Effect of flunarizine on canine cerebral cortical blood flow and vascular resistance post cardiac arrest

Ca paradox in neural injury: a hypothesis

The deleterious effects of Ca ionic entry into neurons has been speculated to be a final common pathway of cell death. However, a direct cause-effect relationship between Ca and neuronal death has been difficult to establish. Cells dying from any cause will accumulate Ca. The entry of Ca into neurons and the subsequent pathological changes associated with Ca entry consequently may be manifestations rather than causes of cell death. Recent work showing that extracellular Ca ionic activity becomes profoundly depressed in injured spinal cord and ischemic cerebral cortex prompted a new hypothesis on Ca mediated damage. We propose that the initial fall in extracellular Ca activity, resulting from the death of some cells in the tissue, increases the susceptibility of the surviving cells to Ca entry when extracellular Ca activity levels normalize and that this accounts for part of the secondary damage that has been observed in neural injury models. Such a phenomenon has been described in cardiac tissues. Dubbed Ca paradox, this phenomenon occurs when heart cells are perfused with Ca-free solutions for several minutes followed by the return to normal Ca-containing solutions. The cardiac cells die and undergo physiological, morphological, biochemical, and other changes. The evidence supporting a Ca paradox phenomenon in injured neural tissues is summarized. The therapeutic implications of Ca paradox in neural tissue injury are discussed.

Ischemic brain injury and cell calcium: morphologic and therapeutic aspects

Histopathological data obtained from different experimental models of hypoxia and ischemia were evaluated in order to extend current knowledge of mechanisms responsible for delayed neuronal cell death. Special attention is given to the distribution of calcium (Ca2+) in vulnerable areas during the postischemic period. Between an initial defensive Ca2+ sequestration, which is completely reversible, and final toxic Ca2+ overload, which is associated with irreversible neuronal necrosis, important Ca2+ shifts could be demonstrated cytochemically. Such shifts occur mainly at excitatory presynaptic sites and seem to precede structural ischemic cell change in postsynaptic areas. Recent results obtained with some Ca2+ entry blockers indicate that prophylactic treatment and postischemic intervention prevent cytosolic Ca2+ overload and reduce delayed brain injury.

Artificial perfusion techniques during cardiac arrest: questions of experimental focus versus clinical need

Contemporary cerebral-cardiopulmonary resuscitation investigations in the experimental laboratory have defined mechanisms for blood flow during closed-chest CPR and have demonstrated that the current CPR technique produces limited systemic perfusion. Modified closed-chest CPR techniques usually improve perfusion. Unfortunately few laboratory CPR studies have actually investigated resuscitation and survival. In addition, the animal model employed (prolonged ventricular fibrillation) may have limited clinical relevance, based on clinical experience and resuscitation practice, and data reporting techniques and their interpretation may be affected by control values that are not normal because of the effects of anesthetics. Closed-chest CPR was intended to buy time until a countershock could be delivered. Clinical and laboratory experience indicate that this goal can be met. Cerebral perfusion during closed-chest CPR is low, but adequacy from a functional perspective following restoration of circulation has not been carefully studied. Preservation of neuronal integrity after restoration of spontaneous circulation may be more important than cerebral perfusion during cardiac arrest and CPR. The role and benefit of open-chest CPR have yet to be determined, because this technique will most likely be used after conventional CPR failure. New and different experimental models are required to meet clinical needs and challenges. The alliance between practitioner and investigator should be strengthened if common goals are to be attained.

Ischemic brain protection

Despite advances in the understanding of the pathophysiology of cerebral ischemia, no single brain resuscitation therapy has yet been shown to be clinically superior to brain-oriented intensive care. Basic concepts in cardiopulmonary-cerebral resuscitation (CPCR) are discussed, as are two specific phases of CPCR, cerebral preservation and cerebral resuscitation. Cerebral preservation is initiated during cardiac arrest (ie, prior to restoration of spontaneous circulation [ROSC]) and includes use of artificial perfusion techniques and drugs to produce cerebral perfusion during this phase. Cerebral resuscitation is brain-oriented therapy initiated after ROSC. Pharmacologic agents currently under study for cerebral resuscitation include the barbiturates, calcium antagonists, and iron chelators. With respect to defining efficacy of the pharmacologic agents, the concept of therapeutic window is important. Although no agent has been proven clinically, several appear to be promising.

Ionized calcium during CPR in the canine model

The purpose of our study was to determine ionized calcium levels during cardiopulmonary resuscitation (CPR). Following placement of ascending aortic catheters in 15 adult mongrel dogs, ventricular fibrillation was induced electrically. After five minutes without therapy, mechanical external CPR was instituted. Animals received either standard CPR (S-CPR, n = 8) or simultaneous compression and ventilation CPR (SCV-CPR, n = 7) for 30 minutes. Ionized calcium levels were obtained prior to fibrillation and every five minutes during CPR. Mean ionized calcium levels during CPR (1.27 +/- 0.06 mmol/L) did not differ significantly from prearrest levels (1.27 +/- 0.07 mmol/L) at any point during CPR. This was true when the dogs were analyzed together (P = 0.1293) and when the animals receiving S-CPR (P = 0.4465) and SCV-CPR (P = 0.5470) were analyzed by groups. Defibrillation was attempted in all animals and resulted in electromechanical dissociation in three. None of these dogs was hypocalcemic either prior to arrest or during CPR, and none developed an effective rhythm with the administration of calcium. Furthermore, three of the four animals receiving calcium developed markedly elevated ionized calcium levels. Hypocalcemia apparently does not occur during CPR. The beneficial effect of calcium in reported cases cannot be explained routinely by correction of hypocalcemia. Further studies are needed to define the role of calcium administration, if any, in CPR.

Open- versus closed-chest cardiac compressions in a canine model of pediatric cardiopulmonary resuscitation

Whether or not the principles of adult resuscitation apply to the pediatric population remains unknown. In order to study this issue, a pediatric animal model was developed using puppies 6-12 weeks of age and 2-8 kg in weight. Hemodynamic status was assessed using standard methods, and measured global cerebral blood flow was assessed using the nitrous oxide (Kety-Schmidt) technique after placement of a catheter in the sagittal sinus. In this initial study, five puppies resuscitated with closed-chest cardiac compression (CCCC) were compared with five receiving open-chest cardiac compression (OCCC). Although mean systolic arterial pressures were equal with both methods during resuscitation (40 versus 49 mm Hg, P = 0.19), OCCC produced a greater cardiac output and a higher cerebral blood flow (5 versus 18 ml/100 g/min, P = 0.008). Only one of five dogs treated with CCCC had a blood flow during resuscitation greater than 15 ml/100 g/min, as compared with four of five receiving OCCC. Finally, three of five dogs in the CCCC group experienced liver lacerations, while none who were resuscitated by OCCC sustained any gross visceral injuries.

The effects of lidoflazine and flunarizine on cerebral reactive hyperemia

Cerebral blood flow in the rat was monitored by a venous outflow technique with an extracorporeal circulation, which allows for the continuous recording of flow over periods of several hours. The bi-fluorophenyl-piperazine derivatives, lidoflazine and flunarizine, enhanced the reactive hyperemia elicited by a brief (30 s) anoxic challenge. They did not alter resting cerebral blood flow rates. Verapamil, a potent calcium slow channel blocker, decreased resting flow rates but did not alter the duration of the reactive hyperemia. As lidoflazine and flunarizine are potent inhibitors of adenosine uptake, whereas verapamil is not, the results are consistent with the hypothesis that adenosine plays a significant role in cerebral vascular autoregulation.

Prolonged cardiac arrest and resuscitation in dogs: brain mitochondrial function with different artificial perfusion methods

Clinical techniques for artificial perfusion have not previously been examined directly for their effects on brain high-energy metabolism. Our study involved 24 large mongrel dogs that were anesthetized, instrumented for central venous intravenous access, and subjected to craniotomy to expose the dura and underlying parietal cortex. The animals were divided into the following six experimental groups of four animals each: nonischemic controls; 15-minute cardiac arrest without resuscitation; 45-minute cardiac arrest without resuscitation; 15-minute cardiac arrest plus 30 minutes resuscitation with conventional cardiopulmonary resuscitation (CPR); 15-minute cardiac arrest plus 30 minutes resuscitation with interposed abdominal compression (IAC) CPR; and 15-minute cardiac arrest plus 30 minutes resuscitation with internal cardiac massage. Cardiac arrest was induced by central venous injection of KCl 0.6 mEq/kg, and it was confirmed by continuous ECG monitoring. The three active resuscitation models included administration of NaHCO3 and epinephrine, but no attempt was made to restart the heart by defibrillation during resuscitation. At the indicated time in each group, a 4- to 5-g sample of brain was removed through the craniotomy, immediately cooled to 0 C and processed for isolation of mitochondria. The mitochondria were studied for their content of superoxide dismutase and for quantitative oxygen consumption with glutamate/malate substrate during resting and ADP-stimulated respiration. Our results show a significant drop in brain mitochondrial superoxide dismutase activity during the first 15 minutes of cardiac arrest. There is minimal injury to brain mitochondrial oxygen consumption during both 15 and 45 minutes of complete ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium-channel blockers in the treatment of migraine

According to classic theory, a migraine attack is initiated by cerebrovascular spasm followed by extracranial vasodilatation. Results of recent studies support this theory and suggest that cerebral blood flow during the initial phase of migraine symptoms is, in fact, decreased and this decrease probably leads to ischemia and hypoxia. Cellular hypoxia, in turn, can cause an increase in the flow of calcium from the extracellular fluid to the intracellular space, resulting in calcium overload and cellular dysfunction. Because calcium-channel blockers selectively inhibit the intracellular influx of calcium ions, investigators have begun evaluating the efficacy of these agents for migraine prophylaxis. Nimodipine, a calcium-channel blocker that exhibits selective effects on cerebral vessels, seems to offer protection against the cerebral ischemia and hypoxia presumed to be operative during migraine attacks. In a double-blind, placebo-controlled study, nimodipine decreased the frequency and duration of migraine attacks by at least half in 69% of patients treated with this agent. Comparable reductions in migraine frequency and duration were attained in 58, 51, 41 and 52% of patients treated with methysergide maleate, pizotifen, clonidine hydrochloride and propranolol, respectively. The piperazine derivative flunarizine also has calcium-channel blocking properties. This agent prevents vasospasm in cerebral arteries and protects against cerebral hypoxia. Results of double-blind studies of migraine prophylaxis with flunarizine demonstrate the beneficial effects of this agent, particularly in younger patients. Flunarizine proved to be superior to pizotifen in decreasing the severity of migraine attacks and comparable to pizotifen in decreasing their frequency.(ABSTRACT TRUNCATED AT 250 WORDS)

Post resuscitation iron delocalization and malondialdehyde production in the brain following prolonged cardiac arrest

Assays for brain tissue malondialdehyde (MDA) and low molecular weight chelated (LMWC) iron were used to examine samples of the cerebral cortex obtained from dogs 2 h after resuscitation from a 15-min cardiac arrest. The effect of post-resuscitation treatment with lidoflazine and/or desferrioxamine was similarly examined. Non-ischemic brain samples had LMWC iron levels (in nmol/100 mg tissue) of 12.32 + 2.60 and MDA levels (in nmol/100 mg tissue) of 8.46 + 1.35. Animals subjected to cardiac arrest and resuscitation and standard intensive care (SIC) had LMWC iron levels of 37.04 + 4.58 (p less than .01 against non-ischemic controls) and MDA levels of 12.24 + 1.9 (p less than .05 against non-ischemic controls). All treatment interventions significantly reduced the LMWC iron (p less than .05), but only treatment with desferrioxamine alone significantly reduced MDA (p less than .05), although a trend toward reduction of the MDA was also evident in animals treated with both desferrioxamine and lidoflazine. LMWC iron levels are increased in the post-ischemic brain, and this increase may be related to lipid peroxidation in the brain following resuscitation from cardiac arrest. These changes are probably pathologic and are amenable to pharmacologic intervention.

Neurological recovery after cardiac arrest: clinical feasibility trial of calcium blockers

In order to determine whether the calcium blockers verapamil and/or magnesium sulfate decrease neurological morbidity after cardiac arrest, all out-of-hospital cardiac arrests (290) occurring during a nine-month period in five participating hospitals were retrospectively studied. Twenty-nine patients met the criteria for inclusion in this study. Each had an unwitnessed, out-of-hospital cardiac arrest and was comatose (no purposeful response to pain) 20 minutes after the restoration of spontaneous circulation (ROSC). Eighteen patients (calcium blocker group) received verapamil and/or magnesium sulfate at some point after ROSC, while eleven patients received standard ACLS therapy (control group). Age, arrest time, cardiopulmonary resuscitation (CPR) time, and cerebral ischemic time were comparable in the two groups. In the calcium blocker group, seven of 18 patients regained consciousness, and six of these seven survived. All six survivors appeared neurologically normal upon discharge and at three and six months of follow-up. While no demonstrably adverse effects were seen after the administration of magnesium sulfate, 56% of the patients who received verapamil had a significant drop in blood pressure. In the control group, three of 11 patients regained consciousness and two of the three left the hospital alive. Both survivors were disabled--one severely and one moderately. Follow-up after three and six months revealed no significant improvement in their disability. Overall, six of 18 patients experienced clinically complete neurological recovery in the calcium blocker group, while none of the 11 patients in the control group made a complete neurological recovery (P = 0.06).

Prehospital use of dexamethasone in pulseless idioventricular rhythm

We investigated the prehospital use of 100 mg dexamethasone for the treatment of cardiac arrest patients with pulseless idioventricular rhythms (PIVR). In the 86 patients studied in this prospective, randomized, double-blind investigation, four of the 46 patients receiving saline and two of the 37 patients receiving dexamethasone survived long enough to be admitted to the hospital intensive care unit. There were no long-term survivors. No benefit from the field use of 100 mg dexamethasone in PIVR could be identified in this study.

Calcium channel blockers in emergency medicine

Diltiazem, nifedipine, and verapamil inhibit calcium entry into cells via different mechanisms with different pharmacologies. They display different relative effects on different cardiovascular functions, a complex interplay of direct actions and adrenergic reflexes. Peripheral arterial vasorelaxation causes adrenergic reflex activity which opposes their direct negative chronotropic, dromotropic, inotropic, and hypotensive actions. Verapamil's most potent activity is electrophysiologic, and nifedipine's effects are hemodynamic; diltiazem acts like a less-potent combination of verapamil and nifedipine. All three drugs are efficacious in angina. These three drugs may not be interchangeable in all patients, but individualization of therapy is possible. Future indications for calcium channel blocker therapy may include hypertrophic cardiomyopathy, cerebral vasospasm, migraine headaches, pulmonary hypertension, asthma, esophageal spasm, intestinal ischemia, Raynaud's phenomenon, dysmenorrhea, and premature labor.

Use of calcium in electromechanical dissociation

Calcium is recommended by American Heart Association standards for the resuscitation of patients with electromechanical dissociation (EMD). Until recently, only anecdotal case reports were offered to support this recommendation. Recent studies examining the question of whether calcium is useful in resuscitating hearts in EMD are reviewed.

Perfusion of the cerebral cortex by use of abdominal counterpulsation during cardiopulmonary resuscitation

Perfusion of the cerebral cortex (rCCBF) during resuscitation from cardiac arrest was studied using 24 large dogs and three different resuscitation models. Conventional cardiopulmonary resuscitation (CPR) was compared with interposed abdominal compression CPR (IAC-CPR) and with IAC-CPR together with infusion of epinephrine. Conventional CPR produced a mean rCCBF of only 11% (0.057 +/- 0.07 ml/min/g) normal perfusion (0.54 +/- 0.14 ml/min/g). Even without epinephrine, IAC-CPR produced mean rCCBF equal to 51% (0.27 +/- 0.17 ml/min/g) of normal. With epinephrine, IAC-CPR produced rCCBF (0.93 +/- 0.49 ml/min/g) statistically indistinguishable from normal. Both models of IAC-CPR were significantly superior to conventional CPR in perfusion of the cerebral cortex.

Asphyxia, cardiac arrest and resuscitation in rats. I. Short term recovery

This study was conducted to investigate the degree of insult from asphyxia leading to total body circulatory arrest, as a model for brain resuscitation studies in rats. Of 78 male rats, 68 were anesthetized with halothane in O2/N2O, controlled ventilated, paralyzed with pancuronium and asphyxiated, 5, 7.5, 10, 12.5 and 15 min, respectively. Asphyxiation led to circulatory arrest in 244 +/- 22 s (mean +/- S.E.M.). Resuscitation was successful in 65% within 60 s using controlled ventilation with 100% O2, extrathoracic compressions and epinephrine intravenously. Subsequent intensive care to 6, 12 or 24 h was successful in 50% of resuscitated rats. At 6, 12 and 24 h of recovery, neurologic deficit scores and light microscopic neuropathology scores of the brain after in vivo fixation of the total body with intraventricular paraformaldehyde 3%, revealed a large scatter variability without a clear pattern. Lesions were located mostly in the frontal cortex and hippocampus (footplate) with ischemic neuronal change as the most frequent structural change. Brain cell necrosis was not seen after successful resuscitation. It seems that both scores were influenced by post-insult stress, as indicated by paroxysmal hypertension and motor activity, by complications, such as obstruction of the tracheotomy cannula by abundant sputum production, and by partial sedation with N2O and paralysis with pancuronium. This study indicates the feasibility of an asphyxial insult in rats for use in resuscitation studies of short duration. Although 24 h post-insult recovery is possible, up to 6 h seems most practical, with asphyxia of 7.5-10 min most successful and controllable. Questions are raised about the effects of irritation during the post-insult intensive care on both neurological deficit and neuropathology scores.

Failure of flunarizine to improve cerebral blood flow or neurologic recovery in a canine model of complete cerebral ischemia

Ten minutes of cerebral ischemia was produced in 12 dogs by temporary ligation of the venae cavae and aorta. After reperfusion the dogs received the calcium entry blocker, flunarizine, 6 micrograms/kg infused over a ten minute period. Cerebral blood flow (CBF) and metabolism (CMRO2) were measured pre-ischemia and for 2 h post-ischemia in 6 dogs. At the end of the study brain biopsies were analyzed for cerebral metabolites. Neurologic recovery was evaluated for up to 48 h post-ischemia in an additional 6 dogs. The results of each study were compared to those previously obtained in untreated animals. The cerebral blood flows (when expressed as a percent of the pre-ischemic control value) of the flunarizine-treated and untreated groups were similar throughout the post-ischemic period. Following an initial hyperemia, the CBF fell to significantly less than the pre-ischemic control values, and remained approximately 26% of control during the final 90 min in both groups. The CMRO2 was also the same for both groups. Cerebral metabolites were similar although abnormal in both groups. Flunarizine produced pulmonary edema in 5 of 6 dogs studied for neurologic recovery. Four of these dogs died within 12 h and another dog demonstrated severe neurologic damage. None of the untreated dogs developed pulmonary edema, but 6 of 7 dogs evidenced severe neurologic damage or were dead at 48 h. Thus, flunarizine failed to improve either cerebral blood flow or neurologic outcome when given after complete cerebral ischemia in the dog. A cardiodepressive effect of flunarizine might have contributed to the poor neurologic outcome.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of lidoflazine on cerebral blood flow following twelve minutes total cerebral ischemia

Lidoflazine, a calcium channel blocker, was administered to dogs following twelve minutes of cerebral ischemia, induced by aortic cross-clamping. The effects of lidoflazine (1 mg/kg i.v.) on cerebral blood flow following ischemia was studied in 15 anesthetized, mechanically ventilated dogs. Cerebral blood flow was measured with the radiolabelled microsphere technique before and 10, 30, 60, 90 and 150 minutes following ischemia. Cerebral blood flow increased in all brain regions following ischemia, but by 60 minutes had decreased to control values. Lidoflazine had no effect on this reperfusion phenomenon, or on the distribution of blood flow within the brain. Regional cerebral blood flow was also not altered by lidoflazine therapy. Our data demonstrate that this dose of lidoflazine has no effect on regional or total cerebral blood flow following 12 minutes of cerebral ischemia in dogs. These data do not support perfusion preservation as a mechanism of amelioration of neurologic injury after ischemia by this calcium channel blocker.

Verapamil in the treatment of asystolic and pulseless idioventricular rhythm cardiopulmonary arrests: a preliminary report

A randomized, double-blinded study was conducted to evaluate the effectiveness of the calcium antagonist verapamil in patients in cardiopulmonary arrest with asystole or pulseless idioventricular rhythm (PIVR). Twenty-one such patients presenting to the emergency department received either verapamil (10 mg) or normal saline placebo in an intravenous bolus as initial therapy. They were then treated according to standard American Heart Association guidelines with the exception that calcium was not used. If these rhythms persisted after ten minutes, a second bolus of verapamil or saline was given. Resuscitation was successful in two of ten patients (20%) receiving verapamil and in one of 11 patients (9%) receiving placebo. This similar outcome (P = .462) in this small series suggests that verapamil may not add to successful resuscitation in these patients. Additional studies are needed to define the role of calcium and its antagonists in the treatment of asystole and PIVR.

Cerebral blood flow and neurologic outcome when nimodipine is given after complete cerebral ischemia in the dog

Ten minutes of complete cerebral ischemia was produced in 26 dogs by temporary ligation of the aorta and the venae cavae. Twenty dogs received nimodipine, a calcium entry blocker, 10 micrograms kg-1 i.v. 2 min after the ischemic period, followed by 1 microgram kg-1 min-1 for 2-3 h. Six dogs received only the solvent used for nimodipine. Fourteen dogs received nimodipine for 3 h and were subsequently evaluated neurologically up to 48 h postischemia. In the 12 other dogs, CBF and metabolism were followed for 2 h postischemia while either nimodipine or the solvent only was infused. The results were compared to previously published results for untreated dogs and dogs given nimodipine before the ischemic event. Nimodipine had the same effect on postischemic CBF whether started before or after the ischemic event, nearly doubling the flow when compared with untreated controls, whereas the solvent alone caused only a slight increase in CBF over control. By contrast, nimodipine initiated in the preischemic period significantly improved the neurologic outcome, but when initiated in the postischemic period the results were equivocal, such that the outcome was not significantly different from either the untreated group or the group in which nimodipine was initiated preischemia. Metabolic measurements did not give any indication of a specific effect of nimodipine, nor could the metabolic results be used as an indicator of neurologic outcome. The results are consistent with a beneficial effect of nimodipine following complete cerebral ischemia; however, evaluation of neurologic functional effects will require a more sensitive model.

Effect of the calcium antagonist nimodipine on the delayed hypoperfusion following incomplete ischemia in the rat

Regional cerebral blood flow (CBF) was measured autoradiographically in the recovery period following 15 min of forebrain ischemia in rats pretreated with either nimodipine (0.1 mg kg-1) or vehicle. The results showed that although nimodipine increased postischemic CBF, the flow enhancement was regionally heterogeneous, sometimes resulting in zones of gross hypoperfusion and overt hyperemia within the same structures. This patchy improvement of delayed postischemic hypoperfusion was not accompanied by recovery of sensory evoked responses, and return of EEG activity was not enhanced.

The use of calcium in cardiac resuscitation

All records of cardiac arrest patients presenting to the Tampa EMS system for the 24-month period of January, 1980, through December, 1982, were reviewed. Paramedics were given direct orders or standing orders to administer calcium intravenously or intracardiac in patients in ventricular fibrillation, asystole, or electromechanical dissociation. Of the 480 patients receiving calcium for the above conditions, only patients with electromechanical dissociation responded to calcium. Twenty-seven EMD patients responded positively with the immediate return of blood pressure and pulse. Fourteen of these patients arrived at the emergency department with stable vital signs; there were three long-term survivors. Adverse rhythm or rate changes were not noted following calcium use, and arrhythmias associated with digitalis excess were not seen in a small group of patients taking digoxin. Although long-term survivors are limited in this group of patients, positive hemodynamic responses were seen following calcium chloride administration in 10% of EMD patients and not at all in patients with asystole or ventricular fibrillation.

Cerebral cortical perfusion during and following resuscitation from cardiac arrest in dogs

Perfusion of the cerebral cortex during closed chest CPR in dogs, generating systolic pressures of 60 to 70 mmHg, is only 10% of pre-arrest blood flow. In contrast, internal cardiac massage produces normal cortical perfusion rates. Following a 20-min perfusion arrest, during pressure controlled reperfusion, cortical flow rates decay to less than 20% normal after 90 min of reperfusion. This appears to be due to increasing cerebral vascular resistance, and is not due to rising intracranial pressure. The post-arrest cortical hypoperfusion syndrome is prolonged with cortical flow remaining below 20% normal up to 18 hr post arrest. The use of a variety of calcium antagonists, including flunarizine, lidoflazine, verapamil, and Mg2+, immediately post-resuscitation maintains cerebral vascular resistance and cortical perfusion at normal levels. A prospective blind trial of the calcium antagonist lidoflazine following a 15-min cardiac arrest in dogs and resuscitation by internal massage, demonstrates amelioration of neurologic deficit in the early postresuscitation period.

Relationship between calcium accumulation and recovery of cat brain after prolonged cerebral ischemia

The relationship between brain tissue calcium content and postischemic electrophysiological and metabolic recovery was investigated in 18 adult normothermic cats, 12 of which were submitted to 1 h of complete ischemia and 3 h of recirculation. Six animals served as controls. Functional recovery was estimated by recording the electrocorticogram (ECoG) and evoked potentials, and biochemical recovery by regional evaluation of ATP, glucose, and pH in intact brain sections. One group of animals was treated with the calcium antagonist flunarizine (0.1 mg/kg i. v., followed by continuous i. v. infusion of 0.1 mg/kg/h during the recirculation phase); another group did not receive this treatment. Evoked potentials in all six untreated animals (and in four also, spontaneous ECoG activity) returned after ischemia. In the animals with ECoG activity, biochemical recovery was homogeneous, as indicated by a return toward normal of regional tissue ATP and glucose content. In one animal without ECoG activity, several small regions were present in which energy metabolism was impaired. In regions with biochemical recovery, brain tissue calcium significantly increased by ∼35% (controls, 0.330 ± 0.045; ischemia, 0.447 ± 0.194 μg/mg protein; means ± SD). Changes were accompanied by a parallel increase in sodium (controls, 7.72 ± 1.92; ischemia, 10.50 ± 2.47 μg/mg protein), a slight decrease of potassium (controls, 29.52 ± 0.85; ischemia, 27.66 ± 2.30 μg/mg protein), and an increase of tissue pH (controls, 7.10 ± 0.096; ischemia, 7.307 ± 0.083). In regions without biochemical recovery, pH fell to 6.288 ± 0.157, and calcium content was 0.602 ± 0.235, sodium content 11.70 ± 4.60, and potassium content 23.00 ± 3.91 μg/mg protein. Treatment with the calcium antagonist flunarizine did not reduce tissue calcium content, nor did it improve functional or metabolic recovery after ischemia: three of six treated animals exhibited ECoG activity, one showed only evoked potentials, and two showed no recovery at all. It is concluded that postischemic accumulation of calcium in brain tissue cannot be prevented by the calcium antagonist flunarizine. However, the observed increase of calcium did not interfere with the early postischemic electrophysiological and biochemical recovery. Its pathophysiological importance, therefore, may be associated with more delayed postischemic disturbances.

Early amelioration of neurologic deficit by lidoflazine after fifteen minutes of cardiopulmonary arrest in dogs

A prospective, controlled, blind study was done to test the effect of a calcium entry blocker on the neurologic integrity of dogs after cardiopulmonary arrest. Ten male mongrel dogs were anesthetized, prepared with sterile technique, and instrumented for pulmonary arterial (PA) and systematic arterial pressure monitoring. A left thoracotomy and pericardotomy were performed. Cardiac arrest was produced by injecting KCl (1 mEq/kg) through the PA line, and the respirator was stopped. Full arrest was maintained for 15 minutes. Thereafter, the dogs were resuscitated with ventilation, internal massage, fluids, bicarbonate, epinephrine, and internal defibrillation. All dogs were resuscitated within 6 to 10 minutes. Five control dogs received saline placebo, and five dogs were treated with lidoflazine (1 mg/kg) IV drip immediately post resuscitation. All dogs were scored neurologically every two hours by a deficit grading scale. All treated dogs had spontaneous ventilation, reactive pupils and corneals, voluntary movements, and responses to tactile stimulation at 12 hours post resuscitation. Four of five control dogs had maximum deficit scores without improvement. The difference in neurologic scores between the treated and control groups became increasingly divergent with time, and was statistically significant (P less than .05) by four hours post resuscitation. Thus the calcium antagonist lidoflazine produces improvement in neurologic recovery in the first 12 hours after cardiopulmonary arrest in dogs.

Prolonged hypoperfusion in the cerebral cortex following cardiac arrest and resuscitation in dogs

Increasing cerebral vascular resistance and brain perfusion failure occur within 90 minutes following cardiac arrest and resuscitation. This study followed cortical perfusion for 18 hours after a 15-minute cardiac arrest. Six dogs were anesthetized with ketamine and gallamine and then mechanically ventilated. They were instrumented for arterial pressure, central venous pressure, and regional cerebral cortical blood flow (rCCBF) determined by thermodilution. A left thoracotomy and pericardiotomy were done. Two dogs served as non-arrest controls. Cardiac arrest was produced in four dogs with an intravenous bolus of KCl at 1 mEq/kg. After 15 minutes of cardiac arrest, the animals were resuscitated with internal massage, NaHCO3, epinephrine, and internal defibrillation. Cortical blood flow was followed for 18 hours. Arterial core temperature was never less than 35 C. Pre-arrest cortical blood flows were 0.86 cc/min/g (+/- 0.11). The two control animals had stable rCCBF (0.74 +/- 0.17) for all determinations during the 18-hour follow-up period. Determinations of rCCBF from 6 to 18 hours in post-arrest animals were 7% to 14% of pre-arrest values. We conclude that the post-resuscitation perfusion failure in the cortex is prolonged. Any potential for neuronal recovery, unless perfusion is protected, would not be realized given this phenomenon.

Use of calcium in prehospital cardiac arrest

All records of patients presenting to the Milwaukee County Paramedic System for the period of January 1 to December 31, 1980 were reviewed retrospectively. One hundred seventy-nine patients initially presented in asystole, and 116 patients initially presented in electromechanical dissociation (EMD). All patients with trauma and poisoning were excluded. The in-field successful resuscitation rates for asystole were 8/105 (8%) in the calcium group versus 8/24 (33%) in the no-calcium group (P less than .002); for EMD they were 10/63 (16%) in the calcium group versus 8/18 (44%) in the no-calcium group (P less than .02). A successful resuscitation is defined as the conveyance of a patient to the emergency department with a pulse and cardiac rhythm. There were no significant differences between the calcium and no-calcium groups in both the asystole and EMD patients. The use of calcium in the prehospital setting in the currently recommended dosage for cardiac arrest with initial arrest rhythms of asystole and EMD is highly suspect.

Nimodipine improves cerebral blood flow and neurologic recovery after complete cerebral ischemia in the dog

Ten minutes of complete ischemia was produced in 11 dogs by temporary ligation of the aorta. Immediately before the ischemic episode, the dogs received nimodipine, a new calcium entry blocker, 10 micrograms kg-1, i.v., followed by an infusion of 1 microgram kg-1 min-1 for 2 h. Post-ischemic cerebral blood flow and metabolism were measured for 120 min in six dogs. Neurologic recovery was evaluated 48 h post-ischemia in five dogs. The results were compared to previously determined controls. Nimodipine nearly doubled cerebral blood flow in the delayed post-ischemic hypoperfusion period, compared to untreated dogs (approximately 45% versus 25% of pre-ischemic control values), but had no significant effect on metabolism. Nimodipine also improved neurologic recovery. Four of five treated dogs were normal and one was moderately damaged, whereas six of seven controls were either severely damaged or dead. This suggests that the delayed hypoperfusion state occurring after complete cerebral ischemia probably does contribute to the ultimate neurologic damage, and that nimodipine offers a potential protective effect.

The role of calcium and the significance of calciumantagonists in some neurological and neurosurgical diseases

Calcium is an important intracellular 'second messenger' in the activation of contractile proteins in vascular smooth muscle cells. Intracellular calcium accumulation probably has a major pathological effect in the occurrence of ischemic cell damage. Calcium antagonists are a heterogenous group of substances with one property in common, that is they interfere with the transmembrane movement of calcium. Their therapeutic usefulness in cerebral vasospasms, migraine and cerebral ischemia is reviewed.