Arteries and veins are coiiiposed of three tissue layers; the outer adventitia of connective tissue, the central media of smooth muscle and elastic fibers, and the inner intima, or endothelial cell layer. The specific response of blood vessels to injury depends on the iiiagnitude of dissipated energy and its duration. Gunshot wounds produce greater injury than do stabs, and high-velocity gunslaots (> 2500 ft/s) result in mas- sive vascular and soft tissue, nerve, and bone destruction, due to their greater kinetic energy than that of low-velocity missiles. Blunt injury causes a similar level of destruccive en- ergy to surrounding tissues, which may disrupt collateral cir- culation and contribute to loss of perfusion and limb loss in any instance of direct vascular injury. Major blood vessels iriay be injured by the indirect force of the dissipating energy or shock wave, even though not directly impacted, an effect not seen in simple stairs or lc›w-velocity gunshot wounds. The remarkably low inciclence of extretnity vascular injury following both blunt and penetrating trauma is due in part to the elasticity of major arteries, which allows them to stretch out of the path of injurious agents. This protective acttoii may itself cause sortie ftorms of vascular injury through vessel wall contusion and intiinal disruption."
There are several types of vessel injuries (Fig. 43—2) - The most common forms of injury to both arteries and vi2iFlS docuiriented in clinical series are lacerations and transec- tions (Table 43---4). Lacerations are full-thickness tears of the vessel in whicla part of the wall reirrains intact and vessel cont inority is maintained. They are classified as mild whf2l4
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