Thomas M. Ringer

Serial MRI After Transient Focal Cerebral Ischemia in Rats: Dynamics of Tissue Injury, Blood-Brain Barrier Damage, and Edema Formation

BACKGROUND AND PURPOSE With the advent of thrombolytic therapy for acute stroke, reperfusion-associated mechanisms of tissue injury have assumed greater importance. In this experimental study, we used several MRI techniques to monitor the dynamics of secondary ischemic damage, blood-brain barrier (BBB) disturbances, and the development of vasogenic edema during the reperfusion phase after focal cerebral ischemia in rats. METHODS Nineteen Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion of 30 minutes, 60 minutes, or 2.5 hours with the suture occlusion model. MRI, including diffusion-weighted imaging (DWI), T2-weighted imaging, perfusion-weighted imaging, and T1-weighted imaging, was performed 5 to 15 minutes before reperfusion, as well as 0.5, 1.5, and 2.5 hours and 1, 2, and 7 days after withdrawal of the suture. Final infarct size was determined histologically at 7 days. RESULTS In the 30-minute ischemia group (and partially also after 60 minutes), DWI abnormalities reversed transiently during the early reperfusion period but recurred after 1 day, probably due to secondary ischemic damage. After 2.5 hours of ischemia, DWI abnormalities no longer reversed, and signal intensity on both DWI and T2-weighted images increased rapidly in the previously ischemic region due to BBB damage (enhancement on postcontrast T1-weighted images) and edema formation. Early BBB damage during reperfusion was found to be predictive of relatively pronounced edema at subacute time points and was probably related to the increased mortality rates in this experimental group (3 of 7). CONCLUSIONS Reperfusion after short periods of ischemia (30 to 60 minutes) appears to be mainly complicated by secondary ischemic damage as shown by the delayed recurrence of the DWI lesions, whereas BBB damage associated with vasogenic edema becomes a dominant factor with longer occlusion times (2.5 hours).

Overexpression of HSP72 after Induction of Experimental Stroke Protects Neurons from Ischemic Damage

The 72-kD inducible heat shock protein (HSP72) can attenuate cerebral ischemic injury when overexpressed before ischemia onset. Whether HSP72 overexpression is protective when applied after ischemia onset is not known, but would have important clinical implications. Fifty-seven rats underwent middle cerebral artery occlusion for 1 hour. Defective herpes simplex viral (HSV) vectors expressing hsp72 with lacZ as a reporter were delivered 0.5, 2, and 5 hours after ischemia onset into each striatum. Control animals received an identical vector containing only lacZ. Striatal neuron survival at 2 days was improved by 23% and 15% when HSP72 vectors were delayed 0.5 and 2 hours after ischemic onset, respectively (P < 0.05). However, when delayed by 5 hours, HSP72 overexpression was no longer protective. This is the first demonstration that HSP72 gene transfer even after ischemia onset is neuroprotective. Because expression from these HSV vectors begins 4 to 6 hours after injection, this suggests that the temporal therapeutic window for HSP72 is at least 6 hours after ischemia onset. Future strategies aimed at enhancing HSP72 expression after clinical stroke may be worth pursuing. The authors suggest that in the future HSP72 may be an effective treatment for stroke.

Early Disruption of the Blood–Brain Barrier After Thrombolytic Therapy Predicts Hemorrhage in Patients With Acute Stroke

Background and Purpose— Leaks of the blood–brain barrier can be detected on postcontrast-enhanced T1-weighted MRIs. Although early disruptions of the blood–brain barrier appear to be an important risk factor for tissue plasminogen activator-related hemorrhages in rodents, little is known about their incidence and consequences in human stroke. Methods— This is a retrospective analysis of a prospectively collected stroke database over the past 6 years. In 52 patients, multimodal MRI (including diffusion-weighted, perfusion-weighted, and postcontrast-enhanced T1-weighted MRI to detect blood–brain barrier changes) had been performed immediately before systemic thrombolysis and in 48 patients within a median of 30 minutes (interquartile range: 30 to 60 minutes) after recombinant tissue plasminogen activator treatment. The incidence of symptomatic hemorrhage (SICH), defined as any parenchymal hemorrhage leading to deterioration in the patient’s clinical condition, was related to several clinical and imaging variables, including early blood–brain barrier changes. Results— Overall, SICH was detected in 9 (9%) patients and among these, 2 died. Although no blood–brain barrier changes were detectable before thrombolysis, 3 of 48 patients (6.25%) had a parenchymal gadolinium enhancement in the areas of initial infarction after tissue plasminogen activator treatment. All 3 patients developed SICHs at sites corresponding to the areas of enhancement. The presence of a parenchymal enhancement was significantly associated with SICH (P<0.01), whereas other clinical and imaging variables did not predict SICH in this series. Conclusion— Early parenchymal enhancement after intravenous tissue plasminogen activator is significantly associated with subsequent SICH and could therefore become a useful imaging sign for the rapid initiation of preventive strategies in the future.

Noninvasive Assessment of Cerebral Perfusion and Oxygenation in Acute Ischemic Stroke by Near-Infrared Spectroscopy

Background: In acute stroke patients, there is a need for noninvasive measurement to monitor blood flow-based therapies. We investigated the utility of near-infrared spectroscopy (NIRS) to determine cerebral perfusion in these patients. Methods: Eleven patients were investigated within 1.4 ± 2.2 days after onset of an ischemic middle cerebral artery infarction by monitoring the kinetics of an intravenous bolus of indocyanine green (ICG). For ICG kinetics, bolus peak time, time to peak (TTP = time between 0 and 100% ICG maximum), maximum ICG concentration, rise time (time between 10 and 90% ICG maximum), slope (maximum ICG/TTP), and blood flow index (BFI = maximum ICG/rise time) were obtained. Perfusion-weighted MRI (PWI) and NIRS measurements were performed within 24 h, and the interhemispherical differences of TTP values were compared. Results: Stroke patients showed an increased bolus peak time (p < 0.02), TTP (p < 0.01), and rise time (p < 0.01), whereas slope (p < 0.01) and BFI (p < 0.01) were diminished at the site of infarction as compared to the unaffected hemisphere. The interhemispherical differences of TTP as measured by PWI and NIRS were closely correlated (r = 0.86). Conclusions: Noninvasive measurements of cerebral ICG kinetics by NIRS provide a useful means of detecting cerebral perfusion deficits in patients with acute stroke, which correlate well with those obtained by PWI.

Serial MRI After Transient Focal Cerebral Ischemia in Rats : Dynamics of Tissue Injury, Blood-Brain Barrier Damage, and Edema Formation Editorial Comment: Dynamics of Tissue Injury, Blood-Brain Barrier Damage, and Edema Formation

BACKGROUND AND PURPOSE With the advent of thrombolytic therapy for acute stroke, reperfusion-associated mechanisms of tissue injury have assumed greater importance. In this experimental study, we used several MRI techniques to monitor the dynamics of secondary ischemic damage, blood-brain barrier (BBB) disturbances, and the development of vasogenic edema during the reperfusion phase after focal cerebral ischemia in rats. METHODS Nineteen Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion of 30 minutes, 60 minutes, or 2.5 hours with the suture occlusion model. MRI, including diffusion-weighted imaging (DWI), T2-weighted imaging, perfusion-weighted imaging, and T1-weighted imaging, was performed 5 to 15 minutes before reperfusion, as well as 0.5, 1.5, and 2.5 hours and 1, 2, and 7 days after withdrawal of the suture. Final infarct size was determined histologically at 7 days. RESULTS In the 30-minute ischemia group (and partially also after 60 minutes), DWI abnormalities reversed transiently during the early reperfusion period but recurred after 1 day, probably due to secondary ischemic damage. After 2.5 hours of ischemia, DWI abnormalities no longer reversed, and signal intensity on both DWI and T2-weighted images increased rapidly in the previously ischemic region due to BBB damage (enhancement on postcontrast T1-weighted images) and edema formation. Early BBB damage during reperfusion was found to be predictive of relatively pronounced edema at subacute time points and was probably related to the increased mortality rates in this experimental group (3 of 7). CONCLUSIONS Reperfusion after short periods of ischemia (30 to 60 minutes) appears to be mainly complicated by secondary ischemic damage as shown by the delayed recurrence of the DWI lesions, whereas BBB damage associated with vasogenic edema becomes a dominant factor with longer occlusion times (2.5 hours).

MRI of subacute hemorrhagic transformation in the rat suture occlusion model

In this study we investigated the utility of different MRI techniques for the detection and predictability of hemorrhagic transformation (HT) in a rat model of transient focal cerebral ischemia. Hemorrhagic infarction was reliably identified with gradient-echo sequences and developed between 2 and 7 days following the insult. None of the investigated early MRI features of the ischemic lesions (including the apparent diffusion coefficient and post-reperfusion blood–brain barrier damage) was a good predictor of HT severity at 7 days. This indicates that subacute HT at 2–7 days occurs independently of the severity of acute tissue and BBB damage.

Serial MRI After Transient Focal Cerebral Ischemia in Rats

BACKGROUND AND PURPOSE With the advent of thrombolytic therapy for acute stroke, reperfusion-associated mechanisms of tissue injury have assumed greater importance. In this experimental study, we used several MRI techniques to monitor the dynamics of secondary ischemic damage, blood-brain barrier (BBB) disturbances, and the development of vasogenic edema during the reperfusion phase after focal cerebral ischemia in rats. METHODS Nineteen Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion of 30 minutes, 60 minutes, or 2.5 hours with the suture occlusion model. MRI, including diffusion-weighted imaging (DWI), T2-weighted imaging, perfusion-weighted imaging, and T1-weighted imaging, was performed 5 to 15 minutes before reperfusion, as well as 0.5, 1.5, and 2.5 hours and 1, 2, and 7 days after withdrawal of the suture. Final infarct size was determined histologically at 7 days. RESULTS In the 30-minute ischemia group (and partially also after 60 minutes), DWI abnormalities reversed transiently during the early reperfusion period but recurred after 1 day, probably due to secondary ischemic damage. After 2.5 hours of ischemia, DWI abnormalities no longer reversed, and signal intensity on both DWI and T2-weighted images increased rapidly in the previously ischemic region due to BBB damage (enhancement on postcontrast T1-weighted images) and edema formation. Early BBB damage during reperfusion was found to be predictive of relatively pronounced edema at subacute time points and was probably related to the increased mortality rates in this experimental group (3 of 7). CONCLUSIONS Reperfusion after short periods of ischemia (30 to 60 minutes) appears to be mainly complicated by secondary ischemic damage as shown by the delayed recurrence of the DWI lesions, whereas BBB damage associated with vasogenic edema becomes a dominant factor with longer occlusion times (2.5 hours).

Neurological Sequelae of Sepsis: I) Septic Encephalopathy

Septic encephalopathy (SE) or sepsis-associated delirium is the most common encephalopathy in ICU patients. It is defined by brain dysfunction due to systemic inflammatory response syndrome and extracranial infection. Clinically, acute impairment in level of consciousness and confusion are primarily defining symptoms. Precise clinical evaluation of brain function is crucial, although the necessary diagnostic tools are limited and require further verification in clinical studies. Therefore, SE is often underestimated and not frequently diagnosed. This review gives an overview of clinical features, epidemiological data, pathophysiological processes, imaging and neuropathological findings as well as diagnostic and therapeutic approaches in SE patients to characterize this severe neurological complication of sepsis.

Assessment of pulmonary function in amyotrophic lateral sclerosis: when can polygraphy help evaluate the need for non-invasive ventilation?

Background Non-invasive positive-pressure ventilation (NPPV) is an established, effective, long-term treatment for patients with amyotrophic lateral sclerosis (ALS), but the correct indicators for the establishment of NPPV have not been defined. Methods In this retrospective study, records (spirometry, nocturnal polygraphy, nocturnal blood gases) of 131 patients with ALS were reviewed in order to evaluate the role of polygraphy for prediction of respiratory failure in ALS. Results The patient group reporting with versus without dyspnoea had significantly lower values on the revised ALS-Functional Rating Scale (ALSFRS-R), vital capacity (VC), forced VC (FVC), arterial oxygen saturation and arterial oxygen tension readings, including a higher apnoea–hypopnoea index. 23 patients, who did not report about dyspnoea, had an FVC of <75%. Nocturnal hypoventilation was observed in 67% of the patients with ALS independent of their ALSFRS-R. The patient group with nocturnal hypoventilation was characterised by a significantly lower VC, FVC and maximal static inspiratory pressure compared with the group without nocturnal hypoventilation. However, also in the absence of nocturnal hypoventilation, 8 patients had a VC <50% as predicted. Discussion Our study shows that in patients not reporting dyspnoea and having an FVC of >75%, nocturnal hypoventilation was observed in nearly every second patient. Therefore, for the question of whether NPPV should be initiated, polygraphy does not provide useful additional information if the FVC is already <75% as predicted. However, in patients with more or less normal lung function parameters or where lung spirometry cannot perform adequately (eg, bulbar ALS), it can provide sufficient evidence for the need of NPPV.

Down-regulation of purinergic P2X7 receptor expression and intracellular calcium dysregulation in peripheral blood mononuclear cells of patients with amyotrophic lateral sclerosis

BACKGROUND Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder associated with intracellular Ca(2+) dysregulation. The P2X receptor family is comprised of ligand-gated ion channels that respond to extracellular adenosine triphosphate (ATP) and increases permeability of calcium into the cell. The underlying mechanisms of purinergic signalling on peripheral blood mononuclear cells (PBMCs) in ALS remain unclear. Herein, we studied the expression of P2X4/P2X7 receptors and calcium homeostasis in blood cells of ALS patients. METHODS We used PBMCs from 42 ALS patients and 19 controls. Purinergic receptors P2X4 (P2X4R) and P2X7 (P2X7R) were examined using western blot analysis. The effect of exogenous ATP on intracellular Ca(2+) homeostasis in monocytes was measured using fluorimetry by Fura-2 on a single-cell level. RESULTS Western blot analysis revealed stable P2X4R expression in patients and controls. P2X7R expression was significantly reduced (p=0.012) in ALS patients. Repetitive long-term ATP stimulation caused a sustained decrease in Ca(2+) levels in the ALS group as measured by the area under the curve, peak amplitude and peak height. CONCLUSION These results confirm our hypothesis that Ca(2+) abnormalities in ALS are measurable in immune cells. These findings suggest that the reduction of P2X7 receptor expression on PBMCs leads to intracellular calcium dysregulation. Our study improves the understanding of ALS pathophysiology and proposes PBMCs as a non-invasive source to study ALS.