Proefschrift_vd_Beek

–12

Levels at initial fitting T-level (dB)

Levels at 1 year

–15

250

12

logDR

M-levels

6

200

DR

0

150

logM- levels

–18

-6

100 Level (CU)

Level (dB)

T-levels

-12

logT- levels

50

-18

a

0

1 + 2

3 + 4

1+2 9 + 10 Electrode duo 5 + 6 7 + 8

1 + 2

9+10 3 + 4

15+16 Electrode duo 9 + 10 13+14 11+12 5 + 6 7 + 8

1 + 2

3 + 4

Electrode duo 9 + 10 5 + 6 7 + 8

7+8

1+2

3+4

5+6

5+6 13 + 14

3+4 11 + 12

7+8

9+10

15 + 16

11 + 12

13 + 14

15 + 16

11 + 12

13 + 14

15+16

13+14

11+12

a

b

Electrode duo

Electrode duo

Fig. 3. T-levels, M-levels and DRs at initial fitting and after 1 year in clinical units ( a ) and in decibels ( b ). Arrows point from the initial fit line towards the 1-year data.

5 In figure 4, speech perception scores are plotted against the ASM and ASV of levels. Figure 4a, c shows a significant correlation between speech perception scores and T-level and DR (r = 0.34, p < 0.01, and r = 0.33, p < 0.01, respectively). No significant correlation of speech perception with the ASM of the M-level was found. Figure 4d–f illustrates the absence of a significant correlation between speech perception and ASV of the T-level, M-level or DR. These panels also show that the ASV was relatively small in most cases, with data clustering around a value of 1 or 2 dB, meaning a relatively flat level profile. The word scores showed a small negative correlation with duration of deafness (3% decrease in word score for a 10-year duration of deafness; r = 0.23, p < 0.01; data not shown). The solid lines in figure 5a show the T-values (in decibels) along the array (measured 1 year postoperatively) for 4 quartile groups of the overall T-level. For all groups, an increase towards the basal end was found, which was independent of the actual overall T-level. A mixed linear model based on the measured T-levels of randomly chosen 70% of the subjects found that the best fit of this increase was given by the following quadratic function with only electrode 2 duo and electrode duo as significant parameters: ited number of cases (>1.5 × IQR). Assuming a normally distributed data set, this means that about 1 out of 50 (the- oretically 2.15%) has a ratio of 10% or below. Further- more, from figure 2a, it can be seen that the ratio was fairly stable along the array. Figure 2b shows that about one third of the variance of the T-/M-level ratio could be predicted by the T-level (r = 0.61, p < 0.01). On the other hand, the T-/M-level ratio did not show any correlation with the M-level (fig. 2c), while it had a significant nega- tive correlation with the DR ( = –0.42, p < 0.01; fig. 2d). The overall T-level turned out to be very weakly cor- related with duration of deafness (approx. 4 CU per de- cade; r = 0.22, p < 0.05) and not correlated at all with age at implantation (p = 0.63). In contrast, the overall M-lev- el was not significantly correlated with duration of deaf- ness (p = 0.57), but a small but significant negative cor- relation was ound with age at implantation (approx. 15 CU per decade; r = 0.23, p < 0.01). The changes in T-level, M-level and DR during the first year are shown in figure 3. Figure 3a show the levels along the electrode array during initial fitting and after 1 year of follow-up, expressed in clinical units. Figure 3b shows the same data, now plotted using a decibel scale. M-levels (fig. 3a) showed a larger increase (40.6 CU; SD 83.8) than T-levels (11.0 CU; SD 24.3), resulting in an in- crease in DR (29.8 CU; SD 73.0). T-and M-levels ex- pressed in decibels (fig. 3b) showed an approximately equal increase (1.8–1.7 dB; SD 3.58–2.78), resulting in a stable DR in the first year (–0.2 dB; SD 3.2). In figure 4, speech perception scores are plotted against the ASM and ASV of levels. Figure 4a, c shows a signifi- cant correlation between speech perception scores and T-level and DR (r = 0.34, p < 0.01, and r = 0.33, p < 0.01, respectively). No significant correlation of speech percep- tion with the ASM f the M-l vel was found. Figure 4d–f illustrates the absence of a significant correlation between speech perception and ASV of the T-level, M-level or DR. These panels also show that the ASV was relatively small in most cases, with data clustering around a value of 1 or 2 dB, meaning a relatively flat level profile. The word scores showed a small negative correlation with duration of deafness (3% decrease in word score for a 10-year du- ration of deafness; r = 0.23, p < 0.01; data not shown). The solid lines in figure 5a show the T-values (in deci- bels) along t r ay (measured 1 year posto eratively) for 4 quartile groups of the overall T-level. For all groups, an increase towards the basal end was found, which was inde- pendent of the actual overall T-level. A mixed linear model based on the measured T-levels of randomly chosen 70% of the subjects found that the best fit of this increase was given Fig. 3. T-levels, M-levels and DRs at initial fitting and after 1 year in clinical units (a) and in decibels (b). Arrows point from the initial fit line towards the 1-year data. by the following quadratic function with only electrode 2 duo and electrode duo as significant parameters: T-level ( electrode duo ) = 0.04 × electrode 2 duo + 0.03 × electrode duo ( in dB ). (1) The interaction of electrode du with the ASM of T-levels did not reach significance (p > 0.05). r-value 0 0.20 0.40 .60 0.80 1.00 b Fig. 5. a Measured and predicted T-levels fitted with a random70% of the population. Data plo ted in quartile groups of ASM. b Dis- tribution of r-values fitting with single T-level measures at differ- ent electrodes (electrodes 2, 5, 9 and 14 not included; electrodes active in less than 33% of the subjects). The interaction of electrode duo with the ASM of T-levels did not reach significance (p > 0.05). To predict the T-level for each 16 separate electrodes for an individual subject, instead of the 8 electrode duos, electrode duo from equation 1 should be substituted by (½ × electrode + ¼). Finally, the overall level can be determined by measuring the T-level measurement of one electrode. It turned out that the best Population-Based Prediction of Fitting Levels Audiol Neurotol 2015;20:1–16 DOI: 10.1159/000362779 Population-Based Prediction of Fitting Levels Audiol Neurotol 2015;20:1–16 DOI: 10.1159/000362779 7 To predict the T-level for for an individual subject, inst electrode duo from equation (½ × electrode + ¼). Finally, termined by measuring the electrode. It turned out that mean correlation coefficient 1 2 3 4 5 6 7 Electrode of

Downloadedby: LeidenUniversity 145.88.209.33 - 11/23/20142:34:38PM

101