Distensibility is a metric of the stiffness of blood vessels. It is defined as

${\displaystyle D={\frac {d_{sys}-d_{dias}}{(p_{sys}-p_{dias})d_{dias}}}}$,

where ${\displaystyle d_{sys}}$ and ${\displaystyle d_{dias}}$ are the diameter of the vessel in systole and diastole, and ${\displaystyle p_{sys}}$and ${\displaystyle p_{dias}}$are the systolic and diastolic blood pressure.^[1]

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