Conduction of Electrical Current to and Through the Human Body: A Review

Objective: The objective of this article is to explain ways in which electric current is conducted to and through the human body and how this influences the nature of injuries. Methods: This multidisciplinary topic is explained by first reviewing electrical and pathophysiological principles. There are discussions of how electric current is conducted through the body via air, water, earth, and man-made conductive materials. There are also discussions of skin resistance (impedance), internal body resistance, current path through the body, the let-go phenomenon, skin breakdown, electrical stimulation of skeletal muscles and nerves, cardiac dysrhythmias and arrest, and electric shock drowning. After the review of basic principles, a number of clinically relevant examples of accident mechanisms and their medical effects are discussed. Topics related to high-voltage burns include ground faults, ground potential gradient, step and touch potentials, arcs, and lightning. Results: The practicing physician will have a better understanding of electrical mechanisms of injury and their expected clinical effects. Conclusions: There are a variety of types of electrical contact, each with important characteristics. Understanding how electric current reaches and travels through the body can help the clinician understand how and why specific accidents occur and what medical and surgical problems may be expected

Toward Virtual Digital Mammograms for Research and Training in Tumor Detection

Research in the processing, compression, transmission, and interpretation of digital radiographic images requires evaluation of a wide variety of test images, varying in format, in spatial resolution, and in anatomic content. To evaluate the diagnostic performance of observers using novel versus conventional image formats, large numbers of test images containing known abnormalities are required. This report describes a method for creating high resolution, virtual digital mammograms from computational models of the human breast that include branched lobulated ducts and suspensory ligaments embedded in fatty subcutaneous tissue. Breast phantoms may include any of three types of simulated tumors (fibroadenomas, invasive ductal carcinomas, and intraductal carcinomas). Virtual mammograms are generated by computing x-ray transmission through a mathematically defined, three dimensional tissue space according to Beer\u27s Law, using a fast ray-tracing algorithm. The resulting test images are adequately realistic, inexpensive, and reproducible at any desired resolution. They may contain precisely defined and localized abnormalities of unlimited subtlety. This approach provides a flexible, easy-to-use research tool to explore digital techniques in mammography, as well as a potential aid to training of radiologists in early breast cancer detection

Theoretical Advantages of Abdominal Counterpulsation in CPR as Demonstrated in a Simple Electrical Model of the Circulation

Animal studies and preliminary clinical observations suggest that the addition of interposed abdominal compressions (IAC) to ventilation and chest compression of standard cardiopulmonary resuscitation (CPR) augments blood flow, blood pressures, and immediate survival. To investigate the physical basis for enhanced circulation during IAC-CPR, we developed an electrical model of the circulation. Heart and blood vessels were modeled as resistive-capacitive networks, pressures as voltages, blood flow as electric current, blood inertia as inductance, and the cardiac and venous valves as diodes. External pressurization of the heart and great vessels, as would occur in CPR, was simulated by application by half-sinusoidal voltage pulses between vascular capacitances and ground. Closed-chest CPR was simulated by pressurization of all intrathoracic capacitances. IAC was simulated by similar pressurization of the inferior vena cava and abdominal aorta, 180 degrees out of phase with chest compression. During simulation of CPR, IAC improved cranial and myocardial perfusion at all levels of chest compression pressure by amounts linearly related to peak abdominal pressure, suggesting that the abdomen can function as a second, independent blood pump during CPR. Brain and heart flow were improved further during simulated vasoconstriction in kidneys, abdominal viscera, and extremities. Based on the fundamental properties of the cardiovascular system represented in the model, abdominal counterpulsation provides a rational basis for flow augmentation during CPR

Methods for Calculating Coronary Perfusion Pressure During CPR

Coronary perfusion pressure (CPP) is a major indicator of the effectiveness of cardiopulmonary resuscitation in human and animal research studies; however methods for calculating CPP differ among research groups. Here we compare the 6 published methods for calculating CPP using the same data set of aortic (Ao) and right atrial (RA) blood pressures. CPP was computed using each of the 6 calculation methods in an anesthetized pig model, instrumented with catheters with Cobe pressure transducers. Aortic and right atrial pressures were recorded continuously during electrically induced ventricular fibrillation and standard CPR. CPP calculated from the same raw data set by the 6 calculation methods ranged from -1 (signifying retrograde blood flow) to 26 mmHg (mean ± SD of 15 ± 11 mmHg). The CPP achieved by standard closed chest CPR is typically reported as 10–20 mmHg. Within a single study the CPP values may be comparable; however, the CPP values for different studies may not be reliable indicators of the relative efficacies of different CPR methods. Electronically derived, true mean coronary perfusion pressure is arguably the gold standard metric for representing coronary perfusion pressure

Cardiac, Thoracic, and Abdominal Pump Mechanisms in Cardiopulmonary Resuscitation: Studies in an Electrical Model of the Circulation

To investigate alternative mechanisms generating artificial circulation during cardiopulmonary resuscitation (CPR), an electrical model of the circulation was developed. Heart and blood vessels were modeled as resistive-capacitive networks; pressures in the chest, abdomen, and vascular compartments as voltages; blood flow as electric current; blood inertia as inductance; and the cardiac and venous valves as diodes. External pressurization of thoracic and abdominal vessels, as would occur in CPR, was simulated by application of half-sinusoidal voltage pulses. Three modes of creating artificial circulation were studied: cardiac pump (CP), in which the atria and ventricles of the model were pressurized simultaneously; thoracic pump (TP), in which all intrathoracic elements of the model were pressurized simultaneously; and abdominal pump (AP), in which the abdominal aorta and inferior vena cava of the model were pressurized simultaneously. Flow was greatest with the CP, less with the TP, and least with the AP mechanism. However, the AP could be practically combined with either the CP or TP by interposition of abdominal compressions between chest compressions (IAC-CPR). Our model predicts that this combined method can substantially improve artificial circulation, especially when cardiac compression does not occur and chest compression invokes only the thoracic pump mechanism

Therapeutic indices for transchest defibrillator shocks: Effective, damaging, and lethal electrical doses

Although prospective studies of defibrillator shock overdose cannot be performed in man, the therapeutic indices of various defibrillating current waveforms can be measured in animals. We determined the ratios TD50/ED50 and LD50/ ED50 (where TD50 = median toxic or damageinducing dose, ED50 = median effective or defibrillating dose, and LD50 = median lethal dose) as measures of the therapeutic index for damped sine wave defibrillator shocks in dogs. Death of an animal and/or any degree of cardiac damage found by gross or microscopic examination were defined as harmful effects of shock, analogous to drug toxicity. In terms of peak current, the ED50, TD50, and LD50 were 1.1, 5.8, and 24 amperes/ kg; the therapeutic indices were TD50/ED50 = 5 for morphologic damage and LD50/ED50 = 22 for death. In terms of delivered energy the ED50, TD50, and LD50 were 1.5, 30, and 470 joules/kg; the therapeutic indices were TD50/ED50 = 20 for damage and LD50/ED50 = 320 for death. These data indicate a reasonable margin of safety for damped sine wave defibrillator shocks in dogs, and are consistent with reported incidences of suspected shockinduced damage in humans

Clinical ROC Studies of Digital Stereo Mammography

The objective of this study was to explore and document the diagnostic utility of digital stereo mammography for the detection of localized breast cancer in women. In it we character­ized the ability of experienced mammographers, general radiologists, and non-radiologists to detect three types of tumor masses embedded within a heterogeneous background of normal tis­sue elements in numerically simulated digital mammograms. The simulated mammograms were displayed to the subjects on a high resolution video display, both in stereo mode and in mono mode. Half of the mammograms contained a single tumor, ranging from 0.3 to 0.8 cm in maxi­mal diameter. Each reader rated 120 images (60 in stereo and 60 in mono) as to the probability of abnormality on scale of 1-5. Observer responses were evaluated using receiver operating characteristic (ROC) analysis to characterize any difference in diagnostic performance between the two viewing modes. The synthesized mammograms and the digital display were highly rated by the participant radiologists as promising tools for future research. The results of ROC analysis, however, indicated no significant difference in tumor detection when the same readers utilized the stereo mode versus the mono mode (Az mono = 0.833 versus, Az stereo = 0.826). The results were similar for readers of all 3 experience levels--mammographers, general radiolo­gists, and non-radiologists

Bostonia: The Boston University Alumni Magazine. Volume 12

Founded in 1900, Bostonia magazine is Boston University’s main alumni publication

Performance of the CMS Cathode Strip Chambers with Cosmic Rays

The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device in the CMS endcaps. Their performance has been evaluated using data taken during a cosmic ray run in fall 2008. Measured noise levels are low, with the number of noisy channels well below 1%. Coordinate resolution was measured for all types of chambers, and fall in the range 47 microns to 243 microns. The efficiencies for local charged track triggers, for hit and for segments reconstruction were measured, and are above 99%. The timing resolution per layer is approximately 5 ns

Performance and Operation of the CMS Electromagnetic Calorimeter

The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented