Instrumentation & Measurement Magazine 24-2 - 54

Progress in the Assessment
of Arterial Stiffness
Miodrag Bolic, Hilmi R. Dajani, Masayoshi Yoshida, and Voicu Z. Groza

n this brief review, we will introduce arterial stiffness,
describe how it is currently measured and point to new
developments that might lead towards arterial stiffness
estimation outside of specialized clinics in the future. In almost
all methods for measuring arterial stiffness, the arterial pulse
plays an important role. Therefore, new developments are related to novel non-invasive sensors for acquiring the arterial
pulse, simulation and modeling of the arterial pulse waves,
parameter estimation of the stiffness parameters through
physical models of the arterial pulse and machine learning
methods for predicting the arterial stiffness.
Arterial stiffness is related to the extent of hardening of the
wall of the artery and is an important and independent predictor of cardiovascular events. Large arteries in our body are
the most elastic arteries, and so they smooth the pressure wave
generated by the contraction of the heart.
Arterial stiffness measurements are indirect and are based
on tonometry, oscillometric cuff measurements, ultrasound
and magnetic resonance imaging. Measurements of arterial
stiffness, unlike measurements of blood pressure, are not yet
commonly performed by general physicians or in the home,
likely because measurement indices are not well-known, devices are not ubiquitous and are relatively expensive, and
measurement methods commonly require using two or more
sensors that may need to be properly placed by a trained
expert.
This review paper is different from existing review papers
on arterial stiffness since it not only emphasizes the existing
systems for estimating arterial stiffness but points to new directions in multiple areas including sensors, modeling, and
machine learning.

Arterial Stiffness Assessment
Why is Arterial Stiffness Important?
Arterial stiffness refers to passive mechanical properties of the
arterial walls that can be modulated by active processes, such
as change in smooth muscle tone around the arteries. Its functional importance is that it is a main determinant of arterial
54

impedance and so it affects the blood pressure and flow in every heartbeat [1].
Aging is one of the strongest factors that affects arterial
stiffness. Increases in systolic pressure and pulse pressure
(the difference between systolic and diastolic pressure) has
traditionally been thought to also contribute to age-related
stiffening of the arteries [2]. Despite the widespread belief that
hypertension causes arterial stiffness, however, there is now
strong evidence that stiffening of the arteries leads to hypertension instead of being a consequence of it [1].
Arterial stiffness has been shown to be a predictor of the
risk of adverse cardiovascular events, cardiovascular disease
and other systemic pathologies, even in patients without high
blood pressure [3].

Challenges in Measuring Arterial Stiffness
Some of the most popular and validated measures of arterial
stiffness, for example carotid femoral pulse wave velocity (cfPWV) described below, usually require a trained operator in
a specialized setting. Other popular measures, such as the
Cardio-Ankle Vascular Index (CAVI) described below, can
be obtained automatically without operator intervention but
currently require relatively expensive specialized equipment.
This hinders the routine measurement of arterial stiffness
by general physicians, or even in the home, as is done with
the measurement of blood pressure. Furthermore, the measurement of PWV depends on the accurate measurement of
the travel distance of the pulse between two locations on the
body (such as between the measurement points at the carotid
and femoral arteries). The challenge here is that the distance
traveled by the pulse wave needs to be estimated based on
measurements made on the body surface which may not accurately reflect the distance along the arterial path. Accurate
measurement of the travel distance using an imaging method
such as Magnetic Resonance Imaging (MRI) or Computerized
Tomography (CT) is possible, but this is currently not cost-effective or practical. As a result, the current recommendation
is to multiply the direct distance between the two recording
points at the carotid and femoral arteries by the factor of 0.8 [1].

IEEE Instrumentation & Measurement Magazine
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April 2021

Instrumentation & Measurement Magazine 24-2

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