Pulse Wave Velocity (PWV)
The aortic pulse wave velocity (PWV) is the most widely validated and universally accepted measure of arterial stiffness. It is known that aortic PWV increases with age and blood pressure. The higher the PWV the higher the arterial stiffness. In addition to hypertension, other risk factors accelerate the age-related stiffening of the aorta. Therefore, aortic PWV is an integrative indicator of cardio-vascular risks. An increased stiffness of the aorta reduces its Windkessel function and increases the load to the heart.
For the determination of aortic PWV it is necessary to define when the arterial blood is injected into the aorta what is the starting point of the arterial pulse wave. It corresponds with the opening of the aortic valve what is characterised by the B-point in the ICG wave form. To detect the arrival of the pulse wave in the femoral artery a cuff is placed on the upper leg which has a constant pressure of about 80 mmHg close to the diastolic blood pressure. This cuff allows to measure a pressure pulse wave in which the slope rise onset is defined (F-point). The time delay between the B-point in the ICG (opening of the aortic valve) and the F-point in the pressure pulse wave (arrival of pulse wave) defines the propagation time (PT) of the arterial pulse wave in the aorta. For the calculation of the aortic pulse wave velocity it is necessary to measure the distance (d) between the middle of the thigh cuff and the Jugulum to approximate the length of the aorta.
In comparison to other non-invasive methods the combination of ICG and a thigh cuff is a unique method which allows to determine the aortic pulse wave velocity very easily and with high accuracy.
The aortic PWV should not be mistaken with peripheral PWV measured on other locations of the body. In comparison to the aorta other and more distal located vessels have a different structure characterised by vascular muscles which influence their elasticity and, consequently, the pulse wave velocity. In the result the peripheral PWV is influenced not only by their general stiffness and the blood pressure but also by a lot of additional factors, such as, vascular tone or temperature. Therefore it is very important to separate between aortic and peripheral PWV when comparing measuring results and standard values.
|PT||Propagation Time||time delay between the opening of the aortic valve (B point in ICG) and the slope rise onset of peripheral pressure pulse wave taken in the upper leg|
|PWV||Pulse Wave Velocity||velocity of propagation of pressure pulse wave in the aorta which is calculated as PWV = d / PT whereby d is the distance between Jugulum and the middle of the thigh cuff|