The Circulatory Disturbance of Spinal Cord Injury and Its Response to Local Cooling Therapy Takashi TSUBOKAWA, Saburo NAKAMURA, Nariyuki HAYASHI, Norikata TAGUMA, Takehito SUGAWARA, Toshikazu GOTO and Nobuo MORIYASU Department of Neurological Surgery, Nihon University School of Medicine, Tokyo, Japan Summary
Thirty adult dogs were subjected to immobilization of the spinal cord under nembutal anes thesia to produce spinal cord injury of two different degrees of severity by means of an impact of 500 G.cm or more and 300 G.cm or less respectively. In one group of animals an assessment was made of the resultant disturbance of spinal cord circulation at its acute stage while registering the serotonin content of the injured segment of the spinal cord as well as the evoked spinal cord potentials in response to peripheral nerve stimulation. The other group underwent local spinal cord cooling (1000 ml/hr.) for a comparison with the nontreated group of the ensuing changes in the circulatory disturbance of the spinal cord. As a result, it was found that the impact on the spinal cord, because of the anatomical constitution of the spinal arteries and veins as well as the specific features of spinal cord circulation, gave rise to rupture of microvessels in the central gray substance along with petechial hemorrhage, which in turn led to elevated serotonin level in the injured area, and that these two phenomena were responsible for the subsequent deteriora tion of spinal cord circulation with increased central necrosis. It was shown that the local cooling method is effective in ameliorating microcirculation and correcting the metabolic acidosis due to the impact and also in inhibiting the formation of serotonin which acts adversely in these respects. Key words: spinal cord injury, blood flow, spinal cord potential, local cooling
lack of valid criteria for the severity of spinal cord injury and occasional necessity for verteb rectomy and fusion due to concurrent fracture Albin et al.1,2,3> reported the usefulness of or luxation. local cooling in spinal cord injuries. White 27) Since the report by Goodkin et al.") and successfully applied a percutaneous-subara White et al.25) of central hemorrhagic necrosis chnoid perfusion system, which can provide as the main lesion associated with spinal cord continuous cooling postoperatively as well as injury, attention has been paid to impaired during laminectomy performed at the acute blood flow in the spinal cord as a factor in the stage of the injury. The mechanism of effectua genesis of the lesions,' 6,5,10,12,6,7,8,9)as well as tion of this procedure remains largely obscure, to lactates, 17) and norepinephrinels,l9> as the however, having only been shown to involve substances that cause hemodynamic disturb depression of neural enzymatic processes with ance in the spinal cord. This paper deals reduced cellular metabolic rate and oxygen with our recent attempt to elucidate the changes requirement.") Howitt and Turnbull 14) even in spinal cord circulation as the principal found local spinal cord cooling useless in labor lesions of experimentally induced spinal cord atory studies. injury and to evaluate the usefulness of local Clinically, there was recovered motor func spinal cord cooling in such lesions. tion of the legs in five cases documented by White et al .26) The same results were also ob Methods tained in some of our cases of central spinal cord injury with paraplegia treated by decom Thirty adult mongrel dogs under nembutal anesthesia (30 mg/Kg, i. p. ) were used in this pressive laminectomy and local cooling. 12,11) No statistical appraisal of local cooling thereapy study. A tube was inserted into a femoral artery has been attempted, however, because of the for blood collection and with a blood pressure Introduction
monitor. The animals were injected intra venously with physiological saline by dropping injection. With the spinal column kept fixed, laminectomy was performed from Th9 through L3 to produce spinal cord injury by the weight dropping method of Allen et al.') Animals used were divided into two groups: 10 of them were given an impact of 300 G. cm or less and the other 20 that of 500 G. cm or more on the epidural surface. The impact was delivered through a sheet of vinyl covering the surface of the spinal cord in animals undergoing opening of the dura to monitor the microcircu lation in the spinal cord. The method employed for local spinal cord cooling involved a pool made up with the dura opened 30 minutes after delivery of the impact to perfuse the spinal cord with 1000 ml of phy iological saline at 7 -10 °C for 30 minutes. Both the non-cooling and the cooling groups were submitted to checkup one hour later under the following terms : (1) micro angi ographic study,") (2) the monoamine content of the spinal cord as determined by Fleming's method,1s,19) (3) the status of vessel wall on the electron micrograph, and (4) spinal cord blood flow as estimated by the C14 antipyrine tech nique. In parallel with these studies and deter minations, a computer (ATAC 501) analysis was made of the evoked spinal cord potentials in response to peripheral nerve stimulation through 50 addition operations for a time span of 125 msec. Results
(1) Circulatory disturbance of spinal cord injury (a) Animals given an impact of 500 G. cm or more. An impact of 500 G. cm or more on the surface of the spinal cord gave rise to marked arterial angiospasm with subarachnoid hemorrhage particularly in the intermediate region between the impacted and normal areas. The veins were found dilated and enlarged in some regions but stenosed or occluded in others. A flock of microcoagulations emerged in small vessels while the radicular artery remained hardly altered. There was increasing subarach noid hemorrhage following spinal cord injury, with arterial angiospasm extending into the
Fig. 1. Decrease of spinal cord blood flow measured by C14 antipyrine method following irreversible injury (500g-cm impact). Left side shows local blood flow rate in normal cat. Right side shows the decrease of blood flow rate at the impact area (0 cm), and both caudal (+1 cm) and cranial parts (-1, -2 cm) of the impact. There is markedly decrease of blood flow rate in the central gray matter and the dorsal column without any increase around the ishemic area.
normal area and the flock of microcoagulations in small vessels becoming less variable in loca tion until 30 minutes after delivery of the im pact, when these changes became established and fixed. During this time, spinal cord blood flow ceased in a region corresponding to the site of of central hemorrhagic necrosis in the central gray substance. The blood flow rate reduced in circumjacent region including the dorsal column. These changes extended up to 2 cm above and below the imacted area. In addi tion, there was no evidence of an increment in spinal cord blood flow in the circumjacent region where blood flow had reduced (Fig. 1). The electron micrograph of vessels in the area of central necrosis and the adjacent region showed the basement membrane to be irregu larly thickened, taking an irregular form against capillary lumen. There was increased pinocy tosis with cavitation and edema formation in the endothelium, which was also irregularly thickened, forming an uneven, narrowed capil lary lumen (Fig. 2a). The microangiogram afforded an overall view of these changes in the vascular system produced by the impact (Fig. 3) : non-uniform, irregular lumen of vessels, extravasation and
Fig. 2-A. Capillary vessel in necrotized central gray matter after spinal cord injury: The capillary vessel shows waving basement membrane, thickened endothelium and narrow capillary lumen. B : basement membrane, E : endothelium, L: capillary lumen.
Fig. 2-B. Capillary vessel in necrotized central gray matter of the spinal cord which was treated by cooling (7'C, 30 min.) : The capillary vessel shows thickened basement membrane, but flat endothelium and widely opened capillary lumen. B : basement membrane, E : endothelium, L: capillary lumen.
marked swelling of the spinal cord. Determinations of the norepinephrine and serotonin levels in the injured area at 30-60 minutes after impacting indicated a mean level of 0.88 ug/g for the former substance, a value slightly higher than the normal mean or 0.6 j g/ g, and 2.10 pg/g for the latter, a level which was more than thrice as high as the normal mean or 0.45 pg/g (Fig. 4). In addition,
it was found
that
the norepine
phrine level was not markedly elevated even in the presence of augmented central necrosis in
Fig. 3. The alterations in microangiogram and evoked spinal cord potentials responded to the tibial nerve stimulation. a: One hour after irreversible impact (500 g• cm) without any treatment. 1: evoked spinal cord potential before impact. 2: evoked spinal cord potential after impact. There is no electrical activity. b : The effects on microangiogram and evoked spinal cord potentials by local cooling 3: evoked spinal cord potential before impact. 4: evoked spinal cord potential at 30 minutes after cooling. A little early components are recorded.
the central gray substance whereas the serotonin level varied in positive proportion with the severity of hemorrhagic necrosis in the central gray substance. A study of the evoked spinal cord potential revealed ansence of all of the potentials or all but P, with the other early components disap pearing completely (Fig. 3). The amplitude of injury potentials, which were observed in the injured and adjacent areas, was decreased with time, but there was no sign of other responses being elicited as before. All animals given an impact of 500 G. cm or more were found to be in a state of permanent paraplegia with the low extremities failing to regain their mobility throughout a one-week period of observation following steroid antifi brinolytic therapy. (b) Animals given an impact of 300 G. cm or less. In this group the microcirculation sustained only changes of mild severity: subarachnoid hemorrhage and mild spasm of the arterial system. Even at 30 minutes after impacting there was no evidence of microcoagulation but rather a tendency toward dilatation of the
Fig. 4. The alterations of both serotonin (5HT) and norepinephrine (NE) in the injured cord at one hour after irreversible impact (500 g• cm), and a half hour after local cooling (cooling), pretreated by phenoxybenzamine and semicarbazide. Serotonin content in the injured cord is markedly increased but it decreases to normal level by the cooling.
venous system. Measurements of the spinal cord blood flow showed it to be decreased in a localized central area of the gray substance that corresponded to the impacted area but to be rather increased in the gray and white substances in the adjacent region. The area of increased blood flow ex tended over the gray and white substances in the anterior column 1-2 cm caudal to the im pacted area (Fig. 5).
Fig. 5. Decrease of spinal cord blood flow measured by C"' antipyrine method following reversible injury (less than 300 g. cm impact). Blood flow rate in the center of central gray matter at the level of impact area, but there is markedly increase of blood flow rate around the ishemic area.
Immediately following delivery of the impact there was instantaneous absence of evoked spinal cord potentials responding to peripheral nerve stimulation. At five minutes, however, the early components including P, though P3 were invariably observable although limited in amplitude and simple in wave form. Further more, both the amplitude and wave form tended to returen to normal with passage of time.The late components preceded the early ones in this regard. The same type of treatmsnt as in the 500 G. cm group brought about recovery of motor function within three days in all the animals in this group. As to the monoamine content in the injured area, no difference from the 500 G. cm group existed in the resultant rise in norepine phrine level. The serotonin level, in contrast, was elevated up to about double the normal level, falling short of 2.0 pg/g in all the in stances. (2) Effect of local cooling therapy on the circulatory disturbance. Spinal cord injury was produced with an impact of 500 G. cm or more delivered on the spinal cord of animals. Ten to 30 minutes later dura was opened for perfusion of the spinal cord with 1000 ml of cooled physiological saline 1000 ml of cooled physiological saline at 7 10°C for 30 minutes. In some animals the physiological saline was kept at a temperature
of 2'C for comparison with the other animals. The ensuing changes in the microcirculation on the surface of the spinal cord include relief of arterial angiospasm, gradual regression of microcoagulation in the venules and disappea rance of luminal narrowing in th venules and disappearance of luminal narrowing in the venous system. The subarachnoid hemorrhage that took place at the time of impacting re mained unaffected, however. Spinal cord swell ing was also alleviated so much as to permit development of a space between the spinal cord and dura (Fig. 3. b). The electron micrograph of vessels in the injured area showed the basement membrane to be more markedly thickened with collagen fibrils appearing in greater amounts than in animals receiving no cooling therapy. No waving of the membrane was observed, however. The endothelium was smooth and free from significant pinocytosis, with the capil lary lumen remaining patent enough (Fig. 2-B). Spinal cord blood flow was rather increased around the area of ischemic non-flow in the central region, a finding which mimicked that of the reversible spinal cord injury caused by an impact of 300 G. cm (Fig. 5). The microangiogram provided a more clear cut picture of the morphological changes described above: it showed the anterior and posterior spinal cord arteries bypassing the sites of microbleeding in the impacted area. The microcirculation in the circumjacent region was improved (Fig. 3) but was still featured by less dense distribution of vessels than in the normal group as well as by a flock of microcoagulations persisting in small vessels. In the cooling group the norepinephrine level in the injured area was essentially as high as normal or 0.59 µg/g on the average, but its peak level was 0.3 pg/g higher than the normal upper limit. Serotonin, on the other hand, gave a mean level of 0.55 ug/g, being 0.1 yg/g in excess of normal mean but one-fourth as high as that for the non-cooling group or 2.1 pg/g (Fig. 4). As to the evoked spinal cord potentials, it was shown that cooling therapy resulted in re-emer gence of the early components that had re mained absent after delivery of the impact, followed ny the late components and then by P 1N 1 (Fig. 3). Only two animals in this series received
steroid-antifibrinolytic therapy in the wake of spinal cord cooling. Both of these two were able to stand up although they were still suf fering from some degree of disability. Discussion
Investigations were made of the circulatory disturbance and the variation in serotonin level and evoked spinal cord potentials that followed spinal cord injury in two groups of animals: those which were capable of standing up within three days of steroid-autifibrinolytic therapy (given an impact of 300 G. cm or less) and those in which recovery of motor function was diffi cult to achieve with the same therapy (given an impact of 500 G. cm or more). In the latter group subarachnoid hemorrhage occurred with petechial hemorrhage in the central gray sub stance immediately following and angiospasm developed simultaneously with the delivery of the impact. These changes were increasingly intensified up to the point of full-fledged central hemorrhagic necrosis. By means of the local cooling technique such circulatory insufficiency was improved and the percent area of hemor rhagic necrosis kept from increasing to 23.3 at two hours and 69.4 % at 24 hours as was described by Osterholm et a]. 18,19) This fact supports the hypothesis advanced by Fairholm et al.10) and Ducker et al.9) that the essence of spinal cord injury may reside in microcirculatory disturbance. The ensuing hy poxia may also be regarded as probably in volved here (Kelly et al.). 16) In parallel with such vascular reactions there was elevated serotonin level immediately after delivery of the impact and over subsequent periods. Osterholm et al.18,19)regarded elevated norepinephrine level as accountable for the hemorrhagic necrosis. Based on the intense traumatic vascular reaction associated with a time-based progression of traumatic spinal lesions, Irvin15) found that norepinephrine increase in the injured area was induced by synaptic vesicles and small vessels and Vise et al.") believed the norepinephrine to be derived from blood sources. It is questionable, however, if norepinephrine is really the cause of the circulatory disturbance, because its peak level was attained at one hour, namely, later than the vascular reaction. The
fact that serotonin level began to rise coinci dently with the emergence of a flock of micro coagulations in the wake of the vascular reaction suggests that the elevated serotonin level resulting from vascular injury may be the main factor in the pathogenesis of microcoagu lation, which in turn led to reduced spinal cord blood flow and changes in vascular endothelial cells. Local spinal cord cooling brought about an improvement in spinal cord circulation with reduced serotonin level, showing that serotonin is involved as a factor in the deteriorated spinal cord circulation. However, serotonin is not the only major factor involved here. Recently Tator et al.21) evaluated the results of spinal cord injury in monkeys perfused with normothermic Elliott's B solution. The grade of neurological recovery after normothermic perfusion seemed consistently better than with hypothermia. Osterholm20) agreed to this on grounds that norepinephrine can thus be washed out. Provided, however, a major causative role is played by norepinephrine or serotonin, then hypothermic perfusion must be more useful in this respect, because the presence of local anoxia or contusion which is mandatory for a rise in the level of these substances will imply the necessity of depressing neural enzymatic process and cellular metabolism to reduce oxygen requirement as well as for measures to be taken against spinal cord swelling. Our study showed that cooling water at 7'C or above can best serve the purpose and that at lower temperatures of cooling water a decrease in spinal cord blood flow and hence impover ished spinal cord circulation will result. In short, it was made clear that the impact on the spinal cord gives rise to hemorrhage as a result of rupture of thin-walled vessels with erythrocyte leakage into the perivascular space in the central gray substance and that the impact also induces an increase in serotonin level in the injured area. These events in turn lead to deterioration of spinal cord circulation with an increasing area of central hemorrhagic necrosis, which gradually deprives the spinal cord of its normal function. These two factors are favor ably affected by local spinal cord cooling, which is effective both in ameliorating the hemodyna mics in the spinal cord and in preventing the spinal cord from losing its normal function.
Conclusion
Spinal cord injury was produced by the method of Allen et al. (1968) in 30 adult dogs to elucidate its pathogenetic process in terms of spinal cord circulation and to evaluate the response of spinal cord circulation to local cooling as one of the therapeutic measures available against spinal cord injury. As a result, it was found that an impact on the spinal cord, because of the anatomical structure of the spinal arteries and the specificity of spinal cord circu lation, gives rise to destruction of microvessels in the central gray substance along with pete chial hemorrhage in the vascular region, which in turn leads to elevated serotonin level in the injured area. These two phenomena together resulted in deteriorated spinal cord circulation with increasing central hemorrhagic necrosis in the gray substance. Local spinal cord cooling favorably affected the changes caused by the impact itself, such as spinal cord edema, angiospasm, luminal narrowing of vessels and metabolic acidosis, and was also useful in sup pressing formation of serotonin which is in volved in the progression of such changes. Local spinal cord cooling can be of thera peutic value in that it can prevent deterioration of spinal cord circulation. Against the primary damage caused by the impact, however, it can be beneficial in no more than removing edema. References 1)
Albin, M. S., White, R. J., Locke, G. E., and Kretchmer, H. E.: Spinal cord hypothermia by localized perfusion cooling. Nature 210: 10591060, 1966.
2)
Albin, M. S., White, R. J., Acosta-Rua, G., and Yashon, D.: Study of functional recovery produced by delayed localized cooling after spinal cord injury in primates. J. Neurosurg., 29: 113-120, 1968. 3) Albin, M. S., White, R. J., Yashon, D., and Harries, L. S.: Effects of localized cooling in spinal cord trauma. J. Trauma. 9: 1000-1008, 1969. 4) Allen, A. R.: Surgery of experimental lesion of spinal cord equivalent to crush injury of fracture dislocation of spinal column. Preliminary report. JAMA, 57: 878-880, 1911. 5)
Assenmacher, D. R. and Ducker, T. B.: Experi mental traumatic paraplegia. The vascular and pathological irreversible
changes spinal cord
seen in reversible and lesions. J. Bone Jt. Surg. ,
53A:
6)
7)
671-680,
1971.
Dohrmann, G. L., Wagner, F. C., and Bucy, P. C.: Transitory traumatic paraplegia: electron micros copy of the early alterations in myelinated nerve fibers. J. Neurosurg., 36: 407-415, 1972. Dohrmann, G. L., Wick, K. M., and Bucy, P. C.: Spinal cord blood flow patterns in experimental traumatic paraplegia. J. Neurosurg., 38: 52-58, 1973.
8)
Ducker, T. B. and Hamit, H. F.: Experimental treatments of acute spinal cord injury. J. Neuro surg., 30: 693-697, 1969.
9)
Ducker, T. B. and Perot, P. L. Jr.: Spinal cord oxygen and blood flow in trauma. Surg. Forum, 22: 413-415, 1971.
10)
Fairholm, D. J. and Turnbull, I. M.: Microangio graphic study of experimental spinal injuries in dogs and rabbits. Surg. Forum, 21: 453-455, 1970.
11)
Fairley, H. Med. Bull., Fried, L. C. observations spinal cord.
12)
B.: Metabolism in hypothermia. Brit. 17: 52-55, 1961. and Goodkin, R.: Microangiographic of the experimentally traumatized J. Neurosurg., 35: 709-714, 1971.
norepinephrine metabolism following experimen tal spinal cord injury. Part 1: Relationship to hemorrhagic necrosis and post-wounding neuro logical deficits. J. Neurosurg., 36: 386-394, 1972. 19) Osterholm, J. L. and Mathews, G. J.: Altered norepinephrine metabolism following experimental spinal cord injury. Part 2: Protection against traumatic spinal cord hemorrhagic necrosis by norepinephrine synthesis blockade with alpha methyl tyrosine. J. Neurosurg., 36: 395-401, 1972. 20) Osterholm, J. L.: The pathophysiological response to spinal cord injury. J. Neurosurg., 40: 5-33, 1974. 21)
Tator, C. H. and Deecke, L.: Value of normo thermic perfusion, hypothermic perfusion, and durotomy in the treatment of experimental acute spinal cord trauma. J. Neurosurg., 39: 52-64, 1973.
22)
Tsubokawa, T., Moriyasu, N., Nakamura, S., and Hayashi, N.: Pathogenesis of spinal cord injury and its application to treatment. Except Med., 293: 109, 1973. Tsubokawa, T., Sugawara, T., Hayashi, N., Nakamura, S., and Moriyasu, N.: Pathogenesis of spinal cord injury. Trauma, 5: 75-87, 1973, (Jap. ed.). Vise, W. M., Yashon, D., and Hunt, W. E.: Mechanisms of norepinephrine accumulation within sites of spinal cord injury. J. Neurosurg., 40: 76-82, 1974. White, R. J., Albin, M. S., and Harris, L. S.: Spinal cord injury sequential morphology and hypothermia stabilization. Surg. Forum, 20: 432434, 1969. White, R. J., Yashon, D., Albin, M. S., and Demian, Y. K.: The technique of localized spinal cord hypothermia in the human. Proceedings of 7th VA spinal cord injury conferance. pp. 58-60, 1971.
23)
13) Goodkin, R. and Campbell, J. B.: Sequential pathologic shanges in spinal cord injury, a pre liminary report. Surg. Forum, 20: 430-432, 1969. 14)
Howitt,
W. M. and
hypothermia experimental 179-186,1972.
Turnbull,
I. M.:
Effects
of
24)
and methysergide on recovery from paraplegia. Canad. J. Surg., 15:
15) Irvin, J. D.: Histofluorescent studies of the normal and injured cat spinal cord. Ph.d thesis, Hahne mann Medical College and Hospital, Philadelphia, 1973.
25)
16)
26)
Kelly,
D. L. Jr., Lassiter,
K. R. L., Vongesvivut,
A. and Smith, J. M.: Effects of hyperbaric oxygene tion and tissue oxygen studies in experimental paraplegia.
17)
18)
J. Neurosurg.,
36: 425-429,
1972.
Locke, G. E., Yashon, D., Feldman, R. A., and Hunt, W. E.: Ischemia in primate spinal cord injury. J. Neurosurg., 34: 614-617, 1971. Osterholm,
J. L. and
Mathews,
G.
J.:
Altered
27)
White, R. J.: Current status of spinal cord cooling. Clin. Neurosurg., 20: 400-408, 1973.
Thirty adult dogs were subjected to immobilization of the spinal cord under nembutal anes thesia to produce spinal cord injury of two different degrees of severity by means of an impact of 500 G.cm or more and 300 G.cm or less respectively. In one group of animals an assessment was made of the resultant disturbance of spinal cord circulation at its acute stage while registering the serotonin content of the injured segment of the spinal cord as well as the evoked spinal cord potentials in response to peripheral nerve stimulation. The other group underwent local spinal cord cooling (1000 ml/hr.) for a comparison with the nontreated group of the ensuing changes in the circulatory disturbance of the spinal cord. As a result, it was found that the impact on the spinal cord, because of the anatomical constitution of the spinal arteries and veins as well as the specific features of spinal cord circulation, gave rise to rupture of microvessels in the central gray substance along with petechial hemorrhage, which in turn led to elevated serotonin level in the injured area, and that these two phenomena were responsible for the subsequent deteriora tion of spinal cord circulation with increased central necrosis. It was shown that the local cooling method is effective in ameliorating microcirculation and correcting the metabolic acidosis due to the impact and also in inhibiting the formation of serotonin which acts adversely in these respects. Key words: spinal cord injury, blood flow, spinal cord potential, local cooling
lack of valid criteria for the severity of spinal cord injury and occasional necessity for verteb rectomy and fusion due to concurrent fracture Albin et al.1,2,3> reported the usefulness of or luxation. local cooling in spinal cord injuries. White 27) Since the report by Goodkin et al.") and successfully applied a percutaneous-subara White et al.25) of central hemorrhagic necrosis chnoid perfusion system, which can provide as the main lesion associated with spinal cord continuous cooling postoperatively as well as injury, attention has been paid to impaired during laminectomy performed at the acute blood flow in the spinal cord as a factor in the stage of the injury. The mechanism of effectua genesis of the lesions,' 6,5,10,12,6,7,8,9)as well as tion of this procedure remains largely obscure, to lactates, 17) and norepinephrinels,l9> as the however, having only been shown to involve substances that cause hemodynamic disturb depression of neural enzymatic processes with ance in the spinal cord. This paper deals reduced cellular metabolic rate and oxygen with our recent attempt to elucidate the changes requirement.") Howitt and Turnbull 14) even in spinal cord circulation as the principal found local spinal cord cooling useless in labor lesions of experimentally induced spinal cord atory studies. injury and to evaluate the usefulness of local Clinically, there was recovered motor func spinal cord cooling in such lesions. tion of the legs in five cases documented by White et al .26) The same results were also ob Methods tained in some of our cases of central spinal cord injury with paraplegia treated by decom Thirty adult mongrel dogs under nembutal anesthesia (30 mg/Kg, i. p. ) were used in this pressive laminectomy and local cooling. 12,11) No statistical appraisal of local cooling thereapy study. A tube was inserted into a femoral artery has been attempted, however, because of the for blood collection and with a blood pressure Introduction
monitor. The animals were injected intra venously with physiological saline by dropping injection. With the spinal column kept fixed, laminectomy was performed from Th9 through L3 to produce spinal cord injury by the weight dropping method of Allen et al.') Animals used were divided into two groups: 10 of them were given an impact of 300 G. cm or less and the other 20 that of 500 G. cm or more on the epidural surface. The impact was delivered through a sheet of vinyl covering the surface of the spinal cord in animals undergoing opening of the dura to monitor the microcircu lation in the spinal cord. The method employed for local spinal cord cooling involved a pool made up with the dura opened 30 minutes after delivery of the impact to perfuse the spinal cord with 1000 ml of phy iological saline at 7 -10 °C for 30 minutes. Both the non-cooling and the cooling groups were submitted to checkup one hour later under the following terms : (1) micro angi ographic study,") (2) the monoamine content of the spinal cord as determined by Fleming's method,1s,19) (3) the status of vessel wall on the electron micrograph, and (4) spinal cord blood flow as estimated by the C14 antipyrine tech nique. In parallel with these studies and deter minations, a computer (ATAC 501) analysis was made of the evoked spinal cord potentials in response to peripheral nerve stimulation through 50 addition operations for a time span of 125 msec. Results
(1) Circulatory disturbance of spinal cord injury (a) Animals given an impact of 500 G. cm or more. An impact of 500 G. cm or more on the surface of the spinal cord gave rise to marked arterial angiospasm with subarachnoid hemorrhage particularly in the intermediate region between the impacted and normal areas. The veins were found dilated and enlarged in some regions but stenosed or occluded in others. A flock of microcoagulations emerged in small vessels while the radicular artery remained hardly altered. There was increasing subarach noid hemorrhage following spinal cord injury, with arterial angiospasm extending into the
Fig. 1. Decrease of spinal cord blood flow measured by C14 antipyrine method following irreversible injury (500g-cm impact). Left side shows local blood flow rate in normal cat. Right side shows the decrease of blood flow rate at the impact area (0 cm), and both caudal (+1 cm) and cranial parts (-1, -2 cm) of the impact. There is markedly decrease of blood flow rate in the central gray matter and the dorsal column without any increase around the ishemic area.
normal area and the flock of microcoagulations in small vessels becoming less variable in loca tion until 30 minutes after delivery of the im pact, when these changes became established and fixed. During this time, spinal cord blood flow ceased in a region corresponding to the site of of central hemorrhagic necrosis in the central gray substance. The blood flow rate reduced in circumjacent region including the dorsal column. These changes extended up to 2 cm above and below the imacted area. In addi tion, there was no evidence of an increment in spinal cord blood flow in the circumjacent region where blood flow had reduced (Fig. 1). The electron micrograph of vessels in the area of central necrosis and the adjacent region showed the basement membrane to be irregu larly thickened, taking an irregular form against capillary lumen. There was increased pinocy tosis with cavitation and edema formation in the endothelium, which was also irregularly thickened, forming an uneven, narrowed capil lary lumen (Fig. 2a). The microangiogram afforded an overall view of these changes in the vascular system produced by the impact (Fig. 3) : non-uniform, irregular lumen of vessels, extravasation and
Fig. 2-A. Capillary vessel in necrotized central gray matter after spinal cord injury: The capillary vessel shows waving basement membrane, thickened endothelium and narrow capillary lumen. B : basement membrane, E : endothelium, L: capillary lumen.
Fig. 2-B. Capillary vessel in necrotized central gray matter of the spinal cord which was treated by cooling (7'C, 30 min.) : The capillary vessel shows thickened basement membrane, but flat endothelium and widely opened capillary lumen. B : basement membrane, E : endothelium, L: capillary lumen.
marked swelling of the spinal cord. Determinations of the norepinephrine and serotonin levels in the injured area at 30-60 minutes after impacting indicated a mean level of 0.88 ug/g for the former substance, a value slightly higher than the normal mean or 0.6 j g/ g, and 2.10 pg/g for the latter, a level which was more than thrice as high as the normal mean or 0.45 pg/g (Fig. 4). In addition,
it was found
that
the norepine
phrine level was not markedly elevated even in the presence of augmented central necrosis in
Fig. 3. The alterations in microangiogram and evoked spinal cord potentials responded to the tibial nerve stimulation. a: One hour after irreversible impact (500 g• cm) without any treatment. 1: evoked spinal cord potential before impact. 2: evoked spinal cord potential after impact. There is no electrical activity. b : The effects on microangiogram and evoked spinal cord potentials by local cooling 3: evoked spinal cord potential before impact. 4: evoked spinal cord potential at 30 minutes after cooling. A little early components are recorded.
the central gray substance whereas the serotonin level varied in positive proportion with the severity of hemorrhagic necrosis in the central gray substance. A study of the evoked spinal cord potential revealed ansence of all of the potentials or all but P, with the other early components disap pearing completely (Fig. 3). The amplitude of injury potentials, which were observed in the injured and adjacent areas, was decreased with time, but there was no sign of other responses being elicited as before. All animals given an impact of 500 G. cm or more were found to be in a state of permanent paraplegia with the low extremities failing to regain their mobility throughout a one-week period of observation following steroid antifi brinolytic therapy. (b) Animals given an impact of 300 G. cm or less. In this group the microcirculation sustained only changes of mild severity: subarachnoid hemorrhage and mild spasm of the arterial system. Even at 30 minutes after impacting there was no evidence of microcoagulation but rather a tendency toward dilatation of the
Fig. 4. The alterations of both serotonin (5HT) and norepinephrine (NE) in the injured cord at one hour after irreversible impact (500 g• cm), and a half hour after local cooling (cooling), pretreated by phenoxybenzamine and semicarbazide. Serotonin content in the injured cord is markedly increased but it decreases to normal level by the cooling.
venous system. Measurements of the spinal cord blood flow showed it to be decreased in a localized central area of the gray substance that corresponded to the impacted area but to be rather increased in the gray and white substances in the adjacent region. The area of increased blood flow ex tended over the gray and white substances in the anterior column 1-2 cm caudal to the im pacted area (Fig. 5).
Fig. 5. Decrease of spinal cord blood flow measured by C"' antipyrine method following reversible injury (less than 300 g. cm impact). Blood flow rate in the center of central gray matter at the level of impact area, but there is markedly increase of blood flow rate around the ishemic area.
Immediately following delivery of the impact there was instantaneous absence of evoked spinal cord potentials responding to peripheral nerve stimulation. At five minutes, however, the early components including P, though P3 were invariably observable although limited in amplitude and simple in wave form. Further more, both the amplitude and wave form tended to returen to normal with passage of time.The late components preceded the early ones in this regard. The same type of treatmsnt as in the 500 G. cm group brought about recovery of motor function within three days in all the animals in this group. As to the monoamine content in the injured area, no difference from the 500 G. cm group existed in the resultant rise in norepine phrine level. The serotonin level, in contrast, was elevated up to about double the normal level, falling short of 2.0 pg/g in all the in stances. (2) Effect of local cooling therapy on the circulatory disturbance. Spinal cord injury was produced with an impact of 500 G. cm or more delivered on the spinal cord of animals. Ten to 30 minutes later dura was opened for perfusion of the spinal cord with 1000 ml of cooled physiological saline 1000 ml of cooled physiological saline at 7 10°C for 30 minutes. In some animals the physiological saline was kept at a temperature
of 2'C for comparison with the other animals. The ensuing changes in the microcirculation on the surface of the spinal cord include relief of arterial angiospasm, gradual regression of microcoagulation in the venules and disappea rance of luminal narrowing in th venules and disappearance of luminal narrowing in the venous system. The subarachnoid hemorrhage that took place at the time of impacting re mained unaffected, however. Spinal cord swell ing was also alleviated so much as to permit development of a space between the spinal cord and dura (Fig. 3. b). The electron micrograph of vessels in the injured area showed the basement membrane to be more markedly thickened with collagen fibrils appearing in greater amounts than in animals receiving no cooling therapy. No waving of the membrane was observed, however. The endothelium was smooth and free from significant pinocytosis, with the capil lary lumen remaining patent enough (Fig. 2-B). Spinal cord blood flow was rather increased around the area of ischemic non-flow in the central region, a finding which mimicked that of the reversible spinal cord injury caused by an impact of 300 G. cm (Fig. 5). The microangiogram provided a more clear cut picture of the morphological changes described above: it showed the anterior and posterior spinal cord arteries bypassing the sites of microbleeding in the impacted area. The microcirculation in the circumjacent region was improved (Fig. 3) but was still featured by less dense distribution of vessels than in the normal group as well as by a flock of microcoagulations persisting in small vessels. In the cooling group the norepinephrine level in the injured area was essentially as high as normal or 0.59 µg/g on the average, but its peak level was 0.3 pg/g higher than the normal upper limit. Serotonin, on the other hand, gave a mean level of 0.55 ug/g, being 0.1 yg/g in excess of normal mean but one-fourth as high as that for the non-cooling group or 2.1 pg/g (Fig. 4). As to the evoked spinal cord potentials, it was shown that cooling therapy resulted in re-emer gence of the early components that had re mained absent after delivery of the impact, followed ny the late components and then by P 1N 1 (Fig. 3). Only two animals in this series received
steroid-antifibrinolytic therapy in the wake of spinal cord cooling. Both of these two were able to stand up although they were still suf fering from some degree of disability. Discussion
Investigations were made of the circulatory disturbance and the variation in serotonin level and evoked spinal cord potentials that followed spinal cord injury in two groups of animals: those which were capable of standing up within three days of steroid-autifibrinolytic therapy (given an impact of 300 G. cm or less) and those in which recovery of motor function was diffi cult to achieve with the same therapy (given an impact of 500 G. cm or more). In the latter group subarachnoid hemorrhage occurred with petechial hemorrhage in the central gray sub stance immediately following and angiospasm developed simultaneously with the delivery of the impact. These changes were increasingly intensified up to the point of full-fledged central hemorrhagic necrosis. By means of the local cooling technique such circulatory insufficiency was improved and the percent area of hemor rhagic necrosis kept from increasing to 23.3 at two hours and 69.4 % at 24 hours as was described by Osterholm et a]. 18,19) This fact supports the hypothesis advanced by Fairholm et al.10) and Ducker et al.9) that the essence of spinal cord injury may reside in microcirculatory disturbance. The ensuing hy poxia may also be regarded as probably in volved here (Kelly et al.). 16) In parallel with such vascular reactions there was elevated serotonin level immediately after delivery of the impact and over subsequent periods. Osterholm et al.18,19)regarded elevated norepinephrine level as accountable for the hemorrhagic necrosis. Based on the intense traumatic vascular reaction associated with a time-based progression of traumatic spinal lesions, Irvin15) found that norepinephrine increase in the injured area was induced by synaptic vesicles and small vessels and Vise et al.") believed the norepinephrine to be derived from blood sources. It is questionable, however, if norepinephrine is really the cause of the circulatory disturbance, because its peak level was attained at one hour, namely, later than the vascular reaction. The
fact that serotonin level began to rise coinci dently with the emergence of a flock of micro coagulations in the wake of the vascular reaction suggests that the elevated serotonin level resulting from vascular injury may be the main factor in the pathogenesis of microcoagu lation, which in turn led to reduced spinal cord blood flow and changes in vascular endothelial cells. Local spinal cord cooling brought about an improvement in spinal cord circulation with reduced serotonin level, showing that serotonin is involved as a factor in the deteriorated spinal cord circulation. However, serotonin is not the only major factor involved here. Recently Tator et al.21) evaluated the results of spinal cord injury in monkeys perfused with normothermic Elliott's B solution. The grade of neurological recovery after normothermic perfusion seemed consistently better than with hypothermia. Osterholm20) agreed to this on grounds that norepinephrine can thus be washed out. Provided, however, a major causative role is played by norepinephrine or serotonin, then hypothermic perfusion must be more useful in this respect, because the presence of local anoxia or contusion which is mandatory for a rise in the level of these substances will imply the necessity of depressing neural enzymatic process and cellular metabolism to reduce oxygen requirement as well as for measures to be taken against spinal cord swelling. Our study showed that cooling water at 7'C or above can best serve the purpose and that at lower temperatures of cooling water a decrease in spinal cord blood flow and hence impover ished spinal cord circulation will result. In short, it was made clear that the impact on the spinal cord gives rise to hemorrhage as a result of rupture of thin-walled vessels with erythrocyte leakage into the perivascular space in the central gray substance and that the impact also induces an increase in serotonin level in the injured area. These events in turn lead to deterioration of spinal cord circulation with an increasing area of central hemorrhagic necrosis, which gradually deprives the spinal cord of its normal function. These two factors are favor ably affected by local spinal cord cooling, which is effective both in ameliorating the hemodyna mics in the spinal cord and in preventing the spinal cord from losing its normal function.
Conclusion
Spinal cord injury was produced by the method of Allen et al. (1968) in 30 adult dogs to elucidate its pathogenetic process in terms of spinal cord circulation and to evaluate the response of spinal cord circulation to local cooling as one of the therapeutic measures available against spinal cord injury. As a result, it was found that an impact on the spinal cord, because of the anatomical structure of the spinal arteries and the specificity of spinal cord circu lation, gives rise to destruction of microvessels in the central gray substance along with pete chial hemorrhage in the vascular region, which in turn leads to elevated serotonin level in the injured area. These two phenomena together resulted in deteriorated spinal cord circulation with increasing central hemorrhagic necrosis in the gray substance. Local spinal cord cooling favorably affected the changes caused by the impact itself, such as spinal cord edema, angiospasm, luminal narrowing of vessels and metabolic acidosis, and was also useful in sup pressing formation of serotonin which is in volved in the progression of such changes. Local spinal cord cooling can be of thera peutic value in that it can prevent deterioration of spinal cord circulation. Against the primary damage caused by the impact, however, it can be beneficial in no more than removing edema. References 1)
Albin, M. S., White, R. J., Locke, G. E., and Kretchmer, H. E.: Spinal cord hypothermia by localized perfusion cooling. Nature 210: 10591060, 1966.
2)
Albin, M. S., White, R. J., Acosta-Rua, G., and Yashon, D.: Study of functional recovery produced by delayed localized cooling after spinal cord injury in primates. J. Neurosurg., 29: 113-120, 1968. 3) Albin, M. S., White, R. J., Yashon, D., and Harries, L. S.: Effects of localized cooling in spinal cord trauma. J. Trauma. 9: 1000-1008, 1969. 4) Allen, A. R.: Surgery of experimental lesion of spinal cord equivalent to crush injury of fracture dislocation of spinal column. Preliminary report. JAMA, 57: 878-880, 1911. 5)
Assenmacher, D. R. and Ducker, T. B.: Experi mental traumatic paraplegia. The vascular and pathological irreversible
changes spinal cord
seen in reversible and lesions. J. Bone Jt. Surg. ,
53A:
6)
7)
671-680,
1971.
Dohrmann, G. L., Wagner, F. C., and Bucy, P. C.: Transitory traumatic paraplegia: electron micros copy of the early alterations in myelinated nerve fibers. J. Neurosurg., 36: 407-415, 1972. Dohrmann, G. L., Wick, K. M., and Bucy, P. C.: Spinal cord blood flow patterns in experimental traumatic paraplegia. J. Neurosurg., 38: 52-58, 1973.
8)
Ducker, T. B. and Hamit, H. F.: Experimental treatments of acute spinal cord injury. J. Neuro surg., 30: 693-697, 1969.
9)
Ducker, T. B. and Perot, P. L. Jr.: Spinal cord oxygen and blood flow in trauma. Surg. Forum, 22: 413-415, 1971.
10)
Fairholm, D. J. and Turnbull, I. M.: Microangio graphic study of experimental spinal injuries in dogs and rabbits. Surg. Forum, 21: 453-455, 1970.
11)
Fairley, H. Med. Bull., Fried, L. C. observations spinal cord.
12)
B.: Metabolism in hypothermia. Brit. 17: 52-55, 1961. and Goodkin, R.: Microangiographic of the experimentally traumatized J. Neurosurg., 35: 709-714, 1971.
norepinephrine metabolism following experimen tal spinal cord injury. Part 1: Relationship to hemorrhagic necrosis and post-wounding neuro logical deficits. J. Neurosurg., 36: 386-394, 1972. 19) Osterholm, J. L. and Mathews, G. J.: Altered norepinephrine metabolism following experimental spinal cord injury. Part 2: Protection against traumatic spinal cord hemorrhagic necrosis by norepinephrine synthesis blockade with alpha methyl tyrosine. J. Neurosurg., 36: 395-401, 1972. 20) Osterholm, J. L.: The pathophysiological response to spinal cord injury. J. Neurosurg., 40: 5-33, 1974. 21)
Tator, C. H. and Deecke, L.: Value of normo thermic perfusion, hypothermic perfusion, and durotomy in the treatment of experimental acute spinal cord trauma. J. Neurosurg., 39: 52-64, 1973.
22)
Tsubokawa, T., Moriyasu, N., Nakamura, S., and Hayashi, N.: Pathogenesis of spinal cord injury and its application to treatment. Except Med., 293: 109, 1973. Tsubokawa, T., Sugawara, T., Hayashi, N., Nakamura, S., and Moriyasu, N.: Pathogenesis of spinal cord injury. Trauma, 5: 75-87, 1973, (Jap. ed.). Vise, W. M., Yashon, D., and Hunt, W. E.: Mechanisms of norepinephrine accumulation within sites of spinal cord injury. J. Neurosurg., 40: 76-82, 1974. White, R. J., Albin, M. S., and Harris, L. S.: Spinal cord injury sequential morphology and hypothermia stabilization. Surg. Forum, 20: 432434, 1969. White, R. J., Yashon, D., Albin, M. S., and Demian, Y. K.: The technique of localized spinal cord hypothermia in the human. Proceedings of 7th VA spinal cord injury conferance. pp. 58-60, 1971.
23)
13) Goodkin, R. and Campbell, J. B.: Sequential pathologic shanges in spinal cord injury, a pre liminary report. Surg. Forum, 20: 430-432, 1969. 14)
Howitt,
W. M. and
hypothermia experimental 179-186,1972.
Turnbull,
I. M.:
Effects
of
24)
and methysergide on recovery from paraplegia. Canad. J. Surg., 15:
15) Irvin, J. D.: Histofluorescent studies of the normal and injured cat spinal cord. Ph.d thesis, Hahne mann Medical College and Hospital, Philadelphia, 1973.
25)
16)
26)
Kelly,
D. L. Jr., Lassiter,
K. R. L., Vongesvivut,
A. and Smith, J. M.: Effects of hyperbaric oxygene tion and tissue oxygen studies in experimental paraplegia.
17)
18)
J. Neurosurg.,
36: 425-429,
1972.
Locke, G. E., Yashon, D., Feldman, R. A., and Hunt, W. E.: Ischemia in primate spinal cord injury. J. Neurosurg., 34: 614-617, 1971. Osterholm,
J. L. and
Mathews,
G.
J.:
Altered
27)
White, R. J.: Current status of spinal cord cooling. Clin. Neurosurg., 20: 400-408, 1973.
