Blood flow in normal and injured monkey spinal cord W. GEORGE BINGHAM, PH.D., M . D . , HAROLD GOLDMAN, PH.D.,
STEWART J. FRIEDMAN, B.S., SHARON MURPHY, B.S., DAVID YASHON, M.D., ANDWILLIAME. HUNT, M.D.
Departments of Surgery (Neurosurgery) and Pharmacology, Ohio State University, Columbus, Ohio ~" The authors used indicator fractionation techniques to determine blood flow in normal and bluntly traumatized spinal cords of Macaca rhesus monkeys. Normal flow rates were determined for several levels of spinal cord as well as differential values for white and gray matter from representative areas. Flow rates in traumatized tissue, obtained at several different time intervals up to 4 hours after injury, demonstrated marked differences in regional perfusion of the white matter and gray matter after trauma. Gray matter perfusion was nearly obliterated while white matter blood flow persisted and in fact was higher than uninjured controls. The findings do not support the concept of ischemia as a factor in white matter failure. If toxic pathobiochemical alterations are induced by trauma, it may be possible to reverse these changes by exploiting the preserved white matter blood flow for chemotherapeutic intervention. KEY WORDS paraplegia 9 spinal cord injury spinal cord blood flow 9 nutritional blood flow ~
URRENT interest in spinal cord physiology engendered in part by the demonstration of Osterholm and Mathews, 19,2~ that a potentially reversible pathobiochemical substrate might be responsible for the devastating processes in paraplegia has disclosed a need for a better understanding of spinal cord blood flow (SCBF). The salient pathological finding following blunt spinal cord trauma, now documented by a number of investigators, is hemorrhagic necrosis of the central gray matter. Osterholm and Mathews observed that the central hemorrhage increased during the first few hours after injury and that occasionally petechial hemorrhages developed
C
]62
9 9 antipyrine-14C
in the white matter. They also found that norepinephrine (NE) levels were elevated in cat spinal cord following trauma, and they speculated that this produced vasoconstriction, which together with the expanding central hemorrhage caused further embarrassment of the microcirculation. Implicit in the theory was the vicious cycle of ischemia, anoxia, acidosis, edema, compression, and further ischemia, a well popularized if less than adequately proven concept. Support for this theory appeared to be provided in their demonstration that cats treated with an NE inhibitor, alpha-methyl-tyrosine, fared better than untreated animals following spinal cord injury?8 J. Neurosurg. / Volume 43 / August, 1975
Blood flow in monkey spinal cord Other investigators3'14'~7 have failed to con- where Ui = indicator uptake in tissue mass i firm the findings of increased NE in spinal at time (T), I = body uptake of indicator, cord tissue following trauma in cats, dogs, or Fi = blood flow to tissue mass i, CO = carmonkeys. Nevertheless, two concepts have diac output, and C'a describes the indicator become entrenched in current thinking on the dilution curve obtained from the real one by problem of spinal cord injury. One concept substituting the extrapolated points for the holds that alteration of the microcirculation real ones after recirculation. is the primary pathological response to acute Equation 1 states, in effect, that when an spinal cord trauma. An implied corollary is indicator such as antipyrine is administered in that if the microcirculation can be supported a single intravenous injection and the killing or restored rapidly enough, paralysis might time is short, the pattern of antipyrine disbe circumvented. The second, perhaps more a tribution in nervous tissue will be the same as hope than a concept, suggests that some in- the pattern of the fractional distribution of jurious metabolic reaction after trauma is the cardiac output. capable of producing paralysis and if this Adult male rhesus monkeys weighing an process is recognized and treated early average of 9 lb received a preanesthetic injecenough, it might be reversed and paralysis tion of atropine (0.1 mg/lb), then were prevented. A third consideration, receiving anesthetized with phencyclidine HC1 (Serless emphasis in the literature, is that primary nylan) (0.5 mg/lb), intubated and maintained alterations of the nerve fibers may be the fun- for the duration of the experiment on N20:O~ damental reaction to injury quite apart from (4:1) mixture from an anesthesia apparatus the vascular response. Perhaps there is some and Harvard respirator.* End-expiratory reluctance to accept this possibility because of CO~ was monitored constantly by a Beckman the classical view that neuronal injury within LB-I infra-red CO2 meter.f Arterial blood the central nervous system (CNS) is irreversi- gases and pH were determined periodically by ble. However, if repair of endothelial mem- a Radiometer blood gas analyzer.$ A femoral branes can be achieved at the molecular level vein was exposed in the upper thigh and PE~ in order to reverse vascular injury, it may be 60 polyethylene catheter of a length sufficient possible that axonal and myelin membranes to contain 0.25 ml was inserted high in the in~ can also be repaired once the basic ferior vena cava. The corresponding femoral artery was cannulated to permit constant pathological process is identified. We report here the regional perfusion of monitoring and recording of blood pressure, the spinal cord as a function of time following pulse, and measurement of the blood gases blunt trauma. and cardiac output. The animal was placed in the prone posiMethods and Materials tion and dorsal laminectomies of T-6 and T-2 The blood flow method is our modification were performed through separate incisions. of Sapirstein's original indicator fractiona- Particular attention was directed toward tion technique;23 its principle is described avoiding trauma to the cord during the elsewhere. ~~ With antipyrine-14C used as the laminectomy and the dura was left intact. indicator, the flow fraction of the cardiac out- Twenty-one animals made up the experimenput perfusing a region is measured tal group and were divided into subgroups of simultaneously with that of the cardiac out- those surviving 5, 15, and 30 minutes and 1, 2, put. The method, therefore, permits estima- and 4 hours posttrauma. The injury was intion not only of the distribution of the cardiac output, but the minimum absolute flow of *Sernylan supplied by Bio-Centic Laboratories, blood that exchanges nutrients with the Inc., St. Joseph, Missouri 64502. Harvard region as well. The basic equation of the in- respirator made by Harvard Apparatus, Inc., 150 dicator fractionation technique states that Dover Road, Millis, Massachusetts. fBeckman LB-1 infrared CO2 meter manufacUi/I = Fi/CO, (1) tureA by Beckman Instruments, Inc., 2500 Harbor Boulevard, Fullerton, California 92634. whenever SRadiometer blood gas analyzer made by Radiometer A/S, 72 Emdrupvej, DK 2400, Copenhagen, Denmark. oITCa dt = 0~C'a dt d. Neurosurg. / Volume 43 / August, 1975
163
W. G. Bingham, et al.
FI6. 1. A 300 gm-cm blunt injury to the T-6 segment produced an immediate response in pulse and blood pressure with bradycardia and hypertension lasting 5 to 10 minutes. Average decrease in pulse rate for all animals was 93/min while average mean arterial pressure rose 55 mm Hg.
flicted at the T-6 level while the T-2 segment served as untraumatized control. Trauma was produced by placing a small, spindle-shaped metal impounder with a 5-mm foot plate onto the dura. The other end of the impounder extended a few millimeters into a hollow Teflon tube held vertically above the exposed cord. A 20-gm weight was dropped 15 cm through the tube onto the impounder inflicting a 300 gmcm injury to the dorsal surface of the cord. Acute, total paralysis in the hind legs as well as typical central hemorrhagic necrosis were seen in all animals. Vital parameters were monitored at the time of impact. At the end of the survival time, T = - 1 min, final blood gases and pressures were recorded, and 0.35 ml heparin, 1:1000 dilution, was injected into the circulation. The arterial cannula was disconnected from the pressure transducer and arterial blood sampiing to determine cardiac output, and plasma volume was begun at 1-second intervals with an automatic collecting device. At zero time, 25 lzCi of antipyrine-14C was flushed smoothly into the circulation with 0.35 ml saline. At T -- 3ff sec, blood collecting was terminated and at T = 40 sec, a 5 cc bolus of saturated KCI was rapidly injected intravenously, producing instant cardiac arrest. Eight additional animals used to establish the validity of the method subsequently provided control blood flow values throughout the entire spinal cord. In those animals the femoral vessels were cannulated as described above and the various vital parameters were recorded. However, no laminectomy was performed prior to the injection of the isotope. Survival intervals were 10, 20, 40 and 60 seconds after injection of the isotope. When the monkey was dead, total laminectomy was 164
performed, the entire cord was removed and several 2-mm segments were taken from each region of the cord. Four monkeys served as additional controls; these had laminectomy without cord trauma prior to death. In the experimental group the traumatized segment and the T-2 control segment were excised quickly following cardiac arrest. The dura and nerve roots were removed and the segment split in half at the ventral fissure. In the traumatized segment the central hemorrhagic area was dissected from the surrounding white matter and the two specimens weighed separately on an electrobalance; the control segment was treated similarly. Dissection of the gray and white matter was facilitated by use of a loupe or dissecting microscope. Tissue indicator was extracted (> 98%) by the scintillation solvent (Bray's) and counted. Results
Blood Pressure and Pulse The effect of the blow to the isolated segment of midthoracic spinal cord (T-6) on blood pressure and pulse was apparent instantly (Fig. 1). Within 10 sec after injury mean pulse rate slowed from a pretrauma value of 179 to 86 while the mean arterial pressure rose from 105 mm Hg to 160 mm Hg. Both pulse and pressure maintained a plateau for the ensuing 20 seconds, followed by a gradual return to pretrauma levels over the next 5 to 10 minutes. A slight drop in the mean arterial pressure occurred and it remained below the pretrauma level (average 95%) for the next 3 hours. The mean pulse remained at baseline level. The instantaneous response in pulse and pressure following J. Neurosurg. / Volume 43 / August, 1975
Blood flow in monkey spinal cord trauma was a constant and highly dependable reaction. Failure to elicit it indicated a defective blow to the cord usually caused by the impounder striking the neighboring bony edge of lamina rather than producing a clean blow on the cord. The response did not depend on the reflex jump caused by contraction of somatic musculature when the cord was struck, since a small paralyzing dose of dimethyl tubocurarine could obliterate the jump without eliminating the vascular response. Cardiac Output Cardiac output (CO) was determined by the indicator-dilution technique2~ with the use of antipyrine-14C. This indicator, which has the same dye-dilution curves as Evan's blue or 8eRb, has been used extensively for determination of CO in rats by Goldman and Sapirstein. 1~It has not been possible to determine CO in unanesthetized monkeys, but in lightly anesthetized animals given an initial injection of phencyclidine and maintained on N20:O~ (4:1), the mean CO dropped rapidly following cord injury reaching a mean of 69 ml/min/kg in 5 minutes (35% of control value) (Fig. 2). This was followed by a rise to a mean of 115 m l / m i n / k g (60% of control) in 15 minutes. A gradual leveling off followed, with relatively little change for the first 3 hours after injury. Around 3 hours a slow upswing occurred, and reached a mean of 153 ml/min/kg (80% of control) at 4 hours. The time sequence of events occurring immediately after the injury is of considerable interest. After the injury, elevation of mean arterial pressure and slowing of pulse occurred instantly, accompanied by a fall in CO. The change in pulse and pressure was short-lived and had returned to near control levels in 5 to 10 minutes when CO was at or near its lowest point. At 15 minutes, pressure and pulse reached a plateau at approximately 95% of control values while, by contrast, CO leveled off at approximately 60% of control values and remained at this level for the succeeding 2 to 3 hours, followed by a slow climb toward control values.
200
..............................................
-
160140g \
/
~
,2o-
80~ 60IHR
2HR
3HR
4HR
F]o. 2. Cardiac output dropped precipitously after trauma and leveled off at slightly more than half the pretrauma va|ue. Injury at arrow. 14" 12" I0" 8" 6" 4
2-
~t
I H~'
2 HR
3 HR
4 HR
FIG. 3. Total spinal cord blood flow expressed as a ratio of injured to control segments (T-6:T-2) showed a biphasic response to trauma reaching its nadir approximately 1 hour postinjury followed by a slow return toward control level. Injury at arrow.
Uninjured, normal control values showed a ratio of 0.91 for total cord, 0.90 for white matter, and 0.98 for gray, since normal SCBF is slightly higher in the upper thoracic segments than in the midthoracic area (Table 1). Within 5 minutes after trauma, total flow in the traumatized segment fell to approximately 80% of untraumatized level. This was followed by an increase to 110% of control levels 15 minutes after injury. This in turn was followed by a second, more gradual, fall to about 75% of control level. Flow remained below normal values for the remainder of the experiment. Thus, a clear-cut biphasic flow pattern occurring within the first hour was Spinal Cord Blood Flow described. Dissection of gray matter from the surIn Fig. 3 spinal cord blood flow (SCBF) is expressed as a ratio of the flow in the injured rounding white matter and separate deterarea (T-6) to that of the control area (T-2). mination of flow patterns for each revealed J. Neurosurg. / Volume 43 / August, 1975
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Bingham, et
al.
TABLE 1 Spinal cord blood flow (SCBF) measurements in five reported series
Authors, Year
Measurement Method
Bingham, et al., 1975
antipyrine-14C
Landau, et al., 1969 Flohr, et al., 1969
autoradiography
Smith, et al., 1969 Griffiths 1973
Species monkey
Anesthesia phencyclidine, N20:02
cat
tihopentone
1311particles
cat
pentobarbital
I~3XEintraspinal
goat
N20:O2
x33XE intraspinal
dog
thiopentone, N20:02
Area Measured* C-3 C-4 C-5 C-6, gray C-6, white C-7 T-2 T-2, gray T-2, white T-3 T-4 T-6, gray T-6, white T-7 T-11 T-12, gray T-12, white L-2 L-3, gray L-3, white L-4 L-5 S-2 white matter gray matter C T LS L T
SCBF (ml/100 gm/min)
48.4 19.7 40.6 18.3 40.6 13.9 37.1 16.2 43.7 21.7
26.0 24.9 26.8 27.4 19.8 20.4 19.5 18.1 18.3 22.1 27.3 28.4 30.4 14.0 63.0 20.3 16.5 23.7 16.2 15.8
* Unless noted, values are for total cord blood flow. Variations in total flow values are due to variations in ratio of gray to white matter. striking differences in these areas. Within 5 minutes after the injury, flow in the central gray matter (Fig. 4) dropped to 62% of control values; this was followed by a rise to 92% of control in 15 minutes and a second and persistent drop to 21% of the control level by 1 hour after injury. Severe disruption of the central gray m a t t e r blood flow is thus indicated and is consistent with the salient pathological finding of central hemorrhagic necrosis which develops gradually during the first hour after trauma/,7,18 A biphasic curve, however, is evident prior to n e a r - t o t a l obliteration of central gray matter blood flow. By contrast, white matter blood flow showed a rather different pattern of perfusion (Fig. 5). Initially, there was a slight drop in flow to 93% of untraumatized control values 166
in the first 5 minutes. This was followed by a m a r k e d rise to 141% of control in 15 minutes. This persisted for the next 20 minutes after t r a u m a . A drop to about 90% of control value by 1 hour was followed again by a gradual, m o r e persistent rise to levels significantly above control levels at the end of the experiment. A clear-cut biphasic response occurs in the white m a t t e r in the first hour. An impressive feature is the m a r k e d increase in perfusion developing 5 minutes after t r a u m a and persisting for a b o u t 20 minutes. S t a n d a r d deviations for specific values were small and the values were significant at the p < .001 level. Perhaps even more noteworthy is that flow rates remain high and in fact exceed normal values for the majority of the 4-hour period of observation. J. Neurosurg. / Volume 43 / August, 1975
Blood flow in monkey spinal cord goats and obtained biexponential washout curves in most instances. They noted that fast 12 and slow components of the clearance curve did not necessarily correspond to flows in discrete anatomical areas (for instance, gray and white matter) and observed that multiexponential curves have been obtained from muscle and cerebral cortex which are "homogenous" tissues. They did not feel that assigning the fast component to gray and slow ~1 I HR 2 HR 3 HR 4 HR component to white matter was a valid FI~. 4. Gray matter blood flow expressed as a assumption. These investigators also noted a ratio of injured to control segments. It is severely wide range of sensitivity of SCBF to pCO2. disrupted by trauma consistent with the central Gritiiths x2.13 used intraparenchymal injechemorrhagic necrosis. Decrease in total flow tions of xenon 133localized to the white matter values is due mainly to loss of gray matter flow. of dog cord to obtain monoexponential "slow Injury at arrow. component" clearance rates in 60% of his animals. These clearance values were presumed to represent flow through white 14 matter and were comparable to values obIZ tained by Flohr, et al., and Smith, et al., for thoracic cord. Griffiths notes that the xenon tss L0 o injection is a traumatic maneuver associated with "small focal hemorrhages." Thus, slight interruption of the microcirculation could in6 terfere with normal washout and produce 4 lower flow rates. 14
2 I HR
FI~. 5. White
2 H,q"
3 HR
4HR
matter blood flow increased
significantly in the first half hour followed by a drop and a second rise above control values which persisted for the duration of the 4 hours. p < 0.001. Discussion Perfusion o f Intact Spinal C o r d
While the gross anatomy of the spinal cord circulation has been described repeatedly and is now rather well understood, 25 information regarding the function of the microcirculation is comparatively meager and knowledge of the effects of disease and trauma on cord blood flow is almost nonexistent, a5 Flohr, et al., 8 using 113x macroaggregated albumin, demonstrated slightly higher flow rates in the cervical and lumbosacral areas than in the thoracic region in cats anesthetized with pentobarbital. A significant correlation was found between flow rates and arterial pCO~ levels in all areas of cord examined. Smith, et aL, 24 injected xenon a33 directly into the parenchyma of the spinal cord of J. Neurosurg. / Volume 43 / August, 1975
Regional Perfusion - - Gray vs. W h i t e M a t t e r
Landau, et al., ~ introduced an autoradiographic technique using radioactive trifluoroiodomethane (CF~I L3~) for determining blood flow of the brain and spinal cord. They were able to obtain separate values for white and gray matter of the cord and both were considerably lower than flow rates for white and gray matter of any portion of the brain. Cerebral and cerebellar white matter values were 23 and 24 ml/100 gm/min, compared to the next lower value of 87 ml/100 gm/min in cerebellar nuclei. Reivich, et al.,2~'22 also employed autoradiography using antipyrine-t~C to measure cerebral blood flow in awake cats. They did not report values for SCBF but their flow rates for other areas of white matter were 21, 20, 24, and 22 ml/100 gm/min for cerebrum, optic tract, cerebellum, and pyramid, respectively. Their values were very close to those reported by Landau, et al., and, in general, were in good agreement with those reported by Flohr, et al., Smith, et al., and Griffiths. Reivich, et al., note that possible sources of error in the autoradiographic technique include thickness variation in the tissue sections '167
W. G. Bingham, et al. and variation in duplicate densitometer readings within a group of sections as well as between series of tissue sections. Flow rates for white matter in the above studies, including our own, generally range from approximately 15 to 25 ml/100 gm/min, whether it be brain, optic nerve, pyramid, or spinal pathway. It is interesting to note the similarity in values for white matter in the various studies employing the different techniques. Gray matter blood flow on the other hand varies considerably, ranging from 138 ml/100 gm/min in the sensorymotor cortex to 63 ml/100 gm/min in the spinal gray matter in the studies of Landau, et al. Reivich, et al., did not report flow values for spinal cord but their flow rate of 65 ml/100 gm/min for pontine reticular formation was essentially the same as that of Landau, et al. By our method, gray matter perfusion appears to be roughly 2.0 to 2.5 times that of the white matter (Table 1). In our T-2 control area, for example, gray flow values averaged 40.3 ml/100 gm/min, while white matter flow averaged 18.3 ml/100 gm/min. Gray:white tissue ratios for total cross-sectional areas occupied by the gray and white matter indicate that there is approximately five times as much white matter as gray at the T-2 level. The volume of the vascular bed based on pointcounting analysis of several cross-sections of this level indicate that the vasculature of the gray matter is approximately six times greater than that of the white matter. Thus, at the T-2 level, one-sixth of the tissue contains approximately 85% of the vascular bed with a blood flow more than twice that of the remaining tissue. By contrast, we have determined that gray matter blood flow is higher in the C-6 segment where the greater volume of central gray matter occupies approximately 30% of the cross-sectional area. The vascular bed of the central gray matter was seven times that of the white matter, while the flow through the gray matter was two and a half times that of the white matter. Effects o f T r a u m a
It is apparent that SCBF cannot be discussed in terms of total flow through an entire cord segment but must be considered in terms of separate flows through the central gray matter and surrounding white matter, par168
ticularly when one considers how these two areas differ in their susceptibility to trauma. Thus, our 300 gm-cm injury produced the typical central gray hemorrhage and resulted in near-total obliteration of the flow of blood to this area. In the white matter, however, there was little if any gross pathological alteration except for an occasional small petechial hemorrhage, and the blood flow was preserved. In fact, during the first hour after injury, the perfusion of white matter was significantly above control levels for much of the time, and after a slight dip below control levels at 1 hour it again rose to and finally exceeded control levels for up to 4 hours after injury. The biphasic nature of the blood flow pattern in traumatized tissue seems to be related to events occurring locally in the cord and unrelated to changes in the systemic circulation. Alterations in blood pressure and pulse occur instantly and are essentially back to near-normal levels at a time when blood flow, cardiac output and blood volume are still undergoing their initial responses and have yet to reach their peak levels. Moreover, while the time relationships of the changes in CO are perhaps more closely related to the changes in SCBF, the shift in CO is markedly downward while SCBF shows an increase, particularly marked in the white matter. That the white matter vasculature is more resilient has also been suggested by the work of Ducker, et al., 8 and by the injection studies of Dohrmann, et al.? ,~ who used the fluorescent dye Thioflavine S which stains vascular endothelium. These investigators demonstrated preservation of vascular channels in white matter following a 400 gm-cm injury, while vessels in the central gray matter were obliterated. Perfusion of white matter had decreased by 15 minutes after trauma; this was replaced by an increase at 30 minutes, which in turn was followed by a slight second decrease in 4 to 8 hours and a return to near normal by 24 hours. Therefore, their technique suggests a biphasic flow pattern with a temporal distribution not too dissimilar from our findings. Since the Thioflavine S technique indicates only those vessels that are open at the time of perfusion and reveals nothing regarding the quantitative capacity of the functioning vessels, the comparison cannot be too rigorously applied. The important consideration is the preserved cord blood flow J. Neurosurg. / Volume 43 / August, 1975
Blood flow in monkey spinal cord following an injury which does appear to reproduce the clinical picture of paraplegia and central necrosis. Fairholm and Turnbull 7 also noted preserved capillaries in traumatized rabbit spinal cord in the area immediately surrounding the central gray matter hemorrhagic necrosis. Interestingly, neuronal and axonal degeneration that followed trauma did not seem to be caused by ischemia initially, but recovery may have depended on the intact microvasculature. The illustrations in the article by Fried and Goodkin 9 show Micropaque in white matter vessels of traumatized monkey cord, but the authors do not discuss this observation. There appears to be adequate evidence, therefore, both anatomical and physiological, that the white matter vasculature is considerably more resilient to blunt trauma than is that of the gray matter. White matter blood vessels are usually associated with septal infoldings of pia which penetrate the white matter and gradually thin out as they approach the central gray matter. The larger vessels possess heavier mesenchymal-supporting investment. 26,27 Electron microscopic studies currently in progress suggest that the microvasculature of white matter possesses a more dense glial investment than vessels of the gray matter. These structural differences may account for greater degrees of resistance to trauma; however, they do not account for the gradual development of the central hemorrhagic necrosis and near total obliteration of gray matter blood flow. The highly simplistic and poorly documented concept of trauma, ischemia, anoxia, edema, compression, ischemia, and so forth as a self-propagating, vicious cycle is not supported by recent findings noted above. According to this theory, the pia is viewed as an inelastic membrane which confines the swollen injured spinal cord, thereby compromising the microcirculation. Since tissue tension studies have not to our knowledge been reported, this view of the role of the pia is purely speculative. That the microcirculation of the white matter is not embarrassed has been adequately demonstrated in our studies as well as those of Fairholm and Turnbull 7 and Dohrmann, et al. 4's While a cause-and-effect relationship between gray matter blood flow and central hemorrhagic necrosis is not defined with certainty by these results, our feeling is that the J. Neurosurg. / Volume 43 / August, 1975
central hemorrhage is produced by the direct effect of trauma on the central microvasculature. The traumatic disruption of the vessels in turn causes decreased flow through the tissue. Our investigations of the ultrastructural alterations of central gray matter microcirculation following trauma have revealed opening of tight junctions of the vascular endothelium, separation of endothelium from basement membranes with recanalization, numerous platelet thrombi, and gross disruption of vessel walls with plasma and cellular extravasation into extracellular spaces? 1 These findings are most certainly the result of direct trauma although they clearly indicate the source of subsequent circulatory obstruction and ischemia in the gray matter. Comparable changes have not been found in white matter. That primary alterations in neuronal structures are produced by trauma and may be progressive for some time following the injury seems quite probable and is suggested by Fairholm and Turnbull's observations of fragmentation and end-bulb formation of the injured axons 2 hours postinjury. The possibility of a toxic, metabolic process other than ischemia is an important consideration. Bingham, et al., ~,2 noted changes in lysosomal enzyme activity in brain tissue following injury. Our preliminary observations on spinal cord tissues, however, fail to show that these enzymes contribute to the cellular injury following acute cord trauma. In addition, the possibility that the accumulation of biogenic amines, specifically norepinephrine, might result in further vascular compromise, ischemia, and cell damage, as proposed by Osterholm and Mathews, x9,2~ has not been supported by more recent studies by Hedeman, et aL?* in dogs, Naftchi, et a l . ) 7 in cats, and Bingham, et al., a in monkeys; all of these investigators showed lowered values for norepinephrine in injured spinal cord tissue. The method employed here estimates for the first time the regional perfusion in both intact and traumatized spinal cord of subhuman primates. It should be noted that this method estimates only that aspect of perfusion which exchanges nutrients with the tissue and, therefore, is most likely to represent metabolic blood flow, it cannot estimate flow through arteriovenous shunts. The observation of preserved flow in white matter, then, regardless of any abnormal channels or ]69
W. G. Bingham, et al. shunts that may be established by trauma, estimates perfusion that has the potential capacity to exchange metabolically with the parenchyma surrounding the microcirculation. Whether freshly traumatized tissue does, in fact, engage in any significant exchange that has metabolic value to the tissue is a moot point. If one judges from cord specimens of chronic injuries, the severe cystic degeneration often seen makes one question the efficacy of this blood flow. Still, if there is some potentially reversible aspect to cord injury, it may be possible to accomplish this reversal by exploiting the preserved white matter blood flow, since the utility of chemotherapy relies on a drug's ability to reach the white matter.
Summary 1. Using antipyrine-14C, the authors determined spinal cord blood flow in monkeys by means of standard indicator fractionation techniques. 2. N o r m a l flow rates were obtained for several areas of the spinal cord as well as differential values for gray and white matter of representative segments. 3. Perfusion of injured spinal cord was determined by subjecting the cord to blunt trauma and obtaining flow rates at various periods up to 4 hours after trauma. 4. T r a u m a causes near obliteration of blood flow to the gray matter, while perfusion of the white matter persists. 5. The results do not support the concept of ischemia as an important factor in failure of white matter.
References 1. Bingham WG Jr, Paul SE, Sastry KSS: Effect of cold injury on six enzymes in rat brain. Arch Neurol 21:649-660, 1969 2. Bingham WG Jr, Paul SE, Sastry KSS: Effect of steroid on enzyme response to cold injury in rat brain. Neurology (Minneap) 21:111-121, 1971 3. Bingham WG, Ruffolo R, Friedman SJ: Catecholamine levels in the injured spinal cord of monkeys. J Neurosurg 42:174-178, 1975 4. Dohrmann G J, Wagner FC Jr, Bucy PC: The microvasculature in transitory traumatic paraplegia. An electron microscopic study in the monkey. J Neurosurg 35:263-271, 1971 5. Dohrmann G J, Wick KM, Bucy PC: Spinal 170
cord blood flow patterns in experimental traumatic paraplegia. J Neurosurg 38:52-58, 1973 6. Ducker TB, Kindt GW, Kempe LG: Pathological findings in acute experimental spinal cord trauma. J Neurosurg 35:700-708, 1971 7. Fairholm D J, Turnbull IM: Microangiographic study of experimental spinal cord injury. J Neurosurg 35:277-286, 1971 8. Flohr HW, Brock M, Christ R, et al: Arterial PCO~ and blood flow in different parts of the CNS of anesthetized cats, in Brock M, Fieschi C, Ingvar DH, et al (eds): Cerebral Blood Flow. Berlin, Springer-Verlag, 1969, pp 86-88 Fried LC, Goodkin R: Microangiographic 9. observations of the experimentally traumatized spinal cord. J Neurosurg 35:709-714, 1971 10. Goldman H, Sapirstein LA: Brain blood flow in the conscious and anesthetized rat. Am J Physiol 224:122-126, 1973 11. Goodman JH, Bingham WG Jr, Hunt WE: Edema formation and central hemorrhagic necrosis following impact injury to primate spinal cord. Surg Forum 25:440-442, 1974 12. Griffiths IR" Spinal cord blood flow in dogs. I. The "normal" flow. J Neural Neurosurg Psychiatry 36:34-41, 1973 13. Griffiths IR: Spinal cord blood flow in dogs: the effect of blood pressure. J Neural Neurosurg Psychiatry 36:914-920, 1973 14. Hedeman LS, Shellenberger MK, Gordon JH: Studies in experimental spinal cord trauma. Part I. Alterations in catecholamine levels. J Neurosurg 40:37-43, 1974 15. Jellinger K: Circulation disorders of the spinal cord. Aeta Neurochir (Wieo) 26:327-337, 1972 16. Landau WM, Freygang WH, Roland LP, et al: The local circulation of the living brain: values in unanesthetized and anesthetized cats. Traos Am Neural Assoc 80:125-129, 1955 17. Naftchi NE, Demeny M, DeCrescito V, et al: Biogenic amine concentrations in traumatized spinal cord of cats. Effect of drug therapy. J Neurosorg 40:52-57, 1974 18. Osterholm JL: The pathophysiological response to spinal cord injury. The current status of related research. J Neorosorg 40:3-33, 1974 19. Osterholm JL, Mathews G J: Altered norepinephrine metabolism following experimental spinal cord injury. I. Relationship to hemorrhagic necrosis and post-wounding neurological deficits. J Neurosarg 36:386-394, 1972 20. Osterholm JL, Mathews G J: Altered norepinephrine metabolism following experimental spinal cord injury. 2. Protection against traumatic spinal cord hemorrhagic necrosis by norepinephrine synthesis blockade J. Neurosurg.
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21. 22.
23. 24. 25.
with alpha methyl tyrosine. J Neurosurg 36:395-401, 1972 Reivich M: Regulation of the cerebral circulation. Ciin Neurosurg 16:378-418, 1968 Reivich M, Hejle J, Sokoloff L, et al: Measurement of regional cerebral blood flow with antipyrine-14C in awake cats. J Appl Physiol 27:296-300, 1969 Sapirstein LA: Regional blood flow by fractional distribution of indicators. Am J Physiol 193:161, 1958 Smith AL, Pender JW, Alexander SC: Effects of PCO2 on spinal cord blood flow. Am J Physioi 216:1158-1163, 1969 Turnbull IM: Blood supply of the spinal cord, in Vinken P J, Bruyn GW (eds): Handbook of
J. Neurosurg. / Volume 43 / August, 1975
Clinical Neurology, Voi 12. Amsterdam, North Holland Publ, 1972 pp 478-491 26. Wagner FC Jr, Dobrmann G J, Bucy PC: Histopathology in transitory traumatic paraplegia in monkey. J Neurosurg 35: 272-276, 1971 27. Wolman L: The disturbance of circulation in traumatic paraplegia in acute and late stages: a pathological study. Paraplegia 2:213-226, 1965 Address reprint requests to: W. George Bingham, Jr., Ph.D., M.D., N-911 University Hospital, Ohio State University, 410 West 10th Avenue, Columbus, Ohio 43210.
171
STEWART J. FRIEDMAN, B.S., SHARON MURPHY, B.S., DAVID YASHON, M.D., ANDWILLIAME. HUNT, M.D.
Departments of Surgery (Neurosurgery) and Pharmacology, Ohio State University, Columbus, Ohio ~" The authors used indicator fractionation techniques to determine blood flow in normal and bluntly traumatized spinal cords of Macaca rhesus monkeys. Normal flow rates were determined for several levels of spinal cord as well as differential values for white and gray matter from representative areas. Flow rates in traumatized tissue, obtained at several different time intervals up to 4 hours after injury, demonstrated marked differences in regional perfusion of the white matter and gray matter after trauma. Gray matter perfusion was nearly obliterated while white matter blood flow persisted and in fact was higher than uninjured controls. The findings do not support the concept of ischemia as a factor in white matter failure. If toxic pathobiochemical alterations are induced by trauma, it may be possible to reverse these changes by exploiting the preserved white matter blood flow for chemotherapeutic intervention. KEY WORDS paraplegia 9 spinal cord injury spinal cord blood flow 9 nutritional blood flow ~
URRENT interest in spinal cord physiology engendered in part by the demonstration of Osterholm and Mathews, 19,2~ that a potentially reversible pathobiochemical substrate might be responsible for the devastating processes in paraplegia has disclosed a need for a better understanding of spinal cord blood flow (SCBF). The salient pathological finding following blunt spinal cord trauma, now documented by a number of investigators, is hemorrhagic necrosis of the central gray matter. Osterholm and Mathews observed that the central hemorrhage increased during the first few hours after injury and that occasionally petechial hemorrhages developed
C
]62
9 9 antipyrine-14C
in the white matter. They also found that norepinephrine (NE) levels were elevated in cat spinal cord following trauma, and they speculated that this produced vasoconstriction, which together with the expanding central hemorrhage caused further embarrassment of the microcirculation. Implicit in the theory was the vicious cycle of ischemia, anoxia, acidosis, edema, compression, and further ischemia, a well popularized if less than adequately proven concept. Support for this theory appeared to be provided in their demonstration that cats treated with an NE inhibitor, alpha-methyl-tyrosine, fared better than untreated animals following spinal cord injury?8 J. Neurosurg. / Volume 43 / August, 1975
Blood flow in monkey spinal cord Other investigators3'14'~7 have failed to con- where Ui = indicator uptake in tissue mass i firm the findings of increased NE in spinal at time (T), I = body uptake of indicator, cord tissue following trauma in cats, dogs, or Fi = blood flow to tissue mass i, CO = carmonkeys. Nevertheless, two concepts have diac output, and C'a describes the indicator become entrenched in current thinking on the dilution curve obtained from the real one by problem of spinal cord injury. One concept substituting the extrapolated points for the holds that alteration of the microcirculation real ones after recirculation. is the primary pathological response to acute Equation 1 states, in effect, that when an spinal cord trauma. An implied corollary is indicator such as antipyrine is administered in that if the microcirculation can be supported a single intravenous injection and the killing or restored rapidly enough, paralysis might time is short, the pattern of antipyrine disbe circumvented. The second, perhaps more a tribution in nervous tissue will be the same as hope than a concept, suggests that some in- the pattern of the fractional distribution of jurious metabolic reaction after trauma is the cardiac output. capable of producing paralysis and if this Adult male rhesus monkeys weighing an process is recognized and treated early average of 9 lb received a preanesthetic injecenough, it might be reversed and paralysis tion of atropine (0.1 mg/lb), then were prevented. A third consideration, receiving anesthetized with phencyclidine HC1 (Serless emphasis in the literature, is that primary nylan) (0.5 mg/lb), intubated and maintained alterations of the nerve fibers may be the fun- for the duration of the experiment on N20:O~ damental reaction to injury quite apart from (4:1) mixture from an anesthesia apparatus the vascular response. Perhaps there is some and Harvard respirator.* End-expiratory reluctance to accept this possibility because of CO~ was monitored constantly by a Beckman the classical view that neuronal injury within LB-I infra-red CO2 meter.f Arterial blood the central nervous system (CNS) is irreversi- gases and pH were determined periodically by ble. However, if repair of endothelial mem- a Radiometer blood gas analyzer.$ A femoral branes can be achieved at the molecular level vein was exposed in the upper thigh and PE~ in order to reverse vascular injury, it may be 60 polyethylene catheter of a length sufficient possible that axonal and myelin membranes to contain 0.25 ml was inserted high in the in~ can also be repaired once the basic ferior vena cava. The corresponding femoral artery was cannulated to permit constant pathological process is identified. We report here the regional perfusion of monitoring and recording of blood pressure, the spinal cord as a function of time following pulse, and measurement of the blood gases blunt trauma. and cardiac output. The animal was placed in the prone posiMethods and Materials tion and dorsal laminectomies of T-6 and T-2 The blood flow method is our modification were performed through separate incisions. of Sapirstein's original indicator fractiona- Particular attention was directed toward tion technique;23 its principle is described avoiding trauma to the cord during the elsewhere. ~~ With antipyrine-14C used as the laminectomy and the dura was left intact. indicator, the flow fraction of the cardiac out- Twenty-one animals made up the experimenput perfusing a region is measured tal group and were divided into subgroups of simultaneously with that of the cardiac out- those surviving 5, 15, and 30 minutes and 1, 2, put. The method, therefore, permits estima- and 4 hours posttrauma. The injury was intion not only of the distribution of the cardiac output, but the minimum absolute flow of *Sernylan supplied by Bio-Centic Laboratories, blood that exchanges nutrients with the Inc., St. Joseph, Missouri 64502. Harvard region as well. The basic equation of the in- respirator made by Harvard Apparatus, Inc., 150 dicator fractionation technique states that Dover Road, Millis, Massachusetts. fBeckman LB-1 infrared CO2 meter manufacUi/I = Fi/CO, (1) tureA by Beckman Instruments, Inc., 2500 Harbor Boulevard, Fullerton, California 92634. whenever SRadiometer blood gas analyzer made by Radiometer A/S, 72 Emdrupvej, DK 2400, Copenhagen, Denmark. oITCa dt = 0~C'a dt d. Neurosurg. / Volume 43 / August, 1975
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W. G. Bingham, et al.
FI6. 1. A 300 gm-cm blunt injury to the T-6 segment produced an immediate response in pulse and blood pressure with bradycardia and hypertension lasting 5 to 10 minutes. Average decrease in pulse rate for all animals was 93/min while average mean arterial pressure rose 55 mm Hg.
flicted at the T-6 level while the T-2 segment served as untraumatized control. Trauma was produced by placing a small, spindle-shaped metal impounder with a 5-mm foot plate onto the dura. The other end of the impounder extended a few millimeters into a hollow Teflon tube held vertically above the exposed cord. A 20-gm weight was dropped 15 cm through the tube onto the impounder inflicting a 300 gmcm injury to the dorsal surface of the cord. Acute, total paralysis in the hind legs as well as typical central hemorrhagic necrosis were seen in all animals. Vital parameters were monitored at the time of impact. At the end of the survival time, T = - 1 min, final blood gases and pressures were recorded, and 0.35 ml heparin, 1:1000 dilution, was injected into the circulation. The arterial cannula was disconnected from the pressure transducer and arterial blood sampiing to determine cardiac output, and plasma volume was begun at 1-second intervals with an automatic collecting device. At zero time, 25 lzCi of antipyrine-14C was flushed smoothly into the circulation with 0.35 ml saline. At T -- 3ff sec, blood collecting was terminated and at T = 40 sec, a 5 cc bolus of saturated KCI was rapidly injected intravenously, producing instant cardiac arrest. Eight additional animals used to establish the validity of the method subsequently provided control blood flow values throughout the entire spinal cord. In those animals the femoral vessels were cannulated as described above and the various vital parameters were recorded. However, no laminectomy was performed prior to the injection of the isotope. Survival intervals were 10, 20, 40 and 60 seconds after injection of the isotope. When the monkey was dead, total laminectomy was 164
performed, the entire cord was removed and several 2-mm segments were taken from each region of the cord. Four monkeys served as additional controls; these had laminectomy without cord trauma prior to death. In the experimental group the traumatized segment and the T-2 control segment were excised quickly following cardiac arrest. The dura and nerve roots were removed and the segment split in half at the ventral fissure. In the traumatized segment the central hemorrhagic area was dissected from the surrounding white matter and the two specimens weighed separately on an electrobalance; the control segment was treated similarly. Dissection of the gray and white matter was facilitated by use of a loupe or dissecting microscope. Tissue indicator was extracted (> 98%) by the scintillation solvent (Bray's) and counted. Results
Blood Pressure and Pulse The effect of the blow to the isolated segment of midthoracic spinal cord (T-6) on blood pressure and pulse was apparent instantly (Fig. 1). Within 10 sec after injury mean pulse rate slowed from a pretrauma value of 179 to 86 while the mean arterial pressure rose from 105 mm Hg to 160 mm Hg. Both pulse and pressure maintained a plateau for the ensuing 20 seconds, followed by a gradual return to pretrauma levels over the next 5 to 10 minutes. A slight drop in the mean arterial pressure occurred and it remained below the pretrauma level (average 95%) for the next 3 hours. The mean pulse remained at baseline level. The instantaneous response in pulse and pressure following J. Neurosurg. / Volume 43 / August, 1975
Blood flow in monkey spinal cord trauma was a constant and highly dependable reaction. Failure to elicit it indicated a defective blow to the cord usually caused by the impounder striking the neighboring bony edge of lamina rather than producing a clean blow on the cord. The response did not depend on the reflex jump caused by contraction of somatic musculature when the cord was struck, since a small paralyzing dose of dimethyl tubocurarine could obliterate the jump without eliminating the vascular response. Cardiac Output Cardiac output (CO) was determined by the indicator-dilution technique2~ with the use of antipyrine-14C. This indicator, which has the same dye-dilution curves as Evan's blue or 8eRb, has been used extensively for determination of CO in rats by Goldman and Sapirstein. 1~It has not been possible to determine CO in unanesthetized monkeys, but in lightly anesthetized animals given an initial injection of phencyclidine and maintained on N20:O~ (4:1), the mean CO dropped rapidly following cord injury reaching a mean of 69 ml/min/kg in 5 minutes (35% of control value) (Fig. 2). This was followed by a rise to a mean of 115 m l / m i n / k g (60% of control) in 15 minutes. A gradual leveling off followed, with relatively little change for the first 3 hours after injury. Around 3 hours a slow upswing occurred, and reached a mean of 153 ml/min/kg (80% of control) at 4 hours. The time sequence of events occurring immediately after the injury is of considerable interest. After the injury, elevation of mean arterial pressure and slowing of pulse occurred instantly, accompanied by a fall in CO. The change in pulse and pressure was short-lived and had returned to near control levels in 5 to 10 minutes when CO was at or near its lowest point. At 15 minutes, pressure and pulse reached a plateau at approximately 95% of control values while, by contrast, CO leveled off at approximately 60% of control values and remained at this level for the succeeding 2 to 3 hours, followed by a slow climb toward control values.
200
..............................................
-
160140g \
/
~
,2o-
80~ 60IHR
2HR
3HR
4HR
F]o. 2. Cardiac output dropped precipitously after trauma and leveled off at slightly more than half the pretrauma va|ue. Injury at arrow. 14" 12" I0" 8" 6" 4
2-
~t
I H~'
2 HR
3 HR
4 HR
FIG. 3. Total spinal cord blood flow expressed as a ratio of injured to control segments (T-6:T-2) showed a biphasic response to trauma reaching its nadir approximately 1 hour postinjury followed by a slow return toward control level. Injury at arrow.
Uninjured, normal control values showed a ratio of 0.91 for total cord, 0.90 for white matter, and 0.98 for gray, since normal SCBF is slightly higher in the upper thoracic segments than in the midthoracic area (Table 1). Within 5 minutes after trauma, total flow in the traumatized segment fell to approximately 80% of untraumatized level. This was followed by an increase to 110% of control levels 15 minutes after injury. This in turn was followed by a second, more gradual, fall to about 75% of control level. Flow remained below normal values for the remainder of the experiment. Thus, a clear-cut biphasic flow pattern occurring within the first hour was Spinal Cord Blood Flow described. Dissection of gray matter from the surIn Fig. 3 spinal cord blood flow (SCBF) is expressed as a ratio of the flow in the injured rounding white matter and separate deterarea (T-6) to that of the control area (T-2). mination of flow patterns for each revealed J. Neurosurg. / Volume 43 / August, 1975
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Bingham, et
al.
TABLE 1 Spinal cord blood flow (SCBF) measurements in five reported series
Authors, Year
Measurement Method
Bingham, et al., 1975
antipyrine-14C
Landau, et al., 1969 Flohr, et al., 1969
autoradiography
Smith, et al., 1969 Griffiths 1973
Species monkey
Anesthesia phencyclidine, N20:02
cat
tihopentone
1311particles
cat
pentobarbital
I~3XEintraspinal
goat
N20:O2
x33XE intraspinal
dog
thiopentone, N20:02
Area Measured* C-3 C-4 C-5 C-6, gray C-6, white C-7 T-2 T-2, gray T-2, white T-3 T-4 T-6, gray T-6, white T-7 T-11 T-12, gray T-12, white L-2 L-3, gray L-3, white L-4 L-5 S-2 white matter gray matter C T LS L T
SCBF (ml/100 gm/min)
48.4 19.7 40.6 18.3 40.6 13.9 37.1 16.2 43.7 21.7
26.0 24.9 26.8 27.4 19.8 20.4 19.5 18.1 18.3 22.1 27.3 28.4 30.4 14.0 63.0 20.3 16.5 23.7 16.2 15.8
* Unless noted, values are for total cord blood flow. Variations in total flow values are due to variations in ratio of gray to white matter. striking differences in these areas. Within 5 minutes after the injury, flow in the central gray matter (Fig. 4) dropped to 62% of control values; this was followed by a rise to 92% of control in 15 minutes and a second and persistent drop to 21% of the control level by 1 hour after injury. Severe disruption of the central gray m a t t e r blood flow is thus indicated and is consistent with the salient pathological finding of central hemorrhagic necrosis which develops gradually during the first hour after trauma/,7,18 A biphasic curve, however, is evident prior to n e a r - t o t a l obliteration of central gray matter blood flow. By contrast, white matter blood flow showed a rather different pattern of perfusion (Fig. 5). Initially, there was a slight drop in flow to 93% of untraumatized control values 166
in the first 5 minutes. This was followed by a m a r k e d rise to 141% of control in 15 minutes. This persisted for the next 20 minutes after t r a u m a . A drop to about 90% of control value by 1 hour was followed again by a gradual, m o r e persistent rise to levels significantly above control levels at the end of the experiment. A clear-cut biphasic response occurs in the white m a t t e r in the first hour. An impressive feature is the m a r k e d increase in perfusion developing 5 minutes after t r a u m a and persisting for a b o u t 20 minutes. S t a n d a r d deviations for specific values were small and the values were significant at the p < .001 level. Perhaps even more noteworthy is that flow rates remain high and in fact exceed normal values for the majority of the 4-hour period of observation. J. Neurosurg. / Volume 43 / August, 1975
Blood flow in monkey spinal cord goats and obtained biexponential washout curves in most instances. They noted that fast 12 and slow components of the clearance curve did not necessarily correspond to flows in discrete anatomical areas (for instance, gray and white matter) and observed that multiexponential curves have been obtained from muscle and cerebral cortex which are "homogenous" tissues. They did not feel that assigning the fast component to gray and slow ~1 I HR 2 HR 3 HR 4 HR component to white matter was a valid FI~. 4. Gray matter blood flow expressed as a assumption. These investigators also noted a ratio of injured to control segments. It is severely wide range of sensitivity of SCBF to pCO2. disrupted by trauma consistent with the central Gritiiths x2.13 used intraparenchymal injechemorrhagic necrosis. Decrease in total flow tions of xenon 133localized to the white matter values is due mainly to loss of gray matter flow. of dog cord to obtain monoexponential "slow Injury at arrow. component" clearance rates in 60% of his animals. These clearance values were presumed to represent flow through white 14 matter and were comparable to values obIZ tained by Flohr, et al., and Smith, et al., for thoracic cord. Griffiths notes that the xenon tss L0 o injection is a traumatic maneuver associated with "small focal hemorrhages." Thus, slight interruption of the microcirculation could in6 terfere with normal washout and produce 4 lower flow rates. 14
2 I HR
FI~. 5. White
2 H,q"
3 HR
4HR
matter blood flow increased
significantly in the first half hour followed by a drop and a second rise above control values which persisted for the duration of the 4 hours. p < 0.001. Discussion Perfusion o f Intact Spinal C o r d
While the gross anatomy of the spinal cord circulation has been described repeatedly and is now rather well understood, 25 information regarding the function of the microcirculation is comparatively meager and knowledge of the effects of disease and trauma on cord blood flow is almost nonexistent, a5 Flohr, et al., 8 using 113x macroaggregated albumin, demonstrated slightly higher flow rates in the cervical and lumbosacral areas than in the thoracic region in cats anesthetized with pentobarbital. A significant correlation was found between flow rates and arterial pCO~ levels in all areas of cord examined. Smith, et aL, 24 injected xenon a33 directly into the parenchyma of the spinal cord of J. Neurosurg. / Volume 43 / August, 1975
Regional Perfusion - - Gray vs. W h i t e M a t t e r
Landau, et al., ~ introduced an autoradiographic technique using radioactive trifluoroiodomethane (CF~I L3~) for determining blood flow of the brain and spinal cord. They were able to obtain separate values for white and gray matter of the cord and both were considerably lower than flow rates for white and gray matter of any portion of the brain. Cerebral and cerebellar white matter values were 23 and 24 ml/100 gm/min, compared to the next lower value of 87 ml/100 gm/min in cerebellar nuclei. Reivich, et al.,2~'22 also employed autoradiography using antipyrine-t~C to measure cerebral blood flow in awake cats. They did not report values for SCBF but their flow rates for other areas of white matter were 21, 20, 24, and 22 ml/100 gm/min for cerebrum, optic tract, cerebellum, and pyramid, respectively. Their values were very close to those reported by Landau, et al., and, in general, were in good agreement with those reported by Flohr, et al., Smith, et al., and Griffiths. Reivich, et al., note that possible sources of error in the autoradiographic technique include thickness variation in the tissue sections '167
W. G. Bingham, et al. and variation in duplicate densitometer readings within a group of sections as well as between series of tissue sections. Flow rates for white matter in the above studies, including our own, generally range from approximately 15 to 25 ml/100 gm/min, whether it be brain, optic nerve, pyramid, or spinal pathway. It is interesting to note the similarity in values for white matter in the various studies employing the different techniques. Gray matter blood flow on the other hand varies considerably, ranging from 138 ml/100 gm/min in the sensorymotor cortex to 63 ml/100 gm/min in the spinal gray matter in the studies of Landau, et al. Reivich, et al., did not report flow values for spinal cord but their flow rate of 65 ml/100 gm/min for pontine reticular formation was essentially the same as that of Landau, et al. By our method, gray matter perfusion appears to be roughly 2.0 to 2.5 times that of the white matter (Table 1). In our T-2 control area, for example, gray flow values averaged 40.3 ml/100 gm/min, while white matter flow averaged 18.3 ml/100 gm/min. Gray:white tissue ratios for total cross-sectional areas occupied by the gray and white matter indicate that there is approximately five times as much white matter as gray at the T-2 level. The volume of the vascular bed based on pointcounting analysis of several cross-sections of this level indicate that the vasculature of the gray matter is approximately six times greater than that of the white matter. Thus, at the T-2 level, one-sixth of the tissue contains approximately 85% of the vascular bed with a blood flow more than twice that of the remaining tissue. By contrast, we have determined that gray matter blood flow is higher in the C-6 segment where the greater volume of central gray matter occupies approximately 30% of the cross-sectional area. The vascular bed of the central gray matter was seven times that of the white matter, while the flow through the gray matter was two and a half times that of the white matter. Effects o f T r a u m a
It is apparent that SCBF cannot be discussed in terms of total flow through an entire cord segment but must be considered in terms of separate flows through the central gray matter and surrounding white matter, par168
ticularly when one considers how these two areas differ in their susceptibility to trauma. Thus, our 300 gm-cm injury produced the typical central gray hemorrhage and resulted in near-total obliteration of the flow of blood to this area. In the white matter, however, there was little if any gross pathological alteration except for an occasional small petechial hemorrhage, and the blood flow was preserved. In fact, during the first hour after injury, the perfusion of white matter was significantly above control levels for much of the time, and after a slight dip below control levels at 1 hour it again rose to and finally exceeded control levels for up to 4 hours after injury. The biphasic nature of the blood flow pattern in traumatized tissue seems to be related to events occurring locally in the cord and unrelated to changes in the systemic circulation. Alterations in blood pressure and pulse occur instantly and are essentially back to near-normal levels at a time when blood flow, cardiac output and blood volume are still undergoing their initial responses and have yet to reach their peak levels. Moreover, while the time relationships of the changes in CO are perhaps more closely related to the changes in SCBF, the shift in CO is markedly downward while SCBF shows an increase, particularly marked in the white matter. That the white matter vasculature is more resilient has also been suggested by the work of Ducker, et al., 8 and by the injection studies of Dohrmann, et al.? ,~ who used the fluorescent dye Thioflavine S which stains vascular endothelium. These investigators demonstrated preservation of vascular channels in white matter following a 400 gm-cm injury, while vessels in the central gray matter were obliterated. Perfusion of white matter had decreased by 15 minutes after trauma; this was replaced by an increase at 30 minutes, which in turn was followed by a slight second decrease in 4 to 8 hours and a return to near normal by 24 hours. Therefore, their technique suggests a biphasic flow pattern with a temporal distribution not too dissimilar from our findings. Since the Thioflavine S technique indicates only those vessels that are open at the time of perfusion and reveals nothing regarding the quantitative capacity of the functioning vessels, the comparison cannot be too rigorously applied. The important consideration is the preserved cord blood flow J. Neurosurg. / Volume 43 / August, 1975
Blood flow in monkey spinal cord following an injury which does appear to reproduce the clinical picture of paraplegia and central necrosis. Fairholm and Turnbull 7 also noted preserved capillaries in traumatized rabbit spinal cord in the area immediately surrounding the central gray matter hemorrhagic necrosis. Interestingly, neuronal and axonal degeneration that followed trauma did not seem to be caused by ischemia initially, but recovery may have depended on the intact microvasculature. The illustrations in the article by Fried and Goodkin 9 show Micropaque in white matter vessels of traumatized monkey cord, but the authors do not discuss this observation. There appears to be adequate evidence, therefore, both anatomical and physiological, that the white matter vasculature is considerably more resilient to blunt trauma than is that of the gray matter. White matter blood vessels are usually associated with septal infoldings of pia which penetrate the white matter and gradually thin out as they approach the central gray matter. The larger vessels possess heavier mesenchymal-supporting investment. 26,27 Electron microscopic studies currently in progress suggest that the microvasculature of white matter possesses a more dense glial investment than vessels of the gray matter. These structural differences may account for greater degrees of resistance to trauma; however, they do not account for the gradual development of the central hemorrhagic necrosis and near total obliteration of gray matter blood flow. The highly simplistic and poorly documented concept of trauma, ischemia, anoxia, edema, compression, ischemia, and so forth as a self-propagating, vicious cycle is not supported by recent findings noted above. According to this theory, the pia is viewed as an inelastic membrane which confines the swollen injured spinal cord, thereby compromising the microcirculation. Since tissue tension studies have not to our knowledge been reported, this view of the role of the pia is purely speculative. That the microcirculation of the white matter is not embarrassed has been adequately demonstrated in our studies as well as those of Fairholm and Turnbull 7 and Dohrmann, et al. 4's While a cause-and-effect relationship between gray matter blood flow and central hemorrhagic necrosis is not defined with certainty by these results, our feeling is that the J. Neurosurg. / Volume 43 / August, 1975
central hemorrhage is produced by the direct effect of trauma on the central microvasculature. The traumatic disruption of the vessels in turn causes decreased flow through the tissue. Our investigations of the ultrastructural alterations of central gray matter microcirculation following trauma have revealed opening of tight junctions of the vascular endothelium, separation of endothelium from basement membranes with recanalization, numerous platelet thrombi, and gross disruption of vessel walls with plasma and cellular extravasation into extracellular spaces? 1 These findings are most certainly the result of direct trauma although they clearly indicate the source of subsequent circulatory obstruction and ischemia in the gray matter. Comparable changes have not been found in white matter. That primary alterations in neuronal structures are produced by trauma and may be progressive for some time following the injury seems quite probable and is suggested by Fairholm and Turnbull's observations of fragmentation and end-bulb formation of the injured axons 2 hours postinjury. The possibility of a toxic, metabolic process other than ischemia is an important consideration. Bingham, et al., ~,2 noted changes in lysosomal enzyme activity in brain tissue following injury. Our preliminary observations on spinal cord tissues, however, fail to show that these enzymes contribute to the cellular injury following acute cord trauma. In addition, the possibility that the accumulation of biogenic amines, specifically norepinephrine, might result in further vascular compromise, ischemia, and cell damage, as proposed by Osterholm and Mathews, x9,2~ has not been supported by more recent studies by Hedeman, et aL?* in dogs, Naftchi, et a l . ) 7 in cats, and Bingham, et al., a in monkeys; all of these investigators showed lowered values for norepinephrine in injured spinal cord tissue. The method employed here estimates for the first time the regional perfusion in both intact and traumatized spinal cord of subhuman primates. It should be noted that this method estimates only that aspect of perfusion which exchanges nutrients with the tissue and, therefore, is most likely to represent metabolic blood flow, it cannot estimate flow through arteriovenous shunts. The observation of preserved flow in white matter, then, regardless of any abnormal channels or ]69
W. G. Bingham, et al. shunts that may be established by trauma, estimates perfusion that has the potential capacity to exchange metabolically with the parenchyma surrounding the microcirculation. Whether freshly traumatized tissue does, in fact, engage in any significant exchange that has metabolic value to the tissue is a moot point. If one judges from cord specimens of chronic injuries, the severe cystic degeneration often seen makes one question the efficacy of this blood flow. Still, if there is some potentially reversible aspect to cord injury, it may be possible to accomplish this reversal by exploiting the preserved white matter blood flow, since the utility of chemotherapy relies on a drug's ability to reach the white matter.
Summary 1. Using antipyrine-14C, the authors determined spinal cord blood flow in monkeys by means of standard indicator fractionation techniques. 2. N o r m a l flow rates were obtained for several areas of the spinal cord as well as differential values for gray and white matter of representative segments. 3. Perfusion of injured spinal cord was determined by subjecting the cord to blunt trauma and obtaining flow rates at various periods up to 4 hours after trauma. 4. T r a u m a causes near obliteration of blood flow to the gray matter, while perfusion of the white matter persists. 5. The results do not support the concept of ischemia as an important factor in failure of white matter.
References 1. Bingham WG Jr, Paul SE, Sastry KSS: Effect of cold injury on six enzymes in rat brain. Arch Neurol 21:649-660, 1969 2. Bingham WG Jr, Paul SE, Sastry KSS: Effect of steroid on enzyme response to cold injury in rat brain. Neurology (Minneap) 21:111-121, 1971 3. Bingham WG, Ruffolo R, Friedman SJ: Catecholamine levels in the injured spinal cord of monkeys. J Neurosurg 42:174-178, 1975 4. Dohrmann G J, Wagner FC Jr, Bucy PC: The microvasculature in transitory traumatic paraplegia. An electron microscopic study in the monkey. J Neurosurg 35:263-271, 1971 5. Dohrmann G J, Wick KM, Bucy PC: Spinal 170
cord blood flow patterns in experimental traumatic paraplegia. J Neurosurg 38:52-58, 1973 6. Ducker TB, Kindt GW, Kempe LG: Pathological findings in acute experimental spinal cord trauma. J Neurosurg 35:700-708, 1971 7. Fairholm D J, Turnbull IM: Microangiographic study of experimental spinal cord injury. J Neurosurg 35:277-286, 1971 8. Flohr HW, Brock M, Christ R, et al: Arterial PCO~ and blood flow in different parts of the CNS of anesthetized cats, in Brock M, Fieschi C, Ingvar DH, et al (eds): Cerebral Blood Flow. Berlin, Springer-Verlag, 1969, pp 86-88 Fried LC, Goodkin R: Microangiographic 9. observations of the experimentally traumatized spinal cord. J Neurosurg 35:709-714, 1971 10. Goldman H, Sapirstein LA: Brain blood flow in the conscious and anesthetized rat. Am J Physiol 224:122-126, 1973 11. Goodman JH, Bingham WG Jr, Hunt WE: Edema formation and central hemorrhagic necrosis following impact injury to primate spinal cord. Surg Forum 25:440-442, 1974 12. Griffiths IR" Spinal cord blood flow in dogs. I. The "normal" flow. J Neural Neurosurg Psychiatry 36:34-41, 1973 13. Griffiths IR: Spinal cord blood flow in dogs: the effect of blood pressure. J Neural Neurosurg Psychiatry 36:914-920, 1973 14. Hedeman LS, Shellenberger MK, Gordon JH: Studies in experimental spinal cord trauma. Part I. Alterations in catecholamine levels. J Neurosurg 40:37-43, 1974 15. Jellinger K: Circulation disorders of the spinal cord. Aeta Neurochir (Wieo) 26:327-337, 1972 16. Landau WM, Freygang WH, Roland LP, et al: The local circulation of the living brain: values in unanesthetized and anesthetized cats. Traos Am Neural Assoc 80:125-129, 1955 17. Naftchi NE, Demeny M, DeCrescito V, et al: Biogenic amine concentrations in traumatized spinal cord of cats. Effect of drug therapy. J Neurosorg 40:52-57, 1974 18. Osterholm JL: The pathophysiological response to spinal cord injury. The current status of related research. J Neorosorg 40:3-33, 1974 19. Osterholm JL, Mathews G J: Altered norepinephrine metabolism following experimental spinal cord injury. I. Relationship to hemorrhagic necrosis and post-wounding neurological deficits. J Neurosarg 36:386-394, 1972 20. Osterholm JL, Mathews G J: Altered norepinephrine metabolism following experimental spinal cord injury. 2. Protection against traumatic spinal cord hemorrhagic necrosis by norepinephrine synthesis blockade J. Neurosurg.
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with alpha methyl tyrosine. J Neurosurg 36:395-401, 1972 Reivich M: Regulation of the cerebral circulation. Ciin Neurosurg 16:378-418, 1968 Reivich M, Hejle J, Sokoloff L, et al: Measurement of regional cerebral blood flow with antipyrine-14C in awake cats. J Appl Physiol 27:296-300, 1969 Sapirstein LA: Regional blood flow by fractional distribution of indicators. Am J Physiol 193:161, 1958 Smith AL, Pender JW, Alexander SC: Effects of PCO2 on spinal cord blood flow. Am J Physioi 216:1158-1163, 1969 Turnbull IM: Blood supply of the spinal cord, in Vinken P J, Bruyn GW (eds): Handbook of
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Clinical Neurology, Voi 12. Amsterdam, North Holland Publ, 1972 pp 478-491 26. Wagner FC Jr, Dobrmann G J, Bucy PC: Histopathology in transitory traumatic paraplegia in monkey. J Neurosurg 35: 272-276, 1971 27. Wolman L: The disturbance of circulation in traumatic paraplegia in acute and late stages: a pathological study. Paraplegia 2:213-226, 1965 Address reprint requests to: W. George Bingham, Jr., Ph.D., M.D., N-911 University Hospital, Ohio State University, 410 West 10th Avenue, Columbus, Ohio 43210.
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