Analysis of the contour of the peripheral pulse to assess arterial properties was first described in the nineteenth century. With the recognition of the importance of arterial stiffness there has been a resurgence of interest in pulse wave analysis, particularly the analysis of the radial pressure pulse acquired using a tonometer. An alternative technique utilizes a volume pulse. This may conveniently be acquired optically from a finger (digital volume pulse). Although less widely used, this technique deserves further consideration because of its simplicity and ease of use.
As with the pressure pulse, the contour of the digital volume pulse is sensitive to changes in arterial tone induced by vasoactive drugs and is influenced by ageing and large artery stiffness. Measurements taken directly from the digital volume pulse or from its second derivative can be used to assess these properties. The arterial pulse waveform is a contour wave generated by the heart when it contracts, and it travels along the arterial walls of the arterial tree. Generally, there are 2 main components of this wave: forward moving wave and a reflected wave.
The forward wave is generated when the heart (ventricles) contracts during systole. This wave travels down the large aorta from the heart and gets reflected at the bifurcation or the across-road of the aorta into 2 iliac vessels. In a normal healthy person, the reflected wave usually returns in the diastolic phase, after the closure of the aorta valves. The returned wave give a notch and it also helps in the perfusion of the heart through the coronary vessels as it pushes the blood through the coronaries.
Therefore the velocity at which the reflected returns becomes very important : the stiffer the arteries are, the faster it returns. This may then enter into the systolic phase and augment final blood pressure reading.