Stiffness

It has been shown that compression devices exerting the same resting pressure have different hemodynamic effects on venous reflux and venous pumping function depending on the elastic property of the material.4 This can be characterized by the stiffness, which plays an important role concerning the performance of a compression device during standing and walking, and which can be measured in vivo.

Stiffness is defined by the increase of compression per centimeter increase in the circumference of the leg, expressed in hectopascals per centimeter and/or millimeters of mercury per centimeter.1 A very appropriate method to measure a dynamic stiffness index during walking has been described by a Dutch group.5 However, this technique requires sophisticated instrumentation and can be performed only in specialized laboratories.

We have proposed a very simple method that is able to differentiate inelastic from elastic material by measuring the difference between the standing pressure and the supine pressure at the B1 region, which is the area where the tendinous part of the medial gastrocnemius muscle changes into the muscular part.6 The standing position is considered to be a snap-shot of the walking cycle. Therefore pressure sensors also may be used that are not able to register continuous pressure changes.

Especially when several textiles are combined in a multilayer bandage, the stiffness of the final bandage will increase because of the friction of the layers.2 The same is true when two compression stockings are donned over each other.

Compared with in vitro measurements stiffness corresponds to the slope of the hysteresis curve in vitro.

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