Hypertension
Hypertension is defined as systolic blood pressure more than or equal to 140 mmHg and or
diastolic blood pressure more than or equal to 90 mmHg, readings taken at least in three
different settings or use of prescribed antihypertensive medication (12). WHO/ISH divides it
into three grades, as shown below (13);
Table: WHO/ISH grading of blood pressure
Blood pressure Grade 1 Grade 2 Grade 3
SBP mmHg 140-159 160-179 ≥180
DBP mmHg 90-99 100-109 ≥110
Hypertension is a leading cause of cardiovascular disease worldwide (14). The burden of
disease in the world caused by hypertension was 4.5% in 2000 (15) and increased to 7% in
2010 (16). This puts hypertension as a significant cause of morbidity and mortality.
Hypertension is now the most common cardiovascular problem in Africa, and it is estimated
that more than 20 million people are affected (17). In Kenya, studies have shown a prevalence
ranging between 6.4% to 50.1% in different populations and age groups (2, 18-20). This
prevalence is of public health concern as hypertension is associated with many complications
with hearing loss being one of them.
Management is by lifestyle modification and medication (21) to lower and maintain blood
pressure less than 140/90mmHg. According to JNC 7 data up to 67% have uncontrolled BP
hence at risk of complications (21). Medications used to treat hypertension are calcium
channel blockers, beta-blockers, angiotensin receptor blockers, diuretics and angiotensin-
converting enzyme inhibitors among others. These are used either singly or in combination.
With proper public awareness, most causes of hypertension are preventable. For those who
already have the disease proper control can significantly reduce complications (22-25),
including hearing loss. Agrawal recommended that efficient treatment for diabetes mellitus
and high blood pressure may delay hearing loss onset (26).
Hypertension and hearing loss
All living cells in the human body depend on a proper supply of oxygen and nutrients in order
to maintain their function. The supply depends on the functional and structural integrity of the
heart and blood vessels. Hypertension facilitates structural changes in the heart and blood
vessels (27). Uncontrolled blood pressure can result in generalized arteriosclerosis. The inner
ear vessels are also affected. Tachibana (28) showed that acute hypertension leads to leakage
of a macromolecule in the temporal bone. In chronic hypertensive states, stria vascularis cells
may be damaged if some substances leak into its extracellular space (29). With a reduced
cochlear blood flow in a rabbit model, distortion product OAEs were reduced (30) and this
may create irreversible damage to cochlear integrity.
Chronic hypertension potentiates noise induced cochlear damage histologically and thus
decrease in cochlear function (31). High pressure in the vascular system may cause inner ear
hemorrhage, which may cause progressive or sudden hearing loss (27). Systemic arterial
hypertension has been shown to cause retinal vascular changes and has been significantly
correlated with hearing loss (32). It may also cause ionic changes in the hair cells and high
action potential thresholds thus causing hearing loss (33).
Fang (34) found out that the vessel changes in patients with age related hearing loss
might be accelerated by atherosclerosis and hypertension. The vessel changes result
from endothelial dysfunction which predisposes to the development of a pro-
thrombotic state. The endothelium malfunction results in development of adhesion
molecules, endothelial progenitor cells and pro-inflammatory vascular conditions
which lead to distortion of the ear microcirculation impairing cochlear functions
(35). Preeclampsia, a vascular disorder in pregnancy characterized by proteinuria
and hypertension, is thought to affect cochlear microcirculation through vasospasm,
endothelial dysfunction and ischaemia (36). Bakhshaee et al (37) has shown a
positive correlation between preeclampsia and hearing loss using TEOAES.
The organ of Corti hugely depends on the spiral artery for oxygenation (38,
39). Patients undergoing cochlear implants may get a worsening of hearing if the
spiral artery is injured during the procedure.
