Influence of body mass index on variables of brain-stem evoked response audiometry in children aged 2-10 year with delayed development of speech attending Bankura Sammilani Medical College

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rainstem evoked respond audiometry (BERA) or brainstem auditory evoked potential (BAEP) parameters are recorded from the scalp as small voltage potentials after passing auditory stimuli through a headphone 1 .There are mainly five BERA waveforms of which waves I, III and V are the most visible and of more significant clinical value.These waves represent the neuro electrical activity that is generated by the neural generators in the auditory pathway between the cochlea and the brainstem.Among the various factors that affect BERA test finding.Age and hearing loss with definitive prolongation of absolute peak latencies are well established in BERA 2   .The effect of sex on BERA parameters like absolute peak latencies (APL) and interpeak latency (IPL) difference showed non-significant differences between 2 and 13 years, whereas between 16 and 45 years, sex differences were evident.These differences can be attributed to hormonal factors, temperature variations and anthropometric components like height, weight and head size 3,4   .In few studies, the effects of BMI and head size was also studied and it was observed that both affected the BERA latencies and IPL differences independently 5,6 .Although the effect of these variables on BERA has been studied extensively outside India, there remains a limitation of data in the Indian context.Further, most studies have not included an important BERA feature, the waveform V:I amplitude ratio, which indicates the involvement of the auditory pathway in hearing loss, whether central or peripheral.In one such study, it was observed that both IV-V/I and IV-V/III amplitude ratios were independent of sex, but the IV-V/I ratio increased significantly with age 7 .
BMI is very important parameters that influence BERA test variables.Although the correlation of BMI with BERA parameters has been studied recently in various group of population, there is no common consensus on it.Some studies show a positive correlation in normal population, whereas others report a weaker correlation.A few studies discuss correlation between BMI and BERA over the children with delayed development of speech.
This cross sectional study tried to examine any possible association of body mass index on variables of brainstem evoked respond audiometry in children aged 2-10 years with delayed development of speech.

Exclusion criteria
Gross developmental anomaly, autism, very low IQ, recent ear infection, head injury, systemic disease or drug toxicity that affects ear were excluded from the study.

Method of study
Written consent was taken from parent or guardian or accompanying caregiver of all participants after explaining purpose and procedure of study.Children were chosen according to the inclusion and exclusion criteria.The participants were made familiar with the equipment and the test was discontinued if they faced any discomfort.History was taken regarding delayed speech/language impairment followed by general health check-up.BERA test was then done.
Measurement of anthropometric parameters: Weight was measured using a standardized electronic weighing machine, with light clothes in standing posture without footwear.The height of the subjects was measured to the nearest centimetre using stadiometer, The body mass index (BMI) Recording of BERA: All participants were subjected to BERA testing according to standard techniques on an RMS Portable Aleron EP-Electromyograph machine manufactured by Recorders and Medicare System (RMS) (Chandigarh, India).Recording of BERA was carried out in a quiet and dimly lit room with the participant in the supine position.Participants were briefly informed about the procedure.Restless, irritable and apprehensive participants were allowed to relax for 5-10 min before testing.
Patients or their parents/guardians were instructed to take/give shampoo bath to the hair on the day of the investigation so that the scalp is oil free.The non-inverting electrode is placed over the vertex B (CZ) of the head and the inverting electrode is placed over the ear lobes (Ai and Ac) or mastoid prominence.One more electrode known as the earthing electrode was placed over the forehead (ground).Monaural auditory stimulus consisting of rarefaction clicks of 100 μsec pulse were delivered through an electrically shielded earphone at a rate of 11.1/s.The contralateral ear was masked with pure white noise 30 dB below that of the BERA stimulus.A band pass of 10-3000 Hz was used to filter out undesirable frequencies in the surrounding.Responses to 2000 click presentations were live averaged to obtain a single BERA waveform pattern.Waveforms were obtained at 40, 60, 90 and 110 dB in each ear.Data of waveforms obtained at 110 dB were used for analysis.APL of waves I, III, V and IPL of I-III, III-V, I-V wave forms were considered for assessment.

Statistical analysis
Statistical analysis was carried out using SPSS version 20.0 (IBM SPSS Inc., Chicago, IL, USA).Descriptive analysis included the calculation of Mean with Standard Deviation and range for various parameters.Pearson's correlation coefficient was used for correlation statistics.

Results
Descriptive statistics of brainstem evoked response audiometry (BERA) parameters among all children are shown in table 1. Unpaired student 't' test was done between the underweight and nonunderweight children.The test showed significant changes (p value <0.05) in APL-I, APL-II and APL-III (Table 1).In underweight children significant correlation were observed between APL-I and V:I ratio with BMI.
There is lack of association between APL-II, APL-III, I-III IPL, I-V IPL and III-V IPL with BMI (Table 2).
In non-underweight children APL-V, III-V IPL and V:I ratio were significantly correlate with BMI and there is lack of association between APL-I, APL-III, I-III IPL and I-V IPL with BMI (Table 2).

Discussion
The present study observed the effect of BMI on different parameters of BERA in children aged 2-10 year.So we had already excluded sex factors from the study, it clearly accounts for the effect of only BMI with variables on BERA.There was significant correlation between any of the BERA parameters and BMI.
Our study show in underweight children APL-I, APL-II and APL-III significantly lower in compare to non-underweight children whereas, I-III IPL slightly higher and only significant correlation were observed between APL-I and V:I ratio with BMI.In patients with a prolonged I-III inter peak latency and a normal III-V inter peak latency, the auditory dysfunction is assumed to be located between the distal part of CN VIII (near the cochlea) and the superior olivary nucleus, ipsilateral to the ear stimulated 11 .
Present study in Non-underweight children APL-V, III-V IPL and V:I ratio were significantly correlate with BMI.In patients with a prolonged III-V inter peak latency and a normal I-III inter peak latency, the auditory conduction defect likely is located between the superior olivary nucleus and the inferior colliculus, ipsilateral to the ear stimulated 11 .
We also explored the V/I amplitude ratio, which is an essential measure for delineation of central and peripheral auditory pathway involvement.The literature suggests that if the amplitude ratio is below 0.5, it may be consistent with central impairment and if it is above 3.0, it may be consistent with peripheral auditory pathway impairment 12 .Thus, with wide differences in the normative values obtained in each study and its importance in delineating the central versus the peripheral auditory pathway, further research in this domain with a large sample size is essential.BMI-related observations in BERA are in accordance with a previous study by Solanki et al 6 In a comparison study of BERA parameters between obese participants (BMI >30) and controls (BMI <30) among healthy young adults, significant differences were observed 13 .These findings were corroborative with observations in present study.But both studies have limitations of smaller sample size and hence results can be extrapolated to generalized population.Hence further studies with larger sample size are required to explore association of BMI with BERA parameters.Although, association of BMI with peripheral neuropathies have been well understood but it is association with cranial neuropathies remains unanswered.

Conclusion
It suggests both APL and IPL difference as more useful tool that affecting the outcome that needs to be considered.The diagnostic utility of BAEPs can be improved by taking into consideration these physiological variables.Utility of BAEP can be optimized by establishing normative data for every setup based on BMI along with age before using it as a clinical tool and needs further elaboration for re enforcement of this observation.

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calculated, then BMI percentile was computed using Centres for Disease Control and Prevention (CDC) growth charts Based on percentiles10 children were grouped into categories as given by Macek and Mitola as (1) underweight (BMI < 5 th percentile) and (2) non-underweight (BMI > 5 th percentile).

Table 1 :
BERA parameters of all children with delayed development of speech APL-absolute peak latency, IPL-inter peak latency

Table 2 :
Correlation between BERA parameters and BMI