Traumatic brain injury creates biphasic systemic hemodynamic and organ blood flow responses in rats

The Neuroprotective Effect of Ethanol Intoxication in Traumatic Brain Injury Is Associated with the Suppression of ErbB Signaling in Parvalbumin-Positive Interneurons

Ethanol intoxication (EI) is a frequent comorbidity of traumatic brain injury (TBI), but the impact of EI on TBI pathogenic cascades and prognosis is unclear. Although clinical evidence suggests that EI may have neuroprotective effects, experimental support is, to date, inconclusive. We aimed at elucidating the impact of EI on TBI-associated neurological deficits, signaling pathways, and pathogenic cascades in order to identify new modifiers of TBI pathophysiology. We have shown that ethanol administration (5 g/kg) before trauma enhances behavioral recovery in a weight-drop TBI model. Neuronal survival in the injured somatosensory cortex was also enhanced by EI. We have used phospho-receptor tyrosine kinase (RTK) arrays to screen the impact of ethanol on TBI-induced activation of RTK in somatosensory cortex, identifying ErbB2/ErbB3 among the RTKs activated by TBI and suppressed by ethanol. Phosphorylation of ErbB2/3/4 RTKs were upregulated in vGlut2⁺ excitatory synapses in the injured cortex, including excitatory synapses located on parvalbumin (PV)-positive interneurons. Administration of selective ErbB inhibitors was able to recapitulate, to a significant extent, the neuroprotective effects of ethanol both in sensorimotor performance and structural integrity. Further, suppression of PV interneurons in somatosensory cortex before TBI, by engineered receptors with orthogonal pharmacology, could mimic the beneficial effects of ErbB inhibitors. Thus, we have shown that EI interferes with TBI-induced pathogenic cascades at multiple levels, with one prominent pathway, involving ErbB-dependent modulation of PV interneurons.

Organ-specific responses during brain death: increased aerobic metabolism in the liver and anaerobic metabolism with decreased perfusion in the kidneys

Hepatic and renal energy status prior to transplantation correlates with graft survival. However, effects of brain death (BD) on organ-specific energy status are largely unknown. We studied metabolism, perfusion, oxygen consumption, and mitochondrial function in the liver and kidneys following BD. BD was induced in mechanically-ventilated rats, inflating an epidurally-placed Fogarty-catheter, with sham-operated rats as controls. A 9.4T-preclinical MRI system measured hourly oxygen availability (BOLD-related R2*) and perfusion (T1-weighted). After 4 hrs, tissue was collected, mitochondria isolated and assessed with high-resolution respirometry. Quantitative proteomics, qPCR, and biochemistry was performed on stored tissue/plasma. Following BD, the liver increased glycolytic gene expression (Pfk-1) with decreased glycogen stores, while the kidneys increased anaerobic- (Ldha) and decreased gluconeogenic-related gene expression (Pck-1). Hepatic oxygen consumption increased, while renal perfusion decreased. ATP levels dropped in both organs while mitochondrial respiration and complex I/ATP synthase activity were unaffected. In conclusion, the liver responds to increased metabolic demands during BD, enhancing aerobic metabolism with functional mitochondria. The kidneys shift towards anaerobic energy production while renal perfusion decreases. Our findings highlight the need for an organ-specific approach to assess and optimise graft quality prior to transplantation, to optimise hepatic metabolic conditions and improve renal perfusion while supporting cellular detoxification.

Treatment of combined traumatic brain injury and hemorrhagic shock with fractionated blood products versus fresh whole blood in a rat model

INTRODUCTION

Treatment of combined traumatic brain injury and hemorrhagic shock, poses a particular challenge due to the possible conflicting consequences. While restoring diminished volume is the treatment goal for hypovolemia, maintaining adequate cerebral perfusion pressure and avoidance of secondary damage remains a treatment goal for the injured brain. Various treatment modalities have been proposed, but the optimal resuscitation fluid and goals have not yet been clearly defined. A growing body of evidence suggests that in hypovolemic shock, resuscitation with fresh whole blood (FWB) may be superior to component therapy without platelets (which are likely to be unavailable in the pre-hospital setting). Nevertheless, the effects of this approach have not been studied in the combined injury. Previously, in a rat model of combined injury we have found that mild resuscitation to MABP of 80 mmHg with FWB is superior to fluid resuscitation or aggressive resuscitation with FWB. In this study, we investigate the physiological and neurological outcomes in a rat model of combined traumatic brain injury (TBI) and hypovolemic shock, submitted to treatment with varying amounts of FWB, compared to similar resuscitation goals with fractionated blood products-red blood cells (RBCs) and plasma in a 1:1 ratio regimen.

MATERIALS AND METHODS

40 male Lewis rats were divided into control and treatment groups. TBI was inflicted by a free-falling rod on the exposed cranium. Hypovolemia was induced by controlled hemorrhage of 30% blood volume. Treatment groups were treated either with fresh whole blood or with RBC + plasma in a 1:1 ratio, achieving a resuscitation goal of a mean arterial blood pressure (MAP) of 80 mmHg at 15 min. MAP was assessed at 60 min, and neurological outcomes and mortality in the subsequent 24 h.

RESULTS

At 60 min, hemodynamic parameters were improved compared to controls, but not significantly different between treatment groups. Survival rates at 48 h were 100% for both of the mildly resuscitated groups (MABP 80 mmHg) with FWB and RBC + plasma. The best neurological outcomes were found in the group mildly resuscitated with FWB and were better when compared to resuscitation with RBC + plasma to the same MABP goal (FWB: Neurological Severity Score (NSS) 6 ± 2, RBC + plasma: NSS 10 ± 2, p = 0.02).

CONCLUSIONS

In this study, we find that mild resuscitation with goals of restoring MAP to 80 mmHg (which is lower than baseline) with FWB, provided better hemodynamic stability and survival. However, the best neurological outcomes were found in the group resuscitated with FWB. Thus, we suggest that resuscitation with FWB is a feasible modality in the combined TBI + hypovolemic shock scenario, and may result in improved outcomes compared to platelet-free component blood products.

Neuroprotective effect of acute ethanol intoxication in TBI is associated to the hierarchical modulation of early transcriptional responses

Ethanol intoxication is a risk factor for traumatic brain injury (TBI) but clinical evidence suggests that it may actually improve the prognosis of intoxicated TBI patients. We have employed a closed, weight-drop TBI model of different severity (2cm or 3cm falling height), preceded (-30min) or followed (+20min) by ethanol administration (5g/Kg). This protocol allows us to study the interaction of binge ethanol intoxication in TBI, monitoring behavioral changes, histological responses and the transcriptional regulation of a series of activity-regulated genes (immediate early genes, IEGs). We demonstrate that ethanol pretreatment before moderate TBI (2cm) significantly reduces neurological impairment and accelerates recovery. In addition, better preservation of neuronal numbers and cFos+cells was observed 7days after TBI. At transcriptional level, ethanol reduced the upregulation of a subset of IEGs encoding for transcription factors such as Atf3, c-Fos, FosB, Egr1, Egr3 and Npas4 but did not affect the upregulation of others (e.g. Gadd45b and Gadd45c). While a subset of IEGs encoding for effector proteins (such as Bdnf, InhbA and Dusp5) were downregulated by ethanol, others (such as Il-6) were unaffected. Notably, the majority of genes were sensitive to ethanol only when administered before TBI and not afterwards (the exceptions being c-Fos, Egr1 and Dusp5). Furthermore, while severe TBI (3cm) induced a qualitatively similar (but quantitatively larger) transcriptional response to moderate TBI, it was no longer sensitive to ethanol pretreatment. Thus, we have shown that a subset of the TBI-induced transcriptional responses were sensitive to ethanol intoxication at the instance of trauma (ultimately resulting in beneficial outcomes) and that the effect of ethanol was restricted to a certain time window (pre TBI treatment) and to TBI severity (moderate). This information could be critical for the translational value of ethanol in TBI and for the design of clinical studies aimed at disentangling the role of ethanol intoxication in TBI.

When friend turns foe: central and peripheral neuroinflammation in central nervous system injury

Injury to the central nervous system (CNS) is common, and though it has been well studied, many aspects of traumatic brain injury (TBI) and stroke are poorly understood. TBI and stroke are two pathologic events that can cause severe, immediate impact to the neurostructure and function of the CNS, which has been recognized recently to be exacerbated by the body’s own immune response. Although the brain damage induced by the initial trauma is most likely unsalvageable, the secondary immunologic deterioration of neural tissue gives ample opportunity for therapeutic strategists seeking to mitigate TBI’s secondary detrimental effects. The purpose of this paper is to highlight the cell death mechanisms associated with CNS injury with special emphasis on inflammation. The authors discuss sources of inflammation, and introduce the role of the spleen in the systemic response to inflammation after CNS injury.

Traumatic brain injury disrupts cerebrovascular tone through endothelial inducible nitric oxide synthase expression and nitric oxide gain of function

BACKGROUND

Traumatic brain injury (TBI) has been reported to increase the concentration of nitric oxide (NO) in the brain and can lead to loss of cerebrovascular tone; however, the sources, amounts, and consequences of excess NO on the cerebral vasculature are unknown. Our objective was to elucidate the mechanism of decreased cerebral artery tone after TBI.

METHODS AND RESULTS

Cerebral arteries were isolated from rats 24 hours after moderate fluid‐percussion TBI. Pressure‐induced increases in vasoconstriction (myogenic tone) and smooth muscle Ca2+ were severely blunted in cerebral arteries after TBI. However, myogenic tone and smooth muscle Ca2+ were restored by inhibition of NO synthesis or endothelium removal, suggesting that TBI increased endothelial NO levels. Live native cell NO, indexed by 4,5‐diaminofluorescein (DAF‐2 DA) fluorescence, was increased in endothelium and smooth muscle of cerebral arteries after TBI. Clamped concentrations of 20 to 30 nmol/L NO were required to simulate the loss of myogenic tone and increased (DAF‐2T) fluorescence observed following TBI. In comparison, basal NO in control arteries was estimated as 0.4 nmol/L. Consistent with TBI causing enhanced NO‐mediated vasodilation, inhibitors of guanylyl cyclase, protein kinase G, and large‐conductance Ca2+‐activated potassium (BK) channel restored function of arteries from animals with TBI. Expression of the inducible isoform of NO synthase was upregulated in cerebral arteries isolated from animals with TBI, and the inducible isoform of NO synthase inhibitor 1400W restored myogenic responses following TBI.

CONCLUSIONS

The mechanism of profound cerebral artery vasodilation after TBI is a gain of function in vascular NO production by 60‐fold over controls, resulting from upregulation of the inducible isoform of NO synthase in the endothelium.

Superimposed traumatic brain injury modulates vasomotor responses in third-order vessels after hemorrhagic shock

BACKGROUND

Traumatic brain injury (TBI) and hemorrhagic shock (HS) are the leading causes of death in trauma. Recent studies suggest that TBI may influence physiological responses to acute blood loss. This study was designed to assess to what extent superimposed TBI may modulate physiologic vasomotor responses in third-order blood vessels in the context of HS.

METHODS

We have combined two established experimental models of pressure-controlled hemorrhagic shock (HS; MAP 50 mmHg/60 min) and TBI (lateral fluid percussion (LFP)) to assess vasomotor responses and microcirculatory changes in third-order vessels by intravital microscopy in a spinotrapezius muscle preparation. 23 male Sprague-Dawley rats (260-320 g) were randomly assigned to experimental groups: i) Sham, ii) HS, iii) TBI + HS, subjected to impact or sham operation, and assessed.

RESULTS

HS led to a significant decrease in arteriolar diameters by 20% to baseline (p < 0.01). In TBI + HS this vasoconstriction was less pronounced (5%, non-significant). At completed and at 60 minutes of resuscitation arteriolar diameters had recovered to pre-injury baseline values. Assessment of venular diameters revealed similar results. Arteriolar and venular RBC velocity and blood flow decreased sharply to < 20% of baseline in HS and TBI + HS (p < 0.01). Immediately after and at 60 minutes of resuscitation, an overshoot in arterial RBC velocity (140% of baseline) and blood flow (134.2%) was observed in TBI + HS.

CONCLUSION

Superimposed TBI modulated arteriolar and venular responses to HS in third-order vessels in a spinotrapezius muscle preparation. Further research is necessary to precisely define the role of TBI on the microcirculation in tissues vulnerable to HS.

Brain death induces renal expression of heme oxygenase-1 and heat shock protein 70

Background

Kidneys derived from brain dead donors have lower graft survival and higher graft-function loss compared to their living donor counterpart. Heat Shock Proteins (HSP) are a large family of stress proteins involved in maintaining cell homeostasis. We studied the role of stress-inducible genes Heme Oxygenase-1 (HO-1), HSP27, HSP40, and HSP70 in the kidney following a 4 hour period of brain death.

Methods

Brain death was induced in rats (n=6) by inflating a balloon catheter in the epidural space. Kidneys were analysed for HSPs using RT-PCR, Western blotting, and immunohistochemistry.

Results

RT-PCR data showed a significant increase in gene expression for HO-1 and HSP70 in kidneys of brain dead rats. Western blotting revealed a massive increase in HO-1 protein in brain dead rat kidneys. Immunohistochemistry confirmed these findings, showing extensive HO-1 protein expression in the renal cortical tubules of brain dead rats. HSP70 protein was predominantly increased in renal distal tubules of brain dead rats treated for hypotension.

Conclusion

Renal stress caused by brain death induces expression of the cytoprotective genes HO-1 and HSP70, but not of HSP27 and HSP40. The upregulation of these cytoprotective genes indicate that renal damage occurs during brain death, and could be part of a protective or recuperative mechanism induced by brain death-associated stress.

Histopathological features of the brain, liver, kidney and spleen following an innovative polytrauma model of the mouse

OBJECT

Among the various introduced experimental traumatic brain injury models, there is a clear paucity of proper experimental polytrauma models. To overcome this experimental gap we introduced such a polytrauma model in the mouse including traumatic brain injury. Here, we report on the histopathological features of the brain, lung, kidney, spleen and liver.

MATERIALS AND METHODS

20 male C57BL mice with a mean weight of 23 g were anesthetized with ketamine and xylazine. The anaesthetized animals were subjected to a controlled cortical impact (CCI) over the left parieto-temporal cortex using rounded-tip impounder for application of a standardized brain injury. Following fracture of the right femur using a guillotine, a volume-controlled hemorrhagic shock was induced. The control groups included animals with CCI only (n=20) and animals with femur fracture plus hemorrhagic shock without CCI (n=20). Subjects were sacrified at 96 h following trauma. Brain, lung, kidney, spleen and liver of the animals underwent histopathological examinations.

RESULTS

The mortality rate at 96 h was 25% in the polytrauma group versus 10% in the control groups. Within the histopathological investigations, polytraumatized animals differ from those with a single trauma (traumatic brain injury or femur fracture with hemorrhagic shock) with various severity.

CONCLUSION

The findings of this study show that such a polytrauma model can be standardized resulting in a reproducible damage. This model fulfills the requirements of a standardized animal model. It allows adequate analogies and inferences to the clinical situation of a polytrauma in humans.

Modified calcium accumulation after controlled cortical impact under cyclosporin A treatment: a 45Ca autoradiographic study

OBJECTIVE

As a neuroprotective drug, cyclosporin A (CsA) has been subject of multiple experimental works in traumatic brain injury (TBI) research. It is well known that CsA inhibits calcium (Ca2+) induced mitochondrial permeability transition (mPT). The aim of this study was to investigate the influence of CsA on the alteration of Ca2+ homeostasis after experimental brain injury.

METHODS

Sprague-Dawley male rats (n = 36) with a mean weight of 330 g (280-350 g) were general anesthetized with isofluran through gas mask. The anesthetized animals (n = 24) were subjected to a controlled cortical impact (CCI) over the left parietotemporal cortex using round-tip impounder with a 5 mm diameter at a velocity of approximately 3.7 m/s and a penetration depth of 2 mm. The sham group (n = 12) underwent anesthesia and craniotomy without CCI. In the CCI groups, CsA (n = 12) or vehicle (n = 12) was administered 15 minutes post-injury with a subsequent i.p. injection after 24 hours. Thirty-three hours after injury or sham craniotomy, 45calcium (45Ca) suspended in physiologic saline solution was injected in the left femoral vein. Five hours after isotope administration, animals were killed and the brain was quickly removed and placed in powdered dry ice. Coronal plane sections (20 microm thick) taken every 400 microm from the frontal cortex through the occipital cortex, were exposed to cyclotron films for 14 days at -18 degrees C. Relative optical density was utilized to provide a relative measure of 45Ca accumulation within seven different structures.

RESULTS

The difference of 45Ca accumulation (measured by relative optical density) in the CsA group was greater by 30-70% in the following structures compared to vehicle treated traumatized animals: temporal cortex, CA1, anteromedial and posteromedial thalamus (p < 0.05).

CONCLUSION

Post-traumatic 45Ca accumulation is modified under CsA. The crucial neuroprotective effect of CsA might be unrelated to a reduction of post-traumatic Ca2+ accumulation, especially with regard to the importance of Ca2+ as an intracellular messenger governing a large number of cellular functions.

Injury severity determines Purkinje cell loss and microglial activation in the cerebellum after cortical contusion injury

Clinical evidence suggests that the cerebellum is damaged after traumatic brain injury (TBI) and experimental studies have validated these observations. We have previously shown cerebellar vulnerability, as demonstrated by Purkinje cell loss and microglial activation, after fluid percussion brain injury. In this study, we examine the effect of graded controlled cortical impact (CCI) injury on the cerebellum in the context of physiologic and anatomical parameters that have been shown by others to be sensitive to injury severity. Adult male rats received mild, moderate, or severe CCI and were euthanized 7 days later. We first validated the severity of the initial injury using physiologic criteria, including apnea and blood pressure, during the immediate postinjury period. Increasing injury severity was associated with an increased incidence of apnea and higher mortality. Severe injury also induced transient hypertension followed by hypotension, while lower grade injuries produced an immediate and sustained hypotension. We next evaluated the pattern of subcortical neuronal loss in response to graded injuries. There was significant neuronal loss in the ipsilateral cortex, hippocampal CA2/CA3, and laterodorsal thalamus that was injury severity-dependent and that paralleled microglial activation. Similarly, there was a distinctive pattern of Purkinje cell loss and microglial activation in the cerebellar vermis that varied with injury severity. Together, these findings emphasize the vulnerability of the cerebellum to TBI. That a selective pattern of Purkinje cell loss occurs regardless of the type of injury suggests a generalized response that is a likely determinant of recovery and a target for therapeutic intervention.

Nitric oxide in traumatic brain injury

Nitric oxide (NO) is a gaseous chemical messenger which has functions in the brain in a variety of broad physiological processes, including control of cerebral blood flow, interneuronal communications, synaptic plasticity, memory formation, receptor functions, intracellular signal transmission, and release of neurotransmitters. As might be expected from the numerous and complex roles that NO normally has, it can have both beneficial and detrimental effects in disease states, including traumatic brain injury. There are two periods of time after injury when NO accumulates in the brain, immediately after injury and then again several hours-days later. The initial immediate peak in NO after injury is probably due to the activity of endothelial NOS and neuronal NOS. Pre-injury treatment with 7-nitroindazole, which probably inhibits this immediate increase in NO by neuronal NOS, is effective in improving neurological outcome in some models of traumatic brain injury (TBI). After the initial peak in NO, there can be a period of relative deficiency in NO. This period of low NO levels is associated with a low cerebral blood flow (CBF). Administration of L-arginine at this early time improves CBF, and outcome in many models. The late peak in NO after traumatic injury is probably due primarily to the activity of inducible NOS. Inhibition of inducible NOS has neuroprotective effects in most models.

Local neutrophil influx following lateral fluid-percussion brain injury in rats is associated with accumulation of complement activation fragments of the third component (C3) of the complement system

Traumatic brain injury can lead to locally destructive secondary events mediated by several inflammatory components. Following lateral fluid-percussion (FP) brain injury in rats, we examined cortical and hippocampal sections for neutrophil infiltration and accumulation of complement component C3. Neutrophil influx into the brain after injury was detected by an improved myeloperoxidase (MPO) microassay and manual cell counting, while C3 accumulation was detected using immunocytochemistry. MPO levels were elevated in the injured cortical tissue, whereas C3 immunoreactivity was increased in both injured cortical and ipsilateral hippocampal sections. These results show that the FP model of head injury leads to an intense local inflammatory reaction and subsequent tissue destruction.

Brain nitric oxide changes after controlled cortical impact injury in rats

Nitric oxide (NO) and the NO end products, nitrate and nitrite, were measured at the impact site after a 5-m/s, 3-mm deformation controlled cortical impact injury in rats. Immediately after the impact injury and the NO and microdialysis probes could be replaced, there was an increase from baseline in NO concentration of 83 +/- 16 (SE) nM, compared with 0.5 +/- 4 nM in the sham injured animals (P < 0.001). This marked increase in NO occurred at the time of the initial rise in blood pressure (BP) and intracranial pressure (ICP) in response to the injury. After the initial increase in BP and ICP, the BP decreased and stabilized at a value which was approximately 20 mmHg below the preinjury values, and ICP plateaued at an average value of 20 mmHg, compared with 8 mmHg in the sham-injured animals. This provided an average cerebral perfusion pressure of 40-50 mmHg, compared with 65-75 mmHg for the sham-injured animals. These values were relatively constant for the remainder of the 3-h monitoring period. The NO values also stabilized during this time period. By 1 h after the impact injury the NO concentration measured directly using the NO electrode had decreased from baseline values by an average value of 25 +/- 6 nM. NO concentration remained significantly lower than baseline values throughout the remainder of the 3-h monitoring period. The concentration of nitrate/nitrite in the dialysate fluid also decreased by an average value of 341 +/- 283 nM 20-40 min after the injury. Dialysate nitrite/nitrate concentrations remained less than the preinjury baseline values throughout the remainder of the 3-h monitoring period. Preinjury treatment with L-nitro-arginine methyl ester (L-NAME) blunted the injury-induced increase in NO and resulted in more severe immediate intracranial hypertension and more severe systemic hypotension at one hour after injury. Mortality was also 67% with L-NAME pretreatment, compared with 1% in untreated animals.

The consequences of traumatic brain injury on cerebral blood flow and autoregulation: a review

In this decade, the brain argueably stands as one of the most exciting and challenging organs to study. Exciting in as far as that it remains an area of research vastly unknown and challenging due to the very nature of its anatomical design: the skull provides a formidable barrier and direct observations of intraparenchymal function in vivo are impractical. Moreover, traumatic brain injury (TBI) brings with it added complexities and nuances. The development of irreversible damage following TBI involves a plethora of biochemical events, including impairment of the cerebral vasculature, which render the brain at risk to secondary insults such as ischemia and intracranial hypertension. The present review will focus on alterations in the cerebrovasculature following TBI, and more specifically on changes in cerebral blood flow (CBF), mediators of CBF including local chemical mediators such as K+, pH and adenosine, endothelial mediators such as nitric oxide and neurogenic mediators such as catecholamines, as well as pressure autoregulation. It is emphasized that further research into these mechanisms may help attenuate the prevalence of secondary insults and therefore improve outcome following TBI.

Changes in organ perfusion after brain death in the rat and its relation to circulating catecholamines

Brain death can have an impact on donor organ function. This is often attributed to an altered hormonal, mainly thyroidal, status after brain death. A second possible explanation is that during the brain death process, blood flow is redistributed, causing ischemic damage in underperfused organs or regions. We investigated blood flow redistribution with colored microspheres in the rat early and late after brain death, induced by inflation of an intracranial balloon, and correlated this with the global hemodynamic situation and plasma catecholamine concentrations. Brain death was proven by the demonstration of lasting absence of brain perfusion in all animals. Myocardial blood flow closely followed the myocardial oxygen need as estimated by the rate-pressure product. The abdominal organs showed intense vasoconstriction early after brain death, which led to significantly decreased perfusion of these organs despite the highly increased perfusion pressure, followed by significant vasodilation. Total plasma catecholamine concentration was 57 times higher at 30 sec after brain death as compared with basal levels. Plasma noradrenaline concentration fell significantly below basal levels late after brain death. We conclude that brain death importantly alters regional perfusion, with possible implications for donor organ function. These changes are probably due to the tremendous alterations in the activity of the sympathetic nervous system.

Lateral cortical impact injury in rats: cerebrovascular effects of varying depth of cortical deformation and impact velocity

Intracranial pressure (ICP), blood pressure (BP), cerebral perfusion pressure (CPP), and cortical perfusion (LDF) of the contralateral parietal cortex were measured after cortical impact injury in 36 rats. Changes in these physiologic parameters were compared using analysis of variance to a group of 11 rats who received a sham impact. In one series of experiments, the velocity and duration of the impact injury were kept constant, and the severity of the injury was determined by varying the depth of cortical deformation from 2 to 3 mm. The peak pressure inside the skull was directly related to the depth of cortical deformation, and was 93 +/- 16, 182 +/- 18, and 268 +/- 57 mm Hg with the 2, 2.5, and 3 mm deformation, respectively, when the impact velocity was 5 m/sec. With the 2 mm depth injury, there was a transient decrease in BP (p < 0.05) and a 12% decrease in LDF after the impact. With the 2.5 mm depth injury, a small transient increase in ICP and decrease in BP and a 30% decrease in LDF occurred (p < 0.05). ICP then gradually increased throughout the 8 h experiment, becoming significantly greater than the sham-injured animals by 5 h after the impact. LDF gradually returned toward normal throughout the experiment. With the 3 mm depth injury, a marked transient increase in ICP (p < 0.05) and BP (p < 0.05) occurred immediately after the impact. The increase in BP lasted < 5 min, and subsequently the BP decreased to approximately 50 mm Hg for the rest of the experiment. The initial marked increase in ICP lasted 15 min and then remained 5-10 mm Hg higher (p < 0.05) than in the sham-injured animals for the rest of the experiment. LDF decreased by an average of 50% (p < 0.05) immediately after the impact and remained lower than that of the sham-injured animals for the rest of the experiment. In another series of experiments, the depth of cortical deformation was kept constant at 2.5 mm, and the severity of the injury was determined by varying the velocity from 1 to 5 m/sec. The peak ICP was significantly related to the impact velocity, averaging 45 +/- 12, 66 +/- 9, and 182 +/- 18 mm Hg with the 1, 3, and 5 m/sec impact injuries, respectively. The 1 m/sec impact had no effect on ICP and only a transient decrease in BP.(ABSTRACT TRUNCATED AT 400 WORDS)

Immediate hypertensive response to fluid percussion brain injury may be related to intracerebral hemorrhage and hypothalamic damage

Fluid percussion brain injury is associated with an immediate rise in mean arterial pressure (MAP). However, the cerebral morphologic basis for this response is still not clear. Thirty-four anesthetized rats were injured using a lateral craniotomy preparation. In 19 rats, impact level was set at 1.73 +/- 0.04 atm, and impact duration was kept at 25 msec to examine the relationship between postinjury hypertensive response and cerebral lesions. MAP was monitored for 1 hour after impact. Fluid percussion produced an increase in MAP from 99 +/- 3 to 134 +/- 4 mm Hg (p less than 0.001), with an increment range of -2 to 87 mm Hg (36 +/- 5 mm Hg) or 0 to 96% increase. The MAP peak occurred at 15 +/- 2 seconds and then rapidly returned to the preimpact level. Histopathological findings, principally hemorrhage, were graded and ranked from 1 to 19 according to relative severity and hypothalamic involvement. There was a significant correlation between MAP rise and the injury ranking (r = 0.52, p = 0.02). No appreciable damage was observed in the brainstem caudal to the diencephalon. Fifteen rats were subjected to higher injury levels. The overall impact magnitude ranged from 1.3 to 3.5 atm. A linear relationship was found between impact magnitude (X, atm) and increment in MAP (Y, mm Hg) (Y = 28.1*X - 14.0, r = 0.62, p less than 0.001). Our study indicates that the immediate postinjury hypertensive response is closely correlated with the impact magnitude and may be related to intracerebral hemorrhage and hypothalamic damage but not necessarily to caudal brainstem damage.