- Email: [email protected]
Effects of Dose-Response of Topical Administration of Nimodipine on Cerebral Vasospasm After Subarachnoid Hemorrhage in Rabbits
BASIC INVESTIGATION
Effects of Dose-Response of Topical Administration of Nimodipine on Cerebral Vasospasm After Subarachnoid Hemorrhage in Rabbits Yu-Hua Yin, MD, Fei Wang, MD, Yao-Hua Pan, MD, Yong Wang, MD, PhD, Yu Wang, MD, Qi-Zhong Luo, MD and Ji-Yao Jiang, MD, PhD
Abstract: Background: To explore the dose-response effects of topical administration of nimodipine on cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH) in rabbits. Methods: The CVS model was established by injection of fresh autologous nonheparinized arterial blood into the subtemporal area of basilar cisterns. The 24 CVS animals were randomly divided into 4 groups, group I (n ⫽ 7): nimodipine original stock solution/normal saline ⫽ 1/19 (0.01 mg/mL); group II (n ⫽ 6): nimodipine original stock solution/normal saline ⫽ 1/9 (0.02 mg/mL); group III (n ⫽ 5): nimodipine original stock solution/normal saline ⫽ 1/4 (0.04 mg/mL); and group IV (n ⫽ 6) with no nimodipine, but 5% ethanol dissolved in normal saline as the control group. The operative area was administrated with nimodipine at different concentrations or alcohol–saline at 3 days after SAH. The blood flow velocity of middle cerebral artery was measured at 5, 15, 30, and 60 minutes after topical administration of nimodipine by transverse cerebellar diameter monitoring. Results: Blood flow velocity of middle cerebral artery in group II (0.02 mg/mL) and in group III (0.04 mg/mL) significantly decreased at 60 and 15 minutes, respectively, after topical administration of nimodipine (P ⬍ 0.05), and even more significantly at 30 and 60 minutes after topical administration of nimodipine in group III (0.04 mg/mL) (P ⬍ 0.01). Conclusion: Topical administration of nimodipine at the concentrations of 1:5 (0.04 mg/mL) and 1:10 (0.02 mg/mL) significantly alleviates CVS after SAH, which indicates that topical administration of nimodipine may be useful for CVS of patients with SAH during surgical clip of intracranial aneurysms. Key Indexing Terms: subarachnoid hemorrhage; cerebral vasospasm; nimodipine. [Am J Med Sci 2009;337(2):123–125.]
M
ore and more clinical studies show that high frequent rate of cerebral vasospasm (CVS) happens after subarachnoid hemorrhage (SAH), which may cause cerebral ischemia and infarction. Cerebral ischemic damage is strongly associated with poor outcome in patients with SAH.1–3 Although CVS has been extensively studied over the past 4 decades, a clinically proved effective treatment still remains elusive. Measures of proven value in decreasing the risk of delayed cerebral ischemia are liberal supply of fluids, avoidance of antihypertensive drugs, and intravascular administration of nimodipine in patients with SAH.4 Several studies have demonstrated that either intraarterial (IA), intravenous (IV), or intrathecal (IT) administration of nimodipine reduced vasospasm.5–7 However, a clinical trial in stroke has shown that IV nimodipine reduced blood pressure and worsened neurologic outcome.8 To From the Department of Neurosurgery, Renji Hospital, Shanghai Jiaotong University, School of Medicine, Shanghai, China. Submitted February 25, 2008; accepted in revised form April 18, 2008. Fei Wang is the co-first author. Correspondence: Ji-yao Jiang, MD, PhD, Department of Neurosurgery, Renji Hospital, Shanghai Jiaotong University, School of Medicine, Shanghai 200127, People’s Republic of China (E-mail: [email protected]).
prevent the hypotension during IV administration of nimodipine, some neurosurgeons attempt to directly perfuse relatively lowdose nimodipine in the surgical field for relieving CVS after clip of intracranial aneurysms. However, there is no report to confirm the topical administration of nimodipine in relieving CVS after SAH. In the present study, we explored the effects of different concentrations of topical administration of nimodipine on relieving CVS after SAH in rabbits.
MATERIALS AND METHODS CVS Model in Rabbits Forty female New Zealand rabbits (2.3–2.7 kg) were anesthetized by intramarginal auricular vein injection of urethane. Animals were then fixed lying down on their left side. A cut was made perpendicular to the zygomatic arc through its midpoint between superior temporal line and 0.5 cm below zygomatic arc. A small window was opened in the skull and a piece of dura was removed. The temporal lobe was lifted and the optic nerve was reached through the major wing of sphenoid bone. A piece of silicone rubber catheter was positioned in basilar cisterns with one end close to the optic nerve, the other fixed to the surface of temporal muscle. One milliliter blood (without anticoagulation agents) taken from the animal’s own central tragal artery was infused through the catheter into basilar cistern.9 Experimental Groups In 40 animals with injection of autologous nonheparinized arterial blood, 24 CVS models were successfully established. The 24 CVS animals were randomly divided into 4 groups by different concentrations of nimodipine tested. Group I (n ⫽ 7): nimodipine original stock solution/normal saline ⫽ 1/19 (0.01 mg/mL); group II (n ⫽ 6): nimodipine original stock solution/normal saline ⫽ 1/9 (0.02 mg/mL); group III (n ⫽ 5): nimodipine original stock solution/normal saline ⫽ 1/4 (0.04 mg/mL); and group IV (n ⫽ 6) with no nimodipine, but 5% ethanol dissolved in normal saline as the control group (because the Nimotop original stock contains 4.75% ethanol). Nimodipine Topical Perfusion Three days after the blood infusion, the surgical sites were reopened and animals were treated by topical perfusion of different concentrations of nimodipine. A total of 20 mL nimodipine (or ethanol–saline control) solution was administrated into the surgical area. Blood Flow Velocity Measurement Blood flow velocity (VBF) was monitored at the middle cerebral artery (MCA) by DWL transcranial Doppler (DWL MultiDop X2, Compumedics, Germany) and a 16-MHz highfrequency continuous mini probe (DWL, 16 MHz, Compumedics) before and 5, 15, 30, and 60 minutes after the drug
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TABLE 1. The blood flow velocity of the middle cerebral artery in each group of rabbits (cm/sec, X ⫾ SD) Group
n
Before perfusion
5 min
15 min
30 min
60 min
I (0.01 mg/mL) II (0.02 mg/mL) III (0.04 mg/mL) IV (Placebo)
7 6 5 6
24.1 ⫾ 4.1 25.3 ⫾ 3.9 23.2 ⫾ 4.0 23.2 ⫾ 2.0
24.7 ⫾ 6.1 21.8 ⫾ 4.1 21.6 ⫾ 2.9 25.3 ⫾ 2.7
22.9 ⫾ 3.0 20.7 ⫾ 4.2 18.6 ⫾ 2.5a 23.2 ⫾ 3.6
21.0 ⫾ 3.8 21.0 ⫾ 3.0 17.4 ⫾ 2.1b 21.5 ⫾ 2.7
20.9 ⫾ 3.3 19.3 ⫾ 3.1a 16.0 ⫾ 2.9b 21.8 ⫾ 3.2
a b
P ⬍ 0.05. P ⬍ 0.01.
application. A technician who measured VBF was blinded to the randomization. Statistical Analysis Data were analyzed in Statistic 6.0 using repeatedmeasures analysis of variance followed by Dunnett test.
RESULTS Establishment of Rabbit CVS Model The mean VBF of MCA in 24 CVS animals was 13.1 ⫾ 3.6 cm/sec before the blood infusion. The mean VBF was significantly increased to 24.3 ⫾ 4.2 cm/sec (P ⬍ 0.01) at 3 days after the blood infusion (before nimodipine perfusion), indicating the successful establishment of CVS model in these 24 animals (60%, 24/40). Effect of Nimodipine Administration on VBF of MCA There were no significant changes of VBF during topical administration in group I (0.01 mg/mL) (P ⬎ 0.05). However, the VBF was significantly decreased at 60 minutes after topical administration of nimodipine in group II (0.02 mg/mL) (P ⬍ 0.05). Furthermore, the VBF showed a decrease at 15 minutes and became more significant at 30 and 60 minutes after topical administration of nimodipine in group III (0.04 mg/mL) (P ⬍ 0.01). There were no significant differences of VBF before and after topical administration in the control group IV (Table 1). Effect of Nimodipine Administration on Blood Pressure There were no significant changes of blood pressure before, during, and after topical administration of nimodipine or placebo in all groups (P ⬎ 0.05) (Table 2).
DISCUSSION In this study, we have successfully established an animal CVS model with injection of blood into cerebral basilar cisterns in 24 rabbits (60%, 24/40). The topical administration of 1:5 (0.04 mg/mL) to 1:10 (0.02 mg/mL), but not 1:20 (0.01 mg/ mL) concentration of nimodipine significantly alleviates CVS at 3 days after SAH. Our data suggest that it may be helpful for
neurosurgeons to use topical administration of nimodipine for relieving CVS during surgical clip of intracranial aneurysms. There are now a couple of ways for administration of nimodipine, including IA, IV, IT, and topical perfusion of cerebral surgical field. Firat et al5 compared the efficacy of IA or IT nimodipine treatment in a rabbit model of chronic CVS. They found that both IA and IT nimodipine were effective in relieving vertebral and basilary vasospasm (P ⬍ 0.05). Marbacher et al6 assessed the efficacy of continuous IT infusions of nimodipine in preventing delayed CVS associated with SAH in an animal model. They found that continuous IT injection of nimodipine prevented SAH-induced CVS. Hui and Lau7 examined the efficacy of IA nimodipine for the treatment of CVS after SAH in CVS patients. The average dose of nimodipine administered per vessel was 3.3 mg. The mean increase in arterial diameter was 66.6% in the vasospastic segment. However, clinical trials show that IA or IV administration of high-dose nimodipine may cause hypotension and worsen the outcome of patients. Ahmed et al randomly divided the patients with ischemic stroke into placebo (n ⫽ 100), 1 mg/hr (low dose) nimodipine (n ⫽ 101), or 2 mg/hr (high dose) nimodipine (n ⫽ 94). Nimodipine treatment resulted in a statistically significant reduction in systolic blood pressure and diastolic blood pressure (DBP) from baseline compared with placebo during the first few days. Furthermore, a significant correlation between DBP reduction and worsening of the neurologic score was found for the high-dose group (P ⫽ 0.048). Patients with a DBP reduction of ⱖ20% in the high-dose group had a significantly increased adjusted odds ratio for the compound outcome variable death or dependency (Barthel Index ⬍60) and death alone compared with all placebo patients. This study suggests that DBP reduction was associated with neurologic worsening after the IV administration of high-dose nimodipine after acute stroke.8 The VBF is determined by the cerebral blood flow volume (Q) and the cerebral vessel caliber (D) as VBF ⫽ 4Q/D2. VBF is inversely correlated to D, when Q is fixed.10 Thus, VBF could be used as an estimate of the degree of vascular stenosis. Higher VBF measured by transverse cerebellar diameter indicates more severe vascular stenosis. Bilateral MCAs have been used as the
TABLE 2. The blood pressure in each group of rabbits (mm Hg) Group
n
Before perfusion
5 min
15 min
30 min
60 min
I (0.01 mg/mL) II (0.02 mg/mL) III (0.04 mg/mL) IV (Placebo)
7 6 5 6
101.86 ⫾ 2.50 102.00 ⫾ 2.28 101.00 ⫾ 3.09 101.17 ⫾ 3.09
102.14 ⫾ 2.39 99.20 ⫾ 1.53 99.67 ⫾ 3.34 99.67 ⫾ 3.34
101.43 ⫾ 2.89 98.20 ⫾ 2.03 99.02 ⫾ 2.87 99.00 ⫾ 2.88
98.43 ⫾ 2.10 99.40 ⫾ 2.13 99.50 ⫾ 2.62 99.50 ⫾ 2.62
100.67 ⫾ 3.01 98.71 ⫾ 2.14 99.20 ⫾ 1.74 98.33 ⫾ 2.32
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optimal location to measure the vascular stenosis in previous studies.11,12 Human MCA is the terminal artery of the internal carotid artery (ICA) with few collaterals and a long straight trunk, which makes it easy to be measured. The VBF in human MCA is well inversely correlated to the vascular caliber. Thus, the degree of human CVS is usually measured by the mean VBF in MCAs. In addition, VBF in proximal extracranial ICA should also be measured. The VBF ratio of MCA/ICA is an important clinical index to assess the degree of CVS. Lindegaard et al10 suggested that the normal ratio of VBF in MCA and extracranial ICA should be less than 3. High MCA/ICA VBF ratios larger than 3 indicates the existence of CVS. The higher the ratio, the more severe the spasm. Rabbits have fewer transcranial perforating vessels, making them ideal animals to study cerebral hemodynamics.13 Recently, 16 to 20 MHz high-frequency continuous mini Doppler probes have been widely used to monitor the VBF in exposed vessels during neurologic surgeries. In this study, we successfully established the CVS model in rabbits with injection of blood into basilar cisterns, which increased VBF ⬎10 cm/sec after SAH compared with pre-SAH as the standard to diagnose the CVS.14 The etiology of post-SAH CVS is still unclear. It is generally believed that multiple factors may be involved, including neuronal, mechanical, and biochemical factors, inflammatory and immune reactions, vascular stenosis caused by the thickening of vessel walls, and calcium overload in the smooth muscle cells of artery.15,16 Nevertheless, these potential mechanisms may share a final common pathway, which results in free Ca2⫹ overload in the cytoplasm of smooth muscle cells of the artery because of the Ca2⫹ influx and the Ca2⫹ release from intracellular calcium stores.17 There are 2 types of calcium channels: voltage-gated and ligand-gated calcium channels. The voltage-gated calcium channels are activated by the membrane depolarization in smooth muscle cells of cerebral arteries after SAH, whereas the ligand-gated calcium channels are activated by internally released chemical agents such as 5-hydroxytryptamine, adrenaline, and others, which bind to their receptors on the smooth muscle cell membrane of cerebral arteries. When calcium channels are activated, the concentration gradient across the cell membrane drives Ca2⫹ into the cell, which concerted with the Ca2⫹ release from internal stores, elevates the intracellular Ca2⫹ concentration, and elicits smooth muscle contraction of cerebral arteries through a cascade of biochemical reactions.17 Mechanisms of nimodipine relieving CVS is not clear. It has been shown that this effect is mediated by the blockade of L-type Ca2⫹-gated Ca2⫹ channels on the smooth muscle cell membrane of arteries. Ca2⫹ influx plays a critical role in the excitation– contraction coupling in vessel wall smooth muscles, especially in cerebral arteries. This may be related to the internal Ca2⫹ stores in smooth muscle cells of cerebral arteries, which can be easily depleted. The Ca2⫹ influx from extracellular space, which requires the normal activities of Ca2⫹ channels on the cell membrane, is the main source of Ca2⫹ to cause muscle contraction. Nimodipine selectively blocks the L-type Ca2⫹ channels on the smooth muscle cell membrane of cerebral arteries and the subsequent Ca2⫹ influx, which thus
© 2009 Lippincott Williams & Wilkins
inhibits the cerebral vasoconstriction and relieves CVS after SAH. REFERENCES 1. Shimidt JM, Rincon F, Fernandez A, et al. Cerebral infarction associated with acute subarachnoid hemorrhage. Neurocrit Care 2007; 7:10 –17. 2. Weidawer S, Lanfermann H, Raabe A, et al. Impairment of cerebral perfusion and infarction patterns attributable to vasospasm after aneurysmal subarachnoid hemorrhage: a prospective MRI and DAS study. Stroke 2007;38:1831– 6. 3. Fergusen S, Muedonald RL. Predictors of cerebral infarction in patients with aneurysmal subarachnoid hemorrhage. Neurosurgery 2007;60:658 – 67. 4. Gijn J, Rinkel GJ. Subarachnoid hemorrhage: diagnosis, causes, and management. Brain 2001;124:249 –78. 5. Firat MM, Gelebek V, Orer HS, et al. Selective intraarterial nimodipine treatment in an experimental subarachnoid hemorrhage model. Am J Neuroradiol 2005;26:1357– 62. 6. Marbacher S, Neuschmelting V, Graupner T, et al. Prevention of delayed cerebral vasospasm by continuous intrathecal infusion of glyceroltrinitrate and nimodipine in the rabbit model in vivo. Int Care Med 2008;34:932– 8. 7. Hui C, Lau KP. Efficacy of intra-arterial nimodipine in the treatment of cerebral vasospasm complicating subarachnoid haemorrhage. Clin Radiol 2005;60:1030 – 6. 8. Ahmed N, Nasman P, Wahlgren NG. Effect of intravenous nimodipine on blood pressure and outcome after acute stroke. Stroke 2000;31: 1250 –5. 9. Zhou ML, Shi JX, Zhu JQ, et al. Comparison between one- and twohemorrhage models of cerebral vasospasm in rabbits. J Neurosci Methods 2007;159:318 –24. 10. Lindegaard KF, Nornes H, Bakke SJ, et al. Cerebral vasospasm diagnosis by means of angiography and blood velocity measurements. Acta Neurochir (wien) 1989;100:12–24. 11. Aasild R, Huber P, Nornes H, et al. Evaluation of cerebrovascular spasm with transcranial Doppler ultrasound. J Neurosurg 1984;60:37– 41. 12. Seiler RW, Nirkko AC. Effect of nimodipine on cerebrovascular response to CO2 on asymptomatic individuals and patients with subarachnoid hemorrhage: a transcranial Doppler ultrasound study. Neurosurgery 1990;27:247–51. 13. Li Y-H, Fu Y, Ai JP, et al. Examination of post-SAH CVS by transcranial Doppler. Chin J Ultras Med 1992;8:418 –9. 14. He D-H, Ma L-T. Comparison between papaverine and Nimotop in the treatment of cerebral vasospasm. J Jinan Univ Nat Sci Med 2002;21: 105– 8. 15. Schwartz HJ. Cerebral vasospasm: a consideration after various cellular mechanisms involved in the pathophysiology. Neurocrit Care 2004;1:235– 46. 16. Borel CO, McKee A, Parra A, et al. Possible role for vascular proliferation in cerebral vasospasm after subarachnoid hemorrhage. Stroke 2003;34:427–33. 17. Wellman GC. Ion channels and calcium signalling in cerebral arteries following subarachnoid hemorrhage. Neurol Res 2006;28:690 –702.
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Effects of Dose-Response of Topical Administration of Nimodipine on Cerebral Vasospasm After Subarachnoid Hemorrhage in Rabbits Yu-Hua Yin, MD, Fei Wang, MD, Yao-Hua Pan, MD, Yong Wang, MD, PhD, Yu Wang, MD, Qi-Zhong Luo, MD and Ji-Yao Jiang, MD, PhD
Abstract: Background: To explore the dose-response effects of topical administration of nimodipine on cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH) in rabbits. Methods: The CVS model was established by injection of fresh autologous nonheparinized arterial blood into the subtemporal area of basilar cisterns. The 24 CVS animals were randomly divided into 4 groups, group I (n ⫽ 7): nimodipine original stock solution/normal saline ⫽ 1/19 (0.01 mg/mL); group II (n ⫽ 6): nimodipine original stock solution/normal saline ⫽ 1/9 (0.02 mg/mL); group III (n ⫽ 5): nimodipine original stock solution/normal saline ⫽ 1/4 (0.04 mg/mL); and group IV (n ⫽ 6) with no nimodipine, but 5% ethanol dissolved in normal saline as the control group. The operative area was administrated with nimodipine at different concentrations or alcohol–saline at 3 days after SAH. The blood flow velocity of middle cerebral artery was measured at 5, 15, 30, and 60 minutes after topical administration of nimodipine by transverse cerebellar diameter monitoring. Results: Blood flow velocity of middle cerebral artery in group II (0.02 mg/mL) and in group III (0.04 mg/mL) significantly decreased at 60 and 15 minutes, respectively, after topical administration of nimodipine (P ⬍ 0.05), and even more significantly at 30 and 60 minutes after topical administration of nimodipine in group III (0.04 mg/mL) (P ⬍ 0.01). Conclusion: Topical administration of nimodipine at the concentrations of 1:5 (0.04 mg/mL) and 1:10 (0.02 mg/mL) significantly alleviates CVS after SAH, which indicates that topical administration of nimodipine may be useful for CVS of patients with SAH during surgical clip of intracranial aneurysms. Key Indexing Terms: subarachnoid hemorrhage; cerebral vasospasm; nimodipine. [Am J Med Sci 2009;337(2):123–125.]
M
ore and more clinical studies show that high frequent rate of cerebral vasospasm (CVS) happens after subarachnoid hemorrhage (SAH), which may cause cerebral ischemia and infarction. Cerebral ischemic damage is strongly associated with poor outcome in patients with SAH.1–3 Although CVS has been extensively studied over the past 4 decades, a clinically proved effective treatment still remains elusive. Measures of proven value in decreasing the risk of delayed cerebral ischemia are liberal supply of fluids, avoidance of antihypertensive drugs, and intravascular administration of nimodipine in patients with SAH.4 Several studies have demonstrated that either intraarterial (IA), intravenous (IV), or intrathecal (IT) administration of nimodipine reduced vasospasm.5–7 However, a clinical trial in stroke has shown that IV nimodipine reduced blood pressure and worsened neurologic outcome.8 To From the Department of Neurosurgery, Renji Hospital, Shanghai Jiaotong University, School of Medicine, Shanghai, China. Submitted February 25, 2008; accepted in revised form April 18, 2008. Fei Wang is the co-first author. Correspondence: Ji-yao Jiang, MD, PhD, Department of Neurosurgery, Renji Hospital, Shanghai Jiaotong University, School of Medicine, Shanghai 200127, People’s Republic of China (E-mail: [email protected]).
prevent the hypotension during IV administration of nimodipine, some neurosurgeons attempt to directly perfuse relatively lowdose nimodipine in the surgical field for relieving CVS after clip of intracranial aneurysms. However, there is no report to confirm the topical administration of nimodipine in relieving CVS after SAH. In the present study, we explored the effects of different concentrations of topical administration of nimodipine on relieving CVS after SAH in rabbits.
MATERIALS AND METHODS CVS Model in Rabbits Forty female New Zealand rabbits (2.3–2.7 kg) were anesthetized by intramarginal auricular vein injection of urethane. Animals were then fixed lying down on their left side. A cut was made perpendicular to the zygomatic arc through its midpoint between superior temporal line and 0.5 cm below zygomatic arc. A small window was opened in the skull and a piece of dura was removed. The temporal lobe was lifted and the optic nerve was reached through the major wing of sphenoid bone. A piece of silicone rubber catheter was positioned in basilar cisterns with one end close to the optic nerve, the other fixed to the surface of temporal muscle. One milliliter blood (without anticoagulation agents) taken from the animal’s own central tragal artery was infused through the catheter into basilar cistern.9 Experimental Groups In 40 animals with injection of autologous nonheparinized arterial blood, 24 CVS models were successfully established. The 24 CVS animals were randomly divided into 4 groups by different concentrations of nimodipine tested. Group I (n ⫽ 7): nimodipine original stock solution/normal saline ⫽ 1/19 (0.01 mg/mL); group II (n ⫽ 6): nimodipine original stock solution/normal saline ⫽ 1/9 (0.02 mg/mL); group III (n ⫽ 5): nimodipine original stock solution/normal saline ⫽ 1/4 (0.04 mg/mL); and group IV (n ⫽ 6) with no nimodipine, but 5% ethanol dissolved in normal saline as the control group (because the Nimotop original stock contains 4.75% ethanol). Nimodipine Topical Perfusion Three days after the blood infusion, the surgical sites were reopened and animals were treated by topical perfusion of different concentrations of nimodipine. A total of 20 mL nimodipine (or ethanol–saline control) solution was administrated into the surgical area. Blood Flow Velocity Measurement Blood flow velocity (VBF) was monitored at the middle cerebral artery (MCA) by DWL transcranial Doppler (DWL MultiDop X2, Compumedics, Germany) and a 16-MHz highfrequency continuous mini probe (DWL, 16 MHz, Compumedics) before and 5, 15, 30, and 60 minutes after the drug
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TABLE 1. The blood flow velocity of the middle cerebral artery in each group of rabbits (cm/sec, X ⫾ SD) Group
n
Before perfusion
5 min
15 min
30 min
60 min
I (0.01 mg/mL) II (0.02 mg/mL) III (0.04 mg/mL) IV (Placebo)
7 6 5 6
24.1 ⫾ 4.1 25.3 ⫾ 3.9 23.2 ⫾ 4.0 23.2 ⫾ 2.0
24.7 ⫾ 6.1 21.8 ⫾ 4.1 21.6 ⫾ 2.9 25.3 ⫾ 2.7
22.9 ⫾ 3.0 20.7 ⫾ 4.2 18.6 ⫾ 2.5a 23.2 ⫾ 3.6
21.0 ⫾ 3.8 21.0 ⫾ 3.0 17.4 ⫾ 2.1b 21.5 ⫾ 2.7
20.9 ⫾ 3.3 19.3 ⫾ 3.1a 16.0 ⫾ 2.9b 21.8 ⫾ 3.2
a b
P ⬍ 0.05. P ⬍ 0.01.
application. A technician who measured VBF was blinded to the randomization. Statistical Analysis Data were analyzed in Statistic 6.0 using repeatedmeasures analysis of variance followed by Dunnett test.
RESULTS Establishment of Rabbit CVS Model The mean VBF of MCA in 24 CVS animals was 13.1 ⫾ 3.6 cm/sec before the blood infusion. The mean VBF was significantly increased to 24.3 ⫾ 4.2 cm/sec (P ⬍ 0.01) at 3 days after the blood infusion (before nimodipine perfusion), indicating the successful establishment of CVS model in these 24 animals (60%, 24/40). Effect of Nimodipine Administration on VBF of MCA There were no significant changes of VBF during topical administration in group I (0.01 mg/mL) (P ⬎ 0.05). However, the VBF was significantly decreased at 60 minutes after topical administration of nimodipine in group II (0.02 mg/mL) (P ⬍ 0.05). Furthermore, the VBF showed a decrease at 15 minutes and became more significant at 30 and 60 minutes after topical administration of nimodipine in group III (0.04 mg/mL) (P ⬍ 0.01). There were no significant differences of VBF before and after topical administration in the control group IV (Table 1). Effect of Nimodipine Administration on Blood Pressure There were no significant changes of blood pressure before, during, and after topical administration of nimodipine or placebo in all groups (P ⬎ 0.05) (Table 2).
DISCUSSION In this study, we have successfully established an animal CVS model with injection of blood into cerebral basilar cisterns in 24 rabbits (60%, 24/40). The topical administration of 1:5 (0.04 mg/mL) to 1:10 (0.02 mg/mL), but not 1:20 (0.01 mg/ mL) concentration of nimodipine significantly alleviates CVS at 3 days after SAH. Our data suggest that it may be helpful for
neurosurgeons to use topical administration of nimodipine for relieving CVS during surgical clip of intracranial aneurysms. There are now a couple of ways for administration of nimodipine, including IA, IV, IT, and topical perfusion of cerebral surgical field. Firat et al5 compared the efficacy of IA or IT nimodipine treatment in a rabbit model of chronic CVS. They found that both IA and IT nimodipine were effective in relieving vertebral and basilary vasospasm (P ⬍ 0.05). Marbacher et al6 assessed the efficacy of continuous IT infusions of nimodipine in preventing delayed CVS associated with SAH in an animal model. They found that continuous IT injection of nimodipine prevented SAH-induced CVS. Hui and Lau7 examined the efficacy of IA nimodipine for the treatment of CVS after SAH in CVS patients. The average dose of nimodipine administered per vessel was 3.3 mg. The mean increase in arterial diameter was 66.6% in the vasospastic segment. However, clinical trials show that IA or IV administration of high-dose nimodipine may cause hypotension and worsen the outcome of patients. Ahmed et al randomly divided the patients with ischemic stroke into placebo (n ⫽ 100), 1 mg/hr (low dose) nimodipine (n ⫽ 101), or 2 mg/hr (high dose) nimodipine (n ⫽ 94). Nimodipine treatment resulted in a statistically significant reduction in systolic blood pressure and diastolic blood pressure (DBP) from baseline compared with placebo during the first few days. Furthermore, a significant correlation between DBP reduction and worsening of the neurologic score was found for the high-dose group (P ⫽ 0.048). Patients with a DBP reduction of ⱖ20% in the high-dose group had a significantly increased adjusted odds ratio for the compound outcome variable death or dependency (Barthel Index ⬍60) and death alone compared with all placebo patients. This study suggests that DBP reduction was associated with neurologic worsening after the IV administration of high-dose nimodipine after acute stroke.8 The VBF is determined by the cerebral blood flow volume (Q) and the cerebral vessel caliber (D) as VBF ⫽ 4Q/D2. VBF is inversely correlated to D, when Q is fixed.10 Thus, VBF could be used as an estimate of the degree of vascular stenosis. Higher VBF measured by transverse cerebellar diameter indicates more severe vascular stenosis. Bilateral MCAs have been used as the
TABLE 2. The blood pressure in each group of rabbits (mm Hg) Group
n
Before perfusion
5 min
15 min
30 min
60 min
I (0.01 mg/mL) II (0.02 mg/mL) III (0.04 mg/mL) IV (Placebo)
7 6 5 6
101.86 ⫾ 2.50 102.00 ⫾ 2.28 101.00 ⫾ 3.09 101.17 ⫾ 3.09
102.14 ⫾ 2.39 99.20 ⫾ 1.53 99.67 ⫾ 3.34 99.67 ⫾ 3.34
101.43 ⫾ 2.89 98.20 ⫾ 2.03 99.02 ⫾ 2.87 99.00 ⫾ 2.88
98.43 ⫾ 2.10 99.40 ⫾ 2.13 99.50 ⫾ 2.62 99.50 ⫾ 2.62
100.67 ⫾ 3.01 98.71 ⫾ 2.14 99.20 ⫾ 1.74 98.33 ⫾ 2.32
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Volume 337, Number 2, February 2009
Effects of Nimodipine on Cerebral Vasospasm
optimal location to measure the vascular stenosis in previous studies.11,12 Human MCA is the terminal artery of the internal carotid artery (ICA) with few collaterals and a long straight trunk, which makes it easy to be measured. The VBF in human MCA is well inversely correlated to the vascular caliber. Thus, the degree of human CVS is usually measured by the mean VBF in MCAs. In addition, VBF in proximal extracranial ICA should also be measured. The VBF ratio of MCA/ICA is an important clinical index to assess the degree of CVS. Lindegaard et al10 suggested that the normal ratio of VBF in MCA and extracranial ICA should be less than 3. High MCA/ICA VBF ratios larger than 3 indicates the existence of CVS. The higher the ratio, the more severe the spasm. Rabbits have fewer transcranial perforating vessels, making them ideal animals to study cerebral hemodynamics.13 Recently, 16 to 20 MHz high-frequency continuous mini Doppler probes have been widely used to monitor the VBF in exposed vessels during neurologic surgeries. In this study, we successfully established the CVS model in rabbits with injection of blood into basilar cisterns, which increased VBF ⬎10 cm/sec after SAH compared with pre-SAH as the standard to diagnose the CVS.14 The etiology of post-SAH CVS is still unclear. It is generally believed that multiple factors may be involved, including neuronal, mechanical, and biochemical factors, inflammatory and immune reactions, vascular stenosis caused by the thickening of vessel walls, and calcium overload in the smooth muscle cells of artery.15,16 Nevertheless, these potential mechanisms may share a final common pathway, which results in free Ca2⫹ overload in the cytoplasm of smooth muscle cells of the artery because of the Ca2⫹ influx and the Ca2⫹ release from intracellular calcium stores.17 There are 2 types of calcium channels: voltage-gated and ligand-gated calcium channels. The voltage-gated calcium channels are activated by the membrane depolarization in smooth muscle cells of cerebral arteries after SAH, whereas the ligand-gated calcium channels are activated by internally released chemical agents such as 5-hydroxytryptamine, adrenaline, and others, which bind to their receptors on the smooth muscle cell membrane of cerebral arteries. When calcium channels are activated, the concentration gradient across the cell membrane drives Ca2⫹ into the cell, which concerted with the Ca2⫹ release from internal stores, elevates the intracellular Ca2⫹ concentration, and elicits smooth muscle contraction of cerebral arteries through a cascade of biochemical reactions.17 Mechanisms of nimodipine relieving CVS is not clear. It has been shown that this effect is mediated by the blockade of L-type Ca2⫹-gated Ca2⫹ channels on the smooth muscle cell membrane of arteries. Ca2⫹ influx plays a critical role in the excitation– contraction coupling in vessel wall smooth muscles, especially in cerebral arteries. This may be related to the internal Ca2⫹ stores in smooth muscle cells of cerebral arteries, which can be easily depleted. The Ca2⫹ influx from extracellular space, which requires the normal activities of Ca2⫹ channels on the cell membrane, is the main source of Ca2⫹ to cause muscle contraction. Nimodipine selectively blocks the L-type Ca2⫹ channels on the smooth muscle cell membrane of cerebral arteries and the subsequent Ca2⫹ influx, which thus
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inhibits the cerebral vasoconstriction and relieves CVS after SAH. REFERENCES 1. Shimidt JM, Rincon F, Fernandez A, et al. Cerebral infarction associated with acute subarachnoid hemorrhage. Neurocrit Care 2007; 7:10 –17. 2. Weidawer S, Lanfermann H, Raabe A, et al. Impairment of cerebral perfusion and infarction patterns attributable to vasospasm after aneurysmal subarachnoid hemorrhage: a prospective MRI and DAS study. Stroke 2007;38:1831– 6. 3. Fergusen S, Muedonald RL. Predictors of cerebral infarction in patients with aneurysmal subarachnoid hemorrhage. Neurosurgery 2007;60:658 – 67. 4. Gijn J, Rinkel GJ. Subarachnoid hemorrhage: diagnosis, causes, and management. Brain 2001;124:249 –78. 5. Firat MM, Gelebek V, Orer HS, et al. Selective intraarterial nimodipine treatment in an experimental subarachnoid hemorrhage model. Am J Neuroradiol 2005;26:1357– 62. 6. Marbacher S, Neuschmelting V, Graupner T, et al. Prevention of delayed cerebral vasospasm by continuous intrathecal infusion of glyceroltrinitrate and nimodipine in the rabbit model in vivo. Int Care Med 2008;34:932– 8. 7. Hui C, Lau KP. Efficacy of intra-arterial nimodipine in the treatment of cerebral vasospasm complicating subarachnoid haemorrhage. Clin Radiol 2005;60:1030 – 6. 8. Ahmed N, Nasman P, Wahlgren NG. Effect of intravenous nimodipine on blood pressure and outcome after acute stroke. Stroke 2000;31: 1250 –5. 9. Zhou ML, Shi JX, Zhu JQ, et al. Comparison between one- and twohemorrhage models of cerebral vasospasm in rabbits. J Neurosci Methods 2007;159:318 –24. 10. Lindegaard KF, Nornes H, Bakke SJ, et al. Cerebral vasospasm diagnosis by means of angiography and blood velocity measurements. Acta Neurochir (wien) 1989;100:12–24. 11. Aasild R, Huber P, Nornes H, et al. Evaluation of cerebrovascular spasm with transcranial Doppler ultrasound. J Neurosurg 1984;60:37– 41. 12. Seiler RW, Nirkko AC. Effect of nimodipine on cerebrovascular response to CO2 on asymptomatic individuals and patients with subarachnoid hemorrhage: a transcranial Doppler ultrasound study. Neurosurgery 1990;27:247–51. 13. Li Y-H, Fu Y, Ai JP, et al. Examination of post-SAH CVS by transcranial Doppler. Chin J Ultras Med 1992;8:418 –9. 14. He D-H, Ma L-T. Comparison between papaverine and Nimotop in the treatment of cerebral vasospasm. J Jinan Univ Nat Sci Med 2002;21: 105– 8. 15. Schwartz HJ. Cerebral vasospasm: a consideration after various cellular mechanisms involved in the pathophysiology. Neurocrit Care 2004;1:235– 46. 16. Borel CO, McKee A, Parra A, et al. Possible role for vascular proliferation in cerebral vasospasm after subarachnoid hemorrhage. Stroke 2003;34:427–33. 17. Wellman GC. Ion channels and calcium signalling in cerebral arteries following subarachnoid hemorrhage. Neurol Res 2006;28:690 –702.
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