These parameters can be obtained using Vasotens Office Stiffness® and Vasotens 24 Stiffness®
The method for determining this parameter is based on identifying the reflection from the aortic bifurcation in the pulse wave shape. During the propagation the reflected wave is retarded relative to the direct wave (it indicated in the figure as RWTT). The path length of a straight and a reflected wave is equal to the 'length of the aorta' L multiplied by 2.
The ejection of blood from the left ventricle at the systole causes a wave of blood pressure that propagates through the arterial vessels. The pressure wave is accompanied by the expansion of the vascular diameter and is defined as a pulse wave.
For people of young and middle age, the velocity of the pulse wave in the aorta is 5.5-8.0 m/s. Cause of increased PWV is increased stiffness of the elastic arteries as a result of degeneration and hyperplasia of the arterial wall.
The PWV is a reliable vascular biomarker for determination of arterial stiffness. Its standard assessment uses the SphygmoCor technique, based on the measurement of pulse waves by sensors installed in the carotid and femoral arteries. Alternatively, for ambulatory estimation, PWV may be derived by multiplying the surrogate length of the aorta (ΔL, jugulum-symphisis distance or superficial morphological distance corresponding to the projection of the aorta on the body surface) by 2 and by a constant (k) and by dividing the result by the reflected wave transit time (RWTT, the time interval between the forward and the reflected wave)
Augmentation index defines the relation between amplitudes of direct and reflected
from aorta bifurcation components of pulse wave. It is expressed as
percentage and as a rule is defined by the following formula
AIx = (PA / RP) * 100%, where:
PA = (B-A) - the augmentation pressure;
RP - pulse wave amplitude;
A is the amplitude determined by the direct wave;
B is the amplitude at the moment of maximum summation of the direct and reflected waves
Normally, for pulsations defined in the brachial artery AIx is negative. In case
of a high artery stiffness or/and high amplitude of the reflected wave AIx value becomes positive.
Pulsation shape for patients with elastic (а) and stiff (b) arteries:
1 – direct component, 2 – reflected from aorta bifurcation component, 3 – echo from aortal valve closing
Maximum speed of blood pressure growth (dP/dt)max. measured in mm Hg/sec (dP/dt)max. It is defined as the maximum derivative of blood pressure in the artery against time (at the rising edge of the pulse wave).
This value indirectly reflects myocardial contractility.
These parameters can be obtained using Vasotens Office CAP® and Vasotens 24 CAP®
Parameters of Central arterial pressure:
Determination of central arterial blood pressure can be done by the noninvasive method
described in many articles. Averaged form of pulsations in brachial artery is formed
first (blue curve in Figure). Discrete Fourier transform (DFT) is applied to this function,
obtained complex spectrum is multiplied by transient function TF and inverse discrete Fourier transformation (IDFT) is fulfilled after that. Obtained function corresponds to averaged form of pulsations in ascending aorta (red curve). Minimum and maximum values on each curve correspond to diastolic and systolic BP in the particular vessel. As far as BP in brachial artery is known after measurements, the value of central BP (in aorta) becomes also known.
Determination of central hemodynamics parameters
Ejection Duration defined as time period Т from the beginning of pulsation to incisura (the
moment when aortic valve closes).
Aortic augmentation index (AIxао) Measured in per cent and is defined by the following
AIx = (AP / PP) * 100%, where:
AP – augmentation pressure (the differenece between the amplitude defined by the direct
wave and the amplitude with the maximum sum of direct and reflected waves);
PP – pulase wave amplitude.
Analysis of pulse wave in aorta
Pulse pressure amplification, Pulse Wave Amplification is relation of pulse pressure in
brachial artery to central pulse pressure:
PPA = PAD / PADao
Subendocardial viability ratio, Buckberg index, Buckberg ratio SEVR measured in per
cent and is defined as relation of areas under pulsation curve in aorta (corresponding to vessel diastole when aorta valve is closed) and vessel systole (when the aorta valve is open):
SEVR = (DPTI / TTI) * 100%
Or as an equivalent (see Figure 16):
SEVR = (Diastolic_area / Systolic_area) * 100%
When using BPStat®, it is possible to obtain a number of experimental parameters that are not available in commercially available products.
It is measured in percentage and is defined as the area under
pulsations curve, corresponding to vessel systole (the period, when aortal valve is opened),
relative to full area of cardiac cycle.
Systolic (S1) and diastolic (S2) areas. The arrow shows the echo from aortal valve closing
Diastolic Area Index (Sdia, DAI). It is measured in percentage and is defined as the area
under pulsations curve, corresponding to vessel diastole (the period when aortal valve is closed), relative to full area of cardiac cycle.
Ssys = S1 / (S1+S2) * 100%
Sdia = S2 / (S1+S2) * 100% = 100% - Ssys
Systolic (S1) and diastolic (S2) areas. The arrow shows the echo from aortal valve closing.