Thomas Swiontek

Measure of tissue resistivity in experimental electrical burns

Studies were conducted in 14 mongrel dogs to compare resistivities in normal muscle with those from muscle subjected to electrical burns. One-ampere, 60-Hz currents were passed between the hind limbs of the dogs producing injury in three measurement regions of the gracilis muscle. Histology, heart rate, body temperature, arterial and pulmonary artery pressure, cardiac output, hematocrit, leukocyte counts, fibrinogen levels, and platelet levels were determined. Muscle resistivity associated with severe tissue necrosis was 70% lower than control values. Resistivity in tissue showing edema and minimal necrosis decreased 20 to 40% from control values. Muscle showing only edema had a 10 to 30% decrease in resistivity.

Experimental electrical injury studies.

Voltages from 10 to 14,000 volts demonstrated currents up to 70 amperes with resistances of approximately 200 ohms in studies in hogs. Below 1,000 volts, a current reduction is observed following arcing and skin necrosis. At the higher voltages, this phenomenon was not observed. The energy required for tissue damage was dependent upon the voltage and time of application. The tissue electrode resistance with stainless steel disc was proportional to the diameter. Skin buring commenced at the periphery of the electrodes and moved inwards. For application of currents between the hindlimbs of the hog, the current per tissue cross-section was greatest in artery and nerve, followed by muscle, fat, bone marrow, and bone cortex.

Spinal Cord Implant Studies

A loaded probe technique was used to measure the current density distribution resulting from application of electrical current to the spinal cords of live anesthetized stumptail macaque monkeys and fresh human cadaver spinal cords via the electrode arrays of four commercially available spinal implant systems used for management of intractable pain.

Current Pathways in High-Voltage Injuries

Studies were done in the hog with limb-to-limb contacts at potentials up to 2000 V. The current density in nerve, vessels, muscle, bone, fat, lungs, heart, kidney, liver, intestines, and spinal cord were determined. The current densities in the leg are largest in nerve and artery, followed by muscle, fat, and bone. The temperature was greatest in fat and nerve. With forelimb-to-hindlimb current application, the current densities were largest in the back region. The spinal cord current density was approximately twice the average cross-sectional value.

Cerebellar Implant Studies

Electrical currents were applied to the cerebellum of anesthetized monkeys using techniques similar to those employed in human cerebellar electrode implant systems. Alterations in the bloodbrain barrier were not observed. Histological damage, when present, appeared secondary to mechanical injury rather than to application of current. Measurement of current density in the monkey and human cerebellum indicated that with the electrode configuration employed, most of the current is retained in the vicinity of the electrodes. In human patients with spasticity and dyskinesia, application of current through implanted cerebellar electrode units relieves spasticity and also has been associated with reduction of somatosensory evoked potential amplitude. The amount of current required for clinical improvement and for alteration of evoked potential amplitude has remained stable in all patients, even those followed for more than a year. These observations suggest that the methods described do not produce appreciable cerebellar damage.

Effects of Contacts in High Voltage Injuries

The current and impedance attendant with accidental power line contact is difficult to reconstruct following an accident. Studies were conducted in the living hog with potentials from 10 to 14,400 volts applied. The contact was made with #2 ACSR, disk, ellipsoidal and annular electrodes. Blisters occurred at 50 to 80 volts. Nonlinear time versus current and voltage versus current relationships were observed for all electrode contacts. The time required for the increase in current following voltage application was inversely proportional to the applied voltage and proportional to the electrode size. Current versus voltage and current versus time plots for elliptical, disk and annolar electrodes were similar for electrodes with the same distance along the edge. Theoretical calculations and experiments in the saline tank confirmed this finding.

Evaluation of Electrode Configurations in Cerebellar Implants

Capacitively coupled currents of 100 Hz, 0.25 msec duration, were applied to multielectrode arrays implanted upon the superior and posterior surfaces of the chimpanzee cerebellum. The current required for 90% reduction in the amplitude of the evoked potential was inversely proportional to the number of electrodes upon the cerebellar surface. A study of various waveforms showed that z Hz, 0.25 msec pulse duration is near optimal for reduction of amplitude of the somatosensory evoked potential. The current densities per electrode were 5--11 mA/cm2 with a charge per pulse of 0.04--0.08 muC in humans with 15--20 electrodes on each superior surface and 10 electrodes on each posterior cerebellar surface.

Instrumentation design for high-voltage electrical injury studies

The experimental study of high-power electrical injuries requires special devices to protect personnel and data recording instruments. A power distribution system is described which was designed to apply 500-20000 V and currents up to 100 A to an experimental preparation and a measurement system for recording 0.02-200.0 V at local sites in the preparation. Data collection and storage are automated with analog and digital devices that minimize personnel contact. For personnel safety, all recording instruments are isolated from the power distribution system by battery-driven standby power supplies and from the experimental high voltages by fiber optic data links. Current-triggering and- interruption mechanisms allow variable-duration voltage applications as short as 25 ms. These applications are also synchronized to the electrocardiogram and can be made to occur during any part of the cardiac cycle.<<ETX>>

Determination of Tissue Viability in Experimental Electrical Injuries

Electrical burns or ischemia (induced by vascular ligation) were produced in the legs of 15 anesthetized dogs to study evolution of tissue changes compared with impedance alterations. After the application of 1-ampere currents at 60 Hz, animals were monitored from 1 to 4 days. Muscle impendance was measured with frequency sweeping to determine tissue destruction. Nuclear magnetic resonance spectroscopy (phosphorus 31) was used to assess metabolic activity, and results were compared to impedance measurements. In burned limbs, 70% reduction in muscle impedance was seen, which corresponds to decreased metabolic activity (absent organic phosphates) and suggests necrosis. Visually viable tissue had impedance decreases of 25% and levels of organic phosphates slightly lower than normal. Relaxation frequencies in dogs with severe burns exceeded 80 kHz; in viable tissue, 30 to 40 kHz (normal: 30 kHz). In ischemic muscle, organic phosphates decreased rapidly (1 to 2 hours); impedance changes evolved more slowly (1 day), but they ultimately reached the same degree of severity. Measurement of impedance may be a valuable adjunct in the evaluation of electrical burns, since significant changes strongly suggest nonviability.

Fibrillation induced at powerline current levels

Because little information is available on short-duration high-current fibrillation, current levels between 1 and 50 A were used to induce ventricular fibrillation in hogs. Application times ranged between 16 nms and 3 s. Fibrillation was only produced when currents were applied during the T-wave period of the cardiac cycle. However, only 50% of the current application during the T-wave caused fibrillation. The total body resistance of the hogs was measured at the high voltages and currents. The average resistance for 90 current applications was 284 Omega . Trends in the data show that the total resistance decreases for increasing voltage, for increasing electrode size, and for current applications following the first current application.<<ETX>>