Hypothermic retrograde jugular perfusion reduces brain damage in rats with heatstroke

Hypothermic neuroprotection against acute ischemic stroke: The 2019 update

Acute ischemic stroke is a leading cause of death and disability worldwide. Therapeutic hypothermia has long been considered as one of the most robust neuroprotective strategies. Although the neuroprotective effects of hypothermia have only been confirmed in patients with global cerebral ischemia after cardiac arrest and in neonatal hypoxic ischemic encephalopathy, establishing standardized protocols and strictly controlling the key parameters may extend its application in other brain injuries, such as acute ischemic stroke. In this review, we discuss the potential neuroprotective effects of hypothermia, its drawbacks evidenced in previous studies, and its potential clinical application for acute ischemic stroke especially in the era of reperfusion. Based on the different conditions between bench and bedside settings, we demonstrate the importance of vascular recanalization for neuroprotection of hypothermia by analyzing numerous literatures regarding hypothermia in focal cerebral ischemia. Then, we make a thorough analysis of key parameters of hypothermia and introduce novel hypothermic therapies. We advocate in favor of the process of clinical translation of intra-arterial selective cooling infusion in the era of reperfusion and provide insights into the prospects of hypothermia in acute ischemic stroke.

Selective cerebral hypothermia induced via hypothermic retrograde jugular vein saline flush in a porcine model

OBJECTIVES

Multiple methods of selective brain cooling have been used to prevent cerebral ischemia secondary to trauma and pathological or iatrogenic cerebral blood flow restriction. In this study, we tested the efficacy of hypothermic retrograde jugular vein flush (HRJVF) in eliciting selective brain hypothermia in a porcine model.

METHODS

Twelve swine were divided into two groups: retrograde jugular vein infusion (RJVI) with cold saline (4°C RJVI, n  =  6) and with room temperature saline (24°C RJVI, n  =  6). For 90 minutes, the following parameters were measured: brain parenchymal temperature, rectal temperature, intracranial pressure (ICP), mean arterial pressure, and heart rate (HR).

RESULTS

Swine receiving 4°C RJVI experienced a drop in mean brain parenchymal temperature of 1·1 ± 0·1°C, compared to 0·1 ± 0·1°C in swine receiving 24°C RJVI. At 90 minutes, mean brain parenchymal temperature in the 4°C RJVI treatment group was 35·5 ± 0·2°C, as compared to 37·1 ± 0·2°C in the 24°C RJVI treatment group (P < 0·001). In the 4°C RJVI group, the brain-systemic temperature gradient peaked 10 minutes after initiation of cooling and remained significantly different when comparing the two experimental groups (P < 0·001) throughout the duration of the 90 minutes experiment. Of note, ICP, mean arterial pressure, and HR remained constant without any significant changes or differences between treatment groups.

DISCUSSION

These results suggest that HRJVF is an effective method for selective brain hypothermia in a large animal model. Clinical application may prove effective in delaying neural ischemia.

Ischemic and oxidative damage to the hypothalamus may be responsible for heat stroke

The hypothalamus may be involved in regulating homeostasis, motivation, and emotional behavior by controlling autonomic and endocrine activity. The hypothalamus communicates input from the thalamus to the pituitary gland, reticular activating substance, limbic system, and neocortex. This allows the output of pituitary hormones to respond to changes in autonomic nervous system activity. Environmental heat stress increases cutaneous blood flow and metabolism, and progressively decreases splanchnic blood flow. Severe heat exposure also decreases mean arterial pressure (MAP), increases intracranial pressure (ICP), and decreases cerebral perfusion pressure (CPP = MAP - ICP), all of which lead to cerebral ischemia and hypoxia. Compared with normothermic controls, rodents with heatstroke have higher hypothalamic values of cellular ischemia (e.g., glutamate and lactate-to-pyruvate ratio) and damage (e.g., glycerol) markers, pro-oxidant enzymes (e.g., lipid peroxidation and glutathione oxidation), proinflammatory cytokines (e.g., interleukin-1β and tumor necrosis factor-α), inducible nitric oxide synthase-dependent nitric oxide, and an indicator for the accumulation of polymorphonuclear leukocytes (e.g., myeloperoxidase activity), as well as neuronal damage (e.g., apoptosis, necrosis, and autophagy) after heatstroke. Hypothalamic values of antioxidant defenses (e.g., glutathione peroxidase and glutathione reductase), however, are lower. The ischemic, hypoxic, and oxidative damage to the hypothalamus during heatstroke may cause multiple organ dysfunction or failure through hypothalamic-pituitary-adrenal axis mechanisms. Finding the link between the signaling and heatstroke-induced hypothalamic oxidative and ischemic damage might allow us to clinically attenuate heatstroke. In particular, free radical scavengers, heat shock protein-70 inducers, hypervolemic hemodilution, inducible nitric oxide synthase inhibitors, progenitor stem cells, flutamide, estrogen, interleukin-1 receptor antagonists, glucocorticoid, activated protein C, and baicalin mitigate preclinical heatstroke levels.

Multiple Organ Failure Following Near Fatal Exertional Heat Stroke

We describe the clinical features of a patient with near-fatal heat stroke who was admitted to our intensive care unit. A 14-year-old girl became convulsive and hyperthermic when participating in a strenuous hike under direct sunlight in a hilly area in Venezuela on a very hot and humid day. During the following days, she developed multiple organ failure, including neurological impairment, acute renal failure, disseminated intravascular coagulation, and extensive hepatic and muscle damage. Treatment consisted of ventilatory support, hemodialysis, corticosteroids, and enteral nutrition. This case of multiple organ failure following near-fatal heat stroke illustrates that although there are no specific techniques and measures for the treatment of this condition, intensive care management and conservative strategies can result in patient survival and complete recovery.

EFFECT OF BRAIN COOLING ON BRAIN ISCHEMIA AND DAMAGE MARKERS AFTER FLUID PERCUSSION BRAIN INJURY IN RATS

Although systemic cooling had recently been reported as effective in improving the neurological outcome after traumatic brain injury, several problems are associated with whole-body cooling. The present study was conducted to test the effectiveness of brain cooling without interference with the core temperature in rats after fluid percussion traumatic brain injury (TBI). Brain dialysates ischemia (e.g., glutamate and lactate-to-pyruvate ratio) and injury (e.g., glycerol) markers before and after TBI were measured in rats with mild brain cooling (33 degrees C) and in the sham control group. Brain cooling was accomplished by infusion of 5 mL cold saline via the external jugular vein under general anesthesia. The weight loss was determined by the difference between the first and third day of body weight after TBI. The maximum grip angle in an inclined plane was measured to determine motor performance, whereas the percentage of maximal possible effect was used to measure blockade of proprioception. The triphenyltetrazolium chloride staining procedures were used for cerebral infarction assay. As compared with those of the sham-operated controls, the animals with TBI had higher values of extracellular levels of glutamate, lactate-to-pyruvate ratio, and glycerol in brain and intracranial pressure, but lower values of cerebral perfusion pressure. Brain cooling adopted immediately after TBI significantly attenuated the TBI-induced increased cerebral ischemia and injury markers, intracranial hypertension, and cerebral hypoperfusion. In addition, the TBI-induced cerebral infarction, motor and proprioception deficits, and body weight loss evaluated 3 days after TBI were significantly attenuated by brain cooling. We successfully demonstrate that brain cooling causes attenuation of TBI in rats by reducing cerebral ischemia and injury resulting from intracranial hypertension and cerebral hypoperfusion. Because jugular venipuncture is an easy procedure frequently used in the emergency department, for preservation of brain function, jugular infusion of cold saline may be useful in resuscitation for trauma patients.

Human umbilical cord blood-derived CD34+ cells cause attenuation of multiorgan dysfunction during experimental heatstroke

Multiorgan dysfunction ensuing from severe heatstroke includes hypotension, hepatic and renal failure, hypercoagulable state, activated inflammation, and cerebral ischemia and injury. We attempted to assess whether human umbilical cord blood-derived CD34+ cell therapy improves survival during experimental heatstroke by attenuating multiorgan dysfunction. Anesthetized rats, immediately after the onset of heatstroke, were divided into 2 major groups and given CD34- or CD34+ cells (1 x 10(5)-5 x 10(5)/mL/kg body weight) i.v. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats were exposed to room temperature (26 degrees C) and used as normothermic controls. Hypotension, hepatic and renal failure (evidenced by increased serum urea nitrogen, creatinine, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase levels in plasma), hypercoagulable state (evidenced by increased prothrombin time, activated partial thromboplastin time, and D-dimer, and decreased platelet count and protein C in plasma), activated inflammation (evidence by increased TNF-alpha levels in serum), and cerebral dysfunction (evidenced by intracranial hypertension, cerebral hypoperfusion and hypoxia, and cerebral ischemia and injury) were monitored. When the CD34- cell-treated or untreated rats underwent heat stress, their survival time values were found to be 19 to 23 min. Resuscitation with CD34+ cells significantly improved survival time (duration, 63-291 min). As compared with normothermic controls, all CD34- cell-treated heatstroke animals displayed hypotension, hepatic and renal failure, hypercoagulable state, activated inflammation, and cerebral ischemia and injury. However, CD34+ cell therapy significantly caused attenuation of all the above-mentioned heatstroke reactions. In addition, the levels of IL-10 in plasma and glial cell line-derived neurotrophic factors in brain were all significantly increased after CD34+ cell therapy during heatstroke. Our data indicate that CD34+ cell therapy may resuscitate persons who had a heatstroke by reducing multiorgan dysfunction or failure.

Human umbilical cord blood cells or estrogen may be beneficial in treating heatstroke

This current review summarized animal models of heatstroke experimentation that promote our current knowledge of therapeutic effects on cerebrovascular dysfunction, coagulopathy, and/or systemic inflammation with human umbilical cord blood cells (HUCBCs) or estrogen in the setting of heatstroke. Accumulating evidences have demonstrated that HUCBCs provide a promising new therapeutic method against neurodegenerative diseases, such as stroke, traumatic brain injury, and spinal cord injury as well as blood disease. More recently, we have also demonstrated that post- or pretreatment by HUCBCs may resuscitate heatstroke rats with by reducing circulatory shock, and cerebral nitric oxide overload and ischemic injury. Moreover, CD34+ cells sorted from HUCBCs may improve survival by attenuating inflammatory, coagulopathy, and multiorgan dysfunction during experimental heatstroke. Many researchers indicated pro- (e.g. tumor necrosis factor-alpha [TNF-alpha]) and anti-inflammatory (e.g. interleukin-10 [IL-10]) cytokines in the peripheral blood stream correlate with severity of circulatory shock, cerebral ischemia and hypoxia, and neuronal damage occurring in heatstroke. It has been shown that intravenous administration of CD34+ cells can secrete therapeutic molecules, such as neurotrophic factors, and attenuate systemic inflammatory reactions by decreasing serum TNF-alpha but increasing IL-10 during heatstroke. Another line of evidence has suggested that estrogen influences the severity of injury associated with cerebrovascular shock. Recently, we also successfully demonstrated estrogen resuscitated heatstroke rats by ameliorating systemic inflammation. Conclusively, HUCBCs or estrogen may be employed as a beneficial therapeutic strategy in prevention and repair of cerebrovascular dysfunction, coagulopathy, and/or systemic inflammation during heatstroke.

Resuscitation from experimental heatstroke by brain cooling therapy

We have used hypothermic retrograde jugular venous flush to cool the brain previously and to provide better resuscitation than peripheral cold saline infusion during heatstroke in the rat. The current study was performed to assess the effects of brain cooling further on production of reactive nitrogen species, reactive oxygen species, tumor necrosis factor-alpha, and interleukin-10 in both serum and brain during heatstroke. Rats, under general anaesthesia, were randomized into the following groups and given: (a) 36 degrees C or (b) 4 degrees C saline infusion in the external jugular vein immediately after onset of heatstroke. They were exposed to an ambient temperature of 43 degrees C for exactly 70 min to induce heatstroke. When the 36 degrees C saline-treated rats underwent heat stress, their survival time values were found to be 21-25 min. Immediately after the onset of heatstroke, resuscitation with an i.v. dose of 4 degrees C saline greatly improved survival (226-268 min). Compared with the normothermic controls, the 36 degrees C saline-treated heatstroke rats displayed higher levels of brain temperature, intracranial pressure, serum and hypothalamic nitric oxide metabolite, tumor necrosis factor-alpha and dihydroxybenzoic acid as well as hypothalamic inducible nitric oxide synthase immunoreactivity. In contrast, the values of mean arterial pressure, cerebral perfusion pressure, and hypothalamic levels of local blood flow, and partial pressure of oxygen were all significantly lower during heatstroke. The cerebrovascular dysfunction, the increased levels of nitric oxide metabolites, tumor necrosis factor-alpha, and dihydroxybenzoic acid in both the serum and the hypothalamus, and the increased levels of hypothalamic inducible nitric oxide synthase immunoreactivity occurred during heatstroke were significantly suppressed by brain cooling. Although the serum and hypothalamic interleukin-10 maintained at a negligible level before stress, they were significantly elevated by brain cooling during heatstroke. These findings suggest that brain cooling may resuscitate persons who had heatstroke by decreasing overproduction of reactive nitrogen species, tumor necrosis factor-alpha, reactive oxygen species and cerebrovascular dysfunction, but increasing production of interleukin-10.

Inhibition of neuronal nitric oxide synthase causes attenuation of cerebrovascular dysfunction in experimental heatstroke

The present study was performed to assess the prophylactic effect of 7-nitroindazole (7-NI), an inhibitor of neuronal nitric oxide synthase (nNOS), in an animal model of heatstroke. Anesthetized rats, immediately before the start of heat stress, were divided into two major groups and given the following: vehicle solution (1 mL per kg body weight) or 7-NI (5-20mg/mL per kg body weight) intraperitoneally. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats were exposed to room temperature (24 degrees C) and used as normothermic controls. Their physiologic and biochemical parameters were continuously monitored. When the vehicle-pretreated rats underwent heat stress, their survival time values were found to be 21-25 min. Pretreatment with intraperitoneal doses of 7-NI significantly improved survival during heatstroke (55-164 min). As compared to those of normothermic controls, all vehicle-pretreated heatstroke animals displayed higher levels of core temperature, intracranial pressure, nitric oxide metabolite (NO(2)(-)), glutamate, glycerol, lactate/pyruvate ratio, neuronal damage score and nNOS expression in the hypothalamus, and tumor necrosis factor-alpha (TNF-alpha) in the serum. In contrast, all vehicle-pretreated heatstroke animals had lower levels of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, and brain PO(2). Administration of 7-NI before the start of heat exposure significantly reduced the hyperthermia, intracranial hypertension, nNOS-dependent NO(2)(-), glutamate, glycerol, lactate/pyruvate ratio, and neuronal damage score in the hypothalamus, as well as overproduction of TNF-alpha in the serum that occurred during heatstroke. The data show that reduction of nNOS-dependent NO(2)(-) with 7-NI causes attenuation of cerebrovascular dysfunction, hyperthermia, and TNF-alpha overproduction during heatstroke in the rat.

Platonin, a cyanine photosensitizing dye, is effective for attenuation of heatstroke in rats

The present study was performed to assess the prophylactic effect of platonin, a cyanine photosensitizing dye and an inhibitor of proinflammatory cytokines, in an animal model of heatstroke. Anesthetized rats were immediately divided into 2 major groups after the start of heat stress and administered either isotonic sodium chloride solution (dose, 1 mL/kg of body weight i.v.) or platonin (dose, 12.5-50 microg/mL per kilogram of body weight i.v.). They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats were exposed to room temperature (26 degrees C) and used as normothermic controls. Their physiological and biochemical parameters were continuously monitored. When the isotonic sodium chloride solution-pretreated rats underwent heat stress, their survival time values were found to be from 20 to 24 min. Pretreatment with intravenous doses of platonin (12.5-50 microg/mL per kilogram of body weight) immediately after the start of heat exposure significantly improved survival time during heatstroke (duration, 63-185 min). As compared with normothermic controls, all vehicle-pretreated heatstroke animals displayed higher levels of creatinine, serum urea nitrogen, alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, tumor necrosis factor alpha, prothrombin time, activated partial thromboplastin time and D-dimer in the plasma, cellular ischemia and injury markers in striatum, and intracranial pressure. In contrast, all vehicle-pretreated heatstroke animals had lower levels of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, brain Po2, and platelet count and protein C in the plasma. Immediately after the start of heat exposure, the previous administration of platonin significantly improved survival time by reducing the systemic inflammation, hypercoagulable state, and tissue ischemia and damage during heatstroke. The results demonstrate that platonin is effective for attenuation of heatstroke reactions.

The flavonoid baicalin protects against cerebrovascular dysfunction and brain inflammation in experimental heatstroke

The present study was performed to assess the prophylactic effect of baicalin, a flavonoid compound, in an animal model of heatstroke. Anesthetized rats, immediately before the start of heat stress, were divided into two major groups and given the following: vehicle solution (1mL per kg body weight) or baicalin (10-40mg per kg body weight) intravenously. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats was exposed to room temperature (24 degrees C) and used as normothermic controls. Their physiologic and biochemical parameters were continuously monitored. When the vehicle-pretreated rats underwent heat stress, their survival time values were found to be 20-28min. Pretreatment with intravenous doses of baicalin significantly improved survival during heatstroke (65-248min). As compared to those of normothermic controls, all vehicle-pretreated heatstroke animals displayed higher levels of core temperature, intracranial pressure, and nitric oxide metabolite (NO(2)(-)), glutamate, glycerol, lactate/pyruvate ratio, and dihydroxybenzoic acid (DHBA) in hypothalamus. In addition, both serum and hypothalamic levels of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) as well as plasma levels of creatinine, serum urea nitrogen, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase and alkaline phosphatase were elevated after heatstroke onset. In contrast, all vehicle-pretreated heatstroke animals had lower levels of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, and brain PO(2). Administration of baicalin before the start of heat exposure significantly reduced the hyperthermia, intracranial hypertension, and the increased levels of NO(2)(-), glutamate, glycerol, lactate/pyruvate ratio, and DHBA in the hypothalamus that occurred during heatstroke. The heatstroke-induced increased levels of IL-1beta and TNF-alpha in both the serum and hypothalamus, and renal and hepatic dysfunction were suppressed by baicalin pretreatment. In contrast, both the serum and hypothalamic levels of IL-10 were significantly elevated by baicalin during heatstroke. We successfully demonstrated that baicalin can be used as a prophylactic agent for heatstroke. In particular, baicalin may protect against cerebrovascular dysfunction and brain inflammation in heatstroke.

BRAIN COOLING CAUSES ATTENUATION OF CEREBRAL OXIDATIVE STRESS, SYSTEMIC INFLAMMATION, ACTIVATED COAGULATION, AND TISSUE ISCHEMIA/INJURY DURING HEATSTROKE

The purpose of the present study was to assess the therapeutic effect of hypothermic retrograde jugular vein flush (HRJVF) on heatstroke. HRJVF was accomplished by infusion of 4 degrees C isotonic sodium chloride solution via the external jugular vein (1.7 mL/100 g of body weight over 5 min). Immediately after the onset of heatstroke, anesthetized rats were divided into 2 major groups and given the following: 36 degrees C or 4 degrees C isotonic sodium chloride solution, i.v. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats was exposed to room temperature (24 degrees C) and used as normothermic controls. When the 36 degrees C saline-treated rats underwent heat exposure, their survival time values were found to be 23 to 28 min. Immediately after the onset of heatstroke, resuscitation with an i.v. dose of 4 degrees C saline significantly improved survival during heatstroke (208-252 min). All heat-stressed animals displayed systemic inflammation and activated coagulation, evidenced by increased tumor necrosis factor alpha, prothrombin time, activated partial thromboplastin time, and d-dimer, and decreased platelet count and protein C. Biochemical markers evidenced cellular ischemia and injury/dysfunction: plasma levels of blood urea nitrogen, creatinine, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and alkaline phosphatase; and striatal levels of glycerol, glutamate, and lactate/pyruvate; dihydroxy benzoic acid, lipid peroxidation, oxidized-form glutathione reduced-form glutathione, dopamine, and serotonin were all elevated during heatstroke. Core and brain temperatures and intracranial pressure were also increased during heatstroke. In contrast, the values of mean arterial pressure, cerebral perfusion pressure, and striatal levels of local blood flow, partial pressure of oxygen, superoxide dismutase, catalase, glutathione peroxidase, and glutathions reductase activities were all significantly lower during heatstroke. The circulatory dysfunction, systemic inflammation, hypercoagulable state, and cerebral oxidative stress, ischemia, and damage during heatstroke were all significantly suppressed by HRJVF. These findings demonstrate that brain cooling caused by HRJVF therapy may resuscitate persons who had a stroke by attenuating cerebral oxidative stress, systemic inflammation, activated coagulation, and tissue ischemia/injury during heatstroke.

CEREBROVASCULAR DYSFUNCTION IS AN ATTRACTIVE TARGET FOR THERAPY IN HEAT STROKE¶

1. The aim of the present review is to summarize clinical observations and results of animal models that advance the knowledge of the attenuation of cerebrovascular dysfunction in the setting of heat stroke. It is a narrative review of selected published literature from Medline over the period 1959-2005. 2. All heat-stressed rodents, even under general anaesthesia, have hyperthermia, systemic inflammation, hypercoagulable state, arterial hypotension and tissue ischaemia and injury in multiple organs. These findings demonstrate that rodent heat stroke models can nearly mirror the full spectrum of human heat stroke. Experimental heat stroke fulfills the empirical triad used for the diagnosis of classical human heat stroke, namely hyperthermia, central nervous system alterations and a history of heat stress. 3. These physiological dysfunctions and survival during heat stroke can be improved by whole-body or brain cooling therapy adopted immediately after the onset of heat stroke. 4. However, in the absence of body or brain cooling, these heat stroke reactions can still be reduced by the following measures: (i) fluid replacement with 3% NaCl solution, 10% human albumin or hydroxyethyl starch; (ii) intravenous delivery of anti-inflammatory drugs, free radical scavengers or interleukin-1 receptor antagonists; (iii) hyperbaric oxygen therapy; or (iv) transplantation of human umbilical cord blood cells. 5. In addition, before initiation of heat stress, prior manipulations with one of the following measures was found to be able to protect against heat stroke reactions: (i) systemic delivery of alpha-tocopherol, mannitol, inducible nitric oxide synthase inhibitors, mu-opioid receptor antagonists, endothelin ETA receptor antagonists, serotoninergic nerve depletors or receptor antagonists, or glutamate receptor antagonists; or (ii) heat shock protein 72 preconditioning. 6. There is compelling evidence that cerebrovascular dysfunction is an attractive target for therapy in heat stroke.

Exertional heat stroke in competitive athletes

Exertional heat stroke (EHS) is a serious medical condition that can have a tragic outcome if proper assessment and treatment are not initiated rapidly. This article focuses on critical misconceptions that pertain to the prevention, recognition, and treatment of EHS, including 1) the randomness of EHS cases, 2) the role of nutritional supplements in EHS, 3) temperature assessment, 4) onset of EHS and the possible lucid interval, 5) rapid cooling, and 6) return to play. Exploration of these topics will enhance the medical care regarding EHS.

Infusion of human umbilical cord blood cells protect against cerebral ischemia and damage during heatstroke in the rat

Intravenously delivered human umbilical cord blood cells (HUCBC) have been previously shown to improve both morphologic and functional recovery of heat-stroked rats. To extend these findings, we examined both the morphologic and functional alterations in the presence of HUCBC or human peripheral mononuclear cells (PBMC) 24 h before initiation of heatstroke. Anesthetized rats, 1 day before the initiation of heatstroke, were divided into three major groups and given the following: (a) serum-free lymphocyte medium (0.3 ml) intravenously; (b) PBMC (5 x 10(6) in 0.3 ml serum-free lymphocyte medium); or (c) HUCBC (5 x 10(6) in 0.3 ml serum-free lymphocyte medium). Another group of rats were exposed to room temperature (26 degrees C) and used as normothermic controls. In vehicle-treated heatstroke rats, their mean arterial pressure, cerebral blood flow, and brain PO(2) were all lower than in normothermic controls after the onset of heatstroke. However, their body temperatures and striatal levels of inducible nitric oxide synthase (iNOS)-dependent NO, ischemia and damage markers (e.g., glycerol, glutamate, and lactate/pyruvate ratio), and neuronal damage in the striatum were all greater. The heatstroke-induced arterial hypotension, cerebral ischemia and hypoxia, and increased levels of iNOS-dependent NO in the striatum were all significantly reduced by pretreatment with HUCBC, but not with PBMC. Moreover, HUCBC were localized by immunohistochemistry and PCR analysis in the injured brain structures and spleen. These findings indicate that HUCBC transplantation, in addition to having therapeutic values, can be a good choice for preventing heatstroke occurrence.

Resuscitation from experimental heatstroke by transplantation of human umbilical cord blood cells

OBJECTIVE

Human umbilical cord blood cells (HUCBCs) are effective in the treatment of conventional stroke in experimental models. In the study described herein, we administered HUCBCs into the femoral vein or directly into the cerebral ventricular system and assessed their effects on circulatory shock, cerebral ischemia, and damage during heatstroke.

DESIGN

Controlled, prospective study.

SETTING

Hospital medical research laboratory.

SUBJECTS

Sprague-Dawley rats (287 +/- 16 g body weight, males).

INTERVENTIONS

Anesthetized rats, immediately after the onset of heatstroke, were divided into four major groups and given the following: a) normal saline or AIM-V medium intravenously (0.3 mL) or intracerebroventricularly (10 microL); b) peripheral blood mononuclear cells (5 x 10 in 0.3 mL AIM-V medium, intravenously, or 5 x 10 in 10 microL AIM-V medium, intracerebroventricularly); or c) HUCBCs (5 x 10 in 0.3 mL AIM-V medium, intravenously, or 5 x 10 in 10 microL AIM-V medium, intracerebroventricularly). Another group of rats, under urethane anesthesia, were exposed to room temperature (26 degrees C) and used as normothermic controls. Urethane-anesthetized animals were exposed to an ambient temperature of 43 degrees C to induce heatstroke. Their physiologic and biochemical parameters were continuously monitored.

MEASUREMENTS AND MAIN RESULTS

When the vehicle-treated rats underwent heat exposure, their survival time values were found to be 21-23 mins. Resuscitation with intravenous or intracerebroventricular doses of HUCBCs, but not peripheral blood mononuclear cells, immediately at the onset of heatstroke significantly improved survival during heatstroke (61-148 mins). As compared with values for normothermic controls, the vehicle-treated heatstroke rats had lower mean arterial pressure, cerebral blood flow, and brain PO2 values but higher intracranial pressure and cerebral ischemia values and more injury markers. The circulatory shock, intracranial hypertension, cerebral hypoperfusion and hypoxia, increment of cerebral ischemia, and damage markers during heatstroke were all significantly attenuated by intravenous or intracerebroventricular delivery of HUCBCs but not peripheral blood mononuclear cells.

CONCLUSIONS

We successfully demonstrate that HUCBC therapy may resuscitate heatstroke victims by reducing circulatory shock and cerebral ischemic injury; central delivery of HUCBCs seems superior to systemic delivery of HUCBCs in resuscitating patients with heatstroke.

HYDROXYETHYL STARCH PRODUCES ATTENUATION OF CIRCULATORY SHOCK AND CEREBRAL ISCHEMIA DURING HEATSTROKE

We hypothesized that hydroxyethyl starch (HES), which maintains colloid osmotic pressure and potentially "seals" capillary leaks, would ameliorate circulatory shock and cerebral ischemia during heatstroke in a rat model. Animals under urethane anesthesia were exposed to high ambient temperature (Ta) of 42 degrees C until mean arterial pressure and local cerebral blood flow in the striatum began to decrease from peak level, which was arbitrarily defined as the onset of heatstroke. Control rats were exposed to 24 degrees C. In rats treated with 1 mL/kg, 11 mL/kg, or 22 mL/kg of normal saline (NS) immediately after the onset of heatstroke, the values for survival time (interval between the initiation of heatstroke and animal death) were found to be 21 +/- 2, 36 +/- 9, or 92 +/- 7 min, respectively. Intravenous administration of 11 mL/kg of HES (about 5 times the volume-expanding effect of 11 mL/kg of NS), but not 2 mL/kg of HES (about the same volume-expanding effect as 11 mL/kg NS), significantly increased the survival time from the control values of 36 +/- 9 min to new values of 181 +/- 13 min. In NS (11 mL/kg)-treated or HES (2 mL/kg)-treated rats after heatstroke onset, the values for mean arterial pressure, stroke volume, total peripheral resistance, cerebral blood flow, blood pH, Paco2, Pao2, and brain Po2 were significantly lower than those of rats kept at Ta 24 degrees C. In contrast, the values for colonic temperature and the extracellular concentrations of glutamate, glycerol, and lactate/pyruvate ratio obtained in striatum were significantly higher than those of controls. The heatstroke-induced arterial hypotension, decreased stroke volume and total peripheral resistance, decreased blood pH and Pao2, decreased brain Po2, and increased levels of striatal glutamate, glycerol, and lactate/pyruvate ratio in NS-treated rats were all attenuated significantly by increasing the volume expansion with 11 mL/kg of HES administered immediately at the onset of heatstroke. Our data suggest that HES therapy seems superior to NS treatment during heatstroke. The benefit of HES therapy during heatstroke might have something to do with volume expansion rather than capillary permeability.

Hypothermic retrograde jugular vein flush in heatstroke rats provides brain protection by maintaining cerebral blood flow but not by hemodilution

OBJECTIVE

To determine the fundamental mechanism of brain protection by hypothermic retrograde jugular vein flush (HRJVF) in heatstroke rats.

DESIGN

Randomized, controlled, and prospective study.

SETTING

University physiology research laboratory.

SUBJECTS

Sprague-Dawley rats (270-320 g, males).

INTERVENTIONS

Rats were randomized into four groups as follows: a) normothermic control (NC, n = 8); b) heatstroke rats without cold saline delivery (HS, n = 8); c) heatstroke rats treated with cold saline via femoral vein (HS+F, n = 8); and d) heatstroke rats treated with HRJVF (HS+J, n = 8). Right external jugular vein and right femoral vein were cannulated in each rat. The cannulation in the jugular vein was with cranial direction. To produce heatstroke, rats were placed in a chamber with an ambient temperature of 43 degrees C. The cold saline (4 degrees C, 1.7 mL/100 g) was delivered via the cannula in either the femoral vein or jugular vein immediately after the onset of heatstroke. Glutamate release in the brain, cerebral blood flow (CBF), and hematocrit of arterial blood were determined.

MEASUREMENTS AND MAIN RESULTS

After onset of heatstroke, HRJVF significantly decreased the glutamate release. In contrast, cold saline delivery via femoral vein could only delay the elevation of glutamate release in the brain. The CBF of HS and HS+F rats decreased rapidly after the onset of heatstroke, but the CBF of HS+J rats was initially elevated by HRJVF and was maintained at baseline 30 mins after onset of heatstroke. Hematocrit in all the rats did not change after testing.

CONCLUSIONS

HRJVF protects the brain by maintaining cerebral blood flow in rats after heatstroke. To preserve brain function and prolong survival after severe heatstroke, maintenance of cerebral blood flow is important in the management of heatstroke.