detection of motor pathway dysfunction after selective reduction of thoracic spinal cord blood flow in pigs

OBJECTIVE

Clinical monitoring of myogenic motor evoked potentials to transcranial stimulation provides rapid evaluation of motor-pathway function during surgical procedures in which spinal cord ischemia can occur. However, a severe reduction of spinal cord blood flow that remains confined to the thoracic spinal cord might render ischemic only the descending axons of the corticospinal pathway. In this situation lower-limb motor evoked potentials could respond relatively late compared with a similar spinal cord blood flow reduction of the lumbar spinal cord that renders predominantly motoneurons ischemic.

METHODS

Selective thoracic and lumbar spinal cord ischemia was induced by sequential clamping of segmental arteries during continuous assessment of laser-Doppler spinal cord blood flow at the thoracic and lumbar spinal cord. Myogenic motor evoked potentials were recorded from the upper and lower limbs. The time to loss of motor evoked potentials was compared (n = 11) during reduction of laser-Doppler spinal cord blood flow below 25% of baseline (ischemic segment), and flow was maintained at greater than 75% of baseline in the nonischemic segment, both during thoracic and lumbar spinal cord ischemia.

RESULTS

Average laser-Doppler spinal cord blood flow in the ischemic segment was similar during thoracic (26% +/- 15% [+/- SD]) and lumbar (26% +/- 16%) ischemia, whereas normal flow was maintained in the nonischemic segment. The time to motor evoked potentials loss was considerably longer after thoracic spinal cord ischemia (15 +/- 11 minutes) than after lumbar spinal cord ischemia (3 +/- 2 minutes, P <.005).

CONCLUSION

In this experimental model of selective spinal cord ischemia, a severe reduction of lumbar spinal cord blood flow results in rapid loss of myogenic motor evoked potentials, whereas a similar blood flow reduction in the thoracic spinal cord results in relatively slow loss of motor evoked potentials. The effectiveness of motor evoked potentials to rapidly assess spinal cord integrity might be limited when spinal cord ischemia is confined to the thoracic segments.

Monitoring of intrathecal oxygen tension during experimental aortic occlusion predicts ultrastructural changes in the spinal cord

OBJECTIVE

To study the correlation between intrathecal PO2 and ultrastructural changes in the spinal cord during thoracic aortic occlusion in pigs.

MATERIAL AND METHODS

In 18 pigs, online intrathecal oxygenation was monitored by a multiparameter Paratrend catheter (Biomedical Sensors, High Wycombe, United Kingdom) during 60 minutes' clamping of the proximal and distal descending thoracic aorta. The animals were randomly divided into 2 groups (A and B) depending on the level of distal aortic clamping. Distal aortic perfusion was restored through an aorto-iliac shunt, which also maintained low thoracic segmental perfusion of the spinal cord in group B. Perfusion-fixation technique was used before harvesting the spinal cord specimens, which later were evaluated with light and electron microscopy by an independent observer. Intrathecal parameters were interpreted as normal if PO2 was more than 0.8 kPa and PCO2 was less than 12 kPa, as intermediate ischemia if PO2 was 0.8 or less or PCO (2) was more than 12 kPa, and as absolute ischemia if PO2 was 0.8 or less and PCO2 was more than 12 kPa.

RESULTS

Among 6 animals with ultrastructural changes of absolute spinal cord ischemia-reperfusion injury, 5 also had absolute ischemia according to variables derived by the Paratrend catheter. The 2 methods were in agreement in 3 of 5 animals with intermediate ischemia-reperfusion changes and in 5 of 6 animals with normal findings. The accuracy of cerebrospinal fluid PO2 and PCO2 to predict electron microscopy-verified intermediate or absolute ischemia-reperfusion injury was 94%.

CONCLUSIONS

Monitoring of intrathecal PO2 after clamping of the descending aorta correlated with ultrastructural changes in the spinal cord in this pig model.

Effects of hypothermia on blood flow and neural activity in rabbit spinal cord during postischemic reperfusion

The effects of hypothermia on blood flow and neural activity were investigated in rabbit spinal cord during the acute phase of ischemia/reperfusion. Rabbits were exposed to ischemia for 10 or 40 min by occluding the abdominal aorta, using a balloon catheter. The body temperature was maintained either at 38 degrees C (normothermia) or 34 degrees C (hypothermia). Hyperperfusion was observed within 10 min after the cessation of ischemia in all rabbits exposed to ischemia. The magnitude of hyperperfusion in spinal cord blood flow (SCBF) was not significantly different between the 10 and 40 min ischemia rabbits, but the time for 50% recovery from the hyperperfusion was longer in the 40 min ischemia group (26.1 +/- 2.5 min) than in the 10 min group (15.1 +/- 2.1 min). The amplitude of evoked spinal cord potential decreased during ischemia and recovered to the baseline level during 8 h of reperfusion in the 10 min ischemia group. However, in the 40 min ischemia group, the amplitude was 40 +/- 8% of the baseline value after 8 h of reperfusion. Hypothermia prevented the delay of recovery from hyperperfusion and the reduction of evoked spinal cord potential. These results suggest that hypothermia plays a beneficial role in protecting tissue injury in the acute phase of ischemia/reperfusion in the spinal cord by shortening the time for recovery from postischemic hyperperfusion.

A new method of intrathecal PO2, PCO2, and pH measurements for continuous monitoring of spinal cord ischemia during thoracic aortic clamping in pigs

BACKGROUND

Impaired spinal cord circulation during thoracic aortic clamping may result in paraplegia. Reliable and fast responding methods for intraoperative monitoring are needed to facilitate the evaluation of protective measures and efficiency of revascularization.

METHODS

In 11 pigs, a multiparameter PO2, PCO2, and pH sensor (Paratrend 7, Biomedical Sensors Ltd, United Kingdom) was introduced into the intrathecal space for continuous monitoring of cerebrospinal fluid (CSF) oxygenation during thoracic aortic cross-clamping (AXC) distal to the left subclavian artery. A laser-Doppler probe was inserted into the epidural space for simultaneous measurements of spinal cord flux. Registrations were made before and 30 minutes after clamping and 30 and 60 minutes after declamping. The same measuring points were used for systemic hemodynamic and metabolic data acquisition.

RESULTS

The mean CSF PO2 readings of 41 mm Hg (5.5 kPa) at baseline decreased within 3 minutes to 5 mm Hg (0.7 kPa) during AXC (P < .01). Spinal cord flux measurement responded immediately in the same way to AXC. Both methods indicated normalization of circulation during declamping. Significant (P < .01) changes were also observed in the CSF metabolic parameters PCO2 and pH.

CONCLUSIONS

In this experimental model of spinal ischemia by AXC, online monitoring of intrathecal PO2, PCO2, and pH showed significant changes and correlated well with epidural laser-Doppler flowmetry (P < .01).

The early protective effects of L-arginine and Ng-nitro-L-arginine methyl ester after experimental acute spinal cord injury. A light and electron microscopic study

The purpose of this study was to investigate the early protective effects of L-arginine and Ng-nitro-L-arginine methyl ester (L-NAME) after acute spinal cord injury. Acute spinal cord injury was performed by epidural application of an aneurysm clip at thoracic (T) 7 - 11 level. L-arginine at a dose of 750 microg/kg/min was administered 10 min before acute spinal cord injury and continued for 30 min to 10 animals (Group II). L-NAME at a dose of 250 microg/kg/min was administered 10 min before acute spinal cord injury and continued for 30 min to 10 animals (Group III). No drug was administered to 10 animals after acute spinal cord injury (Group I). Light and electron microscopic analysis were performed in all of the groups. Oedema of perineural, axoplasm or white matter in the L-arginine-treated group was less than in Group I and Group III. Thickening in the walls of the arterioles and venules in the L-arginine-treated group was much milder than in Group I and Group III. Degeneration of myelinated axons in the L-arginine-treated group was milder than in the control group. But there was no different between Group II and Group III.

Influence of segmental spinal cord perfusion on intrathecal oxygen tension during experimental thoracic aortic crossclamping

PURPOSE

The purpose of this study was to evaluate the possibility of identifying alterations in blood supply to the spinal cord during thoracic aortic crossclamping.

METHODS

In 17 pigs, a multiparameter PO(2), PCO(2,) and pH sensor was introduced into the intrathecal space for continuous monitoring of cerebrospinal fluid (CSF) oxygenation during aortic crossclamping. An epidural laser Doppler probe was used to measure spinal cord flux. After insertion of an aortic shunt from the left subclavian to the left iliac artery and interruption of the right subclavian and lumbar arteries (L2-L5), the thoracic aorta just distal to the left subclavian artery was clamped for 60 minutes. By placement of the distal aortic crossclamping below the level of L1 in group A (n = 9 animals), perfusion of only the abdominal visceral arteries was maintained. In group B (n = 8 animals), the distal aortic crossclamping was above the level of T12, and thus some spinal cord perfusion was maintained through the aortic shunt.

RESULTS

The significant decrease in CSF PO(2) was observed within 3 minutes after the placement of the proximal aortic crossclamping and was normalized in all animals after establishment of the shunt flow. In group A, distal aortic crossclamping caused a decrease in CSF PO(2) with at least 50% of the preclamping values within 3 minutes. The mean CSF PO(2) of 2.99 +/- 0.70 kPa at 60 minutes of distal aortic crossclamping in group B was significantly higher than in group A (0.11 +/- 0.11 kPa; P <. 001). In group A, PCO(2) measurements showed no significant changes in 3 minutes after distal aortic crossclamping but revealed significantly higher values at 30 and 60 minutes compared with group B. Spinal cord flux values showed similar changes as CSF PO(2) during the whole experiment in both groups.

CONCLUSION

In this experimental model of aortic crossclamping, continuous CSF oxygen tension monitoring allows rapid detection of alterations in spinal cord circulation.