Mechanisms of Spinal Cord Stimulation in Ischemia
Object: The goal of this study was to assess the duration of neuroprotection after SCS. Nearly 40 years after the first description of spinal cord stimulation (SCS), the mechanisms underlying its physiological effects remain unclear. It is known that SCS affects activity in the nervous system on a broad scale. Local neurohumoral changes within the dorsal horn of the spinal cord have been described, as have changes in cortical activation in a number of brain regions. Spinal cord stimulation has even been found to have profound effects on sympathetic vascular tone, a discovery that has led to its use in ameliorating blood flow in the limbs, heart, and brain.
Methods: In an effort to delineate the limits of neuroprotection offered by SCS, the authors have studied its use in an experimental model of permanent middle cerebral artery (MCA) occlusion in rats. The investigators applied SCS in a delayed fashion 3, 6, or 9 hours after MCA occlusion. The results are reported and mechanisms underlying the physiological effects of SCS are reviewed, with particular attention being paid to the effect of SCS on cerebral blood flow in the setting of cerebral ischemia.
Conclusions: The authors found that SCS applied as late as 6 hours postischemia significantly reduces stroke volumes, whereas SCS applied 9 hours after ischemia fails to reduce stroke injury.
The development of SCS as a therapeutic modality for the management of chronic pain followed the initial description of the gate control theory of nociception in 1965. Shealy and colleagues reasoned that the electrical "gates" within the dorsal aspect of the spinal cord that were postulated by Melzack and Wall could be artificially stimulated by electrical current applied externally. The technology of SCS has evolved over the succeeding three decades, but the underlying concept remains unchanged. Modern SCS units consist of an electrical lead positioned in the epidural space overlying the dorsal spinal cord and a pulse generator that delivers a high-frequency, square-wave current. When the spinal cord is stimulated, patients describe a vibratory sensation in their extremities. This sensation is associated with a significant reduction of pain in the "stimulated" limbs. Since its introduction in 1967, SCS has been widely used for the treatment of chronic pain. This treatment is believed to alter neuronal inputs and synaptic activity within the dorsal horn of the spinal cord, thereby reducing central transmission of pain. Electrical conduction in the dorsal columns of the spinal cord has been thought to be modified by SCS, although this concept has been challenged. The mechanism of action of SCS is the subject of heated debate, although its efficacy in the alleviation of chronic pain is largely accepted.
Placement of the SCS leads varies widely according to clinical indications and patient anatomy. The leads are routinely placed in the cervical and in the thoracolumbar spine for the treatment of arm and leg pain, respectively. Optimal lead location for the treatment of pain in various regions has been the subject of some investigations. Nevertheless, the location of the SCS lead is usually determined by clinical benefit, and may range from the top of the cervical spine to the conus medullaris at its lower end. Mathematical modeling of SCS has also been done in an effort to predict its effects on the spinal cord. Finite-element modeling work performed by Holsheimer and colleagues has enabled accurate prediction of electrical contact geometries, providing optimal penetration of the dorsal aspect of the spinal cord.
Object: The goal of this study was to assess the duration of neuroprotection after SCS. Nearly 40 years after the first description of spinal cord stimulation (SCS), the mechanisms underlying its physiological effects remain unclear. It is known that SCS affects activity in the nervous system on a broad scale. Local neurohumoral changes within the dorsal horn of the spinal cord have been described, as have changes in cortical activation in a number of brain regions. Spinal cord stimulation has even been found to have profound effects on sympathetic vascular tone, a discovery that has led to its use in ameliorating blood flow in the limbs, heart, and brain.
Methods: In an effort to delineate the limits of neuroprotection offered by SCS, the authors have studied its use in an experimental model of permanent middle cerebral artery (MCA) occlusion in rats. The investigators applied SCS in a delayed fashion 3, 6, or 9 hours after MCA occlusion. The results are reported and mechanisms underlying the physiological effects of SCS are reviewed, with particular attention being paid to the effect of SCS on cerebral blood flow in the setting of cerebral ischemia.
Conclusions: The authors found that SCS applied as late as 6 hours postischemia significantly reduces stroke volumes, whereas SCS applied 9 hours after ischemia fails to reduce stroke injury.
The development of SCS as a therapeutic modality for the management of chronic pain followed the initial description of the gate control theory of nociception in 1965. Shealy and colleagues reasoned that the electrical "gates" within the dorsal aspect of the spinal cord that were postulated by Melzack and Wall could be artificially stimulated by electrical current applied externally. The technology of SCS has evolved over the succeeding three decades, but the underlying concept remains unchanged. Modern SCS units consist of an electrical lead positioned in the epidural space overlying the dorsal spinal cord and a pulse generator that delivers a high-frequency, square-wave current. When the spinal cord is stimulated, patients describe a vibratory sensation in their extremities. This sensation is associated with a significant reduction of pain in the "stimulated" limbs. Since its introduction in 1967, SCS has been widely used for the treatment of chronic pain. This treatment is believed to alter neuronal inputs and synaptic activity within the dorsal horn of the spinal cord, thereby reducing central transmission of pain. Electrical conduction in the dorsal columns of the spinal cord has been thought to be modified by SCS, although this concept has been challenged. The mechanism of action of SCS is the subject of heated debate, although its efficacy in the alleviation of chronic pain is largely accepted.
Placement of the SCS leads varies widely according to clinical indications and patient anatomy. The leads are routinely placed in the cervical and in the thoracolumbar spine for the treatment of arm and leg pain, respectively. Optimal lead location for the treatment of pain in various regions has been the subject of some investigations. Nevertheless, the location of the SCS lead is usually determined by clinical benefit, and may range from the top of the cervical spine to the conus medullaris at its lower end. Mathematical modeling of SCS has also been done in an effort to predict its effects on the spinal cord. Finite-element modeling work performed by Holsheimer and colleagues has enabled accurate prediction of electrical contact geometries, providing optimal penetration of the dorsal aspect of the spinal cord.
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