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. 2020 Feb 17;10(1):2777.
doi: 10.1038/s41598-019-56253-w.

Four-point impedance as a biomarker for bleeding during cochlear implantation

Affiliations

Four-point impedance as a biomarker for bleeding during cochlear implantation

Christofer Bester et al. Sci Rep. .

Abstract

Cochlear implantation has successfully restored the perception of hearing for nearly 200 thousand profoundly deaf adults and children. More recently, implant candidature has expanded to include those with considerable natural hearing which, when preserved, provides an improved hearing experience in noisy environments. But more than half of these patients lose this natural hearing soon after implantation. To reduce this burden, biosensing technologies are emerging that provide feedback on the quality of surgery. Here we report clinical findings on a new intra-operative measurement of electrical impedance (4-point impedance) which, when elevated, is associated with high rates of post-operative hearing loss and vestibular dysfunction. In vivo and in vitro data presented suggest that elevated 4-point impedance is likely due to the presence of blood within the cochlea rather than its geometry. Four-point impedance is a new marker for the detection of cochlear injury causing bleeding, that may be incorporated into intraoperative monitoring protocols during CI surgery.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Illustrations of cochlear implant surgeries with/without trauma to the lateral wall and how the presence of blood cells effects impedance. (A–C) Illustration of a cochlear implant where lateral wall trauma did not occur. (A) Illustration of how four-point impedance is inferred using a cochlear implant. The current is supplied to the outer electrodes in the quartet and the voltage is measured between the two inner electrodes. This is repeated along the whole array, resulting in 19 quartets. (B) Insertion completed with the cochlea filled with perilymph. C) The current paths of the stimulus for a four-point impedance measurement through perilymph. The current has little resistance and therefore the voltage is low. (D–F) Illustration of a cochlear implant where lateral trauma occurred, resulting in the infiltration of blood. (D) Insertion of the cochlear implant where the electrode array comes into contact with the lateral wall and causes damage. (E) Cochlear implant completely inserted with blood pushed into the cochlea along the electrode array. (F) The current paths for the stimulus when blood is present in between the two inner electrodes. The current has more resistance since it does not pass through the cells and the reduction in available ions, resulting in a higher voltage.
Figure 2
Figure 2
Four-point impedance distribution and Receiver Operator Curves, for four-point impedance and total hearing loss. (A) The distribution of four-point impedance immediately following electrode insertion in all 4-electrode measurements for all patients (969 measurements). (B) Receiver operator curve for the immediately-post insertion four-point impedance values predicting total hearing loss by 3-months post-op, point of maximum efficiency represented by red circle.
Figure 3
Figure 3
Clinical four-point impedance and common ground impedance immediately after implantation. (A) Four-point impedance values in 38 patients with ‘low’ four-point impedance, defined as impedances lower than those at the point of maximum efficiency for prediction of total hearing loss on the receiver operator curve (Fig. 2B). Individuals are presented as grey lines. Electrodes are numbered from base of the cochlea. (B) Individual four-point impedances (black line) and common ground impedance (grey line). The dashed line defines the low/elevated four-point impedance transition point, as determined by the ROC point of maximum efficiency (388 Ω). The numbers of patients with total hearing loss, and post-operative vestibular dysfunction in each group is mentioned in each sub-figure.
Figure 4
Figure 4
Experimental Four-point impedance and the introduction of blood into a cochlea. Four-point impedance recordings from 4 of the 11 procedures before and after blood was injected into the cochleostomy. The arrows indicate the time blood was injected. (A,D) show recordings from procedures that injected cold blood and (B,E) are recordings from procedures that blood at body temperature was injected. (C,F), the four-point impedance measurements from the two controlled procedures where blood was not injected into the inner ear. (G) A boxplot representation of the four-point impedance pre- and post- blood injection from 9 of 11 cases that were exposed to blood. 2 of 11 cases resulted in outliers are not shown.
Figure 5
Figure 5
Experimental blood injection histology. Cross sections of a control cochlea (left) that received only a cochlea implant and an experimental cochlea (right) that was implanted and had blood injected into the basal turn. Scale bar for 500 µm.
Figure 6
Figure 6
Four-point impedance measurements corresponding to the cross-sectional area from the insertions into the 3D printed cochlea models. All data points are shown along the respecting cross-sectional area dependent on the location of the electrode array within the cochlea model. The regression line is plotted (y = 726 − 138x), with a Pearson’s coefficient of −0.6652.

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