Figure 1. The pressure and velocity measured in the ascending aorta in an elderly man.
Wave intensity analysis[1] provides a method to calculate the properties of arterial waves that give rise to arterial blood pressure, based on measurements of pressure, P, and velocity, U, waveforms (Figure 1). Wave intensity analysis is applicable to the evaluation of circulatory physiology and quantifying the pathophysiology of disorders such as coronary artery disease.
The method is based on discrete, successive wave fronts (wavelets) and is carried out in the time domain. These wavelets travel forward and backwards in the arteries with amplitudes and . The wave intensity, , of a particular wavelet is defined asIt is related to sound intensity in acoustics and describes the power per unit area carried by the wavelet. From the theory discussed below, there is a relationship between the pressure amplitude and the velocity amplitude of a waveletwhere ρ is the density of blood and c is the wave speed of the wavelet. From these equations, generally known as the water hammer equations, it follows that the wave intensity for forward wavelets and for backward wavelets . The ability to determine the direction of a wavelet from its sign is the basis of the practical utility of wave intensity analysis.
Figure 2. The wave intensity calculated from the measured pressure and velocity measured in the ascending aorta of an elderly man.
^Parker, Kim H. (2009). "An Introduction to Wave Intensity Analysis". Med Biol Eng Comput. 47 (2): 175–88. doi:10.1007/s11517-009-0439-y. PMID 19205773. S2CID 738467.
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