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AngioScan Medical Tests 43
© 2014 AngioScan-Electronics LLC
4.1.4.18 SPa - Systolic Pressure, Aortic
This parameter corresponds to the level of blood pressure in the proximal aorta and brachiocephalic
vessels. Typically, in young people, without cardio-vascular disease, the blood pressure in peripheral
arteries (such as brachial artery) is slightly higher than that in the aorta and brachiocephalic arteries.
This phenomenon is due to the amplification of the pressure amplitude of the peripheral pulse wave, and
helps to maintain a constant blood flow rate to peripheral organs.
With physical exertion or emotional stress, the heart rate increases and the amplification of the blood
pressure increases. This leads to a significant increase in the difference in pulse pressure in peripheral
arteries compared with that in the central arteries [Avolio et al. 2010].
With age or when the arterial stiffness is increased (such as during hypertension and other diseases of
the cardiovascular system), the speed of the reflected pulse wave increases. In this case, the reflected
wave overlaps with the direct wave. This significantly increases the pressure in the proximal aorta. In this
case, the peripheral blood pressure can be significantly lower than the central blood pressure.
An increase in the blood pressure in the arteries supplying the brain is a main factor in the remodeling of
large and small cerebral vessels. This substantially increases the risk of stroke, especially in older
people [Staessen et al. 2000].
An elevated central blood pressure increases the afterload on the myocardium of the left ventricle,
leading to hypertrophy and the relative decrease in heart tissue perfusion. With a simultaneous reduction
in the central diastolic blood pressure and an increase in the central pulse, which is typical for the
elderly, a decrease in coronary and renal blood flow occurs. These factors lead to an increased risk of
heart attack and kidney failure.
Prognostic significance of central blood pressure has been proven in several large studies evaluating the
effectiveness of various combinations of antihypertensive drugs. (LIFE [Dahlof et al. 2002], CAFÉ
[Williams et al. 2006], REASON [DeLuca et al 2004], Strong Heart Study [Roman et al. 2007]). The
authors of these studies have shown that the central aortic pressure is a significant factor in determining
cardiovascular risk. In the elderly and those suffering from diseases such as hypertension and coronary
heart disease, systolic blood pressure in the aorta is more reliable than that obtained with a more
common method of blood pressure measurement at the brachial artery. Therefore, these patients require
monitoring of central blood pressure, both for risk stratification, and for assessing the effectiveness of
therapy.
4.1.4.19 PI - Pulse Index
This parameter reflects the strength of the pulse wave signal. A high quality pulse wave signal is
obtained when PI value exceeds 1%. Smaller values of this index are often associated with a low
temperature of the hand (temperature <30°C). The dry heat is optimal for warming up the extremities.
Other possible reasons for the low values of the pulse index can be a dark finger nail polish or an
incorrectly placed sensor.
4.1.4.20 Level - Signal level
This parameter characterizes the average signal strength from the sensor. When performing tests, make
sure that the signal is in the range of 4 to 60. One of the reasons for a low value of this parameter can be
a dark nail polish.
4.1.4.21 SIr - Reference Stiffness Index
Reference Stiffness Index is one of the parameters describing the stiffness of large arteries in a Contour
Analysis. The SIr parameter relies not on the time interval between the time of arrival of the systolic and
the reflected waves, but on the time interval between the beginning of the pulse wave and the time of
arrival of the reflected wave. This parameter is measured in ms.