INTRODUCTION

Middle ear impedance studies offer a large number of practical diagnostic applications, such as providing accurate information on the functional integrity of the tympanic-ossicular system. Thus, it allows for the differential diagnosis amongst the mixed, conductive and purely sensorineural hearing losses and it also allows the quantitative and objective study of Eustachian Tube functioning. A number of other clinical applications for this method avows its use as of paramount importance in the assessment of patients with otologic disorders (1-3).

Since this is a non-invasive, safe, fast and of simple application procedure, the acoustic impedance has been chosen by many segments of audiology as one of the most efficient methods used to identify carriers of hearing disorders and also for screening purposes, because it is acceptable, valid, reliable and of reasonable cost. Such procedure measures two important aspects: the very mobility of the tympanic-ossicular system when it undergoes pressure variation (tympanometry) and the assessment of tympanic muscle contraction when stimulated by high intensity sounds (acoustic reflexes) (4, 5). Combining the results of these tests we have a more thorough clinical picture of the patient (5).
The acoustic reflex represents the contraction of the tensor tympani and stapedius muscles in order to protect the inner ear; intensity control due to a high intensity sound stimulus; labyrinth pressure regulation and frequency selection (6-8). Stapedial acoustic reflex study is a highly valued basic component of audiologic assessment because it adds to the information given by tympanometry (9-14).

It is expected that all normal hearing patients have the reflex. Any middle ear disease prevents the acquisition of the acoustic reflex, such as a hearing loss that may limit the triggering of these reflexes (10).

The most important parameter related to the acoustic reflex is the acoustic reflex threshold (ART), which may be defined as the lowest stimulus intensity that triggers the contraction of the stapedial muscle, in other words, capable of causing the minimally measurable alteration in middle ear compliance (6, 12).

Many researchers have studied the normal values for the Acoustic Reflex Threshold (ART). As a rule of thumb, it is broadly accepted that the ART varies between 80 and 100 dBHL (decibel hearing level) in normal hearing patients for a pure tone stimulus, and that the ART for the ipsilateral reflex is of approximately 85 dBHL for a pure tone, and 65 dBHL for broad band noises (12). CARVALLO (10) states that the acoustic reflex is seen at 70 to 90 dB SL (decibel sound level) sound stimulus through current procedures. The reflex thresholds for noises are lower than the thresholds for pure tones (15).

In the presence of conductive hearing loss, acoustic reflexes are either null or high due to impaired transmission of sound stimulus to the inner ear and also to reduction in the mobility of middle ear structures, knowing that null or high acoustic thresholds happen when the reflex response is not present at the expected level between 70 ad 90 dB (14).

The stapedial muscle of each ear responds to ipsilateral, contralateral or binaural stimuli. Because of the bilateral nature of the acoustic reflex trajectory, a monoaural stimulation results in bilateral contraction of the stapedial muscle. Thus, the reflex may be measured in the tested ear (ipsilateral reflex) or in the non-tested ear (contralateral reflex) (5,16). Traditionally, methods in which the pure tone is presented to one of the ears (afferent) are employed and the reflex is seen on the opposite side (efferent), where the probe is located. However, with the most modern equipment, it is possible to detect the reflex in the same ear that receives the pure tone, without the use of the contralateral ear and hearing pathways, thus being called ipsilateral reflex (1).

The sensitivity of the muscle reflex seem higher in the ipsilateral stimulation when compared to the contralateral one, regardless of the stimuli to be given to one or both ears (17).

In order to detect hearing loss, the measurement of ipsilateral reflexes provide significant advantages in relation to the contralateral, because of the presence of some unilateral alteration in the middle or external ear the contralateral reflex is usually high or null (16). The differences among the contra and ipsilateral acoustic reflexes are still uncertain (18), however, MÜLLER (17) compares the reflex threshold for ipsilateral and contralateral stimuli and finds that the ipsilateral thresholds are consistently of 2 to 16 dB lower than their contralateral counterparts, meaning that the ipsilateral sensitivity is higher than the contralateral one. LAUKLY AND MEIR (19) did not find significant differences in their research between ipsilateral and contralateral thresholds of the acoustic reflex.
WILSON AND MARGOLIS (18) after a thorough study concluded that the mean/median of the acoustic reflex thresholds in 250; 500; 1,000; 2,000 and 4,000 Hz varied from 80 to 90 dBHL, the upper limit being 95 dBHL from 250 to 2,000 Hz, and between 100 and 105 dBHL for 4,000 Hz (18). For broad band noise, the authors found the average reflex threshold varying from 70 to 75 dBSPL. STEPHENSON et. al. (14) states in his paper that broad band noise is better able to elicit reflexes than the 500 Hz stimulus, and WILSON and MC BRIDE (20) concluded that broad band noise threshold is, in average, 20 dB lower in relation to pure tones.

Besides, it is important to highlight that the difference in reflex thresholds for pure tone and noise stimuli is of 15 dB for normal hearing subjects, being reduced in cases of mild to moderate hearing loss and large in severe hearing losses. For patients with severe hearing loss, this data is confusing, because most of the patients with hearing loss equal to or higher than 70 dB do not have reflexes (16).

According to NEUMANN et al. (12), the acoustic reflex is detected as a change in the middle ear compliance, where the 226 Hz stimulus may be given to the subject in order to measure this compliance, and another tone, of higher frequency and short duration, is used to elicit the acoustic reflex. These authors believe that a number of stimuli may be used in order to elicit the reflex, such as: filtered or broad band noises, pulsating tone or a sequence of pulsating tones.
In clinical applications, the acoustic reflex thresholds are estimated through monitoring impedance alterations using the 226Hz probe, however, many investigations have shown that the acoustic reflex threshold values according to probe frequency0 (21). For instance, the reflex thresholds measured with the 678 Hz were from 2 to 6 dB lower than the acoustic reflexes obtained through the 226Hz probe in WILSON and MC BRIDE's research (20), who concluded that using the 678 Hz probe one achieves more accurate measures.

Although there is much disagreement among the findings of different investigations, RAWOOL (21) states we can be certain that some of the differences in the measurements of the acoustic reflex may really occur due to differences in probe frequencies. After all, both ipsilateral and contralateral signal may interact with the probe tone in such a way as to produce artifacts in the measure, and the closer the activator signal tone frequency is to the probe tone, the greater will be the likelihood of having such interference(18).
STEPHENSON et. al. (14) studied adults with past history of otitis media in their childhood, her states that the use of probes of different tones, stimulus frequency and the use of conductance and susceptibility tympanograms may provide more complete and detailed information on middle ear functioning in these cases.

Aiming at assessing the ART effectiveness in diagnosing the maximum intensity level comfortable for subjects with hearing loss, RAWOOL (22) utilized low and high frequency probes in his research. The author based his choice in a study by WEATHERBY and BENNETT (23) that showed limitations with the 226Hz probe. Among such limitations is the fact that in babies, the reflexes are usually not present when investigated with low frequency probes (226 Hz) and present with high frequency probes. The study of acoustic reflex thresholds carried out with high frequency probes may be very useful in attaining the maximum intensity level yet comfortable for 1,000 and 2,000 Hz in hearing impaired individuals. However we already know of some acoustic reflex study limitations with the use of high frequency probes, because using the 1,000 Hz frequency probe any small movement of the subject may cause a major fluctuation on the impedance base line, what makes it very difficult to measure the reflex threshold. The best correlation was obtained when the value of the probe frequency was, approximately, equal to half of the stimulus frequency (22).

LU (24) carried out a study of ipsilateral acoustic reflexes in 25 adults, changing the probe frequency from 226 Hz to 678 and 1,000 Hz. He found the following threshold averages: 83 dB HL for the 226 Hz probe, 91 dB HL for 678 Hz and 88 dB HL for the 1,000 Hz probe frequency when they underwent the 1,000 Hz stimulus. Moreover, the ipsilateral acoustic reflex of 3 adults was present when the probe frequencies of 226 and 678 Hz were used and absent for the 1,000 Hz probe frequency.
In RAWOOL'S study (21), the elicited acoustic reflex thresholds with the 678 Hz probe were significantly higher than those with the 226 Hz and 1,000 Hz probes. Results showed that both the 226 Hz and the 1,000 Hz frequency probes can be utilized in the measurement of acoustic reflex thresholds elicited by a 'click' in adults. It is necessary to know that other studies have found opposite results to these ones, and this may be due to variations in the criteria used to determine the ART (21).

The acoustic reflex study is of great value in the audiometric assessment of babies, specially the ipsilateral tests because of its ease of application when compared to the contralateral one and because it is not influenced by abnormalities of the contralateral ear (25). CARVALLO'S investigation (26) with infants between zero and eight months of age, all subjects showed acoustic reflexes with the 226 Hz, 1,000 Hz, 2,000 Hz or white noise, and the latter was different from the formers as to the sound intensity capable of causing the acoustic reflex. WEATHERBY and BENETT (23) explored directly the effect of the probe tone frequency in the measurement of acoustic reflex in neonates and observed that as the frequency of the probe tone increased, the proportion of acoustic reflexes also increased and the mean reflex threshold was reduced.

MC MILAN et. al. (27) studied infants between 2 weeks and 12 months of age, the authors detected the ipsilateral acoustic reflex in 95% of these baby's normal ears. They concluded that 220 Hz and 660 Hz frequency probes are equally effective to measure the reflex, besides, the presence of the ipsilateral reflex and the reflex thresholds are not age-related in the first year of life. SPRAGUE et. al. (28) also studied neonates and found that both ipsilateral and contralateral reflexes were more frequently present for the 660 Hz probe than the 220 Hz probe, however the reflex thresholds did not vary significantly between the probes. Besides, they observed that the reflex thresholds for the broad band noise were significantly lower than those for the pure tone and that the ipsilateral thresholds were lower than their contralateral counterparts. The similarity among the acoustic reflex thresholds obtained with the 220 Hz and 660 Hz probes according to SPRAGUE et. al. (28) is contrary to WEATHERBY e BENNETT'S study (23) in which there was a reduction on the thresholds with the increase on probe frequency. Thus, there is no agreement in the literature as to the effect of probe frequency in the acoustic reflex threshold (21).
HALL (29) stated that it is still uncertain the basis for the age effect on the reflex, however, he suggests that a reduction in the efficacy of middle ear muscles may initially reflect on the reduction of its maximum contraction capacity, and that age-related changes in stapedius muscle innervation may also contribute to a reduction in the reflex amplitude in the elderly.

According to RAWOOL (21) most of the static admittance values found for the 678 Hz frequency probe was related to low acoustic reflex thresholds in women, and such correlation was not found in men. It is still uncertain why there is such a difference between genders. This data points to the need to consider the gender factor in ART determination procedures. As to possible inter-aural differences in the reflex threshold, MARGOLIS and WILSON (18) say that there are no significant differences between reflex thresholds of right and left ears, there may be, as it happen in their investigation, an absolute difference between ears varying from 3.4 to 5.1 dB.

In spite of the diagnostic value and the popularity of the acoustic immitance measures in clinical applications, there are limitations as to the reliability of the data supplied by such assessment and variations of these data, and the very existence of such variations does impair the application of this test. For these reasons, it is necessary to have accurate measuring instruments and, most specially, have specifications for test normal variation limits in order to determine when changes in the middle ear function, shown by immitance measures, are due to normal individual variation or to pathological conditions, so as proper clinical decisions may be arrived at (2, 30).
Because many investigations showed that the acoustic reflex threshold varies according to the probe frequency and there is no agreement in the literature as to the effect of this probe frequency in the acoustic reflex threshold, the goal of the present study is to analyze the pattern of ipsilateral acoustic reflexes obtained from adults without hearing complaints, changing the probe frequency from 226 Hz to 678 Hz and 1,000 Hz.

MATERIALS AND METHODS

The acoustic reflex was studied in 30 adult subjects who did not have any hearing complaints, being 15 males and 15 females. The average sample age was 22.53 years (the lowest age was 20 and the highest 26 years) (Table 1). We tried to identify the intensity in decibel hearing level (dBHL), in which the ipsilateral acoustic reflexes were obtained with the 226, 678 e 1,000 Hz probes, elicited through pulsating stimuli of 500, 1,000, 2,000, and 4,000 Hz and broad band noise BBN). Following that we made a comparative analysis of the ipsilateral reflexes obtained, considering the following variables: probe frequency, stimulus frequency, gender and ear.

The subjects were selected among the patients seen in the Clinical Audiology Service of the Research and Teaching Center of Speech Therapy of the Medical School of the University of São Paulo, they all volunteered to participate and signed the Informed Consent Form. This research was approved by the Ethics Committee in Research from the Clinical Board of the University Hospital of the Medical School of the University of São Paulo (CAPPesq, protocol 140/02).

Inclusion criteria:
 No alterations found in the external acoustic meatus.
 Hearing thresholds < 20dBHL in both ears in the frequencies of 250 to 8,000 Hz.
 Tympanometry with a 226 Hz probe in a normal pattern, with curve amplitude between 0.3 and 1.3 ml and tympanometric peak between -60 and +60 daAP.
 Presence of ipsilateral acoustic reflexes with the 226 Hz probe in the frequencies of 500, 1,000, 2,000, 4,000 Hz and broad band noise.
Thus, all the subjects who had their hearing investigated, but did not fit the inclusion criteria were excluded from this study.

The equipment used in this study were the GSI 61- Grason Stadler audiometer and the GSI 33 - Grason Stadler Version 2 middle ear analyzer. This analyzer is micro-processed, and it is able to present different probe frequencies, having stimuli calibration for the acoustic reflexes in decibel hearing level (dBHL), both contra and ipsilateral. The use of ipsilateral stimulus by the Multiplexed technology allows for a reduction in the artifacts because it separates the frequency for the reflex stimulus (500, 1,000, 2,000, 4,000 Hz and broad band noise - BBN) and the impedance probe (226, 678 or 1,000 Hz).

The subjects had their hearing assessed by tonal audiometry in the frequencies from 250 to 8,000 Hz, by the Speech Attention Threshold Study (SATS), speech recognition threshold (SRT) and percentage index of speech recognition (PISR). Tympanometry was also applied in both ears, and if we saw acoustic reflexes with the 226 Hz probe with the 5 different stimuli (500, 1,000, 2,000, 4,000 Hz and RFL), the subjects selected underwent the study of the ipsilateral acoustic reflex (multiplexed) with the 678 and 1,000 Hz for the same 5 stimuli described.

The reflex was considered present whenever the intensity level of the applied stimulus would generate an admittance change equal to an amplitude of 0.2 ml and a reflex with probe negative deflection of 226 Hz, of 0.6 ml with positive deflection on the 678 Hz probe and of 0.9 ml with positive deflexion on the 1,000 Hz probe.
The results were analyzed in a descriptive fashion, using the measures of central trend (mean, standard deviation, median and trend). The probe frequency (678 and 1,000 Hz), stimulus frequency, gender and ear variables that would influence the ipsilateral reflexes thresholds were studied through variance analysis (ANOVA), in order to check whether or not there were variations in the results as the probe frequency was increased. A 5% significance level was used.

RESULTS

Following are the results for the comparisons made among the variables involved.
Table 2 compares the results by stimulus for the three probe frequencies and shows a statistically significant average difference only for the frequencies of 500 Hz and in BBN. The other frequencies did not present evidences that the probes differ in average. For all stimuli, the measurement by the 678 Hz probe resulted in higher thresholds than for the 226 Hz and 1,000 Hz probes. Besides, the reflex threshold for BBN was lower than the one obtained on the other thresholds for all probe frequencies.
There was a statistically significant difference between the two genders with the use of the 226 Hz probe for all the stimuli frequencies, except for BBN, and also with the 1,000 Hz probe for the stimuli of 2,000 and 4,000 Hz. Therefore, in the 678 Hz probe we did not observe statistically significant differences between the genders.
There was no statistically significant difference between the ears for any of the probe frequencies (Table 3 - 226 Hz probe). With the 226 Hz probe, there was an absolute difference between the ears for the averages of reflex thresholds of 500, 1,000, 2,000, 4,000 Hz and BBN that varied in 1.33 dB (for the 4,000 Hz stimulus) in 3.67 dB (for 500 Hz). For the 678 Hz probe, the absolute difference between the ears varied from 0.17 dB to 4.54dB and, for the 1,000Hz probe, between 1.38 dB (for BBN) and 5.33 dB (for 1,000 Hz). Another piece of relevant data is that all the acoustic reflex thresholds for the right ear were high when kept in the left ear.
The two by two comparative analysis among the probes (Table 4) showed a significant difference for the 500Hz and the BBN stimuli with the 678 Hz probe when compared to the 1,000 Hz; and with the 226Hz probe when compared to the 678Hz. For the 1,000Hz stimulus, this difference was only seen between the 226 Hz and the 678 Hz probes.
Table 4 shows the same comparison, but only for females, because males did not have statistically significant differences in comparing the probes two by two. There was a significant difference when comparing the probes two by two. There was a significant difference in comparing the results of 226 and the 678 Hz probes for the 500, 1,000 Hz and BBN stimuli, and it also showed a strong trend towards the difference between the 678 Hz and the 1,000 Hz probes for the BBN stimulus.

DISCUSSION

According to Table 2, the acoustic thresholds measured by the 678 Hz probe were higher when compared to the 226 Hz and the 1,000 Hz probes, both for pure tones as for broad band noise. This data is in agreement with the findings by RAWOOL (21) and LU (24), however, it does not agree with WILSON and MC BRIDE (20) that found 2 to 6 dB lower reflexes with the 678 Hz probe when compared to the 226 Hz probe. The causes that would justify these findings are still uncertain, however it is possible to state that the high thresholds found with the 226 Hz probe can not be attributed to differences in the criteria used to measure the reflex thresholds. One must consider that in this study almost the same criteria used by RAWOOL (21) were accepted, because only when the change in admittance was of 0.06 mmhos acoustics was considered a criteria with the use of the 678 Hz probe, and when the change in admittance was of 0.09 mmhos acoustics for the 1,000 Hz probe.

The acoustic reflex thresholds for broad band noises (BBN) were equally reduced in relation to pure tone thresholds in all probe frequencies, in agreement with SPRAGUE et al. (28). MARGOLIS (16) states that the difference in reflex thresholds for pure tone stimuli and noise is of 15 dB for normal hearing subjects. Our study corroborates this value with the 226 and the 1,000 Hz probes that showed, in average, a difference of 15.67 and 15.5, respectively, between pure tone and BBN thresholds. With the 678 Hz probe, this value was lower (12.9 dB).

WILSON and MC BRIDE (20) concluded that broad band noise threshold is, in average, 20 dB lower than pure tones. Thus, the present study does not agree with this data, because with the 226 Hz probe we obtained averages bellow 15.67 dB of threshold differences between pure tones and BBN. For the broad band noise, WILSON and MARGOLIS (18) found the mean reflex threshold varying from 70 to 75 dBSPL, and this finding is in agreement with the results of the present study for the frequency probes of 226 Hz and 1,000 Hz, that presented, respectively, the mean thresholds of 71.03 dB and 72.07 dB. Once again, the 678 Hz probe did not present results in agreement with the literature, it showed mean reflex thresholds for BBN of 77.67 dB.

STEPHENSON et al. (14) states that the broad band noise is better able to elicit reflexes than the 500 Hz stimulus, thus it is possible to generalize for this study, that BBN have a better potential to trigger the acoustic reflex than all the other pure tone stimuli. No investigation justifies the cause for the BBN reflex threshold be sistematically reduced when compared to pure tone thresholds, however, it is supposed that this happens because this noise is made up of a fundamental frequency, with its many multiples, and for this reason, it is possible that a pure tone frequency, such as the frequency of the probe used, be coincident to three or four cycles of noise component frequencies, and this would produce a "beating sound" or a pulsation in the patient's ear, thus increasing the BBN potential to elicit acoustic reflexes.

The acoustic reflex thresholds in women were equally reduced when compared to their male counterparts for all stimuli. It may be for this reason that women would have more influence over the different results found among the probes, for there was significant difference and a trend towards difference for the same stimuli shown on Table 2 that gathers together the data from both gender groups. Besides, for males, there was no difference among probes for none of the presented stimuli. This threshold difference between males and females is not much explored in the literature, and therefore the explanations for this finding are still uncertain. In RAWOOL'S (21) study, a large part of the static admittance values found for the 678 Hz frequency probe was related to low acoustic reflex thresholds in women, and this same correlation was not found in men. According to this author, the reason for this correlation difference between the genders is still to be ascertained.
One hypothesis that maybe raised as a cause for the acoustic reflexes being lower in women than in men is related to the anatomical differences found in the female auditory apparatus. It has been suggested that the reduced size of the external acoustic meatus in women is responsible for the differences in terms of the external auditory canal volume and its resonance, as well as for the reduced reflex thresholds when compared to men. This data points towards the need to take into account the gender variable in the ART determination procedures.

From the descriptive analysis of the acoustic reflex by gender for each probe, we can infer that the 678 Hz probe is not so sensitive to measure the acoustic reflex threshold as the other probes, for it did not present statistically significant difference between the genders, whilst the 226 Hz and the 1,000 Hz probes presented differences and trends towards difference for the same stimuli (500; 1,000; 2,000 and 4,000 Hz). This finding is in agreement with RAWOOL'S (21) findings that showed acoustic reflex thresholds for the 678 Hz probe significantly higher than the ones obtained with the 226 Hz and the 1,000 Hz probes. These data led the author to conclude that both the 226 Hz and the 1,000 Hz probes may be used to measure the acoustic reflex thresholds triggered by clicks in adults, because they are more sensitive.
Analyzing the results, it is clear that there are no statistically significant differences between the left and the right ear, and this is in agreement with WILSON and MARGOLIS (18). It is worth stressing out that the absolute difference range of the threshold averages between ears was broader in the present study than in the aforementioned authors' study, because for them this range was from 3.4 to 5.1 dB, and this study found it to be from 0.17 to 5.33 dB, considering the three probe frequencies. This difference of results among absolute value ranges for ears threshold averages in this study compared to those from the WILSON e MARGOLIS'S (18), may be due to the fact that these authors performed their study with only one probe frequency. There is no data in the literature that corroborates the finding that right ear average reflex thresholds are always high in relation to the left ear, thus both the truthfulness and the reliability of this finding have to be analyzed with caution in future studies.

Analyzing the results depicted on Table 4, that compares the probes two by two for the stimuli that present statistically significant difference among them, it is clear that the data obtained through the measurement with the 226 and the 1,000 Hz probes do not differ from one another, because in this table there was no significant difference between the two probes for none of the stimuli. Another interesting piece of data is that for the 1,000 Hz stimulus there was statistically significant difference only in the comparison between the 226 Hz and the 678 Hz probes, and not when the 1,000 Hz probe, which coincides with the stimulus frequency, was involved.

Both Table 4 and Table 2 did not show statistically significant difference for the 2,000 and the 4,000 Hz stimulus, and this may be due to the fact that the frequency of these stimuli are not close to those of the probe. This hypothesis is based on RAWOOL'S (22) statement that the best correlation in his study was obtained when the value of the probe frequency was, approximately, half of the stimulus frequency, which was exactly what happened in this study. Therefore, since the 2,000 and the 4,000 Hz stimuli were at least twice the highest value of the probe frequency (1,000 Hz), there was no interaction between the stimulus tone with the probe tone in such a way as to produce artifacts in the measure, as stated by WILSON and MARGOLIS (18), and, maybe for this reason, no statistically significant difference was found among the probes for these two stimuli.

Considering these statements from RAWOLL (22) and WILSON and MARGOLIS (18), it is possible to justify the reason why we had statistically significant difference between the probes only for the 500 Hz, 1,000 Hz and BBN stimuli. Thus, the 500 Hz stimulus showed significant difference when the 226 Hz and the 1,000 Hz probes were involved in the probe to probe comparison (226 Hz X 678 Hz and 678 Hz X 1,000 Hz) because of the 2:1 relation among these values, in other words, because the 226 Hz probe has practically half the stimulus value of the stimulus and the 1,000 Hz has twice the stimulus frequency. In the same way, for the 1,000 Hz stimulus there was significant difference between the probes only in the comparisons that did not involve the 1,.000 Hz probe tone, in other words, there was only difference between the 226 Hz and the 678 Hz probes, because with the probe frequency of 1,000 Hz there may have been an interaction of the stimulus tone with the probe tone in a way as to produce artifacts in the measurement as stated by WILSON and MARGOLIS (18), since the authors stated that the closer the reflex activator signal frequency is to the probe tone, the higher is the likelihood of having an interaction between the two signals, causing the artifact.

Considering still the same theory from RAWOOL (22) that the best correlation is obtained when the probe frequency value is, approximately, half the stimulus frequency than that from WILSON and MARGOLIS (18), it is possible to justify the reason behind the significant differences between the probes for the BBN stimulus, due to the very characteristic of this stimulus of being made up of many multiple frequencies and one fundamental frequency, that being, for any probe frequency used the stimulus carries a frequency that is favoring the 2:1 ratio proposed as ideal one, for instance, when the 1,000 Hz probe is used, it is possible to have a frequency close to 500 Hz in the broad band noise spectrum, and this reduces the likelihood of having an artifact.

Table 4 (probe to probe descriptive analysis of the acoustic reflexes) depicts results which are practically similar to those from the Acoustic Reflexes Descriptive Analysis, probe to probe, for females specifically, because for women the differences occurred for the same stimuli (500 Hz, 1,000 Hz and BBN) of the general Table involving both genders, and this stresses the hypothesis that in this study the female subjects had greater influence than their male counterparts on the results. Thus being, if it is possible to state so, the ones causing this statistically significant difference between the probes.

We still have to stress the fact that the 678 Hz probe was the one that most depicted artifacts and altered configuration; in other words, negative deflection instead of a positive one; when compared to the other probes. It is likely that because of this inconsistence of reflex configuration with the 678 Hz probe, presenting itself sometimes with positive deflexion and other times with negative ones, one may explain the fact that the acoustic reflex thresholds for all the stimuli (pure tones and BBN) were in higher intensities in relation to the probe frequency of 226 Hz and 1,000 Hz.

Thus, this study has allowed us to observe that the probe frequencies of 226 Hz and 1,000 Hz presented similar capabilities to elicit acoustic reflexes in adults without hearing complaints, whilst the 678 Hz probe requires higher intensities to elicit the acoustic reflexes. Since the 226 Hz and the 1,000 Hz probes seem to be the most adequate and sensitive to measure the acoustic reflex threshold in adults without hearing complaints, it is necessary to do a similar study in adults with some hearing disorder in order to confirm or reject the effectiveness and similarity of diagnosis potential between the 226 Hz and the 1,000 Hz probes.


CONCLUSION

The probe frequency change in the acoustic reflexes study may be a valuable diagnostic tool. The 226 Hz and the 1,000 Hz probes present similar efficacy and competence in eliciting acoustic reflexes in adults without hearing complaints, and they may be equally used to study acoustic reflexes in this specific population.

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