ABSTRACT
A portable meter has been developed for measuring low frequency currents that flow in the human body. Although the present version of the meter was specifically designed to measure 50/60 Hz "contact currents," the principles involved can be used with other low frequency body currents. Contact currents flow when the human body provides a conductive path between objects in the environment with different electrical potentials. The range of currents the meter detects is approximately 0.4-800 microA. This provides measurements of currents from the threshold of human perception (approximately 500 microA(RMS)) down to single microampere levels. The meter has a unique design, which utilizes the human subject's body impedance as the sensing element. Some of the advantages of this approach are high sensitivity, the ability to measure current flow in the majority of the body, and relative insensitivity to the current path connection points. Current measurement accuracy varies with the accuracy of the body impedance (resistance) measurement and different techniques can be used to obtain a desired level of accuracy. Techniques are available to achieve an estimated +/-20% accuracy.
Subject(s)
Electricity , Electrophysiology/instrumentation , Environmental Exposure , Magnetics , Adult , Electric Conductivity , Electric Impedance , Equipment Design , Humans , Male , Occupational ExposureABSTRACT
Residential electrical wiring safety practices in the US result in the possibility of a small voltage (up to a few tenths of a volt) on appliance surfaces with respect to water pipes or other grounded surfaces. This "open circuit voltage" (V(OC)) will cause "contact current" to flow in a person who touches the appliance and completes an electrical circuit to ground. This paper presents data suggesting that contact current due to V(OC) is an exposure that may explain the reported associations of residential magnetic fields with childhood leukemia. Our analysis is based on a computer model of a 40 house (single-unit, detached dwelling) neighborhood with electrical service that is representative of US grounding practices. The analysis was motivated by recent research suggesting that the physical location of power lines in the backyard, in contrast to the street, may be relevant to a relationship of power lines with childhood leukemia. In the model, the highest magnetic field levels and V(OC)s were both associated with backyard lines, and the highest V(OC)s were also associated with long ground paths in the residence. Across the entire neighborhood, magnetic field exposure was highly correlated with V(OC) (r = 0.93). Dosimetric modeling indicates that, compared to a very high residential level of a uniform horizontal magnetic field (10 mu T) or a vertical electric field (100 V/m), a modest level of contact current (approximately 18 mu A) leads to considerably greater induced electric fields (> 1 mV/m) averaged across tissue, such as bone marrow and heart. The correlation of V(OC) with magnetic fields in the model, combined with the dose estimates, lead us to conclude that V(OC) is a potentially important exposure with respect to childhood leukemia risks associated with residential magnetic fields. These findings, nonetheless, may not apply to residential service used in several European countries or to the Scandinavian studies concerned with populations exposed to magnetic fields from overhead transmission lines.
Subject(s)
Electromagnetic Fields/adverse effects , Neoplasms, Radiation-Induced/etiology , Child , Humans , Leukemia, Radiation-Induced/epidemiology , Leukemia, Radiation-Induced/etiology , Models, Biological , Radiometry , Risk Factors , United States/epidemiologyABSTRACT
This retrospective study evaluated patients under 18 years of age who underwent major limb replantation between 1976 and 1989 at Louisville Hand Surgery. The age of the 15 patients followed for between 1 and 8.5 years (mean 4.2 years) ranged from 2 to 17 years (mean 9.8). Of amputations, 40% were guillotine, 40% were limited crush-avulsions, 7% were extended crushing, and eight were of an upper extremity and seven of a lower extremity. Average warm/total ischemia times were 4.8/14.8 hr in failures and 1.1/7.5 hours in successful replantation. Overall limb survival was 87%. Among the patients, 93% felt that their replanted limb functioned and looked better than a prosthesis; 87% of patients had a sensory recovery of more than S2+ in the lower extremity or S3 in the upper extremity; and 38% of upper extremity replantation patients had two-point discrimination of less than 15 mm.
