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Unidirectional Propagation
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Tissue Response:
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Tissue Response:Nerve: Page 1

The tissue response of nerves to electrodes include trauma to axons as well as the nature and extent of the encapsulation surrounding the implant. Traumatized axons may not conduct propagating actions potentials and thick encapsulation layers degrade electric field gradients by increasing the separation between the electrode contacts and target axons.
Rigid Cuff Electrodes.

A rigid split-cylinder type cuff electrode is shown in the lower right of the Figure.


On the left, connective tissue developing around the nerve and the interspace can be seen.

 

AAMI Standards call for the nerve cuff inner diameter to be 150% of the outside diameter of the nerve.

 

Tissue Response to Open Cuff Electrode

Cross-section of the connective tissue formed around a “half-cuff”. The horseshoe shaped region in the upper part of the photograph, which is absent tissue, is the space previously occupied by the “half-cuff”. The oval shaped region in the lower part of the figure is the nerve, which has been pushed out of the cuff. Close inspection of the upper portion of the connective tissue on the inner aspect of the cuff reveals layers, like rings on a tree trunk (arrow, right). These layers of connective tissue are presumed to have developed in response to mechanical irritation between the cuff and the local tissues. It appears that the very small blood vessels are repeatedly injured, probably mechanically, causing fibrous tissue to proliferate and push the nerve out of the cuff.

 

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