Fukuda VaSera VS-2000 Series, Operation Manual

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13-2
Chapter 13 Appendix
Measurements
Blood Pressure and Pulse Wave Examinations
[1] CAVI (Cardio-Ankle Vascular Index)
A new index based on stiffness parameter
β
, CAVI is a pressure-independent index indicating the natural stiffness of the blood
vessels. While compliant with Hasegawa PWV method, the Cardio-Ankle Vascular Index calculates the specific stiffness of
arterial walls independent of blood pressure. A larger CAVI implies greater stiffness of the arterial walls.
(1) Stiffness Parameter
β
As shown in the diagrams below, the relationship between internal pressure and inner diameter is nonlinear. b) has
greater extensibility than a) and at the same pressure
Δ
Pa/
Δ
Da >
Δ
Pb/
Δ
Db. However, a comparison of low pressure
regions with high pressure regions show that the relationship between inner diameter and inner pressure is not constant
even for a).
As shown in the diagram on the right, plotting the relationship between natural logarithm for the pressure ratio ln (Px/
Po) and the rate of change in inner diameter (Dx-Do)/Do shows a linear relationship. This oblique straight line is called
stiffness parameter
β
. It is known that this parameter is independent of internal pressure and that a larger
β
indicates
lower extensibility (greater vascular stiffness).
Assessment of carotid arterial distensibility using
β
stiffness index - Nippon Rinsho Vol 62, Suppl 3, 2004
The stiffness parameter
β
is calculated as shown below.
ln(Ps/Pd): Logarithmic pulse pressure (Ps: systolic pressure, Pd: diastolic pressure)
D/
Δ
D: Reciprocal of radius percentage change (D: Vascular radius,
Δ
D: Beat-initiated change in the vascular
radius)
(2) Bramwell-Hill Equation
The Bramwell-Hill equation produces the following formula.
ρ
: Blood density, V: Volume,
Δ
V: Change to volume
PWV: Pulse wave transmission speed (refer to "(4) PWV (Pulse Wave Velocity)" (P13-3))
(3) CAVl Equation
By substituting equation (1) into equation (2), we obtain the following CAVI equation.
Internal Diameter (D
x
ー D
0
) / D
0
Internal Pressure
Slope
···································· ձ
D
D
Pd
Ps
Δ
⋅
⎟
⎠
⎞
⎜
⎝
⎛
=
ln
β
··························· ղ
Pd Ps
PWV D
−
=
2
2
D
࣭
Ǽ
ρ