Dynamics And Sensitivity Analysis Of High-frequency Conduction Block

Title:
Dynamics And Sensitivity Analysis Of High-frequency Conduction Block
Authors:
Ackermann, D. Michael; Bhadra, Niloy; Gerges, Meana; Thomas, Peter J.
Abstract:
The local delivery of extracellular high-frequency stimulation (HFS) has been shown to be a fast acting and quickly reversible method of blocking neural conduction and is currently being pursued for several clinical indications. However, the mechanism for this type of nerve block remains unclear. In this study, we investigate two hypotheses: (1) depolarizing currents promote conduction block via inactivation of sodium channels and (2) the gating dynamics of the fast sodium channel are the primary determinate of minimal blocking frequency. Hypothesis 1 was investigated using a combined modeling and experimental study to investigate the effect of depolarizing and hyperpolarizing currents on high-frequency block. The results of the modeling study show that both depolarizing and hyperpolarizing currents play an important role in conduction block and that the conductance to each of three ionic currents increases relative to resting values during HFS. However, depolarizing currents were found to promote the blocking effect, and hyperpolarizing currents were found to diminish the blocking effect. Inward sodium currents were larger than the sum of the outward currents, resulting in a net depolarization of the nodal membrane. Our experimental results support these findings and closely match results from the equivalent modeling scenario: intra-peritoneal administration of the persistent sodium channel blocker ranolazine resulted in an increase in the amplitude of HFS required to produce conduction block in rats, confirming that depolarizing currents promote the conduction block phenomenon. Hypothesis 2 was investigated using a spectral analysis of the channel gating variables in a single-fiber axon model. The results of this study suggested a relationship between the dynamical properties of specific ion channel gating elements and the contributions of corresponding conductances to block onset. Specifically, we show that the dynamics of the fast sodium inactivation gate are too slow to track the high-frequency changes in membrane potential during HFS, and that the behavior of the fast sodium current was dominated by the low-frequency depolarization of the membrane. As a result, in the blocked state, only 5.4% of nodal sodium channels were found to be in the activatable state in the node closest to the blocking electrode, resulting in conduction block. Moreover, we find that the corner frequency for the persistent sodium channel activation gate corresponds to the frequency below which high-frequency stimuli of arbitrary amplitude are incapable of inducing conduction block.
Citation:
Ackermann, D. Michael, Niloy Bhadra, Meana Gerges, and Peter J. Thomas. 2011. "Dynamics And Sensitivity Analysis Of High-frequency Conduction Block." Journal Of Neural Engineering 8(6): 065007 1-14.
Publisher:
Institute of Physics
DATE ISSUED:
2011-12
Department:
Mathematics
Type:
article
PUBLISHED VERSION:
10.1088/1741-2560/8/6/065007
PERMANENT LINK:
http://hdl.handle.net/11282/310074

Full metadata record

DC FieldValue Language
dc.contributor.authorAckermann, D. Michaelen_US
dc.contributor.authorBhadra, Niloyen_US
dc.contributor.authorGerges, Meanaen_US
dc.contributor.authorThomas, Peter J.en_US
dc.date.accessioned2013-12-23T16:24:41Zen
dc.date.available2013-12-23T16:24:41Zen
dc.date.issued2011-12en
dc.identifier.citationAckermann, D. Michael, Niloy Bhadra, Meana Gerges, and Peter J. Thomas. 2011. "Dynamics And Sensitivity Analysis Of High-frequency Conduction Block." Journal Of Neural Engineering 8(6): 065007 1-14.en_US
dc.identifier.issn1741-2560en_US
dc.identifier.urihttp://hdl.handle.net/11282/310074en
dc.description.abstractThe local delivery of extracellular high-frequency stimulation (HFS) has been shown to be a fast acting and quickly reversible method of blocking neural conduction and is currently being pursued for several clinical indications. However, the mechanism for this type of nerve block remains unclear. In this study, we investigate two hypotheses: (1) depolarizing currents promote conduction block via inactivation of sodium channels and (2) the gating dynamics of the fast sodium channel are the primary determinate of minimal blocking frequency. Hypothesis 1 was investigated using a combined modeling and experimental study to investigate the effect of depolarizing and hyperpolarizing currents on high-frequency block. The results of the modeling study show that both depolarizing and hyperpolarizing currents play an important role in conduction block and that the conductance to each of three ionic currents increases relative to resting values during HFS. However, depolarizing currents were found to promote the blocking effect, and hyperpolarizing currents were found to diminish the blocking effect. Inward sodium currents were larger than the sum of the outward currents, resulting in a net depolarization of the nodal membrane. Our experimental results support these findings and closely match results from the equivalent modeling scenario: intra-peritoneal administration of the persistent sodium channel blocker ranolazine resulted in an increase in the amplitude of HFS required to produce conduction block in rats, confirming that depolarizing currents promote the conduction block phenomenon. Hypothesis 2 was investigated using a spectral analysis of the channel gating variables in a single-fiber axon model. The results of this study suggested a relationship between the dynamical properties of specific ion channel gating elements and the contributions of corresponding conductances to block onset. Specifically, we show that the dynamics of the fast sodium inactivation gate are too slow to track the high-frequency changes in membrane potential during HFS, and that the behavior of the fast sodium current was dominated by the low-frequency depolarization of the membrane. As a result, in the blocked state, only 5.4% of nodal sodium channels were found to be in the activatable state in the node closest to the blocking electrode, resulting in conduction block. Moreover, we find that the corner frequency for the persistent sodium channel activation gate corresponds to the frequency below which high-frequency stimuli of arbitrary amplitude are incapable of inducing conduction block.en_US
dc.publisherInstitute of Physicsen_US
dc.identifier.doi10.1088/1741-2560/8/6/065007en
dc.subject.departmentMathematicsen_US
dc.titleDynamics And Sensitivity Analysis Of High-frequency Conduction Blocken_US
dc.typearticleen_US
dc.identifier.journalJournal Of Neural Engineeringen_US
dc.subject.keywordMedical physicsen_US
dc.subject.keywordBiological physicsen_US
dc.identifier.volume8en_US
dc.identifier.issue6en_US
dc.identifier.startpage065007-1en_US
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