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Page 4 of 9 Abdelhaliem et al. Vessel Plus 2020;4:31 I http://dx.doi.org/10.20517/2574-1209.2020.13

Figure 1. Flow chart detailing steps undertaken in our extensive literature search

Arterial stiffness as a term is inclusive of vascular smooth muscle hyperplasia, an increase in collagen levels,
degradation of elastin including fracture of the elastic lamellae, and intima-media thickening, thereby
altering vascular smooth muscle cell tone, which over time results in the development of increased stiffness
[14]
or arteriosclerosis . Ageing, obesity, diabetes mellitus, and hyperlipidaemia are all factors relating to
[15]
arterial stiffening . Arterial stiffness, which can be measured as either aortic or carotid-femoral pulse wave
velocity or through augmentation index, is now recognised as an important independent predictor of both
future cardiovascular disease and all-cause mortality [16,17] . Augmentation index measures the central pulse
pressure and is typically considered a more complex variable due to a combination of vascular elasticity
[18]
and peripheral resistance . An increase in aortic pulse wave velocity of 1 metre/second is correlated to an
[16]
age, sex and risk factor adjusted increase of 14% for cardiovascular events and 15% for mortality .
The cochlear microcirculation may be impaired by this increased arterial stiffness due to the terminal
nature of this circulation. Yet, this emerged evidence did not yield a shred of conclusive pathophysiological
evidence as to how it pertains to pulsatile tinnitus. It has been shown that increased arterial stiffness may
lead to microvascular damage in the brain and this can manifest itself with a multitude of clinical symptoms
and signs including tinnitus . This had yielded to another entity related to carotid system arterial stiffness
[19]
[8]
implicated in the development and severity of “idiopathic subjective tinnitus” .
Parameters utilized to support this concept from the studies [8,20] that had recruited participants included
serum lipid profile (mg/dL), pure-tone hearing, blood pressure (mmHg), fasting glucose (mg/dL), and
2
body mass index (BMI, kg/m ). Hence, the common carotid artery stiffness index, common carotid intima-
media thickness, Young’s elastic modulus, peak systolic velocity, end-diastolic velocity, resistive index,
vessel diameter, pulsatility index, mean velocity and volume flow were measured in both the right and left
common carotid arteries.