Magnetic field excitation of peripheral nerves and the heart: a comparison of thresholds

Time-varying magnetic fields can theoretically excite the heart or peripheral nerves. Relative excitation thresholds of nerve and heart are compared using ellipsoidal representations of the human torso. Relative magnetic thresholds depend on the excitability of nerve and cardiac tissue, the geometric positions of anatomical features, stimulus waveform features and the direction and spatial distribution of the incident magnetic field. Minimum electric field thresholds for excitation of nerve and heart do not differ greatly. Nevertheless, nerve and heart magnetic thresholds may be disparate because of factors related to body geometry and the dependence of excitability on the stimulus waveform.

Raman shifting of picosecond light pulses in hydrogen gas

Picosecond light pulses are used to generate multiple wavelengths by means of stimulated Raman scattering. A review of the processes involved is presented, followed by a discussion of the experimental apparatus. Stokes and anti-Stokes Raman-shifted lines arising from vibrational and rotational transitions are observed. The polarization of the incident pump laser considerably affects which wavelengths are observed. Some vibrational Raman lines exhibit a splitting that is due to scattering from different initial H(2) rotational states.

Effects of insulin on skeletal muscle glucose storage, oxidation, and glycolysis in humans

The effects of physiological hyperinsulinemia (approximately 75 mU/l) on glucose storage, oxidation, and glycolysis in skeletal muscle were assessed with euglycemic clamps performed in seven healthy volunteers, in conjunction with leg balance for glucose, lactate, alanine, O2, and CO2. Infusion of insulin increased leg glucose uptake, storage, and oxidation but did not alter net release of lactate and alanine. The respiratory quotient (RQ) across the leg increased from a basal value of 0.74 +/- 0.02 to 0.99 +/- 0.02 during hyperinsulinemia. Under conditions of insulin stimulation, 49 +/- 5% of leg glucose uptake was stored, 37 +/- 4% was oxidized, and 14 +/- 2% was released as lactate and alanine. We conclude that during physiological hyperinsulinemia and euglycemia 1) skeletal muscle lipid oxidation is nearly entirely suppressed and glucose becomes the primary oxidative substrate of muscle, 2) glucose storage and oxidation are the major pathways of skeletal muscle glucose metabolism and are quantitatively similar at physiological insulin levels, and 3) the majority of insulin-stimulated glycolysis is oxidized, with only a small portion released as lactate or alanine.

Peripheral nerve stimulation by induced electric currents: exposure to time-varying magnetic fields

The review evaluates thresholds of peripheral nerve stimulation by complex current waveforms. A neuroelectric model employing Frankenhaeuser-Huxley membrane nonlinearities is used to derive excitation thresholds for monophasic and biphasic pulse sequences, as well as sinusoidal stimuli. The model, along with principles of magnetic field induction, is used to derive criteria of acceptability for exposure to time-varying magnetic fields. Applications to pulsed gradient fields from magnetic resonance imaging devices are discussed.

Intramedullary nailing of femoral shaft fractures. Part I: Decision-making errors with interlocking fixation

Dynamic intramedullary fixation depends on the configuration of the fracture for postoperative stability. Unanticipated loss of reduction of the fracture after dynamic intramedullary nailing of the femur may result from errors in surgical decision-making, specifically the failure to insert both proximal and distal interlocking screws. Of 133 dynamic femoral intramedullary nailings that were performed after interlocking techniques became routinely available, fourteen (10.5 per cent) were complicated by loss of postoperative fixation and reduction. Thirteen of the fourteen femora shortened an average of 2.0 centimeters; the remaining femur shortened slightly, with clinical loss of rotational stability. Eight of fourteen patients elected some form of surgical revision, most commonly closed osteoclasis with restoration of femoral length, followed by the insertion of a statically locked nail. Errors in surgical judgment were attributed to inadequate preoperative analysis of the pattern of the fracture; undetected intraoperative comminution during reaming or insertion of the nail, or both; or postoperative failure to recognize an increase in comminution and instability of the fracture. We suggest using high-quality preoperative radiographs to detect non-displaced comminution of the major fracture fragments. Any increase in comminution of the fracture that occurs with reaming of the canal or insertion of the nail is an indication for static interlocking fixation. Radiographs that are made immediately postoperatively should be analyzed while the patient is under anesthesia, and any previously undetected instability of the fracture should be treated by static interlocking fixation. Dynamic intramedullary stabilization of the femur should be reserved for transverse or short oblique fractures at the femoral isthmus that have type-I or type-II comminution.

Disorders of the sacro-iliac joint in children

The cases of seventeen children whose ages ranged from two to eighteen years and who were treated for a disorder of a sacro-iliac joint between 1975 and 1983 were reviewed retrospectively. Thirteen children were acutely ill, with a temperature of more than 38 degrees Celsius, and four had chronic symptoms that had persisted for three weeks to one year. Pain in the hip, thigh, and buttock was the most common symptom. Of the thirteen acutely ill patients, eleven had septic arthritis of a sacro-iliac joint, while one who had ankylosing spondylitis and one who had juvenile rheumatoid arthritis had acutely painful arthritis of a sacro-iliac joint. Of the four patients who had chronic symptoms, two had septic arthritis of a sacro-iliac joint; one, ankylosing spondylitis with sacro-iliac involvement; and one, eosinophilic granuloma of the ilium. Thus, thirteen patients had septic arthritis of a sacro-iliac joint and four had some other disorder. For the seventeen children who had acute or chronic symptoms, at admission the white blood-cell count ranged from 3,500 to 26,200 per cubic millimeter (average, 11,100 per cubic millimeter) and the sedimentation rate, as determined by the Westergren technique, ranged from twenty-two to sixty-five millimeters per hour (average, fifty millimeters per hour). Twelve of the plain radiographs of the seventeen patients were negative. The initial bone scans of all seventeen patients were positive in eleven and negative in six. Of these six, five had septic arthritis and one, juvenile rheumatoid arthritis. A computed tomographic scan was performed in four patients and was positive in all of them: three had septic arthritis and one had ankylosing spondylitis. Organisms were cultured successfully from blood, from material aspirated from the sacro-iliac joint, or from stool of all thirteen patients who had sepsis. The thirteen infections responded well to appropriate antibiotics, which were administered intravenously to seven patients and first intravenously and then orally to six.

The chronically inflamed bursa

Bursitis continues to be a frequent source of disability in the athlete. However, significantly less interest has been focused upon this type of injury than other types of sports injuries. This article presents a review of the problem, starting with anatomy and working through diagnosis to treatment.

Electrocutaneous sensitivity: effects of skin temperature

The effect of human skin temperature on electrocutaneous sensitivity was examined using brief capacitive discharges. Stimuli were designed to ensure that sensory effects would be independent of skin resistance and would reflect underlying neural excitability as closely as possible. Skin temperature was manipulated by immersing the forearm in circulating hot or cold air. Detection thresholds on the arm and fingertip were raised by cooling, but were not altered by heating. Temperature-related sensitivity shifts were described by the same multiplicative factors for both threshold and suprathreshold levels. The temperature coefficient (Q10) for cutaneous sensitivity under these conditions was approximately 1.3.

Orthopedic problems in athletes

Physicians and patients must recognize the demands of the sport involved, as well as the individual's ability to meet those demands. Careful analysis of the sport and examination of the patient to assess recovery and chances of reinjury are mandatory, if he is to enjoy sports after injury. Physicians should become familiar with padding, shoes, warm-up programs, preparticipation examinations, and protective equipment and devices, all of which are helpful in preventing sports injuries. We have touched only briefly on the epidemic problem of quality of life trauma that is part of our society. Because injuries result in punishment to the soul as well as to the body of a person, the sports participant deserves a comprehensive, scientific, multidisciplinary approach in order to return to the state of physical and emotional well-being he enjoyed before the injury. For this reason a physician must examine each patient carefully and with regard for the individual's ability to be sure of the diagnosis for subsequent treatment.

A randomized trial of leukocyte-depleted platelet transfusion to modify alloimmunization in patients with leukemia

In an effort to determine whether the use of leukocyte (WBC) depleted platelets could modify the development of alloimmunization, 98 adult patients with acute nonlymphocytic leukemia receiving initial induction therapy were randomized to receive standard pooled platelet concentrates (PC) or WBC-depleted PC. WBC depletion was produced by an additional centrifugation of pooled PC, with removal of 81% of WBC and an associated platelet loss of 27%. Lymphocytotoxic antibody (LCTAb) levels were monitored as a serologic marker of alloimmunization. Overall, 5 of 25 evaluable patients receiving WBC-depleted PC developed LCTAb, compared to 13/31 receiving standard PC (p = 0.071). There was no significant difference in alloimmunization rate in the subgroup of patients who had no previous exposure to histocompatibility antigens by pregnancy or prior transfusions (4/15 alloimmunized receiving WBC depleted versus 4/12 receiving standard PC). There was no difference in the number of patients in each group who required HLA-matched platelets during induction therapy. In view of the significant loss of platelets with WBC depletion, the expense and difficulty of providing WBC-poor RBC, the absence of impact on the need for HLA-matched platelets during induction, and the small potential benefit from this approach, WBC-depleted platelets should not be utilized to prevent alloimmunization in patients with leukemia.