MATERIALS AND METHODS: A retrospective repeated crosssectional study was conducted by recruiting patients with cochlear implants presenting to the Dr. Cipto Mangunkusumo National General Hospital, Jakarta, Indonesia between 2017 and 2021. Basal (b1, b2) and apical (a1, a2) electrodes, representing the outermost and innermost parts of the cochlear implant electrodes, were measured at switch on and at 1 year post-implantation.
RESULTS: A total of 123 patients, with a total of 123 cochlear implant samples, were included in the analysis. We found a substantial change in electrical impedance between switch on and follow-up periods, where the impedance levels of basal electrodes decreased (b1: mean difference (MD) -1.13 [95% confidence interval (CI): -1.71, -0.54], p<0.001; b2: MD -0.60 [95%CI: -1.17, -0.03], p=0.041) and those of apical electrodes increased (a1: MD 0.48 [95%CI: -0.28, 0.99], p=0.064; a2: MD 0.67 [95%CI: 0.12, 1.22], p=0.017). We also found that the choice of surgical approaches for implant insertion may affect the electrode impedance. Cochleostomy approach resulted in a higher impedance than round window in basal (b1) and apical (a2) electrodes both at switch on and follow-up (b1 at switch on and at follow-up: p=0.019 and p=0.004; a2 at follow-up: p=0.012). Extended round window approach also resulted in a higher impedance than round window in basal (b1) and apical (a2) electrodes at follow-up (p=0.013 and p=0.003, respectively).
CONCLUSION: Electrical impedance of cochlear implant electrodes may change over time, highlighting the importance of regular impedance assessments for cochlear implant users to ensure optimal device function. The round window approach resulted in better initial and long-term impedance levels compared to cochleostomy, and better long-term impedance levels than extended round window. Extended round window approach also gives better impedance level than cochleostomy. Further research should investigate the potential interplay between surgical approach and other factors that may impact impedance levels to confirm our findings.
METHODS: We formulated body capacitive index (BCI), C(BMI) (capacitance × height(2)/weight), body resistive index (BRI), R(BMI) (resistance × weight/height(2)), and CH(2) (capacitance × height(2)). We also studied H(2)/R, R/H, and reactance of a capacitor/height (X(C) /H). There are 3 components in this study design: (1) establishment of normal values in a control Malaysian population, (2) comparison of these with a CAPD population, and (3) prediction of survival within a CAPD population. We initially performed a BIA study in 206 female and 116 male healthy volunteers, followed by a prospective study in a cohort of 128 CAPD patients [47 with diabetes mellitus (DM), 81 non-DM; 59 males, 69 females] for at least 2 years. All the parameters during enrolment, including BIA, serum albumin, peritoneal equilibrium test, age, and DM status, were analyzed. Outcome measurement was survival.
RESULTS: In healthy volunteers, both genders had the same BCI (2.0 nF kg/m(2)). On the contrary, female normal subjects had higher BRI than male normal subjects (median 15 642 vs 13242 Ω kg/m(2), p < 0.001) due to higher fat percentage (35.4% ± 0.4% vs 28.0% ± 0.6%, p < 0.001), resulting in a lower phase angle (mean 5.82 ± 0.04 vs 6.86 ± 0.07 degrees, p < 0.001). Logistic regression showed that BCI was the best risk indicator in 128 CAPD patients versus 322 normal subjects. In age- and body mass index (BMI)-matched head-to-head comparison, BCI had the highest χ(2) value (χ(2) = 102.63), followed by CH(2) (or H(2)/X(C); χ(2) = 81.00), BRI (χ(2) = 20.54), and X(C)/H (χ(2) = 20.48), with p value < 0.001 for these parameters. In comparison, phase angle (χ(2) = 11.42), R/H (χ(2) = 7.19), and H(2)/R (χ(2) = 5.69) had lower χ(2) values. 35 (27.3%) patients died during the study period. Univariate analysis adjusted for DM status and serum albumin level demonstrated that non-surviving patients had significantly higher CH(2) (245 vs 169 nF m(2), p < 0.001) and BCI (4.0 vs 2.9 nF m(2)/kg, p = 0.005) than patients that survived. CH(2) was the best predictor for all-cause mortality in Cox regression analysis, followed by BCI, phase angle, and X(C)/H.
CONCLUSION: Measures that normalize, such as BCI and CH(2), have higher risk discrimination and survival prediction ability than measures that do not normalize, such as phase angle. Unlike phase angle, measurement of BCI overcomes the gender effect. In this study, the best risk indicator for CAPD patients versus the general population is BCI, reflecting deficit in nutritional concentration, while CH(2) reflects total nutritional deficit and thus is the major risk indicator for survival of CAPD patients.