An improved technique for measurement of spinal cord blood flow

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.

Evidence that nitric oxide- and opioid-containing interneurons innervate vessels in the dorsal horn of the spinal cord of rats

In the dorsal horn of the spinal cord, activation of small fibre nociceptive afferents leads to the release of nitric oxide and enkephalins by interneurons. In this work we encountered unexpected relationships among local spinal cord dorsal horn blood flow, specific forms of afferent input, nitric oxide and intrinsic opioids. Selective rises in rat lumbar dorsal cord blood flow using laser Doppler flowmetry and microelectrode hydrogen clearance polarography were generated by ipsilateral, 'nociceptive' low (3 Hz) frequency stimulation of sciatic afferents. Inhibitors of nitric oxide synthase (NOS) prevented rises in flow during stimulation without influencing baseline flow. Ipsilateral hindpaw intradermal injection of capsaicin, a nociceptive activator, also generated large rises in flow sensitive to NOS inhibition. During NOS blockade or morphine administration there were unexpected acute declines in the dorsal cord blood flow strictly confined to low frequency stimulation epochs. This acute vasoconstrictive effect was prevented by administration of an opioid receptor antagonist. Using immunohistochemistry, terminals apparently innervating dorsal spinal cord blood vessels were labelled with antibodies against neuronal NOS and met-enkephalin. We conclude that local nitric oxide and opioids, probably from interneurons, have competitive actions on dorsal horn microvessels once interneurons are activated during a nociceptive barrage. Collateral innervation of blood vessels may explain this property.

[Methods for measuring spinal cord blood flow]

This study aimed to review the techniques used most currently for measuring spinal cord blood blow flow (SCBF) in animals, i.e. the hydrogen clearance, labelled microspheres, 133Xe clearance and 14C-antipyrine autoradiographic methods. All four techniques may only be used in animals, because of their invasiveness. Flow figures varied greatly with the method, the spinal level at which measurements were carried out, and the species of animal. However, results tend to suggest that SCBF is very similar to cerebral blood flow in that it is controlled by chemical, autoregulatory and metabolic factors. Approaches to measuring SCBF in man may be made using stable xenon-enhanced computed tomographic imaging (Xes-CT) in the same way as for measuring cerebral blood flow. The calculation of SCBF is based on Fick's principle transformed by Kety and Schmidt. After a reference CT section has been obtained, twelve 8 mm thick sections are carried out whilst the patient breathes a 30% xenon-70% air/oxygen mixture. This series of views enables the SCBF to be calculated in four steps. Quantitative analysis in eight human subjects gave a mean SCBF of 58.8 +/- 5.96 ml x 100 g-1 x min-1. However, this method has a low signal to noise ratio. Moreover, the qualitative analysis of the parametric views of flow demonstrate tissue heterogeneity, partly due to the patient's movements (breathing movements). However, the method is non invasive, safe, and reproducible. As it can measure very low values of blood flow, the study of ischaemic spinal lesions is made possible, although some technical and software improvements are still required.

Preliminary report of localization of spinal cord blood supply by hydrogen during aortic operations

One source of paraplegia after aortic operations is the failure to reattach the spinal cord blood supply, the origins of which are not evident at operation. This report is concerned with a rapid new method of identifying these vessels intraoperatively. In 9 pigs, a specially designed catheter with platinum and stainless steel electrodes was inserted intrathecally. Saline solution saturated with hydrogen was injected sequentially into arterial ostia at T-15 to L-4 inclusive, and the generated current impulses from the conditioned platinum electrode were recorded. Of 90 potential segmental arteries supplying the spinal cord, 28 gave rise to spinal radicular arteries. Hydrogen-induced current impulses correctly located 25 of the radicular arteries and all those larger than 180 microns in diameter. When injected with indigo carmine, the vessels localized by the hydrogen-induced current impulses filled the entire anterior spinal artery from the low thoracic to the sacral region, whereas injection of the other vessels did not show filling. After refinement and testing for safety, this method has been employed clinically to rapidly localize and reattach routes of critical cord circulation.

Effect of regional spinal cord blood flow and central control in recovery from spinal cord injury

Forty-two cats were subjected to decerebration, thoracic and lumbar laminectomies, and isolation of the sciatic nerves. Spinal evoked potentials in response to bilateral sciatic nerve stimulation were recorded at L-3, and the spinal cord blood flow (SCBF) was measured by the hydrogen clearance technique. Thoracic cordotomy did not alter the lumbar SCBF or the central conduction time as determined by spinal evoked potentials. Thoracic cordotomy significantly lowered the lumbar spinal cord injury threshold. Continuous sciatic nerve stimulation increased the lumbar SCBF in normal and traumatized animals; however, it did not affect the spinal cord injury threshold as measured by recovery of the spinal evoked potentials. It appears that rostral spinal cord integrity is far more significant in recovery from spinal cord injury than the maintenance of regional SCBF.

Effect of aminophylline on postischemic edema and brain damage in cats

We attempted to ameliorate postischemic edema and brain tissue injury in cats by administering aminophylline to reduce the reactive hyperemia that supposedly aggravates both these sequelae. Forty-one cats were subjected to 1 hour of middle cerebral artery occlusion and were killed after 3 hours, 3 days, or 14 days of recirculation; one half of the cats received 0.916 ml/kg of a 25 mg/ml solution of aminophylline by infusion at a constant rate via the femoral vein starting 10 minutes before release of the occlusion and continuing for 5 minutes after initiation of recirculation; the other half received saline. Regional cerebral blood flow was monitored by the hydrogen clearance method and water content was evaluated by specific gravity measurements after 3 hours of recirculation; the status of the blood-brain barrier was assessed with Evans blue tracer. Morphologic observations were carried out in cats killed after 3 or 14 days of recirculation. Aminophylline-treated cats killed after 3 hours of recirculation showed significantly reduced hyperemia and edema and no leakage of Evans blue, which was present in all untreated cats killed after 3 hours or 3 days of recirculation. Morphologic observations revealed conspicuously more severe ischemic brain tissue damage in the untreated than in the aminophylline-treated cats after 3 and 14 days of recirculation. Our studies indicate the beneficial effect of administration of aminophylline in the amelioration of postischemic edema and brain tissue injury, which is presumably achieved by reduction of reactive hyperemia.

Hydrogen clearance method for determining local cerebral blood flow. II. Effect of heterogeneity in cerebral blood flow

The time course of hydrogen uptake and washout was followed simultaneously in extracranial arterial blood, cortex, subcortical white matter, and caudate nucleus of the cat brain to study intercompartmental hydrogen concentration differences. A clear delay of 1-2 min was seen between the onsets of concentration increase in arterial blood and low-flow brain tissues. Equilibration time was dependent on local CBF and varied between 3 and 34 min. Hydrogen was not cleared simultaneously from the regions under detection. This led to considerable concentration differences within the cerebral tissue during washin and washout phases. Analysis of the clearance curves revealed that secondary equilibration occurs during washout. Hydrogen concentration in the external carotid artery was not a reliable reflection of tracer input in the brain tissues. The consequences of these observations for other techniques of CBF measurement using less diffusive gases and external detection are discussed.

Hydrogen clearance method for determining local cerebral blood flow. I. Spatial resolution

To define the effective spatial resolution of the hydrogen clearance method, serial local CBF (LCBF) measurements were performed at different distances from the cortico-white matter junction of the cat brain. Twenty-five platinum-wire microelectrodes with a sensitive surface of 0.07 mm2 were inserted into the cerebral cortex of three cats through burr holes in the skull and advanced toward the ear-to-ear level in 1- or 0.1-mm steps. Most electrodes passed from high-perfusion regions into low-perfusion areas, indicating that the cortico-white matter junction had been traversed. Whereas within the gray and white matter the LCBF values were fairly constant, a striking decrease of CBF was registered at the cortico-white matter junction. Here the mean LCBF from 12 electrodes showed significant differences in flow between two locations 1 mm apart. On two occasions, a significant difference in CBF was found for locations only 0.1 mm apart. Despite this high spatial resolution, monoexponential clearance curves were detected only in the vicinity of the cortico-white matter junction. It is therefore assumed that factors other than flow might influence H2 clearance.

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.

The effects of local cooling on canine spinal cord blood flow

The internal spinal cord blood flow was measured in dogs at the site of local cooling using hydrogen polarography. Blood flow decreased to 50% of the normothermic values during cooling of the cord to a central temperature of 16 degrees Celsius. Upon cessation of cooling internal blood flow rapidly returned to normal values. Implications of this finding for the treatment of spinal cord injury are discussed.

Spinal cord and cerebral blood flow responses to subarachnoid injection of local anesthetics with and without epinephrine

Subarachnoid anesthesia with lidocaine, mepivacaine, or tetracaine with and without added epinephrine (1:100 000) produced no demonstrable changes in average cerebral (CBF) or segmental spinal cord blood flow (SCBF) in 38 cats anesthetized with pentobarbital. Blood flow was measured by the injection of radioactive microspheres. Seven groups of cats received either lidocaine 15 mg, lidocaine 15 mg with epinephrine, mepivacaine 10 mg, mepivacaine 10 mg with epinephrine, tetracaine 5 mg, tetracaine 5 mg with epinephrine, or saline with epinephrine 1:100 000. Mean arterial pressure (MAP) decreased significantly (P less than 0.05) in Groups I-VI. Added epinephrine had no effect on the decrease in MAP. Amplitude of the somatosensory cortical evoked response decreased significantly in Groups I-VI, but did not change from control in Group VII. No significant change in CBF or SCBF was demonstrated in any group at any time. Plasma lidocaine and mepivacaine levels were significantly less at 5 min after subarachnoid injection in the groups receiving epinephrine compared to those not receiving epinephrine (P less than 0.05). The data appear to support the hypothesis of a vasoconstrictive reduction in systemic absorption of intrathecal local anesthetics, but suggest that significant segmental spinal cord ischemia does not occur. Maintenance of total flow in the face of a decrease in MAP suggests that autoregulation in brain and spinal cord may be maintained. Changes in regional SCBF or CBF may have been present but were not examined in this study. Further studies of brain and spinal cord blood flow dynamics, regional flow changes, and regulation of flow after intrathecal agents are necessary.

The biphasic opening of the blood-brain barrier to proteins following temporary middle cerebral artery occlusion

The behavior of the blood-brain barrier (BBB) was studied in cats following release after 1-h middle cerebral artery (MCA) occlusion. The regional cerebral blood flow (rCBF) was determined by hydrogen clearance method in the caudate nucleus and the cerebral cortex. The BBB was assayed with Evans blue (EB) tracer and by immunohistochemical peroxidase-antiperoxidase (PAP) method. Following release of MCA occlusion, there were two openings of the BBB, separated by a refractory period. The first opening, occurred shortly after recirculation; this was associated with rCBF below 15 ml/100 g/min during the ischemic period and a pronounced reactive hyperemia promptly following release of MCA occlusion. A refractory period of the BBB was indicated by the absence of EB leakage in cats injected with the tracer 30 min before killing at 3 h after recirculation, although the rCBF values in these animals were even lower (6 +/- 1 ml/100 g/min) during occlusion, and all of them showed a pronounced hyperemia after recirculation. The occurrence of the previous BBB opening in these animals was confirmed by the PAP staining. The second opening of the BBB was observed at 5 and 72 h after recirculation in cats which were injected with EB 30 min before killing, and which showed rCBF below 15 ml/100 g/min during occlusion, followed by a pronounced reactive hyperemia. No EB extravasations were observed at any time in cats in which the rCBF during occlusion was above 15 ml/100 g/min and which failed to show a marked reactive hyperemia.

Regional spinal cord blood flow in the rabbit, cat and monkey

Regional blood flow in the spinal cord was measured in rabbits, cats and monkeys with radioactively labelled microspheres. The reproducibility of the method was tested in rabbits by 3 consecutive determinations with differently labelled microspheres within the different cord regions, and was found to be good. In all 3 species, the blood flow was higher in the lumbar part of the cord than in the thoracic part, and in rabbits and monkeys it was also higher in the cervical than in the thoracic part. The flow values for the cervical, lower thoracic and lumbar parts of the cord in rabbits were 33.3, 24.7, and 27.3 ml X min-1 X 100 g-1, respectively, and in monkeys the respective figures were 14.9, 10.5 and 19.7 ml X min-1 X 100 g-1. Corresponding values for cats were only obtained during moderate hyperventilation, and were 12.2, 10.6, and 15.4 ml X min-1 X 100 g-1, respectively. The results are in good accordance with those of previous studies of the blood flow in the spinal cord in which other techniques have been employed.

Local blood flow, oxygen tension, and oxygen consumption in the rat spinal cord. Part 1: Oxygen metabolism and neuronal function

A reliable and reproducible microelectrode technique provided consistent simultaneous measurements of local spinal cord blood flow (local SCBF), tissue oxygen tension (TO2), and tissue oxygen consumption (TO2C) in the rat. Local SCBF was measured by the hydrogen clearance technique, local TO2 was measured polarographically, and local TO2C was calculated from the declining slope of local TO2 following temporary arrest of local SCBF. Mean local TO2 values varied only slightly between gray and white matter, while local TO2C and SCBF maintained a 3 to 1 ratio between gray and white matter areas. Measurements were also made of these parameters in specific white matter tracts and laminae of Rexed. Local white matter SCBF was relatively homogeneous throughout the ventral, lateral, and dorsal funiculi. Gray matter blood flow was more variable with topography. The highest local SCBF was recorded in areas rich in internuncial neurons. The somatic motor regions had values slightly higher than recorded in sensory regions.

Local blood flow, oxygen tension, and oxygen consumption in the rat spinal cord. Part 2: Relation to segmental level

Using a reliable and reproducible microelectrode technique, consistent simultaneous measurements of local spinal cord blood flow (SCBF), tissue oxygen tension, and tissue oxygen consumption were made at cervical, thoracic, and lumbar levels in the rat spinal cord. These observations showed that the metabolic state is maintained constant along the cord, despite significant variations in vasculature. The physiological and anatomical aspects of these findings are discussed.

Simultaneous measurement of local blood flow and tissue oxygen in rat spinal cord

Measurement of local blood flow by hydrogen clearance is a useful technique and is compatible with simultaneous measurement of oxygen tension over long periods. However, existing methods present serious limitations of spatial resolution due to high diffusion rates and other factors. Improved methods permit local measurements in both gray and white matter of the rat spinal cord that correlate well with data from autoradiographic techniques, and indeed distinguish between individual gray matter laminae. Applications of similar methods should be useful in other systems where high spatial resolution is required.

Effect of sympathectomy on spinal blood flow autoregulation and posttraumatic ischemia

✓ The hypothesis that the paravertebral sympathetic ganglia play a role in spinal blood flow regulation was tested in cats. Five cats were subjected to paravertebral sympathectomy, two to combined sympathectomy-adrenalectomy, three to adrenalectomy alone, and five controls received no treatment. Laminectomy was carried out to expose the T4–10 cord, and autoregulation was tested by measuring blood flow from the lateral columns with the hydrogen clearance technique during manipulation of systemic pressure with intravenous saline infusion and nitroprusside administration. The cord was then contused at T-7 with a 400 gm-cm impact injury. Posttraumatic blood flow was recorded, and neurophysiological function was assessed with somatosensory evoked potential (SEP) monitoring.

Before injury, blood flow in the untreated (control) group had no consistent relationship with mean systemic pressure over the range 80 to 160 mm Hg. In contrast, in all cats with paravertebral sympathectomy, whether accompanied by adrenalectomy or not, blood flows increased with systemic pressure (correlation coefficient 0.86, p < 0.01). After injury, the control and adrenalectomized cats showed blood flow decreases of > 60% to 4 to 6 ml/100 gm/min (p < 0.01) by 2 to 3 hours. However, cats with paravertebral sympathectomy maintained blood flow above 9 ml/100 gm/min for up to 3 hours after injury. All the sympathectomized cats recovered their SEP by the 3rd hour after injury, compared with none of the controls.

Thus, in the absence of the paravertebral sympathetic ganglia, spinal blood flow autoregulation was impaired and the typical posttraumatic loss in blood flow did not occur. The sympathectomy also protected the spinal cords from the neurophysiological loss usually seen in 400 gm-cm injury. The data suggest the need for caution in using acetylcholine blocking agents to paralyze animals in experimental spinal injury, since these agents alter sympathetic activity and may influence the injury process. The spinal cord is an excellent model in which to investigate sympathetic regulation of central nervous system blood flow.

Effect of naloxone on posttraumatic ischemia in experimental spinal contusion

The effect of naloxone on blood flow and somatosensory evoked potentials was studied in cats subjected to 400 gm-cm contusion injuries of the thoracic spinal cord. Eight cats were treated with 10 mg/kg naloxone 45 to 60 minutes after injury, 11 cats were given 10 ml of saline instead of naloxone, and six cats were neither injured nor treated. Hydrogen clearance was used to measure blood flow in the lateral white columns at the contusion site. Naloxone, given intravenously, significantly inproved the blood flow rates in the lateral column white matter. At 2 hours after injury, the mean blood flow in the saline-treated cats fell to 50% (p greater than 0.01) of preinjury flow rates, whereas it increased 6% (p greater than 0.50) in naloxone-treated cats, and 12% (p greater than 0.50) in uninjured cats. At the 3rd hour after injury, the respective flows fell 47% (p less than 0.01), and 6% (p greater than 0.50), and increased 15% (p greater than 0.50) of the preinjury flow rates. The naloxone-treated cats had striking preservation of sensory function and somatosensory evoked potentials at 24 hours after injury. At 24 hours, responses had returned in all the naloxone-treated cats and in only 11% of the saline-treated cats. The probability of this combination of events occurring by chance is 0.0030. The authors conclude that naloxone may be useful for the treatment of spinal cord injury. The mechanism of the effect is unknown.

Spinal cord function in Paget's disease of spine

The adverse influence of diminished spinal cord blood flow has been well documented. There is increased skeletal blood flow in Paget's disease of bone, with a corresponding reduction in the size of the anterior spinal artery. Use of salmon calcitonin results in rapid reduction in the bone perfusion. The recovery of cord function following calcitonin therapy in patients with paraplegia due to Paget's disease of the vertebral column is likely to be due to enhanced spinal cord perfusion.

H2 clearance measurement of blood flow: a review of technique and polarographic principles

H2 clearance is a powerful method for monitoring blood flow. Simple and inexpensive to implement, the method allows multiple in situ determinations of blood flow from any tissue in which a small electrode can be implanted. There is, however, evidence to suggest that H2 clearance is neither as accurate nor as local a measure of blood flow as generally supposed. Both in theory and practice, it probably cannot accurately determine blood flow rates greater than 100 ml/100 gm/min or localize blood flow to tissue volumes of less than 5 ml. Moreover, its experimental application is complicated by many technical problems hitherto largely ignored by workers in the field. Some of these problems arise from the limitations of the steady state polarographic technique used to measure tissue H2 concentrations. Other problems stem from the failure to consider possible sources of error in H2 clearance monitoring; these induce interference with the H2 signal by spurious electrode and tissue currents, and contributions from tissue ascorbate and O2. Nevertheless, with the appropriate safeguards and qualifications, H2 clearance is a valid and important approach to measuring blood

Comparison of hydrogen clearance and 14C-antipyrine autoradiography in the measurement of spinal cord blood flow after severe impact injury

Spinal cord blood flow was measured by two different techniques in normal and traumatized cat spinal cord. Flow was measured in the thoracic cord after severe (500-gm-cm) impact injury at T-6. Blood flow was measured sequentially at two sites for 7 hours after trauma using the hydrogen clearance technique, and spatially at many sites but at selected times by means of the 14C-antipyrine autoradiographic method. The two techniques gave similar results. Control white-matter blood flow in the lateral funiculus was 11.13 +/- 1.29 ml/min/100 gm in the hydrogen clearance series, and 11.07 +/- 3.16 gm blood/min/100 gmin the antipyrine series. Following injury, blood flow remained in the control range until 1 hour after trauma, when ischemia became the major pattern. From 4 to 8 hours following trauma, several categories of flow patterns emerged. In one group of animals, white-matter blood flow returned to control levels at some points along the length of cord surveyed, but remained depressed at adjacent cord levels. In another category of animals, most sites in the white matter had flows approaching control levels by 7 to 8 hours. In yet another group, all sites examined, although a limited number, showed ischemia. In contrast, gray-matter ischemia appeared earlier (25% of control levels at 1 hour), had a sharper focus, and persisted in the period examined. The differences in blood flow between gray and white matter and the longitudinal variation in white-matter flow suggested that the hydrogen clearance method should be verified by autoradiography for accuracy of spatial flow patterns.

Spinal cord blood flow in experimental transient traumatic paraplegia

✓ Blood flow in the lateral funiculus of the thoracic spinal cord was measured in 24 anesthetized cats using the hydrogen clearance method. In a control series of eight nontraumatized animals, blood flow measurements were taken from the T-5 and T-6 segments for 6 consecutive hours. The mean spinal cord blood flow (SCBF) in the control group was 12.8 ± 3.51 (SD) ml/min/100 gm on the basis of 107 measurements over 6 hours. In the experimental groups, 16 animals were similarly prepared. The spinal cords of these animals were then traumatized by dropping a 20-gm weight 5 cm (100 gm-cm trauma) or 13 cm (260 gm-cm trauma) onto the T-5 segment. Previous experiments have shown that these trauma levels lead to a transient paraplegia of less than 10 and 30 days' duration, respectively. Two hundred blood flow measurements from T-5 and T-6 were taken over the 6 hours following trauma. In the seven animals of the 100 gm-cm group, mean SCBF after trauma from the T-5 segment was 12.6 ± 3.45 (SD) ml/min/100 gm on the basis of 50 measurements taken over 6 hours; not significantly different from the controls (p > 0.70). In the 260 gm-cm group, mean SCBF from T-5 for 6 hours after trauma was 17.3 ± 6.60 (SD) ml/min/100 gm; significantly higher than controls (p < 0.001). Mean SCBF 3 to 6 hours after trauma was significantly elevated over controls (p < 0.05). The mean hyperemia in the 260 gm-cm group was found to be due to marked hyperemia in only four animals of the series, while five animals maintained blood flows in the normal range.

This experiment provides quantitative evidence that white matter ischemia does not occur in spinal cord injuries that can be expected to produce only transient paraplegia. The data support the concept that white matter ischemia in the acute phase of severe spinal cord trauma may be related to secondary injury and subsequent permanent paraplegia.

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.

Alteration of posttraumatic ischemia in experimental spinal cord trauma by a central nervous system depressant

Blood flow after severe experimental injury to the thoracic spinal cord was studied in cats, using a modification of the hydrogen clearance technique. Gamma hydroxybutyrate, a central nervous system depressant, was shown to markedly alter the ischemic response to injury if given during the early posttraumatic period. Other vasoactive drugs investigated had no effect on posttraumatic ischemia. Therapeutic intervention during the early posttraumatic period aimed at increasing blood flow while decreasing the metabolic requirements of the injured cord may prove of value in reversing or limiting some elements of long-tract dysfunction due to the secondary ischemic insult.

Altered blood flow and secondary injury in experimental spinal cord trauma

A modification of the hydrogen clearance technique was used to study blood flow in the dorsolateral funiculus of traumatized thoracic spinal cord in cats. The result of this study show that ischemia occurred in all animals both at the level of trauma, and 1 cm below the site of trauma. There was, however, a period of over 1 hour after trauma during which blood flow was maintained at both sites. This investigation not only confirms the presence of ischemia in the lateral funiculus of the injured spinal cord but suggests that a period of time exists in the posttraumatic period during which pharmacological intervention may alter the ischemic response and possibly prevent secondary injury resulting from the ischemia.