The effect of blood pressure on inner ear blood flow

Association between hypertension and hearing impairment in health check-ups among Japanese workers: a cross-sectional study

OBJECTIVES

Prevention of hearing impairment (HI) is important because recovery of hearing is typically difficult. Epidemiological studies have examined the risk factors for HI. However, the association between hypertension and HI remains unclear. We aimed to clarify the association between hypertension and HI.

DESIGN

Cross-sectional study.

SETTING

Japanese workers in an information and communication technologies company.

PARTICIPANTS

Of 24 823 employees of the same company, we recruited 13 475 participants who underwent hearing testing by audiometry in annual health check-ups and did not have missing data regarding body measurement, blood test results and drinking/smoking status (mean age: 49.4 years; males: 86.4%).

PRIMARY OUTCOMES

Hearing tests were performed at two frequencies (1 kHz, 4 kHz). We defined the inability of participants to respond to 30 dB at 1 kHz and/or 40 dB at 4 kHz as overall moderate HI. We also defined moderate HI at 1 or 4 kHz as an abnormal finding at 1 or 4 kHz. We defined hypertension as ≥140 mm Hg systolic blood pressure and/or ≥90 mm Hg diastolic blood pressure and/or taking medication for hypertension. We examined the association between hypertension and HI after adjusting for age, sex, body mass index, smoking/drinking status, diabetes mellitus, hyperlipidaemia and proteinuria.

RESULTS

Moderate HI was identified in 980 participants (7.3%). Of these, 441 participants (3.3%) exhibited moderate HI at 1 kHz, and 787 participants (5.8%) exhibited moderate HI at 4 kHz. Subjects with hypertension showed a higher prevalence of any HI. The prevalence of overall moderate HI, moderate HI at 1 kHz and moderate HI at 4 kHz among subjects with hypertension was 8.7%, 4.3% and 6.8%, while those among subjects without hypertension was 6.9%, 3.0% and 5.6% (p<0.01, p<0.01 and p=0.01, respectively).

CONCLUSIONS

Hypertension was associated with moderate HI in Japanese workers.

Cochlear blood flow in relation to age in normotensive and spontaneously hypertensive rats

Cochlear blood flow was studied with the microsphere method in young and old normotensive and spontaneously hypertensive rats. The young animals were 3-6 months old and the old ones 18-24 months. The cochlear blood flow in young rats was 1.64 microliter/min/cochlea for the normotensive and 1.51 for the spontaneously hypertensive rats. In the old rats, the cochlear blood flow rates were 1.40 and 1.29 microliter/min/cochlea, respectively. The differences were not significant between the age groups, nor between the normotensive and spontaneously hypertensive rats. However, there was a tendency towards lower cochlear blood flow with increasing age, especially among the spontaneously hypertensive rats. The difference between young normotensive and old spontaneously hypertensive rats was significant (p less than 0.05). The group of old hypertensive rats was also the only one with evident morphological changes in the organ of Corti.

Cochlear blood flow in the rat. A methodological evaluation of the microsphere method

With the microsphere method it is possible to quantify the blood flow in various organs. The blood flow in the cochlea is only a very small part of the cardiac output and only relatively few microspheres are caught in this organ, which necessitates large groups of animals for such studies. The method has, however, not been fully evaluated for studies of small organs in small animals. In this study, 130 rats of various ages with normal or arterial hypertension were investigated. The blood flows of 97 animals were possible to evaluate. It was found that physiological parameters, such as PCO3, pH, PO2 and mean arterial blood pressure within the rather wide limits usually present in the anesthetized animal did not affect the cochlear blood flow to any great extent and that the method is feasible for studies of the blood flow through the inner ear in small animals.