Transient Aortic Occlusion Research Articles

Abstract Mo100: Predictive Accuracy of Rightward Extrapolation of the Left Ventricular End-Diastolic Pressure-Volume Relationship in Healthy Swine

Objective: Myocardial stiffness is a primary determinant of left ventricular (LV) diastolic function and can be quantitatively described by the end-diastolic pressure-volume relationship (EDPVR). The EDPVR is traditionally derived by measuring LV end-diastolic pressure (EDP) and volume (EDV) during transient reductions in venous return (preload). However, the accuracy of this approach in predicting changes in LVEDP in response to a rise in LVEDV via rightward extrapolation has not been directly studied. Accordingly, we sought to assess the predictive accuracy of preload reduction-derived EDPVRs in estimating LV diastolic stiffness (ΔLVEDP/ΔLVEDV) in healthy swine. Methods: LVEDP and LVEDV were measured in swine (n=6) at rest and during transient inferior vena cava (IVC) occlusion (reduced preload), transient aortic occlusion (increased afterload), and intravenous phenylephrine (PE; 0.5 mg/kg/hr; increased afterload and preload). Pressure-volume data collected during IVC occlusion were used to generate the EDPVR, the accuracy of which was determined via comparison to measurements of ΔLVEDP/ΔLVEDV during aortic occlusion and PE. Results: The LV diastolic stiffness coefficient was greater when derived via aortic occlusion vs. IVC occlusion (0.057±0.013 vs. 0.022±0.004; p=0.03). As a result, IVC occlusion-derived EDPVRs underestimated the rise in LVEDP during aortic occlusion (7.6±2.2 vs. 13.5±2.1 mmHg; p=0.08). Similarly, ΔLVEDP/ΔLVEDV in response to aortic occlusion (0.96±0.28 mmHg/mL) tended to be higher than that predicted from the IVC occlusion-derived EDPVR (0.44±0.09 mmHg/mL; p=0.12). Compared with aortic occlusion, PE elicited a greater rise in LVEDV (31.5±5.4 vs.18.6±4.2 mL; p=0.08) and LVEDP (20.8±1.3 vs. 13.5±2.1 mmHg; p=0.01) but ΔLVEDP/ΔLVEDV was comparable between each condition (0.78±0.16 mmHg/mL vs. 0.96±0.28 mmHg/mL; p=0.60). However, ΔLVEDP/ΔLVEDV derived from PE tended to be higher than that from IVC occlusion (0.78±0.16 mmHg/mL vs. 0.44±0.09 mmHg/mL; p=0.10). Conclusions: Rightward extrapolation of the EDPVR derived via IVC occlusion underestimates the rise in LVEDP when LVEDV is increased in the normal heart. This was observed with increased afterload as well as when afterload and preload were simultaneously increased via PE. These findings reinforce the importance of assessing the hemodynamic response to increased LV loading directly, rather than extrapolating from EDPVRs created via transient preload reduction.

Abstract 361: Effect of Percutaneous Ventricular Assisted Device on a Recovery of Myocardial Function in Swine Model With Prolonged Cardiac Arrest

Background: Percutaneous ventricular assist device (pLVAD) support and Transient aortic balloon occlusion (AO) can preserve cerebral and cardiac blood flow during cardiopulmonary resuscitation (CPR), but it remains unclear if pLVAD reduces post-cardiac arrest myocardial dysfunction. Hypothesis: pLVAD support immediately after the return of spontaneous circulation (ROSC) improves early recovery of myocardial function following prolonged cardiac arrest. Aims: Evaluate the association between early post-ROSC pLVAD support and recovery of myocardial function in a swine model of prolonged cardiac arrest. Methods: This is a secondary analysis of a subset of animals that achieved ROSC in a study comparing pLVAD, transient AO or both during CPR after prolonged cardiac arrest. pLVAD, aortic occlusion, or both were initiated after 24 minutes of ventricular fibrillation cardiac arrest (8 min no-flow and 16 min mechanical CPR). AO was discontinued post-ROSC, and pLVAD support or standard care were continued. Beginning 60 minutes post-ROSC, pLVAD support was weaned to <1.0 L/min while maintaining a MAP >70 mmHg, and subsequently removed at 4 hours when feasible. The primary outcome was the recovery of cardiac index (CI) and left ventricular ejection fraction (LVEF) at 4 hours post-ROSC. Data are shown as mean (standard error). Results: Seventeen animals achieved ROSC without complication and were included in this analysis (pLVAD group, n = 11 [8 were removed from pLVAD], and standard care group, n = 6). For the primary outcome, the pLVAD group had significantly higher CI of 4.2(0.3) vs. 3.1(0.4) L/min/m2 (p=0.043) and LVEF 60(3) vs. 49(4) % (p=0.029) at 4 hours after ROSC, respectively, when compared with the standard care group. Focusing on the early period within 60 minutes after ROSC when maximum pLVAD flow was maintained, the pLVAD group had significantly higher coronary perfusion pressure (62[4] vs. 47[5] mmHg, p=0.019), lower LV stroke work index (3.9[3.0] vs. 14.9[4.4] cJ/m2, p=0.043), and lower total pulmonary resistance index (13.2[4.8] vs. 21.5[14.4] Wood Unit, p=0.001). Conclusion: These results suggest that early pLVAD support after ROSC is associated with better recovery myocardial function compared to standard care after prolonged cardiac arrest.

Effect of percutaneous ventricular assisted device on post-cardiac arrest myocardial dysfunction in swine model with prolonged cardiac arrest

BackgroundIt remains unclear if percutaneous left ventricular assist device (pLVAD) reduces post-cardiac arrest myocardial dysfunction. MethodsThis is a prespecified analysis of a subset of swine that achieved return of spontaneous circulation (ROSC) in a study comparing pLVAD, transient aortic occlusion (AO), or both during cardiopulmonary resuscitation (CPR). Devices were initiated after 24 minutes of ventricular fibrillation cardiac arrest (8 min no-flow and 16 min mechanical CPR). AO was discontinued post-ROSC, and pLVAD support or standard care were continued. Beginning 60 minutes post-ROSC, pLVAD support was weaned to < 1.0 L/min and subsequently removed at 240 minutes. The primary outcome was cardiac index (CI), stroke volume index (SVI), and left ventricular ejection fraction (LVEF) at 240 minutes post-ROSC. Data are shown as mean (standard error). ResultsSeventeen swine achieved ROSC without complication and were included in this analysis (pLVAD group, n = 11 and standard care group, n = 6). For the primary outcomes, the pLVAD group had significantly higher CI of 4.2(0.3) vs. 3.1(0.4) L/min/m2 (p = 0.043) and LVEF 60(3) vs. 49(4) % (p = 0.029) at 240 minutes after ROSC when compared with the standard care group, while SVI was not statistically significantly different (32[3] vs. 23[4] mL/min/m2, p = 0.054). During the first 60 minutes post-ROSC, the pLVAD group had significantly higher coronary perfusion pressure, lower LV stroke work index, and total pulmonary resistance index. ConclusionThese results suggest that early pLVAD support after ROSC is associated with better recovery myocardial function compared to standard care after prolonged cardiac arrest.

USP18 overexpression protects against spinal cord ischemia/reperfusion injury via regulating autophagy

BackgroundSpinal cord ischemia–reperfusion injury (SCII) is usually caused by spinal surgery, often leading to severe neurological deficits. The ubiquitin-specific protease 18 (USP18) plays a significant role in neurological diseases. ObjectiveThe present study was designed to assess the effects and mechanisms of USP18 on SCII. MethodsBy inducing transient aortic occlusion and subsequent reperfusion, a rat model of SCII was successfully established. The Basso-Beattie-Bresnahan scores, the inclined plane test, and hematoxylin and eosin (HE) were used to measure locomotor activity and histological changes in the injured spinal cords. Moreover, the SCII cell model was established using PC12 cells under oxygen-glucose deprivation and reoxygenation (OGD/R). Proinflammatory factors (TNF-α, IL-6, and INF-α) were examined using an ELISA kit. Cell apoptosis was assessed by Annexin V-FITC/PI double-staining and TUNEL assays. Western blot was used to detect the expression levels of proteins related to apoptosis and autophagy. ResultsUSP18 expression was decreasedin vivo and in vitro SCII models. The upregulation of USP18 ameliorated hind limbs' motor function, inhibiting inflammation and apoptosis after SCII in rats. USP18 overexpression in vitro may protect PC12 cells from OGD/R-induced damage by modulating inflammatory responses and apoptosis. Moreover, Overexpression of USP18 enhanced autophagy to inhibit cell apoptosis induced by SCII in vivo and in vitro. ConclusionsIn summary, USP18 overexpression protects against SCII via regulating autophagy.

Distinct Polarization Dynamics of Microglia and Infiltrating Macrophages: A Novel Mechanism of Spinal Cord Ischemia/Reperfusion Injury.

PurposeRecent studies indicate that microglia and monocyte-derived macrophages (MDMs) have different roles in diseases such as stroke and spinal cord injury, yet their respective polarized phenotypes and roles remain unclear in spinal cord ischemia/reperfusion injury (SCIRI).MethodsWe established a mouse model of SCIRI by transient aortic occlusion followed by reperfusion. Basso mouse scale (BMS) scores were used to test the locomotor functions. The histopathological changes in spinal cord were assessed by hematoxylin-eosin staining and NF-200 immunohistochemistry. Real-time PCR, immunofluorescence and flow cytometry were employed to analyze the polarized phenotypes of the microglia and infiltrating MDMs, and the resulting inflammatory responses. Furthermore, the role of infiltrating MDMs were investigated by MDMs depletion using systemic administration of clodronate-liposomes.ResultsSCIRI significantly impaired locomotor function of mice, accompanied with progressed necrosis, infiltration of inflammatory cells and neuron loss in the spinal cord. M1-related pro-inflammatory markers (iNOS, CD16, CD86 and TNF-α) increased dramatically in the early phase following SCIRI. In contrast, M2-related anti-inflammatory markers (CD204 and CD206) elevated at later stage. Besides, the invading MDMs were principally pro-inflammatory M1 type, transiently restricted to the first week after SCIRI. In contrast, microglia were the main source of anti-inflammatory M2 type. Furthermore, depletion of MDMs by clodronate-liposomes significantly preserved neurological functions and relieved neuronal damage caused by SCIRI.ConclusionThese findings suggested distinct polarized status of resident microglia and MDMs following SCIRI. Inhibition of the invading MDMs may represent a novel approach for SCIRI treatment.

Direct in vivo assessment of global and regional mechanoelectric feedback in the intact human heart

BackgroundInhomogeneity of ventricular contraction is associated with sudden cardiac death, but the underlying mechanisms are unclear. Alterations in cardiac contraction impact electrophysiological parameters through mechanoelectric feedback. This has been shown to promote arrhythmias in experimental studies, but its effect in the in vivo human heart is unclear.ObjectiveThe purpose of this study was to quantify the impact of regional myocardial deformation provoked by a sudden increase in ventricular loading (aortic occlusion) on human cardiac electrophysiology.MethodsIn 10 patients undergoing open heart cardiac surgery, left ventricular (LV) afterload was modified by transient aortic occlusion. Simultaneous assessment of whole-heart electrophysiology and LV deformation was performed using an epicardial sock (240 electrodes) and speckle-tracking transesophageal echocardiography. Parameters were matched to 6 American Heart Association LV model segments. The association between changes in regional myocardial segment length and activation-recovery interval (ARI; a conventional surrogate for action potential duration) was studied using mixed-effect models.ResultsIncreased ventricular loading reduced longitudinal shortening (P = .01) and shortened ARI (P = .02), but changes were heterogeneous between cardiac segments. Increased regional longitudinal shortening was associated with ARI shortening (effect size 0.20 [0.01–0.38] ms/%; P = .04) and increased local ARI dispersion (effect size –0.13 [–0.23 to –0.03] ms/%; P = .04). At the whole organ level, increased mechanical dispersion translated into increased dispersion of repolarization (correlation coefficient r = 0.81; P = .01).ConclusionMechanoelectric feedback can establish a potentially proarrhythmic substrate in the human heart and should be considered to advance our understanding and prevention of cardiac arrhythmias.

Transient Aortic Occlusion Augments Collateral Blood Flow and Reduces Mortality During Severe Ischemia due to Proximal Middle Cerebral Artery Occlusion.

Cerebral collateral circulation provides alternative vascular routes for blood to reach ischemic tissues during stroke. Collateral therapeutics attempt to augment flow through these collateral channels to reduce ischemia and brain damage during acute ischemic stroke. Transient aortic occlusion (TAO) has pre-clinical data suggesting that it can augment collateral blood flow and clinical data suggesting a benefit for patients with moderate cortical strokes. By diverting blood from the periphery towards the cerebral circulation, TAO has the potential to augment primary collateral flow at the circle of Willis and thereby improve outcome even during large, hemispheric strokes. Using proximal middle and anterior cerebral artery occlusion in rats, we demonstrate that TAO reduces mortality and improves collateral blood flow in severely ischemic animals. As such, TAO may be an effective therapy to reduce early mortality during severe ischemia associated with proximal occlusions.

Clinical indicators of paraplegia underplay universal spinal cord neuronal injury from transient aortic occlusion

Paraplegia following complex aortic intervention relies on crude evaluation of lower extremity strength such as whether the patient can lift their legs or flex the ankle. Little attention has been given to the possible long-term neurologic sequelae following these procedures in patients appearing functionally normal. We hypothesize that mice subjected to minimal ischemic time will have functional and histological changes despite the gross appearance of normal function.Male mice underwent 3min of aortic occlusion (n=14) or sham surgery (n=4) via a median sternotomy. Neurologic function was graded by Basso Motor Score (BMS) preoperatively and at 24h intervals after reperfusion. Mice appearing functionally normal and sham mice were placed on a walking beam and recorded on high-definition, for single-frame motion analysis. After 96hrs, spinal cords were removed for histological analysis.Following 3min of ischemia, functional outcomes were split evenly with either mice displaying almost normal function n=7 or near complete paraplegia n=7. Additionally, single-frame motion analysis revealed significant changes in gait. Histologically, there was a significant stepwise reduction of neuronal viability, with even the normal function ischemic group demonstrating significant loss of neurons.Despite the appearance of normal function, temporary ischemia induced marked cyto-architectural changes and neuronal degeneration. Furthermore high-definition gait analysis revealed significant changes in gait and activity following thoracic aortic occlusion. These data suggest that all patients undergoing procedures, even with short ischemic times, may have spinal cord injury that is not evident clinically.

Cilostazol attenuates spinal cord ischemia-reperfusion injury in rabbits.

The aim of this study was to evaluate the pretreatment effect of cilostazol on spinal cord ischemia-reperfusion injury. Prospective, interventional study. Research laboratory, single institution. Twenty-four New Zealand white rabbits. Twenty-four rabbits were divided into 3 equal groups: group I (sham), group II (ischemia-reperfusion, control group), and group III (cilostazol, administered orally 30 mg/kg/day for 3 days before the surgery). Spinal cord ischemia was induced by clamping the aorta both below the left renal artery and above the iliac bifurcation for 30 minutes. Seventy-two hours postoperatively, the motor function of the lower limbs was evaluated in each animal according to the modified Tarlov score. Spinal cord and blood samples were taken for histopathologic and biochemical analyses at the 72nd hour of reperfusion. All rabbits in the ischemia-reperfusion group (group II) showed severe neurologic deficits. The median (IQR) Tarlov scores postoperatively at 72 hours in groups I, II, and III were 5.0(-), 2.0(1.0), and 4.5(1.0), respectively. Administration of cilostazol resulted in a significant reduction in motor dysfunction when compared with the ischemia-reperfusion group (p<0.001). In the ischemia-reperfusion group, serum and tissue glutathione peroxidase and superoxide dismutase activity were significantly less compared with the sham group (group I) (p<0.05). Serum and tissue glutathione peroxidase and superoxide dismutase levels in the cilostazol-treated group (group III) were higher compared with the ischemia-reperfusion group (p<0.05). In the cilostazol-treated group, serum and tissue malondialdehyde levels were lower compared with the ischemia-reperfusion group (p<0.05). Histopathologic analysis found decreased neuronal injury in the cilostazol group when compared with the ischemia-reperfusion group (p< 0.05). This study showed that pretreatment with cilostazol significantly ameliorated neurologic functional outcome and attenuated neuronal histopathologic injury after transient aortic occlusion in rabbits.

Effects of Cilostazol on Oxidative Stress, Systemic Cytokine Release, and Spinal Cord Injury in a Rat Model of Transient Aortic Occlusion

Cilostazol is a phosphodiesterase inhibitor that has anti-inflammatory potential in addition to vasodilator and antiplatelet effects. The aim of this study was to determine the influence of cilostazol on biochemical markers of oxidative damage, proinflammatory cytokine release, and spinal cord injury after transient aortic occlusion in rats. Animals were randomized into 3 groups. Sham group rats were subjected to laparotomy without aortic occlusion. Control group rats were pretreated with intraperitoneal dimethyl sulfoxide, and cilostazol group rats received intraperitoneal cilostazol (20 mg/kg/day) for 3 days before the induction of ischemia. Ischemia was induced by clamping of the infrarenal aorta, and 48 hours after reperfusion, Tarlov grades were assessed and spinal cord conduction velocities (SCCVs) were measured using epidural electrical stimulation. Erythrocyte superoxide dismutase (SOD) and catalase activities and plasma malondialdehyde, serum tumor necrosis factor-α, interleukin-1β, and interleukin-6 levels were analyzed. Spinal cord histopathology was examined to determine neuronal damage and tissue inflammation. Aortic occlusion caused significant increases in SOD, catalase activities, and malondialdehyde and cytokine levels accompanied by spinal cord injury. Cilostazol significantly reduced malondialdehyde levels but did not significantly alter the activations of antioxidant enzymes, levels of proinflammatory cytokines, or histologic severity of inflammation. The differences regarding the results of Tarlov grading, SCCVs, and neuronal viability between the ischemic and cilostazol pretreated groups were statistically nonsignificant. The present experimental study indicated that cilostazol pretreatment used in this study before aortic occlusion decreased lipid peroxidation, which may be related to the reduction of reactive oxygen species. Cilostazol did not significantly suppress systemic cytokine release and prevent spinal cord inflammation and injury; however, it did show some benefit. Additional investigations might be needed to determine the critical dose of cilostazol for clarifying the protective role of this drug in spinal cord ischemia/reperfusion injury.

Augmenting Collateral Blood Flow during Ischemic Stroke via Transient Aortic Occlusion

Collateral circulation provides an alternative route for blood flow to reach ischemic tissue during a stroke. Blood flow through the cerebral collaterals is a critical predictor of clinical prognosis after stroke and response to recanalization, but data on collateral dynamics and collateral therapeutics are lacking. Here, we investigate the efficacy of a novel approach to collateral blood flow augmentation to increase collateral circulation by optically recording blood flow in leptomeningeal collaterals in a clinically relevant model of ischemic stroke. Using high-resolution laser speckle contrast imaging (LSCI) during thromboembolic middle cerebral artery occlusion (MCAo), we demonstrate that transiently diverting blood flow from peripheral circulation towards the brain via intra-aortic catheter and balloon induces persistent increases in blood flow through anastomoses between the anterior and middle cerebral arteries. Increased collateral flow restores blood flow in the distal middle cerebral artery segments to baseline levels during aortic occlusion and persists for over 1 hour after removal of the aortic balloon. Given the importance of collateral circulation in predicting stroke outcome and response to treatment, and the potential of collateral flow augmentation as an adjuvant or stand-alone therapy for acute ischemic stroke, this data provide support for further development and translation of collateral therapeutics including transient aortic occlusion.

Intrathecal transplantation of bone marrow stromal cells attenuates blood-spinal cord barrier disruption induced by spinal cord ischemia-reperfusion injury in rabbits

Intrathecal administration of bone marrow stromal cells has been found to produce beneficial effects on ischemia-reperfusion injury to the spinal cord. The blood-spinal cord barrier is critical to maintain spinal cord homeostasis and neurologic function. However, the effects of bone marrow stromal cells on the blood-spinal cord barrier after spinal cord ischemia-reperfusion injury are not well understood. This study investigated the effects and possible mechanisms of bone marrow stromal cells on blood-spinal cord barrier disruption induced by spinal cord ischemia-reperfusion injury. This was a prospective animal study conducted at the Central Laboratory of the First Affiliated Hospital, China Medical University. The study used 81 Japanese white rabbits (weight, 1.8-2.6 kg). Spinal cord ischemia-reperfusion injury was induced in rabbits by infrarenal aortic occlusion for 30 minutes. Two days before the injury was induced, bone marrow stromal cells (1 × 10(8) in 0.2-mL phosphate-buffered saline) were transplanted by intrathecal injection. Hind-limb motor function was assessed using Tarlov criteria, and motor neurons in the ventral gray matter were counted by histologic examination. The permeability of the blood-spinal cord barrier was examined using Evans blue (EB) and lanthanum nitrate as vascular tracers. The expression and localization of tight junction protein occludin were assessed by Western blot, real-time polymerase chain reaction, and immunofluorescence analysis. Matrix metalloproteinase-9 (MMP-9) and tumor necrosis factor-α (TNF-α) expression were also measured. Intrathecal transplantation of bone marrow stromal cells minimized the neuromotor dysfunction and histopathologic deficits (P < .01) and attenuated EB extravasation at 4 hours (5.41 ± 0.40 vs 7.94 ± 0.36 μg/g; P < .01) and 24 hours (9.03 ± 0.44 vs 15.77 ± 0.89 μg/g; P < .01) after spinal cord ischemia-reperfusion injury. In addition, bone marrow stromal cells treatment suppressed spinal cord ischemia-reperfusion injury-induced decreases in occludin (P < .01). Finally, bone marrow stromal cells reduced the excessive expression of MMP-9 and TNF-α (P < .01). Pre-emptive intrathecal transplantation of bone marrow stromal cells stabilized the blood-spinal cord barrier integrity after spinal cord ischemia-reperfusion injury in a rabbit model of transient aortic occlusion. This beneficial effect was partly mediated by inhibition of MMP-9 and TNF-α and represents a potential therapeutic approach to mitigating spinal cord injury after aortic occlusion. Clinical thoracoabdominal aorta surgery may trigger spinal cord ischemia-reperfusion injury, resulting in paraplegia as well as bladder, bowel, and sexual dysfunction. Transplantation of bone marrow stromal cells has attracted increasing attention in the field of nervous system protection, but its mechanisms have not been elucidated completely. The blood-spinal cord barrier plays a crucial role to maintain normal spinal cord function. This study suggested that intrathecal transplantation of bone marrow stromal cells stabilized blood-spinal cord barrier integrity through inhibiting the upregulation of matrix metalloproteinase-9 and tumor necrosis factor-a and ameliorated spinal cord ischemia-reperfusion injury. This may provide a novel train of thought to enhance the protective effects of bone marrow stromal cells on spinal cord injury.

Rapid Ischemic Preconditioning with a Short Reperfusion Time Prevents Delayed Paraplegia in a Rabbit Model

Surgery for thoracic and thoracoabdominal aortic aneurysms can be complicated by a significant incidence of neurogenic deficits due to spinal cord ischemia. In this study, we investigated whether ischemic preconditioning (IPC) improves neurologic outcome in a rabbit model. Forty rabbits underwent infrarenal aortic occlusion. The IPC group (n = 20) had 10 minutes of aortic occlusion to induce spinal cord ischemia, 40 minutes of reperfusion, and 30 minutes of ischemia, whereas the control group (n = 20) had only 30 minutes of ischemia. Tarlov scoring (0, paraplegia; 4, normal) was used to evaluate neurologic functions 7 days later, and spinal cord segments (L4-L6) were stained with hematoxylin and eosin for histologic evaluation. Complete paraplegia (grade 0) occurred in 15 (75%) of the 20 control animals, whereas in the IPC group, 13 (65%) of 20 animals were completely normal (grade 4) (P < .05). IPC is beneficial for protecting against neurologic damage after transient aortic occlusion in a rabbit model; however, the protective mechanisms are not clear.

Of Mice and Men: Essential Considerations in the Translation of Collateral Therapeutics

To the Editor: Shin and colleagues detail an elegant study of collateral perfusion in the ischemic penumbra of mice treated with induced hypertension after distal middle cerebral artery occlusion (MCAO).1 Using optical imaging techniques, they demonstrate that early augmentation of systemic blood pressure with phenylephrine after MCAO improves collateral flow from ipsilateral leptomeningeal branches of the anterior and posterior cerebral arteries. Such collateral perfusion is noted to markedly improve cerebral blood flow (CBF) in penumbra and core, with associated enhancement of oxygenation and cerebral metabolic rate of oxygen in these ischemic regions. After prompt reversal of distal MCAO, infarct size is reduced by induced hypertension in concentric fashion around a focus emanating from the site of distal MCAO. There are subtle yet critical details embedded in this sophisticated cerebrovascular pathophysiology experiment that must be considered regarding the potential of induced hypertension and other therapeutic approaches using collateral perfusion in acute ischemic stroke patients.2 Changes …

Measurement of Peripheral Muscle Resistance in Rats with Chronic Ischemia-Induced Paraplegia or Morphine-Induced Rigidity Using a Semi-Automated Computer-Controlled Muscle Resistance Meter

In experimental and clinical studies, an objective assessment of peripheral muscle resistance represents one of the key elements in determining the efficacy of therapeutic manipulations (e.g. pharmacological, surgical) aimed to ameliorate clinical signs of spasticity and/or rigidity. In the present study, we characterize a newly developed limb flexion resistance meter which permits a semi-automated, computer-controlled measurement of peripheral muscle resistance (PMR) in the lower extremities during a forced flexion of the ankle in the awake rat. Ischemic paraplegia was induced in Sprague-Dawley rats by transient aortic occlusion (10 min) in combination with systemic hypotension (40 mm Hg). After ischemia the presence of spasticity component was determined by the presence of an exaggerated EMG activity recorded from gastrocnemius muscle after nociceptive or proprioceptive afferent activation and by velocity-dependent increase in muscle resistance. Rigidity was induced by high dose (30 mg/kg, i.p.) of morphine. Animals with defined ischemic spasticity or morphine-induced rigidity were then placed into a plastic restrainer and a hind paw attached by a tape to a metal plate driven by a computer-controlled stepping motor equipped with a resistance transducer. The resistance of the ankle to rotation was measured under several testing paradigms: (i) variable degree of ankle flexion (40 degrees, 50 degrees, and 60 degrees), (ii) variable speed/rate of ankle flexion (2, 3, and 4 sec), (iii) the effect of inhalation anesthesia, (iv) the effect of intrathecal baclofen, (v) the effect of dorsal L2-L5 rhizotomy, or (vi) systemic naloxone treatment. In animals with ischemic paraplegia an increased EMG response after peripheral nociceptive or proprioceptive activation was measured. In control animals average muscle resistance was 78 mN and was significantly increased in animals with ischemic spasticity (981-7900 mN). In ischemic-spastic animals a significant increase in measured muscle resistance was seen after increased velocity (4 > 3 > 2 sec) and the angle (40 degrees > 50 degrees > 60 degrees) of the ankle rotation. In spastic animals, deep halothane anesthesia, intrathecal baclofen or dorsal rhizotomy decreased muscle resistance to 39-80% of pretreatment values. Systemic treatment with morphine induced muscle rigidity and corresponding increase in muscle resistance. Morphine-induced increase in muscle resistance was independent on the velocity of the ankle rotation and was reversed by naloxone. These data show that by using this system it is possible to objectively measure the degree of peripheral muscle resistance. The use of this system may represent a simple and effective experimental tool in screening new pharmacological compounds and/or surgical manipulations targeted to modulate spasticity and/or rigidity after a variety of neurological disorders such as spinal cord traumatic or ischemic injury, multiple sclerosis, cerebral palsy, or Parkinson's disease.

Heat stress increases the effectiveness of early ischemic preconditioning in spinal cord protection

This study was aimed to test the hypothesis that the combination of heat stress and early ischemic preconditioning (IP) applied before aortic occlusion would be protective against spinal cord ischemic injury. Thirty Whister-Albino rats were randomly divided into three groups. In group 1 (n=10), aorta was clamped just distal to the left renal artery and above the iliac bifurcation for 45 min. Group 2 (n=10) had 5 min of transient aortic occlusion and 30 min later underwent an additional 45 min. In group 3 (n=10), animals were heated to 41 degrees C and maintained at this temperature for 15 min. Twenty-four hours later, this hyperthermia pretreated group underwent the same early IP model of aortic occlusion. Neurologic status was assessed on postoperative 24 and 48 h by using the 15-point neurologic performance scale. Spinal cords were harvested for histopathological grading (1-4) and evaluated for the presence of heat shock protein-ubiquitin staining. At 24 and 48 h, the mean neurologic performance scores of the group 1 were found to be significantly lower than those of groups 2 and 3. Although the neurologic assessment of rats performed on the 24h did not reveal statistically significant difference between groups 2 and 3 (P=0.069); on 48 h, the mean neurologic scores of the group 3 were significantly higher than those of group 2 (P=0.005). At 48 h, a delayed neurologic deterioration was seen in groups 1 and 2 when compared to the results obtained at 24h. Histologic evaluation correlated well with the neurologic outcome with the least cellular damage in group 3. There were six rats with ubiquitin expression and this was detected only in animals pretreated with sublethal heat stress. An early IP model with a short reperfusion interval does not give the minimal required time for the HSPs expression and is associated with a delayed neurologic deterioration. Neuroprotection provided by heat stress combined with an early IP model lasts up to 48 h and heat shock protein-ubiquitin induction may be responsible in this phenomenon.

Neuroprotective Effect of Epidural Electrical Stimulation against Ischemic Spinal Cord Injury in Rats

Electroconvulsion therapy is likely to serve as an effective preconditioning stimulus for inducing tolerance to ischemic brain injury. The current study examines whether electrical stimuli on the spinal cord is also capable of inducing tolerance to ischemic spinal cord injury by transient aortic occlusion. Spinal cord ischemia was induced by occlusion of the descending thoracic aorta in combination with maintaining systemic hypotension (40 mmHg) during the procedure. Animals implanted with epidural electrodes were divided into four groups according to electrical stimulation and sham. Two groups consisted of rapid preconditioning (RE group, n = 8) and sham procedure (RC group, n = 8) 30 min before 9 min of spinal cord ischemia. In the two groups that underwent delayed preconditioning, rats were exposed to 9 min of aortic occlusion 24 h after either pretreatment with epidural electrical stimulation (DE group, n = 8) or sham (DC group, n = 8). In addition, rats were exposed to 6-11 min of spinal cord ischemia at 30 min or 24 h after epidural electrical stimulation or sham stimulation. The group P50 represents the duration of spinal cord ischemia associated with 50% probability of resultant paraplegia. Pretreatment with electrical stimulation in the DE group but not the RE group protected the spinal cord against ischemia, and this stimulation prolonged the P50 by approximately 15.0% in the DE group compared with the DC group. Although the optimal setting for this electrical preconditioning should be determined in future studies, the results suggest that epidural electrical stimulation will be a useful approach to provide spinal protection against ischemia.

Intrathecal gene delivery of glial cell line-derived neurotrophic factor ameliorated paraplegia in rats after spinal ischemia

Paraplegia is a catastrophic complication of thoracic aortic surgery. At present, there is no effective mean to prevent the ischemia-induced spinal cord trauma. Gene delivery of neurotrophic factors may hold promises for prevention of spinal injury. In the present study, we evaluated the effect of glial cell line-derived neurotrophic factor (GDNF) gene delivery on prevention of the pathological changes due to spinal ischemia. Recombinant adenovirus vectors encoding GDNF (Ad-GDNF) and green fluorescent protein (Ad-GFP) were used for gene transfer studies. Treatment with cobalt chloride induced dose-dependent bcl-2 and synaptophysin downregulation in spinal neuronal cells, which could be effectively reversed by GDNF gene transfer. Intrathecal injection of Ad-GDNF led to maximal GDNF expression in spinal cord within 2–7 days. Thus, after intrathecal administration of adenovirus vectors for 3 days, Sprague–Dawley rats received transient aortic occlusion to induce spinal ischemia and were monitored for behavior deficits. The Ad-GDNF-treated rats showed significantly lower paraplegia rate (40%) than that of Ad-GFP- or saline-treated groups (75–85%; P < 0.01). In addition, the Ad-GDNF-treated rats exhibited significantly improved locomotor function comparing with rats of control groups ( P < 0.001). Histological analysis revealed that GDNF gene delivery profoundly attenuated the infiltration of leukocytes in spinal cord after ischemic insults. Furthermore, GDNF gene delivery prominently attenuated the ischemia-induced neuronal loss in dorsal horn lamina VI–VIII and reduction in synaptophysin expression in spinal cords. In conclusion, GDNF gene transfer confers protection to the neuronal cells and synapses networks, thereby alleviated the paraplegia due to spinal ischemia.

Rapid Ischemic Preconditioning for Spinal Cord Protection after Transient Aortic Occlusion

Rapid Ischemic Preconditioning for Spinal Cord Protection after Transient Aortic Occlusion

The role of early ischemic preconditioning in spinal cord protection after transient aortic occlusion

I read with great interest the article titled ‘Ischemic preconditioning and nicotinamide in spinal cord protection in an experimental model of transient aortic occlusion’ [1]. I congratulate Isbir and associates on their study of ischemic preconditioning (IPC) and nicotinamide utilization to provide spinal cord protection. IPC is a biphasic phenomenon with an early and a late phase of protection. These two phases have been documented in the spinal cord [2 – 4]. In this study Isbir et al. evaluated the effect of either early IPC (group 2) or nicotinamide (group 3) or combined IPC and nicotinamide (group 4) on spinal cord protection in a rat model. In this model, rats underwent 5 min IPC, followed by 45 min of reperfusion before a 45 min duration of infrarenal aortic cross-clamping. They found that early IPC or combined IPC and nicotinamide reduced spinal cord injury at 48 h when compared with the controls (mean Tarlov score: 2.75 for early IPC, 3.13 for combined IPC and nicotinamide vs. 0.88 in the control group; P ¼ 0:004). In a recent published study, our group demonstrated that early IPC without hypotension prevents spinal cord injury in a porcine model of descending thoracic aortic occlusion [2]. We used 20 min IPC, 80 min of reperfusion and the duration of descending thoracic aortic occlusion was 35 min. In our study, it was very important to maintain the arterial systolic blood pressure higher than 100 mmHg during the 80 min reperfusion interval. Two animals had an arterial systolic blood pressure of 80 –9 0 mmHg during the reperfusion period. Although they had a Tarlov score of 4 at 24 h postoperatively, these two animals became paraplegic at 48 h. In another study by Caparrelli et al. [5], in a rabbit model (5 min brief ischemia, 30 min of reperfusion and 20 min of infrarenal aortic occlusion), when six animals with early IPC were compared with seven controls, IPC failed to protect the spinal cord at either 24 or 48 h. In this study it is shown that there was a level of hypotension during the reperfusion interval in the IPC group, and this hypotension may be an explanation for the failure of early IPC to protect the spinal cord. In most studies of spinal cord injury after aortic occlusion there is an aggravation in neurologic scores from 24 to 48 h [2 –5]. In the study of Isbir et al. there is an improvement in paraplegia from 24 to 48 h (groups 2 and 3 from 25% to 12% and group 4 from 12% to 0%). How do the authors explain this improvement? Also, it is mentioned in the published manuscript that the arterial blood pressure and heartbeat were continuously monitored throughout the procedure. It would be of great interest if the authors could provide the proximal to the aortic occlusion arterial blood pressure.