European Journal of Cardiovascular Medicine

According to the World Health Organization, an estimated 1.28 billion adults, aged 30–79 years, have hypertension worldwide, and a majority (two-thirds) of them live in low- and middle-income countries (1). The Global Burden of Disease study has reported that in 2019, high systolic BP accounted for 10.8 million deaths and 235.4 million disability-adjusted life years (DALYs) across the world (2). In India, an estimated 207 million (25.3%) adults, aged 18+ years and above, had hypertension (3). According to data from the National Health and Nutrition Examination Survey, the prevalence of hypertension among adults aged 40-59 is around 54.5%. This means that more than half of individuals in this age group are likely to have hypertension (4). 

The prevalence of hearing loss in the 40-60 age group in India is estimated to be around 40.7%. Severe hearing loss was seen in 46.7% and 68.3% of study participants in 40–59 and >60 years' age group, respectively. Severe hearing loss was seen in 55.3% males and 42.8% females, respectively (5).

Chronic hypertension is known to have a profound impact on multiple organ systems including auditory system. Blood pressure variations and sustained hypertension can affect hearing function by modifying cochlear and brainstem microcirculation patterns (6,7,8,9). ABR functions as an electrophysiological examination of the auditory pathway between the ear to auditory brainstem with objective measurements which include absolute wave latencies when coupled with interpeak latencies (IPL) and wave amplitudes (10,11). Hypertension may result in slower or abnormal ABR waveforms, indicating delayed or impaired transmission of auditory information (12,13,14,15,16). It is known that Hypertension is associated with changes in frequency specific hearing sensitivity (17) but the detailed relationship between the affected ABR parameters and the entities of Hypertension remains indistinct. This study aims to explore the relationship between hypertension and auditory brainstem responses in male adults aged 40-60 years by comparing the brainstem evoked response audiometry of hypertensive and normotensive subjects in terms of absolute wave latencies, interpeak latencies, and morphology of waves.

A cross sectional, case control study was conducted where subjects were selected by screening of known hypertensive patients from the Outpatient Departments of Medicine in Lady Hardinge Medical College and Associated Hospitals, New Delhi. Before participation, all the subjects gave their written informed consent for the study which had prior approval of the Institutional Ethics Committee. Thirty known hypertensive male patients who were between 40-60 years of age attending the Medicine OPD and on antihypertensive medications (except loop diuretics) were included in this study. The duration of the disease in the hypertensive patients ranged from as short as one week to as long as fifteen years. All subjects with a history of hearing loss or any middle or inner ear pathology or familial hearing loss, acoustic and cranial trauma; besides, any medical diseases which affect or are suspected to affect hearing (e.g. endocrine disorders, autoimmune diseases, renal disorder, noise exposure, or use of ototoxic drug therapy) were excluded. The hypertensive patients on loop diuretics, which are known for ototoxicity, were also excluded from the study. Each participant underwent detailed history taking and thorough clinical assessment. From the hospital staff, an apparently healthy normotensive group of 30 male participants was recruited.

Blood pressure measurement

Blood pressure was measured in both the groups at the time of inclusion in the study. An average of two or more properly measured, seated, blood pressure readings was taken as the actual reading.

Auditory Brainstem Evoked Response Audiometry (ABR)

ABR was done using Hortmann Neurootometry – BERA Soft ©1995 by Hortmann GMBH. Three surface electrodes were applied; one over each mastoid and third over the forehead after cleaning the area and applying the conduction facilitating gel (Elektroden Gel). Stimuli were given in the form of Broad Band Clicks in the rarefaction phase at the intensity of 80 dBnHL. 2000 such Clicks at the rate of 21.1/sec. were given to the ear being tested. The contralateral ear was suitably masked by white noise. Waves I, III & V (Jewett and Williston's nomenclature), were looked for the absolute latency, interpeak latency and morphology. Similar procedure was repeated on the other ear of same subject.

Statistical analysis

Intergroup Comparison was done by applying unpaired ‘t’ test whereas intragroup comparison between the two ears was analysed by paired ‘t’ test. Correlation between the parameters was done by Pearson’s

coefficient of correlation analysis. The results were evaluated as statistically significant when the p-value fell below 0.05.

The age, height and weight (mean±SD) of the normotensive group were 48.83±6.44 yrs., 5.46±0.19 ft. and 64.4±12.38 kg respectively. The age, height and weight (mean±SD) of the hypertensive group were 51.73±6.11 yrs., 5.55±0.18 ft. and 70.93±13.82 kg respectively. There was no statistical difference between the age, height and weight of the two groups (p value > 0.05). Hence, both the healthy normotensive and known hypertensive male groups were comparable for the study.

This study analysed the three testing waveforms (I, III, V) and interpeak differences (I-III, III-V, I-V) between normal blood pressure subjects and those with high blood pressure. The research demonstrated no statistically significant variations in any measured variable (p > 0.05) as presented in Table 1. No significant correlation was found of the absolute wave latencies and interpeak latencies with systolic or diastolic blood pressure, both in the normotensives and hypertensives shown in Table 2

.

To see the integrity of the ascending auditory pathway, amplitudes of individual ABR waves have been measured. The amplitude of wave I and wave V was considered, as in some patients, only the peaks could be identified but not the troughs in the Wave III tracings. Amplitude measurement typically requires identification of both the peak and the succeeding trough. No significant difference was found between the average amplitudes of wave I and V of right & left ear in both the groups (P>0.05). Therefore, an average of amplitudes of two ears were calculated in both the groups for wave I & V. It was observed that the amplitudes of wave I & V showed non-Gaussian distribution therefore non- parametric test i.e.  Wilcoxen Signed Rank test and Mann Whitney ‘U’ test were employed for intragroup and intergroup analysis of amplitudes respectively. No significant difference was found between the amplitude of wave I and wave V in normotensive and hypertensive group. Regression analysis did not show any significant relation of amplitudes of wave I and wave V with either systolic or diastolic blood pressure as shown in Table 3.

To have a more insight into the relationship between hypertension and auditory functions in hypertensives, the hypertensive group was again divided into two sub groups C & UC on the basis of controlled and uncontrolled hypertension respectively according to JNC classification (18). Each subgroup contained 15 patients; the details being displayed in Table 4. Unpaired student’s ‘t’ test was applied to compare various parameters in the two subgroups. No statistically significant difference (p value > 0.05) was found in these parameters between the two subgroups; therefore, the controlled and uncontrolled group are comparable for the study. The mean absolute wave latencies and interpeak latencies of ABR were compared in controlled and uncontrolled hypertensives. No statistically significant difference was found between the two groups (p value >0.05). Regression analysis showed no significant correlation between the absolute wave latencies and interpeak latencies with systolic or diastolic blood pressure both in the controlled and uncontrolled hypertensives shown in Table 5. It was observed that no significant difference was found between the amplitude of wave I and wave V in controlled and uncontrolled hypertensives, shown in Table 6. Regression analysis showed no statistically significant relation between the amplitude of wave I&V with systolic or diastolic BP in both the groups in shown in Table 7.

The results demonstrate hypertension does not seem to induce significant changes in auditory brainstem responses among patients in this blood pressure range though results also indicate potential changes occur at elevated blood pressure points indicating more investigations needed to study populations with diverse hypertension ranges.

Table 1: Comparison of ABR Latency and IPL between Normotensive and Hypertensive Groups

Table 2- Pearson Coefficient of Correlation between the ABR parameters with Systolic or Diastolic BP in Normotensives & Hypertensives

Table 3 - Pearson Coefficient of Correlation between the amplitudes of Wave I & Wave V with systolic or diastolic BP in Normotensives and Hypertensives

Table 4 - Various parameters of Blood Pressure & ABR (Mean + SD) in the Controlled and Uncontrolled Hypertensives Subgroups

Table 5 - Pearson Coefficient of Correlation of BERA parameters with systolic or diastolic BP in Controlled & Uncontrolled Hypertensives.

Table 6. Amplitude of BERA waves in the Controlled and Uncontrolled Hypertensives

Table 7. Pearson coefficient of correlation of Amplitude with systolic or diastolic BP in Controlled & Uncontrolled Hypertensives.

p value > 0.05 Not Significant, *p value < 0.05 Significant, **p value < 0.01 Highly Significant, ***p value < 0.001 Very Highly Significant

Our study aimed to determine how high blood pressure influences the auditory brainstem responses among 40 - 60 years old male participants.  Its findings showed that hypertensive patients and normotensive patients had comparable wave latencies as well as IPLs and wave amplitude values and did not demonstrate any significant difference in the parameters of brainstem evoked response audiometry in hypertensive and normotensive group. No significant correlation was found between any of the ABR parameters and the systolic or diastolic blood pressures in the hypertensives.

In the present study, we were not able to find any significant difference in the parameters of Auditory brainstem evoked response audiometry between hypertensive and normotensive subjects. This finding is also supported by the findings of Tandon and colleagues (15) as in their study didn’t find any difference between the ABR findings of hypertensive and normotensive subjects except in one patient whose blood pressure more than 180/110mmHg. In our study there was no single patient with blood pressure above 160/90, this might be the reason why we were not able to find any effect on ABR parameters due to hypertension. The studied hypertension range shows no significant impact on auditory neural conduction per this research while demonstrating consistency with this particular previous finding but in disagreement to studies linking hypertension as a possible factor (10,11,12,14). Scientific evidence provides several theoretical explanations regarding how hypertension affects hearing abilities. Hypertension produces arterial rigidity along with diminished brainstem blood flow and restricted oxygen availability thus affecting auditory neural transmission (19,20,21). Excessive blood pressure causes oxidative stress as well as inflammatory reactions which damage neural conductive pathways (22,23).ABR measurements from this study did not show variations between groups thus promoting the hypothesis that moderate hypertension stages either have minimal effects on brainstem neural pathways or need extensive disease evolution to produce meaningful changes.

Antihypertensive medications require attention as an important factor. The participants in the hypertensive group were primarily taking antihypertensive medicines but loop diuretics were omitted from analysis because they have known ototoxic effects. The protective effect of partial peroxisome proliferator-activated receptor γ (PPAR γ) agonist angiotensin II receptor blockers (ARB), angiotensin-converting enzyme (ACE) inhibitors together with calcium channel blockers has been suggested to reduce hypertension harm on auditory pathways (24,25,26). The lack of observed ABR changes in our study participants might be attributed to the neuroprotective properties of antihypertensive medications.

Our study has certain limitations. The study relied on a modest subject number and enrolled exclusively male participants which reduces the scope to which these research results can be applied to demographics outside the sample group. The study design did not permit researchers to identify extended consequences of hypertension on hearing function. However, we consider it to be an incentive for a more detailed study, on a larger population. Longitudinal research using larger participant numbers that include male and female subjects at different hypertension levels should be conducted to study how prolonged high blood pressure affects ABR measurements.

This research discovered that hypertension does not affect ABR measurements in middle-aged male participants who control their blood pressure or who have mild increases in blood pressure. Further research is essential to understand how hypertension affects auditory neural conduction primarily within uncontrolled and long-term hypertension cases. Hypertension, a multicausal and multifactorial disease, may be a risk factor for hearing loss, such possibility should be explored in hypertensives at an early stage when the diagnosis of hypertension is established so that appropriate strategies for preventive care and health maintenance may be applied to improve the quality of life in elderly.

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