Electrophysiological hazards

Coupling without galvanic tissue contact is covered in Section 7.4.2. However, electromagnetic hazards are outside the scope of this book. There is a vast amount of experimental data on this subject, and the interested reader is recommended the CRC Handbook of Biological Effects of Electromagnetic Fields (Barnes and Greenbaum, 2006). 

Tlie risk of sudden death is related to stimulating the cells of three vital organs of the body the heart, the lungs, and the brain stem. Involuntary movements may indirectly lead 

The current path is important, and organs without current flow are only indirectly affected to be directly dangerous for the healthy heart, the current must pass the heart region. 

Heat effects are certainly related to current density in volume conductors, but this is not necessarily so for nerve and muscle excitation. Excitation under a plate electrode on the skin is more highly correlated to current than current density (see Section 10.16.1). The stimulus summation in the nerve system may reduce the current density dependence if the same current is spread out over a larger volume of the same organ. Therefore, and for practical reasons, safe and hazard levels are more often quoted as current, energy or quantity of current in the external circuit, and not current density in the tissue concerned. 

The heart and the brain stem are particularly sensitive for small areas of high current density. Small area contacts occur, for example, with pacemaker electrodes, catheter electrodes, and current-carrying fluid-filled cardiac catheters. Small area contact implies a monopolar system with possible high local current densities at low current levels in the external circuit. This is called a microshock situation. The internationally accepted 50/60 Hz safety current limit for an applied part to the heart is therefore 10 pA in normal mode, and 50 pA under single fault condition (e.g., if the patient by insulation defects is in contact with mains voltage). The difference between macro- and microshock safety current levels is therefore more than three decades. 

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Myers VB. 1983. Remedial activities at the Miami Drum site, Florida. In National conference on management of uncontrolled hazardous waste sites. Silver Springs, MD Hazardous Materials Control Research Institute, 354-357. Nachtman JP, Couri D. 1984. An electrophysiological study of 2-hexanone and 2,5-hexanedione neurotoxicity in rats. Toxicol Lett 23 141-145. 

Kenneback G, Bergfeldt L, ValUn H, Tomson T, Edhag O. Electrophysiologic effects and clinical hazards of carbamaze-pine treatment for neurologic disorders in patients with abnormahties of the cardiac conduction system. Am Heart J 1991 121 (5) 1421-9. 

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