Measuring arterial stiffness with oscillometric method
How does oscillometric measurement work? How it possible to measure “speed” with a single cuff?
We collect information by analyzing the pulse pressure curve registered in the upper arm with a simple upper arm cuff, via oscillometric method.
The pulse pressure waves are recorded through the upper arm tissues in the air chamber in the cuff. The measuring device amplifies this, the data are transferred via wireless communication to the computer and the attached software analyzes it.
The special, so-called stop-flow method, i.e. the complete occlusion of the brachial artery eliminates the distortion of the pressure curve. The recording is absolutely painless, as the occlusion is only for some seconds. The determination of the position and the amplitude of the reflective wave enable simultaneous and simple determination of pulse wave velocity, the augmentation index and the central blood pressure, as well as complementing the traditional blood pressure measurement data (systolic and diastolic blood pressure, mean arterial pressure, heart rate) with further hemodynamic parameters.
Thus the stop-flow method describes the detailed curve exclusively illustrating the pressure changes.
The curve can be divided into systolic and diastolic segments. In the systole, after the ventricular ejection a direct wave and a late systolic wave (reflected wave, arriving from the periphery) can be differentiated.
The principle is based on the hypothesis that the reflected wave can be identified. It comes from the periphery, as a summation of all the reflections arriving from all reflective points, primarily reflected from the aortic bifurcation. Hypothetical calculation (aortic length approx. 50cm, PWV value ~5-15m/s calculated back from the late reflective wave arrival time (~150-250ms)) and invasive tests support this. V=s/t, i.e. if we know the time of the wave’s return, in order to calculate pulse wave velocity the software needs a distance value (path), which we manually insert into the program while taking patient data. The measurement of the distance between the jugulum and the symphisis has in practice also been proven to match aortic length – this is the measure we need to take into account.
With the identification of the wave peak amplitude, the relationship between the pressure peaks provides the Aix.
The program automatically identifies the wave peaks, and based on this it makes the calculations.