Monday 23 March 2009
The passage of an electric current through the body may be without effect; may cause sudden death by disruption of neural regulatory impulses, producing, for example, cardiac arrest; or may cause thermal injury to organs interposed in the pathway of the current. Many variables are involved, but most important are the resistance of the tissues to the conductance of the electric current and the intensity of the current. The greater the resistance of tissues, the greater the heat generated. Although all tissues of the body are conductors of electricity, their resistance to flow varies inversely with their water content. Dry skin is particularly resistant, but when skin is wet or immersed in water, its resistance is greatly decreased. Thus, an electric current may cause only a surface burn of dry skin but may cause death by disruption of regulatory pathways when it is transmitted through wet skin, producing, for example, ventricular fibrillation or respiratory paralysis without injury to the skin.
The thermal effects of the passage of the electric current depend on its intensity. High-intensity current, such as lightning coursing along the skin, produces linear arborizing burns known as lightning marks. Sometimes intense current is conducted around the victim (so-called flashover), blasting and disrupting the clothing but doing little injury. When lightning is transmitted internally, it may produce sufficient heat and steam to explode solid organs, fracture bones, or char areas of organs. Focal hemorrhages from rupture of small vessels may be seen in the brain. Sometimes, death is preceded by violent convulsions related to brain damage. Less intense voltage may heat, coagulate, or rupture vessels and cause hemorrhages or, in solid organs such as the spleen and kidneys, cause infarctions or ruptures.