Parameterizing the Vasodilation Response

In the last few years there has been a growing interest in understanding the link between endothelial function and several aspects of cardiovascular diseases (CVD). It is known that impaired endothelial function is associated with a number of disease states, including CVD and its major risk factors [28-31]. Also, endothelial dysfunction seems to precede by many years other more manifest symptoms and may itself be a potentially modifiable CVD risk factor. Therefore, it promises to have not only diagnostic value but also use as an instrument for patient monitoring during treatment.

Once that ongoing research establishes the role and value of FMD in clinical practice, and that computerized tools like the one presented in this chapter become extensively validated and accepted in clinical protocols, it will be possible to move one step further and use the information contained in FMD curves to derive new clinical indexes of endothelial function. In this section we provide our initial experience in this direction and suggest a possible approach to parameterize FMD curves.

In most clinical papers, FMD is classically measured according to the expression

0basal where 0max and 0basai are the maximal and basal arterial diameters, respectively. One of the problems generally not discussed in the clinical literature is that manually measuring these diameters can be cumbersome without access to the whole dilation curve. Estimation of 0max by visual inspection of the ultrasound image sequence is time-consuming and subjective, given the small magnitude of the measured dilations. However, using a computerized technique like the one presented here can not only simplify this issue but also provide richer information about the dynamics of the dilation process.

There is still a problem on how to summarize the information present in FMD curves with only a few informative and intuitive parameters. To this end we propose the use of principal component analysis.

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