The New England journal of medicine, Vol. 353, No. 14. (6 October 2005), pp. 1516-22.
PJ Neumann, AB Rosen, MC Weinstein
Medicare and cost-effectiveness analysis
Medicare News, Syndicated
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Feb 212009
The New England journal of medicine, Vol. 353, No. 14. (6 October 2005), pp. 1516-22.Biophysical Mechanisms of Stroke
Stroke, Syndicated
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Feb 132009
Stroke, Vol. 28, No. 10. (1 October 1997), pp. 2067-2077.
Background Stroke is the third leading cause of death and the leading cause of long-term disability in the United States. Although a host of genetic, biochemical, physiological, anatomic, and histological factors have been implicated, to varying degrees, in the pathogenesis of stroke, biophysical factors are believed to play a significant role in the development, diagnosis, and therapy of stroke. The purpose of this review article is to identify, describe, and illustrate these causes and biophysical and hemodynamic mechanisms predisposing a person to stroke, which often form the basis for novel methods of diagnosis and therapy. Summary of Review This mini-review begins by describing the physical principles that govern the flow of blood through normal and stenosed carotid artery bifurcations. In addition to the tortuosity, curvature, and tensile forces of the carotid artery bifurcation, the effects of biophysical phenomena from flowing blood such as viscous forces, pressure forces, velocity, kinetic energy, momentum, impulse, shear stress, and vibrational displacements exerted by the flowing blood on the vessel wall are conducive to abnormal flow behavior and patterns, degrading the vessel wall and creating the potential for stroke. Conclusions Recent advances in the treatment of stroke are based on increasing knowledge of its underlying biophysical mechanisms, as well as on better-publicized advances in imaging instrumentation and procedures for the management and treatment of patients.
George Hademenos, Tarik Massoud
Background Stroke is the third leading cause of death and the leading cause of long-term disability in the United States. Although a host of genetic, biochemical, physiological, anatomic, and histological factors have been implicated, to varying degrees, in the pathogenesis of stroke, biophysical factors are believed to play a significant role in the development, diagnosis, and therapy of stroke. The purpose of this review article is to identify, describe, and illustrate these causes and biophysical and hemodynamic mechanisms predisposing a person to stroke, which often form the basis for novel methods of diagnosis and therapy. Summary of Review This mini-review begins by describing the physical principles that govern the flow of blood through normal and stenosed carotid artery bifurcations. In addition to the tortuosity, curvature, and tensile forces of the carotid artery bifurcation, the effects of biophysical phenomena from flowing blood such as viscous forces, pressure forces, velocity, kinetic energy, momentum, impulse, shear stress, and vibrational displacements exerted by the flowing blood on the vessel wall are conducive to abnormal flow behavior and patterns, degrading the vessel wall and creating the potential for stroke. Conclusions Recent advances in the treatment of stroke are based on increasing knowledge of its underlying biophysical mechanisms, as well as on better-publicized advances in imaging instrumentation and procedures for the management and treatment of patients.
George Hademenos, Tarik Massoud
Longitudinal study of motor recovery after stroke: recruitment and focusing of brain activation.
Stroke, Syndicated
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Feb 122009
Stroke, Vol. 33, No. 6. (June 2002), pp. 1610-1617.
BACKGROUND AND PURPOSE: The goal of this study was to characterize cortical reorganization after stroke and its relation with the site of the stroke-induced lesion and degree of motor recovery using functional MRI (fMRI). METHODS: Fourteen stroke patients with an affected upper limb were studied longitudinally. Three fMRI sessions were performed over a period of 1 to 6 months after stroke. Upper limb recovery, Wallerian degeneration of the pyramidal tract, and responses to transcranial magnetic stimulation were assessed. RESULTS: Two main patterns of cortical reorganization were found. Pattern 1 was focusing, in which, after initial recruitment of additional ipsilateral and contralateral areas, activation gradually developed toward a pattern of activation restricted to the contralateral sensorimotor cortex in 9 patients. Five patients were found to have pattern 2, persistent recruitment, in which there was an initial and sustained recruitment of ipsilateral activity. Occurrence of recruitment or focusing seemed to depend mainly on whether the primary motor cortex (M1) was lesioned; persistent recruitment was observed in 3 of 4 patients with M1 injury, and focusing was seen in 8 of 10 patients with spared M1. These patterns had no relation to the degree of recovery; in particular, focusing did not imply recovery. However, there was a clear relation between the degree of recovery and the degree of Wallerian degeneration. CONCLUSIONS: These results suggest that ipsilateral recruitment after stroke corresponds to a compensatory corticocortical process related to the lesion of the contralateral M1 and that the process of compensatory recruitment will persist if M1 is lesioned; otherwise, it will be transient.
A Feydy, R Carlier, A Roby-Brami, B Bussel, F Cazalis, L Pierot, Y Burnod, MA Maier
BACKGROUND AND PURPOSE: The goal of this study was to characterize cortical reorganization after stroke and its relation with the site of the stroke-induced lesion and degree of motor recovery using functional MRI (fMRI). METHODS: Fourteen stroke patients with an affected upper limb were studied longitudinally. Three fMRI sessions were performed over a period of 1 to 6 months after stroke. Upper limb recovery, Wallerian degeneration of the pyramidal tract, and responses to transcranial magnetic stimulation were assessed. RESULTS: Two main patterns of cortical reorganization were found. Pattern 1 was focusing, in which, after initial recruitment of additional ipsilateral and contralateral areas, activation gradually developed toward a pattern of activation restricted to the contralateral sensorimotor cortex in 9 patients. Five patients were found to have pattern 2, persistent recruitment, in which there was an initial and sustained recruitment of ipsilateral activity. Occurrence of recruitment or focusing seemed to depend mainly on whether the primary motor cortex (M1) was lesioned; persistent recruitment was observed in 3 of 4 patients with M1 injury, and focusing was seen in 8 of 10 patients with spared M1. These patterns had no relation to the degree of recovery; in particular, focusing did not imply recovery. However, there was a clear relation between the degree of recovery and the degree of Wallerian degeneration. CONCLUSIONS: These results suggest that ipsilateral recruitment after stroke corresponds to a compensatory corticocortical process related to the lesion of the contralateral M1 and that the process of compensatory recruitment will persist if M1 is lesioned; otherwise, it will be transient.
A Feydy, R Carlier, A Roby-Brami, B Bussel, F Cazalis, L Pierot, Y Burnod, MA Maier
A functional MRI study of subjects recovered from hemiparetic stroke
Stroke, Syndicated
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Feb 112009
Stroke, Vol. 28, No. 12. (1 December 1997), pp. 2518-2527.
Background and Purpose Stroke recovery mechanisms remain incompletely understood, particularly for subjects with cortical stroke, in whom limited data are available. We used functional magnetic resonance imaging to compare brain activations in normal controls and subjects who recovered from hemiparetic stroke. Methods Functional magnetic resonance imaging was performed in ten stroke subjects with good recovery, five with deep, and five with cortical infarcts. Brain activation was achieved by index finger-tapping. Statistical parametric activation maps were obtained using a t test and a threshold of P<.001. In five bilateral motor regions, the volume of activated brain for each stroke subject was compared with the distribution of activation volumes among nine controls. Results Control subjects activated several motor regions. During recovered hand finger-tapping, stroke subjects activated the same regions as controls, often in a larger brain volume. In the unaffected hemisphere, sensorimotor cortex activation was increased in six of nine stroke subjects compared with controls. Cerebellar hemisphere contralateral and premotor cortex ipsilateral to this region, as well as supplementary motor areas, also had increased activation. In the stroke hemisphere, activation exceeding controls was uncommon, except that three of five cortical strokes showed peri-infarct activation foci. During unaffected hand finger-tapping, increased activation by stroke subjects compared with controls was uncommon; however, decreased activation was seen in unaffected sensorimotor cortex, suggesting that this region's responsiveness increased to the ipsilateral hand and decreased to contralateral hand movements. Use of a different threshold for defining activation (P<.01) did not change the overall findings (kappa=.75). Conclusions Recovered finger-tapping by stroke subjects activated the same motor regions as controls but to a larger extent, particularly in the unaffected hemisphere. Increased reliance on these motor areas may represent an important component of motor recovery. Functional magnetic resonance imaging studies of subjects who recovered from stroke provide evidence for several processes that may be related to restoration of neurologic function.
SC Cramer, G Nelles, RR Benson, JD Kaplan, RA Parker, KK Kwong, DN Kennedy, SP Finklestein, BR Rosen
Background and Purpose Stroke recovery mechanisms remain incompletely understood, particularly for subjects with cortical stroke, in whom limited data are available. We used functional magnetic resonance imaging to compare brain activations in normal controls and subjects who recovered from hemiparetic stroke. Methods Functional magnetic resonance imaging was performed in ten stroke subjects with good recovery, five with deep, and five with cortical infarcts. Brain activation was achieved by index finger-tapping. Statistical parametric activation maps were obtained using a t test and a threshold of P<.001. In five bilateral motor regions, the volume of activated brain for each stroke subject was compared with the distribution of activation volumes among nine controls. Results Control subjects activated several motor regions. During recovered hand finger-tapping, stroke subjects activated the same regions as controls, often in a larger brain volume. In the unaffected hemisphere, sensorimotor cortex activation was increased in six of nine stroke subjects compared with controls. Cerebellar hemisphere contralateral and premotor cortex ipsilateral to this region, as well as supplementary motor areas, also had increased activation. In the stroke hemisphere, activation exceeding controls was uncommon, except that three of five cortical strokes showed peri-infarct activation foci. During unaffected hand finger-tapping, increased activation by stroke subjects compared with controls was uncommon; however, decreased activation was seen in unaffected sensorimotor cortex, suggesting that this region's responsiveness increased to the ipsilateral hand and decreased to contralateral hand movements. Use of a different threshold for defining activation (P<.01) did not change the overall findings (kappa=.75). Conclusions Recovered finger-tapping by stroke subjects activated the same motor regions as controls but to a larger extent, particularly in the unaffected hemisphere. Increased reliance on these motor areas may represent an important component of motor recovery. Functional magnetic resonance imaging studies of subjects who recovered from stroke provide evidence for several processes that may be related to restoration of neurologic function.
SC Cramer, G Nelles, RR Benson, JD Kaplan, RA Parker, KK Kwong, DN Kennedy, SP Finklestein, BR Rosen
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