Nov - Dez - English

arbosa

596

ssoc

ras

2014; 60(6):591-598

at 50 dB at 2000 Hz and 60 dB at 4000 Hz. In this study

we considered three thresholds denominated Threshold1,

Threshold2 and Threshold3 where:

•

Threshold1 (Lim1) = lowest intensity studied whe-

re the signal/noise ratio is greater than or equal to

3dB;

•

Threshold2 (Lim2) = lowest intensity studied whe-

re the signal/noise ratio is greater than or equal to

3dB and 2F1-F2 with a positive value; and

•

Threshold3 (Lim3) = lowest intensity studied whe-

re the signal/noise ratio is greater than or equal to

3dB and subsequent intensities also present a S/N

ratio greater than or equal to 3dB, with the emer-

gence threshold considered when it appeared in 70%

of cases.

Therefore, the responses were better at 2000 Hz compa-

red to 4000 Hz such as those obtained in the aforemen-

tioned study.

When comparing the left ear with the right ear, the

differences were not significant due to the number of new-

borns composing the sample, which was not sufficient

for this purpose. These results compare to those obtai-

ned by Leme and Carvallo

and Costa et al..

There are

studies already established in the literature that show that

OAE responses are better in the right ear for the female

gender compared to the left ear for the male gender, Leme

and Carvallo,

Aidan et al..

and Durante et al.

The results obtained in the DPOAE growth curves in

this study were used to calculate the mean responses for

each intensity, using 2F1-F2 and the signal to noise ratio

at the frequencies of 2000 Hz and 4000 Hz, in order to

obtain an average curve profile for newborns and to iden-

tify the occurrence of any compression pattern for the

responses in this age group. To obtain the mean, the grou-

ped results of the left and right ears at each intensity and

frequency were used, given that there was no significant

difference between them in this study.

The DPOAE GC were obtained for paradigms P1 and

P2 based on the hypothesis that the slope would be higher

(greater incline of the curve) in weak sounds (20 to 40dB

SPL) and lower (lower incline of the curve) in midrange

sounds (40 to 65dB SPL). According to Gorga et al.

coch-

lear gain is higher for weaker stimulus levels, decreasing

as the level increases. That is, the cochlea is more com-

pressive when stimuli are of medium intensity. In this

work, the slope values obtained at 2000 Hz were lower

in P1 than P2 in both ears, and at 4000 Hz in the right

ear P1 was higher than P2, and in the left ear P1 was lo-

wer than P2, as in 2000 Hz. These differences were not

significant. However, visually, the slope in P1 is greater

than in P2. The slope value was higher on average at 2000

Hz than 4000 Hz (except for the slope obtained in P1 in

the right ear at 4000 Hz, which was greater than the cor-

responding slope at 2000 Hz). If the DPOAE growth cur-

ve enables detection of the presence of cochlear compres-

sion upon calculating the slope, the numerical results of

this study did not make it possible to prove the presence

of cochlear compression in the sample, though looking

at the growth curve graphs a decrease was seen in the slo-

pe of the curves at midrange intensities.

It was not possible to make comparisons with other

slope studies obtained in two paradigms, as no work using

DPOAE GC in this way was found in the literature. Ho-

wever, a study by Almeida

noted a change in the incline

of the curve of the slope from 65 dB, which would be the

compression point for the frequencies studied (the DPOAE

GC was outlined with stimuli a variation range between

35 and 75 dB with 5 dB intervals at 2000 Hz and 4000 Hz).

Comparing these results with the present study was not

possible, because 65dB was the largest stimulus used in

the paradigms presented. In studies with adults, the com-

pression point was between 50 and 60 dB.

3,15,22

When using the general paradigm the slope values

were higher than those obtained in paradigms 1 and 2,

but the comparison was not made because of the use of

different criteria.

The slope values varied from3 to 4 on average, reaching

15 in some cases. These maximum values can be attributed

to the fact that they were obtained in the newborn popula-

tion where the OAE responses are better than in other age

groups. This fact was discussed with the technical team of

the equipment manufacturer (Otodynamic), Peter Bray and

Lee Van Middlesworth, who still have no explanation for

this finding due to the small number of studies performed

with the newborn population. The general paradigm was

only applied to part of the sample, and only at 2000 Hz; the-

refore, it was not compared with the other paradigms (P1

and P2), and the General P slope values were higher than

those obtained in P1 and P2. The mean General P slope va-

lue was 10.05 in the right ear and 8.85 in the left ear.